Protection and Restoration Strategies for Watersheds and Tributaries

1. Section Scope

This section reviews, assesses, and summarizes the potential strategies investigated in past scientific and technical research for positively affecting the watersheds and tributaries draining to Puget Sound. The review and assessment covers strategies for both protecting resources that remain and recovering or improving resources that have been impaired. Concentration is on presenting the level of effectiveness of the candidate strategies, as established by the research, and the relative certainty associated with the reported effectiveness. Of particular interest is identifying strategies that reduce multiple threats to the Puget Sound ecosystem.

This section covers the scientific and technical aspects of potential restoration and protection strategies for application in watersheds, whether they drain to tributary fresh waters or to the estuarine and marine waters of Puget Sound. It also encompasses strategies that can be applied within freshwater bodies to affect positively their overall aquatic ecosystems. This scope excludes policy and socioeconomic considerations associated with implementation of the strategies.

A watershed is a unit providing a convenient and practical framework for implementing ecosystem management1. Watersheds capture the basic ecological, hydrological, and geomorphological relationships that can be affected by land uses in their drainage catchments (Montgomery, Grant, and Sullivan 1995; National Research Council 1999; Brooks et al. 2003). The concept of a watershed as used in this chapter is a broad one, encompassing the full range of scales that may come into play in describing and evaluating protection and restoration strategies.

Most fundamentally, a watershed is an area of land from which all of the surface and subsurface water drains to a common point. Depending on where the point of interest is located, watershed size can range very widely. The U.S. Geological Survey (USGS) delineates watersheds in the United States using a nationwide system based on surface hydrologic features. This system divides the nation into regions, subregions, accounting units, and cataloging units (National Research Council [NRC] 2009). These hydrologic units are arranged within each other, from the smallest (cataloging units) to the largest (regions). Puget Sound comprises both a subregion and an accounting unit divided into 21 cataloging units ranging in area from 648 to 6634 km2. The large rivers draining to Puget Sound, or extensive reaches of them, constitute some of these units; others are large tributaries to these rivers; while some are parts of the Sound itself or direct drainages not passing through a major river system. The system put forth by USGS provides a starting point. Ultimately, though, in any particular case a watershed is best defined with reference to specific biogeophysical conditions and problems and management objectives intended to address them. In many cases these considerations will point to a watershed delineation much smaller than a USGS cataloging unit, tens of km2 down to as small as less than 1 km2. Of course, relatively small watersheds are nested within larger ones, the components of which are likely to share many characteristics and be amenable to common strategies. This section discusses strategies in relation to their scale of application as appropriate.

Watershed Protection and Restoration within Context of the Puget Sound Partnership’s Action Agenda

As outlined in the Introduction to Chapter 4 of the Puget Sound Science Update, the Puget Sound Partnership’s (PSP) Action Agenda presented an extensive list of prospective strategies to protect and restore Puget Sound and called out a subset of near-term actions. The technical memorandum Using Results Chains to Develop Objectives and Performance Measures for the 2008 Action Agenda (Neuman et al .2009) incorporated many of these strategies, in some cases supplementing them with others, and grouped them in seven broad categories. The memorandum related strategies to outcomes, threats to the Puget Sound ecosystem, and effects on ecological components, setting up a “results chain” showing how a particular action is thought to lead to some desired result. This section is concerned with the demonstrated effectiveness and relative certainty of some strategies in the Land Protection, Flow Protection, River and Floodplain Restoration, Stormwater, and Wastewater categories.

2. Organization of this Section

The progression of the section is from general strategies appropriate at relatively large scales, to strategies meant for specific water body types, to management practices for application to particular types of threats. The general strategies apply to scales near or at the USGS cataloging unit level, or even to the entire subregion, and are related primarily to certain strategies in the Land Protection category (Neuman et al. 2009). The section discusses water body-specific strategies for streams (creeks and rivers), wetlands, and lakes. Threat-related strategies are presented for stormwater and wastewater. The stormwater coverage first focuses on urban runoff and is followed by discussions of strategies regarding two other urban issues: municipal and on-site domestic wastewater. The section concludes with a summary of strategies related to runoff from agricultural and forestry production areas.

The identified strategies arise out of the peer-reviewed literature of the subject, which generally requires extensive explanation. Each segment concludes with a synthesis bringing together the threads drawn from the literature. While strategies are usually multi-faceted, an attempt is made at that point to encapsulate the key elements in a relatively brief statement to capture the essence and serve as a touchstone for the strategy.

3. Terminology

This section has a dual interest in the protection and restoration of the fresh waters tributary to Puget Sound. In the section’s usage, “protection” means retaining the ecological state at its existing level, whatever that may be, without diminishment of any indicators of the health of that state, terrestrial or aquatic, structural or functional. The section applies the term “restoration” in the broad sense to mean any level of improvement in the state. This usage is consistent with the definition in Merriam-Webster’s Online Dictionary3, “bringing back to a former position or condition.” That definition and the usage in this section carry no connotation of necessarily returning the system to its original state, i.e., pre-human influence, although such an objective is a theoretical possibility. Should such an objective be under consideration, the section refers to the case as “full restoration,’ by which it means reestablishment of the structure and function of an ecosystem, including its natural diversity (Cairns 1988, NRC 1992). The section also employs “rehabilitation,” when an author has selected that term or for variety of discourse, as a synonym for restoration (Merriam-Webster’s defines to rehabilitate as “to restore to a former state”).

When referring to lotic (flowing) waters in general, in this section the term “stream” is usually used, which can indicate channels of any size and stream order. When the scale or size is an issue, the section references the order or an actual or approximate range of orders. There are several systems of assigning stream order, but their distinctions are generally not great enough to affect the discussion within the scope of this section. In Strahler’s (1952) system, a headwaters stream with no tributaries is first-order, two confluent first-order streams form one of second order, joining with another second-order stream (but not one of first order) becomes a third-order stream, etc.

4. Framework for Watershed-based Strategies


The National Research Council (NRC) of the National Academy of Sciences convened a committee in 2007, at the request of USEPA, to review its current permitting program for stormwater discharges under the Clean Water Act and provide suggestions for improvement. The broad goals of the study were to understand better the links between stormwater pollutant discharges and ambient water quality, to assess the state of the science of stormwater management, and to make associated policy recommendations. While the committee’s charge focused on stormwater and discharge permitting, its report (NRC 2009) offered recommendations more widely applicable to comprehensive water resources management, of which regulatory permitting is of course a key component. This segment of Chapter 3 summarizes the relevant recommendations, in the process building a rationale for a watershed basis and extracting strategies advancing the PSP’s Action Agenda and Results Chain process. The approximately 30-year history of stormwater management in the United States has been organized, almost invariably, according to local jurisdictional (city, county) boundaries, with state or USEPA oversight through permitting during the latter half of that period. This organizational principle extends, for the most part, to management of other pollutant-bearing discharges as well. Early in this decade USEPA began to take note of the disadvantages of this practice and the potential benefits of an alternative, in a policy statement (USEPA 2003a) embracing, “... a detailed, integrated, and inclusive watershed planning process ...,” with a basis in, “... clear watershed goals ...” Subsequent to the policy statement, USEPA published two guidance documents laying out a general process for setting up Clean Water Act permits on a watershed basis (USEPA 2003b, 2007a). The NRC committee recognized the benefits of and general principles applying to USEPA’s concept but concluded that its guidance did not go nearly far enough toward bringing it to fruition. The committee developed an approach fitting within the general framework outlined by USEPA but greatly expanding it in scope and detail. It is intended to replace the present structure, instead of being an adjunct to it, and to be uniformly applied nationwide.

5. Framework Elements and Their Relationship to PSP Results Chain Strategies

Appendix 4A, Box A1 presents the major elements of effective watershed-based, water resources management and permitting in the committee’s approach (NRC 2009), which are elaborated in substantial detail in its report. The list is annotated with identical or similar strategies directly represented in Neuman et al. (2009). These elements represent the following key strategy: Develop a comprehensive watershed-based management system.

6. Comprehensive Watershed Analysis and Management Guidance

A key element in the framework presented above, and in the PSP Action Agenda (PSP 2008), is watershed analysis at an advanced scientific and technical level. Many watershed plans completed over the last 40 years have not been successfully implemented. Davenport (2003), drawing heavily on a survey of practitioners by the Center for Watershed Protection, presented and commented on the main reasons cited for these failures (Box 1).

Box 1. Reasons for failures of past watershed plans (Davenport 2003).

  • The plan’s scale was too large2.
  • The plan represented a one-time study instead of a long-term commitment.
  • The process lacked local ownership.
  • The plan skirted real issues about land-use regulation.
  • The budget was low or unrealistic.
  • Planning focused on the tools of watershed analysis instead of outcomes.
  • The document was too long or complex (the backup science and technology should be placed in a separate document).
  • The plan failed to assess critically the adequacy of existing programs to implement it.
  • Recommendations were too general.
  • Regulatory authority for implementation was insufficient.
  • Key stakeholders were not involved.
  • From the technical standpoint, the plan focused on aggregated averages instead of finer-scale processes, obscuring vulnerable locations and watershed elements that should have been targeted for attention.

Ideas for promising approaches to watershed analysis and management can be found in a number of extended works that have been published over the years explicating multiple aspects of watershed analysis and management. Some of these works are potentially useful to assist the PSP and its collaborators in going forward with the challenging task of strategizing on the watershed level. None is sufficient alone, and none should be used uncritically. Table 1 lists the major, general-purpose works of this type published over the last 15 years and summarizes their characteristics.



Topics Covered




General Features



Data Collection







Stormwater Management





Heathcote (2009)

For management professionals, broad scope, interdisciplinary, relatively high level

1-5, 7-9








USEPA (2008)

For agency staff, qualitative treatment with advice to involve quantitative specialists

1, 4, 7, 8


1-2, 4, 5






DeBarry (2004)

For science, engineering, and planning professionals, broad scope, interdisciplinary, relatively high level

1-5, 7


1, 2






Brooks et al. (2003)

More forest land than urban emphasis, relatively high level

1-2, 5-6


1-3 (brief)

Not explicitly





Davenport (2003)

Planning orientation mainly for regulators and regulated parties

1, 8


2, 4






NRC (1999)

Synoptic coverage on a national scale









Center for Watershed Protection (1998)

Planning process approach at a semi-technical level









Terrene Institute (1996)

General coverage at a lay level for decision makers, urban emphasis



















a 1—hydrology, 2—water quality, 3—physiography, 4—soils, 5—hydrogeology, 6—sediment transport, 7—ecosystems, 8—land use, 9—social systems

b 1—geographic information systems, 2—modeling, 3—statistics, 4—monitoring, 5—mapping, 6—field rapid assessment techniques

It may be seen in Table 1 that no single reference covers all of the principal subjects in detail. However, two relatively recent books, Heathcote (2009) and DeBarry (2004), together do provide quite comprehensive coverage at the level appropriate to the analytical emphasis advocated by NRC (2009). These references would make excellent additions to the library of any scientist, engineer, or planner, or regulator who will be working on Puget Sound issues. Those working on highly forested watersheds should also consider acquiring Brooks et al. (2003). The older material in the table could still benefit those desiring a broader view or who are specialists in the areas stressed by a particular reference. As a manifestation of modern watershed-based, strategy-oriented practice, it is instructive to summarize Heathcote’s (2009) general approach. The approach is highly consistent with PSP’s strategic emphasis and the NRC (2009) framework (Box 2).

Box 2: General Approach to watershed-based, strategy-oriented management practices proposed by Heathcote (2009).

  • Develop an understanding of watershed components and processes and water uses and users.
  • Identify or rank problems to be solved or beneficial uses to be protected or restored.
  • Set clear and specific goals.
  • Develop a set of planning constraints and decision criteria (appropriately weighted).
  • Identify an appropriate method of comparing management alternatives.
  • Develop a list of management options.
  • Eliminate options that are not feasible based on constraints and criteria.
  • Test the effectiveness of remaining feasible options using the results of preceding steps.
  • Determine the environmental and economic impacts and legal implications of the feasible management options.
  • Develop several good management strategies, each encompassing one or more options, for the consideration of decision makers.
  • Develop clear and comprehensive implementation procedures for the plan preferred by decision makers.

Four other volumes of a more specialized nature also deserve mention. Field, Heaney, and Pitt (2000) published extended engineering guidance pertaining to urban stormwater management. Its systematic approach has an implicit watershed orientation, although it is not built around watershed assessment and planning in the way that the works in Table 1 generally are. It does cover institutional arrangements and financing, but its treatment of stormwater best management practices (BMPs) is now rather dated, with little explicitly on LID methods. Reimold (1998) compiled material by multiple authors very broad in coverage geographically and by issues. While it gives some attention to analytical and planning tools, this volume is most useful for its regional and problem-area case studies. Pacific Salmon and Their Ecosystems: Status and Future Options, a collection of contributions by many authors edited by Stouder, Bisson, and Naiman (1997), has a fisheries emphasis more suitable for Section 4-4 but is mentioned here because of the watershed-based content in its restoration section. Naiman (1992) edited a volume with the principal title Watershed Management giving many different views of national and even international scope on integrated watershed management and mitigation and restoration.

7. Strategies for Managing Streams in a Watershed Framework

Research Basis

The condition of streams in urban areas became a subject of study over four decades ago (e.g., Larimore and Smith 1963, Hynes 1970, 1974, Tramer and Rogers 1973, Trautman and Gartman 1974). By the 1990s the effects of watershed urbanization on streams were well documented. They include extensive changes in basin hydrologic regime, channel morphology, and physicochemical water quality associated with modified rainfall-runoff patterns and anthropogenic sources of water pollutants. The cumulative effects of these alterations produce an in-stream habitat considerably different from that in which native fauna evolved. In addition, development pressure has a negative impact on riparian forests and wetlands, which are intimately involved in stream ecosystem functioning (Naiman and Décamp 1997). Much evidence of these effects exists from studies of urban streams in the Puget Sound region and around the United States (e.g., Klein 1979, Richey 1982, Karr, Toth, and Dudley 1985, Pedersen and Perkins 1986, Scott, Steward, and Stober 1986, Garie and McIntosh 1986, Steedman 1988, Booth 1990, Booth 1991, Limburg and Schmidt 1990, Booth and Reinelt 1993, Weaver and Garmen 1994).

Here we report on the findings of two investigations, Booth et al. (2001) and Horner May and Livingston (2003) that address linkages between watershed and aquatic ecosystem elements and the capabilities of prevailing management strategies to influence these relationships. These studies covered primarily second- and third-order streams and their contributing watersheds throughout the region. These streams were chosen because of their instrumental role in supporting both the spawning and rearing life stages of several anadromous salmonid species. Together, the two studies collected data on over 200 reaches on almost 90 streams. Both sought not only to understand the connections among watershed conditions, stream habitat characteristics, and aquatic biology, but also to identify strategies to protect and restore these resources.

Stream Management Strategies Derived from Puget Sound Watershed Research

Both Booth et al. (2001) and Horner,May and Livingston(2003) concluded their work with specific recommendations that supply strategies consistent with the Puget Sound Partnership’s Action Agenda and Results Chain strategies. Each study’s strategies were highly consistent with one another (see Appendix 4B) and provide the basis for the following key strategy: Manage stream watersheds using a data- and objective-based approach with appropriate, strategies for streams depending on their levels of ecological condition.

Table B1 (Appendix 4B) assimilates the recommendations of the contributing studies into a catalogue of strategies set up to meet the intent of the Puget Sound Science Update and fit with the Results Chain memo’s structure. Major thrusts of the strategies are reducing the quantities of wet-weather discharges from urban lands and improving the quality of any remaining discharge. Successful implementation of such strategies reduces threats through keeping stream habitats intact, reducing the physical stresses of high flows on stream biota, and decreasing sediment transport resulting from eroded stream channels.

8. Strategies for Stream Restoration


Work to restore the physical habitat and biological communities of streams stretches back decades. This work and its results have been highly documented and the experiences interpreted to formulate extensive guidance on how to perform restoration. Despite this, failures to restore habitats, or even improve them over longer time scales have occurred frequently. Potential reasons for these shortcomings include: the extraordinary complexity of highly dynamic natural systems, the many driving forces operating in these systems not only internally but throughout the climatic and hydrological regimes influencing them, the relative magnitudes and unpredictability of variability in these driving forces and in the biotic and abiotic respondents to them all contribute to the challenges facing restoration efforts. Success in meeting restoration objectives is thus very unlikely if these factors are not appreciated, correctly analyzed, and managed through informed decision making throughout the development of restoration projects.

This segment of Section 3 is concerned with the literature most helpful to understanding the interconnected nature of streams and their contributing watersheds, considerations related to variability, and the techniques available and what they can accomplish.

The prevailing trend in the past has been building in-stream rehabilitation projects to correct localized problems with the objective of improving habitat damaged by altered land use and land cover in the watershed. Isolated problems, such as an improperly sized or configured culvert, are relatively easily identified and corrected. Reversing the consequences of watershed changes, such as channel widening and incision, is a considerably greater challenge, if conditions that led to stream degradation remain unchecked. Nevertheless, many in-stream projects have been constructed in urban or urbanizing basins, attempting to reverse physical and biological degradation in a relatively straightforward and economical manner without addressing the more complex and expensive causes. These projects account for a large share of the failures. All of the references cited here make the point, in one way or another, that the success of any but the most localized in-stream rehabilitation projects is a function of watershed influences. There is no peer-reviewed reference located in the search performed in preparing this chapter claiming otherwise.

The Washington Department of Fish and Wildlife’s (WDFW) Stream Habitat Restoration Guidelines (Saldi-Caromile et al. 2004) observed that stream habitat degradation can be caused by: (1) direct physical modification of the stream corridor; (2) changes in channel boundary conditions upstream, downstream, or laterally; (3) physical constraints placed on natural channel adjustment; or (4) changes in watershed management or land uses. Of course, a combination of any or all of those causes might contribute. These categories also broadly delineate sets of techniques that can be brought to bear to rehabilitate habitat. The circumstances that led to ecosystem decline must be identified, followed by developing a set of realistic goals and objectives to reverse or mitigate the decline. Because of limited resources, it is often necessary to prioritize these goals and objectives to target the dominant factors that prevent the reestablishment of the intended ecological conditions (Saldi-Caromile et al. 2004).

Nilsson et al. (2007) addressed the subject of realistic expectations in restoration efforts, stating that it is not self-evident that restoration should try to mimic attributes of previous ecosystems. They pointed out the issue that humans often have priorities contrary to achieving or approaching a pristine ecosystem state, and that human involvement is much more influential now than ever before. Also, the status of previous systems is difficult to establish for several reasons: (1) often, there are no suitable reference systems to mimic, (2) many catchment qualities have changed since the time period chosen for a historic reference system, (3) changes in climate and biota have been continuous in the past, (4) expected climate change is of uncertain magnitude, (5) non-native species cannot be avoided, and (6) landscape context changes through time. To reduce the risk of mistakes, Hughes et al. (2005) recommended that restoration projects should moderate the ambition of identifying specific target states and instead formulate trajectories that accommodate some levels of both variability and unpredictability; i.e., function in an adaptive management framework.

This discussion of stream restoration proceeds, first, to covering key works to guide the conduct of restoration projects, emphasizing those most pertinent to Puget Sound but also covering references of national and international scope. The section then turns to reports on the effectiveness and relative certainty of restoration. Following a passage on climate change implications to stream restoration, it sums up the lessons offered by the literature in relation to the strategies applicable to Puget Sound’s streams.

Stream Restoration Guiding Principles: Puget Sound

Extended works on stream restoration tend to be of two types: emphasizing principles and case studies, or offering a practices handbook, guiding the selection and installation of materials and processes to be applied for various purposes. The major references mirror the broad reach and complexity of the subject, described above, and present strategies as diverse as the streams and their watersheds. Hence, exposition of detailed aspects of their coverage and highly specific strategy discussions are beyond the scope of this review. Instead, our review concentrates on the general features and areas of coverage from past studies and focuses how they can be used by Puget Sound practitioners.

Guidance Emphasizing Principles and Case Studies

Montgomery et al. (2003) supplies strong intellectual underpinning for assessing, planning, and designing restoration projects for Puget Sound’s streams. The volume provides a highly systematic and well grounded treatment of the subject by multiple authors, proceeding from geological and geomorphological controls on stream characteristics and dynamics; to aquatic biological aspects; onward to chapters addressing social constraints on action; and then to the application of concepts from fluvial geomorphology, civil engineering, riparian ecology, and aquatic ecology to restoration projects. While not comprehensive on structural tools, Montgomery et al. (2003) does have three chapters on various aspects of using wood, a key element of Puget Sound streams often missing or greatly reduced in degraded systems in the region. Rather, it concentrates more on the criteria that must be applied and why (e.g., the complete and prioritized design criteria for an actual project presented by Miller and Skidmore (2003). The book concludes by raising five large questions (Box 3) that the authors recommend be kept in mind to guide restoration, the answers to which they believe will determine the likelihood of success (Bolton, Booth, and Montgomery 2003). The reader is directed to locations within the text to find guidance in formulating answers:

Box 3. Five large questions to guide restoration of rivers and streams in the Puget Sound (from Montgomery et al. 2003)

  1. What is the physical template upon which restoration will take place?
  2. Is the watershed urbanized, agricultural, or forested?
  3. Is the river being restored large or small?
  4. Is there a thorough watershed assessment that identifies historic and current habitat-forming processes and fish distribution?
  5. Has a monitoring plan been developed in concert with the planned restoration action?

Wissmar and Bisson (2003) provided another, more specialized reference of substantial potential use to Puget Sound-region stream efforts. Composed of 12 papers by mostly regional authors, this book’s concern is variability and uncertainty in applying stream restoration strategies. With effective restoration of aquatic habitat depending upon reestablishing watershed and stream processes to a range of variability that maintains dynamic equilibrium (Saldi-Caromile et al. 2004), these considerations are obviously crucial to success, and are informed in theoretical and applied models by the papers collected by Wissmar and Bisson (2003).

Additionally, Darby and Sear (2008) took up the theme of Wissmar and Bisson in 14 more papers on the subject. Most papers include case studies from Europe and North America.

Guidance Emphasizing Practices

WDFW’s Stream Habitat Restoration Guidelines (Saldi-Caromile et al. 2004) begin with a chapter covering watershed processes and stream and floodplain processes and attributes. It lays out some important fundamentals in approaching stream restoration, which are paraphrased here:

Box 4. Fundamentals in approaching stream restoration from Saldi-Caromile (2004)

Channel and floodplain structure, and aquatic habitat, are created, maintained, and destroyed by the energy inherent in high flows. Complex patterns of the resulting sediment erosion and deposition underlie diverse, productive aquatic and riparian habitat. A stream reach in dynamic equilibrium has developed a geometry that balances the energy available for sediment transport with the supply of sediment being delivered to the reach. With this balance, individual channel and floodplain features are created and destroyed but overall channel characteristics such as sinuosity, gradient, width/depth relationships, and pool and riffle frequency are maintained. The stabilizing role of vegetation in channel development and maintenance cannot be overemphasized. Channel complexity, having a large effect on energy dissipation, exerts a major influence on erosion, sediment transport, and deposition, and hence on dynamic equilibrium.

A stream reach undergoing simplification of overall channel characteristics falls into disequilibrium. If the disturbances are temporary, the stream will often recover its former characteristics. Chronic alterations to watershed and stream processes exceeding the natural range of variability of those processes will inevitably alter the stream habitat and ecosystem, eventually to a new, often simplified, equilibrium state. Effective restoration of aquatic habitat depends upon reestablishing watershed and stream processes to a range of variability that maintains a complex channel/floodplain system in dynamic equilibrium.

The lesson for one who would restore a stream, then, is to understand the habitat requirements of the target biota, understand the tolerances of variability to maintain those habitat attributes, and create conditions remaining within those ranges of tolerance. Gaining this understanding implies a need to perform careful watershed, floodplain, and channel assessments as a prerequisite for restoration planning and design. Unfortunately, the WDFW’s assessment chapter remains in a draft, incomplete form. However, stream assessment protocols are numerous; Somerville and Pruitt (2004), contracted by USEPA, reviewed 45 protocols developed for national or regional application. They concluded that a protocol should have the followingcharacteristics:

  • Classification: Stream assessment should be preceded by classification to narrow the natural variability of physical stream variables.
  • Objectivity: The assessment procedure should remove as much observer bias as possible by providing well-defined procedures for objective measures of explicitly defined stream variables.
  • Quantitative methods: The assessment procedure should utilize quantitative measures of stream variables to the maximum extent practicable.
  • Fluvial geomorphological emphasis: Stream assessments undertaken to prioritize watersheds or stream reaches for management or aid the design of stream enhancement or restoration projects should be based on fluvial geomorphic principles.
  • Data management: Data from stream assessments should be catalogued by designated entities in each region of the country.

There has been no Puget Sound regional agreement on a full assessment protocol to support stream restoration. The advice of the USEPA-sponsored review should be taken to settle on the best instrument for the region’s purposes and insert it in the WDFW guidance.

The WDFW manual (Saldi-Caromile et al. 2004) is much more complete in presenting restoration strategies compared to its coverage of assessment. It guides developing and prioritizing goals, objectives, and activities for habitat preservation, restoring habitat-forming processes and connectivity, and modifying and creating stream habitats. It then goes on to elaborate factors to consider when identifying and selecting ecosystem recovery alternatives. Specific approaches are given for restoring sediment supply, the flow regime, energy inputs, water quality, incised and aggrading channels, and salmonid spawning and rearing habitat. The final chapter, the appendices, and a separate series of white papers cover the many techniques, in 15 categories, for achieving restoration goals and objectives. Presentation of each technique includes a description, potential positive and negative physical and biological effects, appropriate applications, risk and uncertainty, design guidance, permitting, construction considerations, costs, monitoring, maintenance, and examples. It also offers general cautionary and cogent advice relevant to any restoration undertaking.

Allied with the WDFW Stream Habitat Restoration Guidelines (Saldi-Caromile et al. 2004) is The Integrated Streambank Protection Guidelines, also from WDFW (WDFW 2003a). These guidelines use a series of sequential or hierarchic matrices to aid in selection of practices applying to the specific restoration task of treating eroding stream banks.

National and International Guidance

The Natural Resources Conservation Service’s (NRCS, 2007a) Stream Restoration Design, National Engineering Handbook, Part 654 is a key reference on the national scale. The handbook is very comprehensive and detailed; but, as its authors regularly caution, the approaches and techniques are not necessarily appropriate in all circumstances. That caution should be particularly taken under consideration in working with Puget Sound’s unique salmonid streams.

Table 2 summarizes the areas of coverage of major works published over the last 15 years devoted mainly to stream restoration principles and general strategies and case studies. All have multiple authorships. The Federal Interagency Stream Restoration Working Group (1998) manual includes coverage of stream assessment and specific techniques for in-stream application, although not in the detail of the NRCS handbook.



Restoration Principles

Stream Processes

General Strategies



Case Study Scope

Brierley and Fryirs (2008)






de Waal, Large, and Wade (1998)






Federal Interagency Stream Restoration Working Group (1998)





None fully developed

Williams, Wood, and Dombeck (1997)





United States

Brookes and Shields (1996)





United States, Europe

9. Effectiveness and Relative Certainty of Stream Restoration

Assessment of In-Stream Habitat Restoration Projects

The tendency throughout most of the history of stream restoration has been to place structures intended to rehabilitate habitat. As a result, most effectiveness evaluations found in the literature concern these practices. Frissell (1997) compiled the results of seven studies of restoration project failures or unanticipated outcomes performed between 1956 and 1992. These projects involved placement of deflectors, check dams, gabions, and/or cover structures in western United States streams draining watersheds disturbed by grazing, mining, or logging without upland mitigation. Majorities of the emplaced structures were damaged or destroyed in every one of the six cases registering physical conditions within 1 to 18 years after installation. Two studies recorded biological (fish or frog) residence, which declined from pre-restoration in both cases. The author attributed the poor results on failure to appreciate the difference between “strategy,” by which he meant comprehensive, large-scale, long-term actions, and “tactics,” which he defined to be a localized, short-term approach.

Brown (2000) examined 22 different types of in-stream restoration practices, involved in more than 450 total installations, classified in four categories: (1) bank protection, (2) grade control, (3) flow deflection or concentration, and (4) bank stabilization. He evaluated each in the field according to the visual criteria structural integrity, function, habitat enhancement, and vegetative stability. He found about 90 percent the practice types to be appropriate for use in the applications investigated, and that around the same proportion of the individual installations remained intact after an average of four years. Unintended scouring or sediment deposition occurred in 20-30 percent of the cases, and less than 60 percent fully achieved habitat enhancement objectives. Most failures were associated with projects that attempted to create different channel plan-form geometry, generally a pre-disturbance channel morphology type superimposed on a stream in a disturbed watershed.

Jacobsen et al. (2007) assessed 163 in-stream and riparian projects completed by the Western Oregon Stream Restoration Program on 285 km (178 miles) of stream during 2002-2004 to boost coho salmon and/or steelhead production. The majority of projects were large wood placements (116), followed by stream fencing (20), fish passage (15), riparian planting (seven) and boulder placement (two). The assessments documented physical changes expected to be beneficial to stream function and productivity of salmonids (there was no direct measurements of fish presence). Most surveys were conducted within one year following treatment. The restoration activities were effective at improving overall habitat complexity and ecological conditions, although a significant increase in quality of over-wintering habitat for juvenile coho salmon was not observed. Fish habitat models (Habitat Limiting Factors Model Version 7.0 and HabRate Version 2.0) did not demonstrate a large increase in habitat quality, apparently at least in part because the amount of off-channel and slow-water pool habitat did not increase significantly, although the treatments increased the complexity of pool habitat.

Installation of large woody debris (LWD) or boulders has become one of the most common techniques to improve fish habitat and compensate for its simplification. LWD, defined4 as a loghaving a mid-point diameter of at least 10 cm, a length of 2 meters, and protruding into the bank-full channel (although sometimes with variations in those dimensions), is particularly important in Pacific Northwest streams. It provides roughness that regulates velocity, cover to fish, and aid in forming pools in which fish feed and rest (McMahon and Hartman 1989). LWD also influences bank stability, sediment retention, and channel grade (Montgomery et al. 1995, Beechie and Sibley 1997, Nelson 1999).

Booth et al. (2001) investigated restoration efforts at six streams, determining the response of invertebrates to LWD placement. The six projects lay in physically similar watersheds but with widely different levels of human disturbance. No anchored LWD moved at any of the project reaches, and where over half of the unanchored logs were key pieces (individual logs with attached root wads) there was also no substantial LWD movement. In the projects with unanchored LWD and few or no key pieces, however, LWD movement was documented. Both types of LWD addition raised pool numbers, at least slightly, towards those of less disturbed streams; but post-project pool spacing was not correlated to LWD loading. Addition of LWD had little demonstrable effect on biological condition as measured by Benthic-Index of Biological Integrity (B-IBI). B-IBI did not increase either when sampling sites were located within or downstream of project boundaries. These results indicate that, although projects several hundreds of meters long improved an important measure of physical habitat (pool spacing) in a stream reach over a time scales of 2-10 years, they had little influence on the benthic invertebrate assemblage.

The effectiveness reports cited thus far lack evaluation of restoration project success in increasing fish productivity. James (2007) attempted to make this connection for Washington State projects having the objective of salmonid population increases. He found that fish passage projects increased adult coho salmon relative abundance and juvenile salmonid densities, but the increases were not statistically significant. In-stream habitat improvement projects significantly increased residual pool metrics, LWD volume, and water surface area. Multiple regression analyses showed relationships between habitat features and fish species distribution, but the author did not report on population changes of the target species before and after restoration projects. James’ (2007) major conclusion was that demonstration of biological outcomes requires monitoring involving more spatial and temporal replication and detailed data using a suite of metrics.

Assessment of a Broad Range of Stream Restoration Techniques

Roni et al. (2002) presented an influential paper that reviewed a wide range of stream restoration techniques and proposed a hierarchical strategy for prioritizing restoration in Pacific Northwest rural watersheds moderately modified by activities like logging and rangeland practices. They placed the techniques in six broad categories: (1) habitat reconnection (e.g., culvert improvements, off-channel connections), (2) road work (e.g., removal, improvement), (3) riparian vegetation restoration, (4) in-stream habitat restoration (e.g., wood and boulder placement), (5) nutrient enhancement, and (6) habitat creation (e.g., in-stream with wood and boulders, off-channel).

In their review, Roni et al. (2002) found that reconnecting isolated off-channel habitats or blocked tributaries provides a quick biological response, is likely to last many decades, and has a high likelihood of success. They recommended that these types of restoration activities be undertaken before methods that produce less consistent results. Riparian restoration or road improvement may not produce results for many years or even decades. Roni et al. (2002) reviewed eight studies documenting LWD or boulder persistence in a functioning state. Two of these studies were also reviewed by Frissell (1997), but seven of the eight in the review of Roni et al. (2002) were more recent, from the 1990s. These authors found a higher rate of success by that point in time, with 85 percent of artificially placed wood remaining in place and contributing to habitat formation. They attributed the improvement to an increased emphasis on replicating natural architecture of wood in streams (creating natural jams or pinning logs between riparian trees), instead of employing artificial structures (e.g., weirs, deflectors), although they noted that the supporting studies were of short duration. The available evidence still suggests that most in-stream structures persist for less than 20 years.

Roni et al. (2002) cite 11 papers summarizing biological evaluations of 29 in-stream restoration projects for anadromous fish in the Pacific Northwest. Post-treatment juvenile abundance for at least one species or life stage increased significantly in 12 streams or was higher in treatment reaches than in control reaches. However, in only five of these studies (six streams) were populations monitored for more than 5 years.

In summarizing their review of the literature on in-stream habitat restoration techniques, Roni et al. (2002) concluded that LWD projects are effective at creating juvenile coho salmon rearing habitat and increasing juvenile densities, but the response of other species is less clear. Although increased spawner densities have been reported in some studies, there are no thorough evaluations of the response of spawning adults to structure placement. Artificial structures such as log weirs and deflectors appear to have moderate-to-high failure rates, and their benefits to fish may be temporary. Therefore, placement of LWD and other material in the stream channel should mimic natural processes by using and placing materials consistent in size, type, location, and orientation to that found in natural channels.

Roni et al. (2002) presented a flow chart depicting a hierarchical strategy for prioritizing specific restoration activities. They advocated implementing first those techniques that have a high probability of success, low variability among projects, and relatively quick response time. As noted above, habitat reconnection was found to meet those criteria best. Riparian restoration and road improvement should be considered after reconnecting high quality, isolated habitats. In-stream LWD and other structural placements should either be undertaken after or in conjunction with reconnection of isolated habitats and efforts to restore watershed processes. The authors noted that their framework may need modification for use in highly altered agricultural and urban watersheds, where some processes cannot be reliably restored or where water quality and hydrologic changes may compromise the effectiveness of many of the commonly employed restoration techniques.

Roni et al. (2002) also note that, while they focused on restoration, it is important not to overlook the need to protect high-quality habitats. This protection should be given priority over habitat restoration, because it is far easier and more successful to maintain good habitat than to recreate or restore degraded habitat.

The reports on in-stream structural projects to improve habitat discussed earlier do not strongly encourage optimism for effective restoration with much certainty. However, the work of Roni et al. (2002) gives a brighter picture, at least for restoring streams not affected by highly altered watershed conditions. The authors’ hierarchical strategy places the major categories of stream restoration activities in context and proper order. They sensibly recommend withholding the prevailing technique of in-stream structural placement at least until habitat reconnection is accomplished, and then implementing that technique by mimicking natural materials and processes. Their advice on giving priority to protection over restoration is particularly pertinent to streams in areas subject to urbanization, which they believe are at a considerable disadvantage for restoration compared to the mostly rural streams in their database.

Further Quantification of Restoration Effectiveness and Relative Certainty

Recently published work further develops the assessment of restoration effectiveness and relative certainty. Two studies (Palmer et al. 2010 and Miller et al. 2010) used statistical and numerical analysis techniques to examine broadly biological responses to restoration actions intended to recover habitat heterogeneity. A third contribution (Stewart-Koster et al. 2010) presented a quantitative decision-making tool to select among restoration alternatives in an environment subject to multiple driving forces.

Palmer et al. (2010) evaluated studies that quantitatively examined the reach-scale response of invertebrate species richness to restoration actions that increased channel complexity and habitat heterogeneity. Adopting these objectives to regain biodiversity has become a dominant paradigm in ecological restoration. This paradigm is reflected in stream restoration projects through the common practice of re-configuring channels to add meanders and adding physical structures such as boulders and artificial riffles. They also evaluated studies that used manipulative or correlative approaches to test for a relationship between physical heterogeneity and invertebrate diversity in streams that were not in need of restoration.They also used habitat and macroinvertebrate taxa richness data from 78 independent stream restoration projects described by 18 different author groups. Most projects were successful in enhancing physical habitat heterogeneity; however, only two showed statistically significant increases in biodiversity rendering them more similar to reference reaches or sites. Studies manipulating structural complexity in otherwise healthy streams were generally small in scale, and less than half showed a significant positive relationship with invertebrate diversity. Only one-third of the studies that attempted to correlate biodiversity to existing levels of in-stream heterogeneity found a positive relationship. Across all the studies evaluated, there is no evidence that habitat heterogeneity was the primary factor controlling stream invertebrate diversity, particularly in a restoration context. The findings indicate that physical heterogeneity should not be the driving force in selecting restoration approaches for most degraded waterways (Palmer et al. 2010). Evidence suggests that much more must be done to restore streams impacted by multiple stressors than simply re-configuring channels and enhancing structural complexity with meanders, boulders, wood, or other structures (Palmer et al. 2010).

Palmer et al. (2010) concluded by observing that, as integrators of all activities on the land, streams are sensitive to a host of stressors, including, depending on the watershed, impacts from urbanization, agriculture, deforestation, invasive species, flow regulation, water extractions, and mining. The impacts of these factors individually or in combination typically lead to a decrease in biodiversity because of reduced water quality, biologically unsuitable flow regimes, dispersal barriers, altered inputs of organic matter or sunlight, degraded habitat, etc. Despite the complexity of these stressors, a large number of stream restoration projects focus primarily on physical channel characteristics. They asserted that this practice is not a wise investment if ecological recovery is the goal and that managers should critically diagnose the stressors impacting an impaired stream and invest resources first in repairing those problems most likely to limit restoration (Palmer et al. 2010). It might be added to the authors’ conclusions that if correcting such problems would require more resources than available, then protection or restoration activities should be pursued elsewhere, where the resources that can be marshaled can make a positive impact with more certainty.

Miller et al. (2010) employed meta-analysis to examine the relationship between restoring physical habitat heterogene¬ity and macroinvertebrate response in terms of diversity and density. Meta-analysis compares results among studies through computation of a common-size effect, scaled by unit variance and weighted by sample size. They analyzed monitoring results from 12 replicated and 14 un-replicated projects, the majority intended to reverse or mitigate the effects of stream channelization. The researchers determined that increasing habitat heterogeneity had significant, positive effects on macroinvertebrate richness. Macroinvertebrate density also increased, although not statistically significantly (Miller et al. 2010). Large woody debris additions produced the largest and most consistent responses, whereas responses to boulder additions and channel reconfigurations were positive, yet highly vari¬able. For example, in the replicated studies richness and density increases were, respectively, 83 and 75 percent greater on average for LWD compared to boulder additions. Among all strategies, the strength and consistency of macroinvertebrate responses were related to land use orwatershed-scale conditions, but appeared independent of project size, stream size, or recovery time.

Stewart-Koster et al. (2010) proposed and demonstrated a solution to the problem of making restoration decisions in the face of multiple system alterations and stressors (e.g., changes in flows, catchment and riparian land-use, habitat degradation, modification of stream energy regimes). Their solution predicts not only the effectiveness of alternative actions but also the relative certainty associated with them. They employed Bayesian networks as a decision support tool for considering the influence of multiple factors on aquatic ecosystems and the relative benefits and costs of various restoration options.

A Bayesian network is a probabilistic graphical model representing a set of factors of a system (nodes) as random variables and their conditional dependencies. The dependencies are depicted as directed links connecting a “parent node” to a “child node.” The network is quantified by populating conditional probability tables associated with the nodes in the network. The table entries can be specified by experts or derived from data. Efficient algorithms exist to draw inferences and perform decision analysis in Bayesian networks. Stewart-Koster et al. (2010) also modified the Bayesian networks to incorporate the relative costs and benefits of potential management actions. Such models are known as Bayesian decision networks and are used interactively to identify the most appropriate decision (here, restoration action) given estimated costs and benefits. A key advantage of Bayesian techniques is that they can easily be operated to give the relative certainty of the predictions.

Reconnecting Habitat by Removing Blockages to Fish Passage

Roni et al. (2002), with some subsequent support by James (2007), established that habitat reconnection projects in general, and fish passage improvement works in particular, are the most effective and certain restoration strategies to improve fish production. Roni et al.(2002) recommended them for first priority among the suite of strategies. Because of their primacy, this segment of the chapter gives brief attention to some specifics of their implementation.

Roni et al. (2002) observed that, among the alternatives for removing blockages, bridges generally allow the free passage of materials and formation of a natural stream channel but are costly. Open-bottom culverts or embedded (e.g., countersunk) pipe-arch culverts allow a natural substrate to form within the channel and are effective at passing both juvenile and adult salmonids (citing Furniss et al. 1991 and Clay 1995). However, such culverts can constrain the stream channel, if the culvert size does not account for large flows or the volume of sediment and wood transported by the stream (citing Robison 1999). Other design options include backwatering culverts at the outlet or inlet and placing baffles within the culvert to reduce flow velocity.

Roni et al. (2002) gave a useful summary of various stream crossing structures and whether or not they allow for juvenile and adult salmonids fish passage and the transport of sediment and LWD or impact stream morphology by constraining the channel (Table 3). The advantage of bridges shows clearly in the table. Otherwise, the bottomless pipe arch and squash pipe or countersunk culvert types supply the most passage benefits, although they still constrain the channel.


Provides Fish Passage For:




Stream Crossing Type























Bottomless pipe arch






Squash pipe or countersunk






Round corrugated, baffled






Round corrugated, no baffles

Yes or Nob

Yes or Nob




Smooth (round or box)






a The degree of constraint depends upon the size of the culvert or bridge relative to the channel and floodplain width.

b Fish passage depends upon culvert slope and length.

The references cited below can be used by qualified scientific and technical personnel to work through an entire fish passage project development, from collecting the needed data, to analyzing and selecting among options, through design, and on to construction and long-term maintenance.

Clay (1995) reviewed fish passage and the techniques to effectuate it under a broad range of circumstances, including at road crossings. He provides an initial primer on culvert designs and methods for retrofitting impassible culverts, although not in sufficient detail for design.

WDFW’s Design of Road Culverts for Fish Passage (WDFW 2003b)serves as guide for designing permanent road-crossing culverts to facilitate upstream fish migration (the manual does not explicitly cover downstream migration). It provides guidance for projects involving new culvert construction as well as retrofitting or replacing existing culverts, laying out the consecutive design steps most likely to be required in a culvert project. The guide emphasizes, as a first step, determining if a culvert is a suitable solution for providing fish passage at the particular site in question. Wherever a roadway crosses a stream, it creates some level of risk to fish passage, water quality or specific aquatic or riparian habitats. Any and all alternatives should be investigated to minimize the number of sites where a roadway crosses a stream, including designing road alignments to avoid crossings and consolidating crossings, with bridges preferred where crossings must occur.

The WDFW handbook (WDFW 2003b) recognizes three design options: (1) No-Slope Design Option, (2) Hydraulic Design Option, and (3) Stream-Simulation Design Option. The No-Slope Design Option results in reasonably sized culverts without requiring much calculation. The Hydraulic Design Option requires hydrologic and open-channel hydraulic calculations, but it usually results in smaller culverts being required than the No-Slope Design Option (smaller culverts may trap more debris, however, and a factor of safety must be applied). The Hydraulic Design Option is based on velocity, depth and maximum turbulence requirements for a target fish species and age classes. The Stream-Simulation Design Option involves constructing an artificial stream channel inside the culvert, thereby providing passage for any fish that would be migrating through the reach. It is difficult in most situations, if not impossible, to comply with velocity criteria for juvenile fish passage using the Hydraulic Design Option. The No-Slope and Stream-Simulation Design options, on the other hand, are assumed to be satisfactory for adult and juvenile passage; thus, they tend to be used more frequently at sites where juvenile fish passage is required. Application of the No-Slope Design Option was determined to be most effective for relatively short culverts at low-gradient sites (WDFW 2003b)

Frei (2006) produced a university thesis that became Federal Highway Administration Hydraulic Engineering Circular (HEC) – 26, a design reference for the classification, design, and installation or retrofit of a stream crossing (culvert or bridge) ensuring fishpassage. The document assumes no particular set of passage criteria; rather, it compiled design options endorsed in different geographic regions to allow the user to select the most appropriate design method for their situation. A collection of design examples and case histories illustrates the design methodology selection. The manual follows a logical progression to guide the reader through the assessment and design process. Culvert and bridge analysis, design, and retrofit techniques are then described, followed by case histories and design examples. Specific requirements of the fish species in question and the hydrologic and geomorphologic circumstances demand that the design for fish passage be considered on a site-by-site basis, all but eliminating the possibility of a “cookie-cutter” design approach. The author noted the diverse expertise needed for a stream crossing effective for fish passage, generally including stream ecology; fish biology; hydrology; and hydraulic, structural, and geotechnical engineering (Frei 2006).

The Federal Highway Administration (FHWA, 2007) issued a synthesis report covering design for fish passage at stream crossings. Extending from HEC – 26, it places culvert design techniques into four categories based on design premise and objectives: (1) No-Impedance techniques, which span the entire stream channel and floodplain; (2) Geomorphic-Simulation techniques, which create fish passage by matching natural channel conditions within the culvert crossing; (3) Hydraulic-Simulation techniques, which attempt to resemble hydraulic diversity found in natural channels through the use of natural and oversized substrate; and (4) Hydraulic-Design techniques, which may utilize roughness elements such as baffles and weirs to meet species-specific fish passage criteria. Preliminary chapters covering the topics of fish biology and capabilities, culverts as barriers, fish passage hydrology, and design considerations aid in the selection of appropriate design techniques based on hydraulic, biological, and geomorphic considerations. A further section presents examples of design techniques fitting the defined design categories. Design examples and case histories for a selection of design techniques are presented next, and are followed by a discussion on construction, maintenance, monitoring, and future research needs. The FHWA synthesis (FHWA 2007) provides comprehensive, highly quantitative guidance and amply represents Washington State methods and examples.

Climate Change and Stream Restoration

The Climate Impacts Group (CIG 2009) used Intergovernmental Panel on Climate Change (IPCC) data predicting Pacific Northwest average temperature and precipitation increases (covered in Chapter 3 of the Puget Sound Science Update) to forecast effects on Washington State hydrology and water resources (CIG 2009). Projections show seasonal river flow timing shifting substantially in snowmelt-dominated and rain-snow mixed watersheds. Although anticipated overall increases are relatively small, a shift is expected to more precipitation in the cooler, wetter season and less in the warmer, drier season. This shift translates to proportionately greater runoff increases, because of the higher efficiency of cool-season precipitation in producing runoff, a phenomenon associated with the lower available soil moisture storage capacity and vegetative demand for water in the cooler season.

The CIG (2009) runoff predictions were applied to estimate stream flow for four snow-rain mixed Puget Sound rivers (the Cedar, Sultan, Tolt, and Green rivers). Stream flow is a quantity related to but differing from runoff, because of the time-lag effect associated with the intervening hydrologic processes. Modeling showed a consistent shift in the hydrographs of all four basins toward higher cool-season and lower warm-season discharges (CIG 2009)

The aforementioned temperature and hydrologic predictions were applied to evaluate the sensitivity of Pacific salmon (Oncorhynchus spp.) (Mantua et al. 2009). It is expected that the combined effects of warming stream temperatures and altered flows will reduce the reproductive success of many salmon populations, but vary according to life histories and watershed characteristics. Populations with extended freshwater rearing periods (steelhead [Oncorhynchus mykiss], coho [Oncorhynchus kisutch], sockeye [Oncorhynchus nerka], and summer Chinook [Oncorhynchus tshawytscha]) were forecast to experience large increases in summer-time thermal and hydrologic stresses (Mantua et al. 2009). Other populations with brief freshwater rearing periods were projected to exhibit the greatest productivity declines in snow-rain mixed rivers, where anticipated increased winter flood magnitudes and frequencies will reduce egg-to-fry survival rates. Summer chum salmon (Oncorhynchus keta) are especially vulnerable because of their reliance on small, shallow streams in the late summer and early fall (Mantua et al. 2009). The Lake Washington Ship Canal is already thermally impaired and inhibiting to certain adult and juvenile salmon migrations, a condition expected to be aggravated in the future.

Mantua et al. (2009) note that many of the hydrologic processes highly sensitive to climate change are also known to be similarly sensitive to land and water use impacts. They went on to recommend as strategies to mitigate stream temperature increases:

  1. Reducing water withdrawals in warm, low-flow periods
  2. Restoring floodplain functions that recharge aquifers
  3. Protecting and restoring thermal refugia provided by groundwater and tributary inflows, undercut banks, and deep pools
  4. Restoring riparian shade
  5. Protecting and enhancing summer in-stream flows (e.g., by strategic reservoir releases)

Their recommended strategies to reduce risks to salmon by elevated fall and winter flows included:

  1. Protection and restoration of off-channel habitat in floodplains as refugia
  2. Limiting expansion of effective impervious area
  3. Retaining watershed forest cover
  4. Operating reservoirs to reduce flooding.

Ormerod (2009) put forth similar recommendations in considering river management on the world-wide scale in the climate-change era, emphasizing increasing landscape-scale connectivity, reducing population vulnerability to other negative effects, and strengthening protected-area networks.

Battin et al. (2007), preceding the work by CIG (2009), used a series of linked models of climate, land cover, hydrology, and salmon population dynamics to investigate the impacts of climate change on the effectiveness of proposed habitat restoration efforts designed to recover depleted Chinook salmon populations in the Snohomish River basin. Their results were in accord with the subsequent work in predicting thermal impacts and hydrologic shifts negatively affecting salmon spawning and incubation, a large negative impact on freshwater salmon habitat, and the particular vulnerability of snow-rain mixed rivers. With the most pronounced effects expected to occur in high-elevation streams with a generally high level of protection through federal ownership and little restoration potential, restoration efforts will be mounted at lower elevations. The authors expect that the combination of extensive impacts high in watersheds and restoration concentrated at lower altitudes will cause a spatial shift in salmon abundance (Battin et al. 2007).

Battin et al. (2007) also used their suite of models to examine the interaction between climate andrestoration effects for three future (i.e., 2025) land-use scenarios: a scenario representing no change from “current” (2001) conditions, one based on a linear future projection of current land-use change and population trends that includes the completion of current restoration projects but no further restoration (“moderate restoration”), and a scenario in which all restoration targets in the restoration plan are met (“full restoration”). The moderate restoration scenario resulted in slightly higher minimum spawning flows and incubation peak flows but lower pre-spawning temperatures than the current scenario. The full restoration scenario resulted in somewhat lower incubation peak flows, with little change in pre-spawning temperatures. Spawning flows decreased slightly under the full restoration scenario because of greater evapotranspiration from the increased forest cover. The authors concluded that although expected climate impacts cannot be mitigated entirely, habitat restoration can play an important role in offsetting those effects.

Palmer et al. (2009) wrote that the anticipation of climate change impacts requires a proactive management response if valuable river assets are to be protected. Furthermore, a proactive response requires sound monitoring and predicting capabilities at the scales that management actions can be applied, which, they believe, is almost always at the local watershedscale (Palmer et al. 2009). They recommend such an approach because of evidence that factors such as urbanization will interact with climate change in ways that are likely to determine the impacts to aquatic biota (Nelson et al. 2009). Increased efforts at both protection and restoration are major components of the program they recommend. In lower-elevation areas, they contend that increasing protection of and restoring floodplains and riparian corridors will not only provide protection for river ecosystems but also will reduce the impacts of both floods and droughts on humans. Giving more watersheds protected status, particularly those at higher elevations expected to experience the most dramatic climate changes, can thus provide refuge habitat for species under multiple threats (Palmer et al. 2009).

10. Synthesis of Stream Restoration Strategies

In-stream restoration strategies summarized here directly address multiple threats to Puget Sound’s tributary streams, including restriction of anadromous fish passage, salmon spawning and rearing habitat degradation, and stream food web disruption. To the extent that watershed restoration accompanies in-stream rehabilitation, strategies address the additional threats of stream channel modification; acute and chronic toxicity effects on aquatic organisms from metal and organic pollutants; and increased pollutant loadings to all downstream waters, including Puget Sound.

The strategies are drawn from the literature reviewed above and are framed in a process of assessment of problems and conditions, development of restoration concepts, and design of restoration elements. In general, problems fit into the categories of physical modification of the stream corridor, changes in channel boundary conditions, physical constraints on channel adjustment, watershed changes in management, or a combination (see Saldi-Caromile et al. 2004). Montgomery et al. (2003) can be consulted to guide assessment of the type and extent of problems, and then to move toward concept development. The forecasts of the Climate Impacts Group (2009) and future work by that group can inform future assessment and concept development.

The literature exhibited a strong consensus that, before restoration proceeds, consideration be given to protecting well functioning streams and their habitats as well as necessary actions in the contributing watershed to achieve restoration goals and objectives. A corollary is that if these actions are infeasible for any reason and cannot be performed, that goals and objectives be adjusted to what is attainable without mitigation of watershed-based problems.

A key component of overall watershed restoration is rehabilitation of the riparian zone, which as shown by the research reported above, must be relatively wide, continuous, and covered by mature vegetation to advance effective restoration of the adjacent stream. Once possible in-stream options are identified, the hierarchical strategy of Roni et al. (2002) is a mechanism to prioritize among them in relation to assessment results. That strategy emphasizes habitat reconnection as generally the most effective and certain of in-stream strategies, where prior disconnection is among the problems. The strategy then guides a user through consideration of riparian restoration and road improvements, with in-stream structural placements to follow or occur simultaneously with any of the other actions, as appropriate.

In complex cases involving multiple stressors, including climate change, the Bayesian approach of Stewart-Kloster et al. (2009) holds promise as a means of objectively assessing effectiveness and relative certainty of alternative actions. Papers in Wissmar and Bisson (2003) and Darby and Sear (2008) can also assist in grappling with variability and uncertainty.

Key Strategy: Synthesis of guiding principles for stream restoration
  • Protect well functioning streams and their habitats, where they exist.
  • Consider which actions are necessary in the contributing watershed to achieve restoration goals and objectives.
  • Identify in-stream restoration options and apply the hierarchical strategy of Roni et al. (2002) to prioritize among them. That strategy emphasizes habitat reconnection as generally the most effective and certain of in-stream strategies, where prior disconnection is among the problems. The strategy then guides a user through consideration of riparian restoration and road improvements, with in-stream structural placements to follow or occur simultaneously with any of the other actions, as appropriate.

11. Strategies for Wetlands Management


Over the past half century it has been recognized that wetlands, once thought to be nuisances, perform functions beneficial to the broader environment and its inhabitants, including humans. Functions are defined as the physical, biological, chemical, and geologic interactions among different components of the environment that occur within a wetland. There are many valuable functions that wetlands perform but they can be grouped into three broad categories: functions that improve water quality, functions that change the water regime in a watershed, and functions that provide habitat for plants and animals (Box 5)(Sheldon et al. 2005).

Box 5. Examples of wetland ecological functions (from Sheldon et al. 2005)

  • Capture pollutants that would otherwise travel farther;
  • Store flood waters;
  • Recharge groundwater in some cases and provide a passageway for groundwater to supplement surface flows in others;
  • Produce food through plant photosynthesis that is often exported to nourish downstream waters; and
  • Provide breeding grounds, feeding sites, and sometimes permanent homes for invertebrates, amphibians, birds, and mammals.

A great deal of work has been devoted to methods to establish the type and extent of the functions performed by wetlands. This work culminated in the development of the Hydrogeomorphic Method (HGM, Brinson 1993), which classifies a wetland based on its landscape setting, water source, and internal water dynamics. HGM was adapted for regional application by the Washington State Wetlands Function Assessment Project5

As a consequence of their functions, threats to wetlands become threats not only to their internal ecosystems but also to waters and even terrestrial environments associated with them throughout the Puget Sound ecosystem. Therefore, protection and restoration of wetlands very broadly counters threats associated with their many functions (see Box 5). In turn, strategies to protect and restore wetlands support an array of broader strategies, essentially all of those discussed earlier in this chapter because of the intimate association of wetlands with streams. Protecting or recovering specific functions, at particular levels, is the natural basis for setting wetland restoration objectives.

While it is obvious that creating something new is generally a harder task than improving something already at least partially functioning, success in protecting, restoring, and creating wetlands depends on the principles put forth by Sheldon et al. (2005): the system must have the structural elements needed to support the intended functions. These elements are the general climate, the geomorphology (topography, landforms, soils, and geology), the source of water, and the movement of water. These factors affect wetland functions directly or through a series of secondary factors, including nutrients, salts, toxic contaminants, temperature, and the connections created between different patches of habitat (Sheldon et al. 2005).

Here we employ the general term “wetlands management” to refer to protection, restoration, and creation of wetlands, when the subject pertains to all of those facets. This selection of terminology is because of the overlapping nature of many considerations for success in any of these areas and a desire to avoid repetition of the three in many places.

Wetlands science and management are very well developed in Washington State. The Washington Department of Ecology (WDOE) has had an active wetlands program for many years. WDOE, with other partners, has supported extensive research to advance the science on specific questions and inform its management and regulatory efforts. The program has assimilated the results of this regional research, as well as findings from the broader literature, to report on virtually every aspect of wetlands science and management pertinent to this valuable Puget Sound resource. WDOE went on to develop guidance for its own and local government staff and private parties regarding the protection and restoration of wetlands and mitigation of their losses. The resulting documents total many hundreds of pages rich in information. More important than their length is their rooting in “best available science.” Recapping this record is beyond the scope of this review and, moreover, is unnecessary given its effective reporting in the source documents. Accordingly, the review is confined to drawing out strategies related to the PSP Action Agenda and Results Chain memorandum and pointing out supporting material in these documents.

A major study performed under WDOE and other sponsorship was the Puget Sound Wetlands and Stormwater Management Research Program. This work spanned 11 years and produced numerous papers and a book recounting the entire process and its results, conclusions, and recommendations (Azous and Horner 2001). It was designed similar to the stream research covered extensively earlier, in that physical, chemical, and biological variables were measured in wetlands subject to a broad range of watershed urban development.

Wetlands Management Guidance

Two principal documents published by the Washington Department of Ecology provide background and guide protection and restoration of Puget Sound’s wetlands (Sheldon et al. 2005, Granger et al. 2005). First, Sheldon et al. (2005) describe the state’s wetlands and how they function. The authors elucidate how human activities disturb wetlands and the resulting negative impacts on their functioning. They then turn to the science behind wetlands management, including mitigation, and the effectiveness of the available tools. The management section emphasizes wetland buffers, relatively undisturbed surround lands offering important protective benefits. They also examine cumulative impacts and recommended responses to counter them. Second, Granger et al. (2005) lay out a framework for managing wetlands using best available science. They emphasize that the first step is analyzing wetlands in a landscape context, which they frame as a series of questions with guidance to obtaining the needed answers (Granger et al. 2005). Individual chapters cover regulatory and non-regulatory solutions to reduce and risks from human activities. They conclude by discussing implementation, monitoring, and adaptive management (Granger et al. 2005).

For mitigating wetlands losses, two additional, more specialized documents are available from WDOE: “Wetland Mitigation in Washington State, Part 1: Agency Policies and Guidance” (WDOE 2006a) and “Wetland Mitigation in Washington State, Part 2: Developing Mitigation Plans” (WDOE 2006b). Part 1 explains the regulatory requirements, and Part 2 provides a more qualitative and descriptive basis for developing mitigation plans. Designed for use by qualified and experienced technical experts, the two-part series is topically comprehensive to bring in the full range of considerations that must be considered to produce effective mitigation for losses of wetland area and functions including mechanisms like mitigation banking and in lieu payments to compensate for losses. More general information is contained within Wetlands by Mitsch and Gosselink (2007) and its companion volume, Wetland Ecosystems by Mitsch et al. (2009).

Effectiveness and Relative Certainty of Wetlands Management Efforts

Research Basis for Effectiveness and Certainty Assessment

The Puget Sound Wetlands and Stormwater Management Research Program has performed research with the goal of deriving strategies that protect wetland resources in urban and urbanizing areas, while also benefiting the management of urban stormwater runoff that can affect those resources (Chin 1996, Horner et al. 1997, Reinelt et al. 1998, Azous and Horner 2001). The research consisted of long-term comparisons of wetland ecosystem characteristics before and after their watersheds wereurbanized, and between a set of wetlands that became affected by urbanization (treatment sites) and a set whose watersheds did not change (control sites). This work was supplemented by shorter term and more intensive studies of pollutant transport and fate in wetlands and several laboratory experiments. These research efforts were aimed at defining the types of impacts that urbanization can cause and the degree to which they develop under different conditions, in order to identify means of avoiding or minimizing impacts that impair wetland structure and functioning. The program's scope embraced both situations where urban drainage incidentally affects wetlands in its path, as well as those in which direct stormwater management actions change wetlands' hydrology, water quality or both.

A major finding of the Puget Sound Wetlands and Stormwater Management Research Program was a decline in the biotic diversity of wetlands associated with increase in water level fluctuations (WLF) and increasing total impervious area (TIA) within the contributing basins (Chin 1996, Horner et al. 1997, Reinelt et al. 1998, Azous and Horner 2001) (see Appendix 4C for supporting material).

Horner et al. (1997) found that an increase of mean annual WLF above 20 cm and a near certainty with TIA > 21 percent resulted in significant decreases in wetland biodiversity (Horner et al. 1997). WLF above 22cm was also negatively correlated with vegetation species richness in emergent vegetation and scrub-scrub wetland habitats. Species richness for both wetland plants and amphibians in wetlands exhibited the same trends as invertebrates and fish in streams with respect to watershed urbanization such that higher levels of wetland health were observed only in watersheds with less urbanization but allow-urbanization sites did not necessarily have healthy wetlands; on the other hand, a lower levels of biological integrity were consistently observed at high levels of urbanization (Horner et al. 1997).

Wetland “hydroperiod” comprises not only the extent but also the frequency and duration of water level fluctuations. In wetlands studied before and after urbanization increased, the frequency and duration of excursions (deviations from) a certain level above or below the pre-existing mean water level were also associated with biodiversity decline (Azous and Horner 2001). Marked plant species richness decrease was seen whenmore than six excursions per year were > 15 cm above or below the pre-existing level, and with any excursion of that magnitude lasting more than 72 hours. Those conditions occurred in the majority of cases when mean annual WLF rose above 24 cm and 20 cm, respectively. Fewer plant species were also recorded if the summer dry period increased or decreased by more than two weeks from the pre-existing length. For amphibians, decrease in species numbers occurred with excursions of > 8 cm for more than 24 hours in any 30 day period in the breeding season (February 1 to May 31) (Azous and Horner 2001).

Other research efforts have found wetland hydrology and hydrodynamics to be functions not only of characteristics of the contributing watershed but also of three aspects of the wetland geomorphology: (1) hydrodynamic type (open water or flow through), (2) outlet constriction (high, moderate, or low), and (3) wetland-to-watershed area ratio (Reinelt et al. 2001, Reinelt and Taylor 2001). Wetlands were classified as the open-water type if substantial pools without emergent vegetation were present, channelization was largely absent, and water velocities were predominantly low (< 5 cm/s). High outlet constriction was characterized by having an undersized culvert or confining beaver dam or by being a completely closed depression. Low constriction was marked by free discharge as sheet flow, over a broad bulkhead, or via an oversized culvert. Wetlands small in area compared to their watersheds (comprising < 5 percent of total area) tend to be dominated by surface inflows, whereas groundwater influence assumes greater importance with relative enlargement of the wetland. Outlet constriction was found to the most important geomorphic variable in controlling WLF (Reinlet and Taylor 2001).

Another major result of the Puget Sound Wetlands and Stormwater Management Research Program was cataloging the maximum, median, and minimum water levels at which nearly 100 vegetation species were found (Cooke and Azous 2001; for details see Appendix 4C, Table C1). While many species occurred over a wide hydrologic range, others were only observed within a narrow range.

Wetland management guidelines were formulated from these and other results of the Puget Sound Wetlands and Stormwater Management Research Program (Horner et al. 2001) and were adopted into the Washington Department of Ecology’s Stormwater Management Manual for Western Washington (WDOE 2005). Wetland protection efforts, as well as attempts to restore wetlands or create new ones, can be designed with the use of this information; and their prospective effectiveness and its relative certainty can be judged accordingly. Another important feature of the guidelines was advice on protecting wetlands from adverse impacts resulting from altering the quantity or quality of entering water (WDOE 2005).

Reported Wetland Mitigation Effectiveness

The Washington State Wetland Mitigation Evaluation Study (Johnson et al. 2000, Johnson et al. 2002) was developed in two phases to evaluate the success of projects intended to compensate (mitigate) for wetlands lost to development activities in the state of Washington. In the first phase of the study Johnson et al. (2000) examined the compliance of 45 randomly selected projects with their permit requirements. Permit compliance for each of the 45 compensatory wetland mitigation projects was evaluated relative to three questions: 1) Was the compensatory mitigation project implemented, 2) Was it implemented according to plan. and 3) Was it meeting its performance standards. They found that overall, 29 percent of projects were in full compliance with all three criteria (Johnson et al. 2000). Forty-two projects (93 percent) were implemented, and of those, 55 percent were implemented according to plan. However, only 35 percent were meeting all performance standards (Johnson et al. 2000).

In the second phase of the study, Johnson et al. (2002) examined the ecological functions of a subset of 24 projects. The ecological success of mitigation projects was evaluated based on two factors, each with its own criteria: First, achievement of ecologically relevant measures (establishing the required wetland area, attaining ecologically significant performance standards, and fulfilling goals and/or objectives); and second, adequate compensation for the loss of wetlands (contribution of the mitigation activity to the potential performance of functions, comparison of the type and scale of functions provided by the mitigation projectwith the type and scale of lost wetland functions). They found that based on these criteria, only 13 percent of the projects were judged to be fully successful, 33 percent were moderately successful, 33 percent were minimally successful, and 21 percent were unsuccessful. Created wetlands were found to be more successful thanprevious studies had shown, with 60 percent at least moderatelysuccessful and only one project unsuccessful. In contrast, no enhancement projects were fully successful, while eight out of nine (89 percent) enhanced wetlands were minimally successful or unsuccessful. For wetland restoration and creation projects together only 65 percent ofthe total acreage of wetlands lost was replaced (Johnson et al. 2002).

The NRC committee on compensating for national wetlands losses reported that from 1993 to 2000 approximately 24,000 acres of wetlands were permitted for filling, and around 42,000 acres of compensation was specified (NRC 2001). However, because of lack of recorded data, the committee was unable to establish the original wetland functions lost or even how much of the specified area was actually restored or created. Nevertheless, their investigations produced a number recommendations that if adopted would likely improve mitigation success. Key scientific recommendations relative to wetland functioning, in summary form are listed in Box 6.

Box 6. Recommendations for improving mitigation success from NRC (2001)

  • Wetland conservation and mitigation should be pursued on a watershed scale.
  • Biological dynamics should be evaluated in terms of population present in reference wetlands for the region and the ecological requirements of those species.
  • Hydrologic functioning should be incorporated into mitigation design and should also be based on comparison to reference sites.
  • Provide appropriate, heterogeneous topography.
  • When establishing vegetation, pay particular attention to planting elevation, depth, seasonal timing, and soil.
  • Mitigation goals must be clear, and those goals should be carefully specified in terms of measurable performance standards.
  • Third-party compensation approaches (e.g., mitigation banks, in lieu fee programs) offer some advantages over permittee-responsible mitigation and should be further evaluated according to a taxonomy developed by the committee.

Climate Change Implications for Wetlands

The anticipated results of climate change covered earlier with reference to streams also have implications for wetlands. The expected shift to more precipitation in the cooler, wetter season and less in the warmer, drier season was projected to produce proportionately greater runoff increases, because of the higher efficiency of cool-season precipitation in producing runoff, and higher cool-season and lower warm-season stream flows (Elsner et al. 2009). These effects could increase the magnitude, frequency, and duration of wetland water level fluctuations. To the extent these increases alter conditions outside their preferred and tolerated ranges, wetland plant and amphibian communities could be affected, generally in the direction of reduced species richness. Such occurrences would make more difficult the protection of existing biodiversity and wetland functions and restoration efforts to recover higher levels.

The projected higher summer temperatures and lower runoff would together tend to increase wetland drying, perhaps introducing a dry period in wetlands where one previously did not happen and increasing its length in those already experiencing one. As the research revealed, plant species presence is likely to be lower with any lengthening beyond two weeks (Azous and Horner 2001).

Synthesis of Strategies for Wetlands Management

The two WDOE volumes covering wetlands management overall (WDOE 2006a, WDOE 2006b) and two additional mitigation documents (Johnson et al. 2000 and Johnson et al 2002), introduced earlier, provide guiding frameworks to implement wetlands protection, restoration, and creation strategies. These works can be supplemented by specific results from the literature and the expertise to put them into appropriate use to achieve the set objectives. The Mitsch and Gosselink (2007) text, the HGM-based functional assessment procedure built into WDOE’s program, the recommendations from NRC (2001), and the Puget Sound Wetlands and Stormwater Management Research Program results reported here are foundations for designing and implementing strategies to manage Puget Sound’s wetlands to advance the PSP’s program.

Together, these studies demonstrate that the physical tolerances of target biological communities must be met in orderto retain or recover these communities, which can only occur if the major factors controlling those influences (climate, geomorpology, and the source and movement of water) are consistent with supplying them. Urbanization and the projected climate change effects described here will clearly have a bearing and must be considered in strategies for wetland protection, restoration, and creation.

Importantly, the body of research we discuss here points to the primacy of hydrologic and hydroperiod preferences and tolerances in governing community maintenance and development and provides specific quantitative specifications supportive of plants and amphibians (e.g., Chin 1996, Horner et al. 1997, Reinelt et al. 1998, Azous and Horner 2001). Establishing hydrologic and hydroperiod variables usually requires the use of computerized models capable of continuous pattern simulations based on meteorological input data, especially for restoration and wetland creation projects. The Western Washington Hydrologic Model (WDOE 2005) is one such model available for this task. Exerting control over those variables will require the application of stormwater management strategies described later in this chapter.

As pointed out above, wetland geomorphology includes the topography, landforms, soils, and geology (Reinelt et al. 2001, Reinelt and Taylor 2001). Scientists and engineers working to protect, restore, or create wetlands have a relatively high degree of control over the first two of those variables. They also have some influence over soils, which can be altered in wetland restoration and creation projects through mineral and organic amendments.

The general topography of a wetland is best represented by its side slopes, which tend to be quite gradual (e.g., ~12 horizontal:1 vertical) in natural wetlands. Wetlands have often been created on more of a “farm pond” model with much steeper side slopes (e.g., ~4 horizontal:1 vertical). If these two configurations received identical inflow volumes, the resulting depth would be much greater (on the order of twice, depending on dimensions) in the latter compared to the first case. It is highly likely in this scenario that the preferences and tolerances of some biota present in the first wetland would not be reproduced in the second, meaning those organisms probably would not thrive there or would be absent entirely. This single factor is probably the leading explanation for some of the numerous documented wetland mitigation failures. A strategy of designing structural features of created and restored wetlands according to those seen in one or more reference natural wetlands can avoid these errors.

Hydrological features such as outlet constriction, pool-and-channel pattern, and wetland-to-watershed area ratio have all been demonstrated toaffect hydrology and hydroperiod (Reinelt et al. 2001, Reinelt and Taylor 2001). If the outlet is unfavorable to internal conditions, it is relatively easy to change it, to protect existing wetland functions, or design one conducive to the functional objectives being pursued in a restoration or creation project. The latter activities also give latitude to form or reform the internal structure. There is less possible control over the area ratio, but designers must be cognizant of its strong influence on hydrology, quantify that influence properly, and design to manage it in relation to objectives.

Key Strategy: Protect, restore, and create wetlands according to the known preferences and tolerances of target biological communities, particularly geomorphic, hydrological, and hydroperiod requirements.

12. Strategies for Management of Lakes

As the location of one of the most well-known lake eutrophication and recovery episodes in the world, the Puget Sound area has long been a center of research on the negative effects of waste discharges to lakes, the resulting deterioration, and restoration strategies. Lake Washington had received discharges from municipal wastewater treatment plants around its shore for approximately 10 years when its deteriorating condition became increasingly evident. Two references that generally describe the recovery process and the shift in nutrient dynamics, algal populations and water clarity are Cooke et al. (2005) and Welch and Jacoby (2004). The entire decline and recovery was meticulously studied and documented by Thomas Edmondson and his associates at the University of Washington and provided some of the most complete and conclusive early evidence of the role of phosphorus in lake trophic (nutritional) dynamics.

Lake Washington’s recovery was rapid for several reasons: its relatively great depth, rapid flushing rate, short history of enrichment, and the low phosphorus content of its major tributary, the Cedar River. These circumstances are not typical, and neither is the pattern of recovery. Lake Sammamish also went through a eutrophication episode, related to a municipal treatment plant and dairy waste, and recovered more slowly because of differing conditions but eventually to about the same degree. This experience, and others in many lakes, produced sufficient understanding that the results of changing the enrichment of a lake, in either the positive or negative direction, are fairly predictable. A number of restoration techniques exist. While a lake’s particular situation determines the best selection and its prospects for success, the state of lake science is such that a strong basis exists to assess the situation, select a technique, and forecast the results with a greater degree of certainty than often is the case with natural ecosystems.

Excellent resources exist to guide lake analysis and restoration assessment. Because of the extensive work here, they have a strong regional flavor. Among many volumes that could be consulted for analysis, Welch and Jacoby (2004), and specifically its Part II on Effects of Pollutants in Standing Water, is recommended for comprehensiveness, practicality, and blend of regional and worldwide content. Chapter 7 (Eutrophication) provides straightforward mathematical expressions and criteria to classify a lake’s trophic status and begin to make decisions about its management and possible restoration. Cooke et al. (2005) provide the detailed science on lake restoration, covering the full range of methods with a similar approach, numerous case studies, and coverage of issues of effectiveness and relative certainty. They divide their presentation of restoration strategies into algal biomass control, control of macrophytes (emergent, submergent, or floating aquatic plants), and treatments for multiple benefits (see Appdendix 4D, Box D1 for details of algal biomass control) and form the basis for the following key strategy: Key Strategy: Protect and restore lakes applying the established specific strategies of algal biomass and macrophyte control.

13. Urban Stormwater Management Strategies


Stormwater runoff in general, and the component of that runoff from urban lands in particular, has emerged as an issue of widespread concern in the Puget Sound region since urban stormwater runoff is a major source of toxic chemicals in the marine waters of Puget Sound (HartCrowser 2007, Envirovision 2008, WDOE 2008, PSP 2010).

Both national (e.g., the Nationwide Urban Runoff Program [NURP], USEPA 1983) and regional research (e.g., Mar et al. 1982) have shown that storm runoff from developed lands threatens not only flooding but also the water quality of streams, lakes, and marine waters receiving the discharge. With their roots in flood control engineering, it was natural than early stormwater managers would turn to structural solutions to the newly recognized problems. Holding runoff in a detention pond for a time and releasing it more slowly than flow off urban surfaces became the favored response to reduce peak flow rates, and hence the erosive shear stress built up in streams. For water quality improvement USEPA’s (1983) NURP highlighted “wet ponds,” basins that maintain a permanent (or semi-permanent) pool and hold runoff for an extended period, giving pollutant removal mechanisms an opportunity to function. These measures prevailed over the first 20 years of modern stormwater management, until ideas about “low-impact development” began to coalesce, at first in Maryland (Prince George’s County 1999). As explained in much more detail below, low-impact development (LID) is a system of practices aimed at avoiding runoff above pre-development quantities and its contaminants from being generated in the first place or preventing it from discharging off-site by exploiting the capabilities of vegetation and soil to mimic pre-development site hydrology. This approach contrasts with traditional methods, which are oriented more toward structural end-of-pipe control.

A National Academy of Sciences committee recently reviewed the entire history and status of the nation’s urban stormwater management program. The committee’s report (NRC 2009) identified numerous problems with the program and made many corrective recommendations, some of which are listed in Box 7. These recommendations lay the groundwork for the specification of detailed strategies to counter the multiple negative effects of urban stormwater runoff on Puget Sound and its tributary waters.

Box 7. Recommendations from NRC (2009) for urban stormwater management:

  • Individual controls on stormwater discharges are inadequate as the sole solution to stormwater in urban watersheds. Storm-water control measure (SCM)6 implementation need to be designed as a system, integrating structural and nonstructural SCMs and incorporating watershed goals, site characteristics, development land use, construction erosion and sedimentation control, aesthetics, monitoring, and maintenance.
  • Nonstructural SCMs such as product substitution, better site design, downspout disconnection, conservation of natural areas, and watershed and land-use planning can dramatically reduce the volume of runoff and pollutant load from a new development. Such SCMs should be considered first before structural practices.
  • SCMs that harvest, infiltrate, and evapotranspire stormwater are critical to reducing the volume and pollutant loading of small storms.

The most effective solutions are expected to lie in isolating, to the extent possible, receiving water bodies from exposure to impacts such as stream channel modification, degradation of salmon spawning and rearing habitat, disruption of the stream food web, exposure to toxic pollutants, and increased pollutant loading to downstream waters including the Puget Sound. In particular, low-impact design methods, termed Aquatic Resources Conservation Design (ARCD) in this report, should be employed to the fullest extent feasible and backed by conventional SCMs when necessary.

Here we first explore the most highly recommended LID-based strategies followed by the conventional end-of-pipe practices. Available effectiveness and relative certainty data are presented for both strategy categories. This account supports development of PSP Results Chain strategies for flow protection and stormwater control enumerated in Neuman et al. (2009).

Aquatic Resources Conservation Design (ARCD) Strategies7

Aquatic Resources Conservation Design (ARCD) Strategies (NRC (2009) are more encompassing than Low-Impact Development (LID) because ARCD signifies that the principles and many of the methods apply to both building on previously undeveloped sites as well as redeveloping and retrofitting existing development. Additionally, incorporating aquatic resources conservation helps reinforce the main reason for improving stormwater regulation and management. ARCD encompasses the all practices that can be used to reduce negative imp1acts of urban runoff ; i.e., “… the full suite of practices that decrease surface runoff peak flow rates, volumes, and elevated flow durations, as well as those that avoid or at least minimize the introduction of pollutants to any surface runoff produced” (NRC 2009, p. 406). Reducing the concentration of pollutants and volume of runoff reduces the cumulative amount of pollutants released into receiving waters.

According to the NRC (2009) report “…ARCD practices begin with conserving existing vegetation and soils, as well as natural drainage features (e.g., depressions, dispersed sheet flows, swales). Clustering development to affect less land is a fundamental practice advancing this goal. Conserving natural features would further entail performing construction in such a way that vegetation and soils are not needlessly disturbed and soils are not compacted by heavy equipment. Using less of polluting materials, isolating contaminating materials and activities from contacting rainfall or runoff, and reducing the introduction of irrigation and other non-stormwater flows into storm drain systems are essential. Many ARCD practices fall into the category of minimizing impervious areas through decreasing building footprints and restricting the widths of streets and other pavements to the minimums necessary. Water can also be harvested from impervious surfaces, especially roofs, and put to use for irrigation and gray water system supply. Harvesting is feasible at the small scale using rain barrels and at larger scales using larger collection cisterns and piping systems. Relatively low traffic areas can be constructed with permeable surfaces such as porous asphalt, open-graded Portland cement concrete, coarse granular materials, concrete or plastic unit pavers, or plastic grid systems. Another important category of ARCD practices involves draining runoff from roofs and pavements onto pervious areas, where all or much can infiltrate or evaporate in many situations” (NRC 2009, p.407).

Following the initial application of ARCD, any excess site runoff could be a candidate an array of techniques to reduce the quantity through infiltration and evapotranspiration (ET) and improve the quality of any remaining runoff. “Natural soils sometimes do not provide sufficient short-term storage and hydraulic conductivity for effective surface runoff reduction because of their composition but, unless they are very coarse sands or fine clays, can usually be amended with organic compost to serve well” (NRC 2009, p. 407).

The NRC (2009) report recommends that “ARCD practices be designed to be applied as close to sources as possible to stem runoff and pollutant production near the point of potential generation. However, these practices must also work well together and, in many cases, must be supplemented with strategies operating farther downstream. For example, the City of Seattle, in its “natural drainage system” retrofit initiative, built serial bioretention cells flanking relatively flat streets that subsequently drain to “cascades” of vegetated stepped pools created by weirs were installed along more sloping.streets. The upstream components are highly effective in attenuating most or even all runoff. Flowing at higher velocities, the cascades do not perform at such a high level, although under favorable conditions they can still infiltrate or evapotranspire the majority of the incoming runoff (Horner et al. 2001, 2002, 2004, Chapman 2006, Chapman and Horner 2010). [The cascades] extract pollutants from remnant runoff through mechanisms mediated by vegetation and soils. The success of Seattle’s natural drainage systems demonstrates that well designed ARCD practices can mimic natural landscapes hydrologically, and thereby avoid raising discharge quantities above pre-development levels.” (NRC 2009, p407)

In cases where ARCD approaches are not feasible, conventional SCMs such as retention/detention basins, biofiltration, and sand filters can be used to augment ARCD strategies. As pointed out in the NRC (2009) report, a “…watershed-based program emphasizing ARCD practices would convey benefits beyond improved stormwater management. ARCD techniques overall would advance water conservation, and infiltrative practices would increase recharge of the groundwater resource. ARCD practices can be made attractive and thereby improve neighborhood aesthetics and property values. Retention of more natural vegetation would both save wildlife habitat and provide recreational opportunities. Municipalities could use the program in their general urban improvement initiatives, giving incentives to property owners to contribute to goals in that area while also protecting water resources.” (NRC 2009, p. 407-408)

ARCD practices are numerous and expanding as existing configurations are applied in new ways. Table 5 presents a catalogue adapted from USEPA (2007b) and NRC (2009). This catalogue contains practices that are not equally applicable in all settings; e.g., residential, industrial, and commercial land uses; or new development, redevelopment, and retrofit stages. Nevertheless, each category offers practices applicable in each of these circumstances.




Source control

Minimizing pollutants or isolating them from contact with rainfall or runoff

  • Substituting less for more polluting  products
  • Segregating, covering, containing, and/or enclosing pollutant-generating materials, wastes, and activities
  • Avoiding or minimizing fertilizer and pesticide applications
  • Removing animal wastes deposited outdoors
  • Conserving water to reduce non-stormwater discharges

Conservation site design

Minimizing the

generation of runoff by preserving open space and reducing the amount of land disturbance and impervious surface

  • Cluster development
  • Preserving wetlands, riparian areas, forested tracts, and porous soils
  • Reduced pavement widths (streets, sidewalks, driveways, parking lot aisles)
  • Reduced building footprints

Conservation construction

Retaining vegetation and avoiding removing topsoil or compacting soil

  • Minimizing site clearing
  • Minimizing site grading
  • Prohibiting heavy vehicles from driving anywhere unnecessary

Runoff harvesting

Capturing rainwater, generally from roofs, for a beneficial use

  • Storage and distribution system for gray water and/or irrigation supply for a public building
  • Cistern for residential garden watering



  • Examples

Practices for temporary runoff storage followed by infiltration and/or evapotranspirationa

Use of soil pore space and vegetative tissue to increase the opportunity for runoff to percolate to groundwater or vaporize to the atmosphere

  • Bioretention cell (rain garden)
  • Vegetated swale (channel flow)
  • Vegetated filter strip (sheet flow)
  • Planter box
  • Tree pit
  • Infiltration basin
  • Infiltration trench
  • Roof downspout surface or subsurface dispersal
  • Permeable pavement
  • Vegetated (green) roof

ARCD landscapingb

Soil amendment and/or plant selection to increase storage, infiltration, and evapotranspiration

  • Organic compost soil amendment
  • Native, drought-tolerant plantings
  • Reforestation
  • Turf conversion to meadow, shrubs, and/or trees

aSome of these practices are also conventional stormwater BMPs but are ARCD practices when ARCD landscaping methods are employed as necessary to maximize storage, infiltration, and evapotranspiration. The first five examples can be constructed with an impermeable liner and an underdrain connection to a storm sewer, if there is a good reason to do so (see further discussion later). Vegetated roofs store and evapotranspire water but offer no infiltration opportunity, unless their discharge is directed to a secondary, ground-based facility.

bSelection of landscaping methods depends on the ARCD practice to which it applies and the stormwater management objectives, but amending soils unless they are highly infiltrative and planting several vegetation canopy layers (e.g., herbaceous growth, shrubs, and trees) are generally conducive to increasing storage, infiltration, and evapotranspiration.

The best strategy for choosing among and implementing these practices is a decentralized, integrated one; i.e., selecting practices that fit together as a system, working from at or near sources through the landscape until management objectives are met. This strategy makes maximum possible use of practices in source control, conservation site design and conservation construction, which then can help prevent stormwater quantity and quality problem. Source control and preservation of existing vegetation and soils obviously avoid post-development runoff quantity and prevent pollutant runoff. Among all strategies, these best maintain pre-development hydrology (infiltration and ET patterns) and yield of materials flowing from the site. This preventive strategy is supplemented by creating as little impervious cover as possible. The remaining practices then contend with the excess runoff and pollutants over pre-development levels generated by the development.

For the practices that infiltrate water, a site’s infiltration capability can be determined through infiltration rate testing and excavation to determine the pattern of soil layers and if groundwater approaches the surface too closely for effective operation. Because of the often substantial variability of conditions around a site, these determinations need to be made at multiple points. Guidance cited below provides procedures for these tasks. If the natural infiltration rate is insufficient, generally regarded as < 0.5 inch/hour (< 1.25 cm/h, Geosyntec 2008), in many situations the soil can be amended, usually with organic compost, to apply an infiltrative practice.

Less predictable than infiltration at this point in time is evapotranspiration. Evidence gathering from available performance research, presented later, is that ET can be substantial but is difficult to quantify at a given site without more research. Therefore, designs of these facilities cannot be optimized now for maximum performance. Meanwhile, designing on the basis of infiltration rate, set considering soil amendment if any, is conservative and is likely to yield better than predicted performance as a result of ET.

Strategies for Implementing ARCD Practices

No single manual on LID provides up-to-date comprehensive selection, design, installation, and maintenance advice covering the full range of practices listed in Table 5. Both the USEPA8 and the Center of Low Impact Development9 websites list several manuals, but they are somewhat dated and focused on specialized applications.

Regionally, the Puget Sound Action Team (PSAT) produced a guidance manual (Hinman 2005) that emphasized site design and construction practices most appropriate for residential land use. This manual guides site assessment and planning, covering conservation construction, soil amendment, and aspects of conservation site design; and provides detailed specifications for bioretention cells, permeable pavement, vegetated roofs, and roof water harvesting. Hinman (2007) supplemented the manual with a handbook aimed at homeowners who wish to create small-scale rain gardens.

Further information on ARCD can be gained from the Post-Construction BMP Technical Guidance Manual of the City of Santa Barbara, California (Geosyntec Consultants 2008), which emphasizes ARCD techniques over conventional ones. This manual encompasses many major urban land use categories although it does not cover source control. Volume IV of WDOE’s (2005) Stormwater Management Manual for Western Washington fills that gap well for commercial and industrial areas. Box 8 provides other resources on various aspects of ARCD.

Box 8. Aspects of ARCD of interest to Puget Sound practitioners.

  • Green Roofs for Stormwater Runoff Control (Berghage et al. 2009)—report on comprehensive studies of green roof performance at Pennsylvania State University, with recommendations pertaining to future designs;
  • Innovative Approaches for Urban Watershed Wet-Weather Flow Management and Control: State-of-the-Technology: Interim Report (Struck, Rowney, and Pechacek 2009)—presents a global information search to identify state-of-the-technology approaches, including case examples and conclusions and recommendations to guide future research, development, and demonstration initiatives;
  • Managing Wet Weather with Green Infrastructure Action Strategy (USEPA 2008)— an outline of a national strategy to develop and implement ARCD; and
  • Reducing Stormwater Costs through Low Impact Development (LID) Strategies and Practices (USEPA 2007b)—presents five case studies from the Pacific Northwest and 12 more nationally with design, performance, and cost information.

See Appendix 4E for supporting information on ARCD strategies and stages of urbanization

Effectiveness and Relative Certainty of ARCD Strategies

Most of the ARCD practices in Table 5 are preventive; i.e., they avoid the generation of surface runoff above pre-development levels and additions of pollutants over pre-development amounts to whatever surface runoff still occurs. If these practices are applied effectively, they could be 100 percent effective for any land area covered. For example, if a development is clustered and an existing forest is untouched by it, the forest’s runoff production and characteristics should not change. Likewise, shielding a previously outdoor industrial activity from contact with rainfall and runoff would eliminate the contamination from that operation. The question of effectiveness and relative certainty, therefore, apply mainly to the last two groups of practices in the table, those for temporary runoff storage followed by infiltration and/or evapotranspiration, and the associated ARCD landscaping practices.

To express hydrologic performance, the most common measures seen in the literature are cumulative surface runoff volume reduction between inflow and outflow over a period that includes multiple storms, and peak flow rate reduction statistics. In their recent paper on the performance of one of Seattle’s natural drainage systems, Chapman and Horner (2010) reported water quality performance in terms of long-term pollutant mass loading reductions, reliable effluent pollutant concentrations, and irreducible minimum effluent concentrations. Mass loading represents a cumulative burden on the receiving water, while the maximum expected discharge concentration expresses the highest acute stress exerted on aquatic life. The irreducible minimum concentration indicates the best performance that can be expected. It is now well established that quantifying stormwater BMP performance in relation to concentration reduction (influent to effluent) statistics can be misleading for several reasons (Strecker et al. 2001), a key one being that devices are often observed to put out somewhat consistent effluent pollutant levels in the face of relatively variable influent levels (Barrett 2005). In that situation a device receiving a relatively “cleaner” flow would not register a performance efficiency as high as one getting a “dirtier” influent, even if their effluent concentrations are identical.

Seattle Natural Drainage System Effectiveness and Relative Certainty

There has been more study of some form of bioretention than any other ARCD practice. This method is applied in a variety of configurations, in some cases with elements of swales and filter strips in addition to or even instead of a depressional form. The City of Seattle’s natural drainage system program10 exemplifies this approach. As described earlier, Seattle uses two basic models: serial bioretention cells for relatively flat streets, and “cascades” of vegetated stepped pools created by weirs along more sloping streets. The former are quiescent, while the cascades often have flow at visible velocity, and hence are “swale-like.”

The best known flat-street cellular installation is the 2nd Avenue Northwest Street Edge Alternatives (SEA Streets) project. This project’s performance has been widely reported regionally, nationally, and internationally, although not in any peer-reviewed journal form because of the straightforwardness of the results. The following account comes from a report to the city by the University of Washington (Horner and Chapman 2007). The street was redesigned to reduce impervious cover, and also traffic speeds, while converting previous asphalt and gravel right of way to vegetated swales and detention areas. Built largely in compost-amended soils, this natural drainage system was designed to reduce peak runoff rates and volumes conveyed to Pipers Creek. While providing these environmental benefits, the system landscaping was also intended to offer a neighborhood aesthetic benefit.

Prior to construction of the SEA Streets project baseline flow monitoring occurred during the period March 19-June 18, 2000 and embraced 35 events totaling 6.32 inches (161 mm) of precipitation. The catchment discharged in all events, delivering a total of 8601 ft3 (244 m3) of runoff to the downstream drainage system leading to Pipers Creek. As a crude measure of yield, the street generated 1361 ft3 of runoff per inch of rain (1.52 m3 per mm).

Monitoring of the completed SEA Streets project began on January 20, 2001. Over the next approximately two years (through March 31, 2003) the system experienced 162 events producing 76.9 inches (1954 mm) of precipitation. The new street discharged runoff during only 11 storms (6.8 percent), yielding 1948 ft3 (55 m3) of runoff, or 25.3 ft3 of runoff per inch of rain (0.028 m3 per mm). This yield is just 1.9 percent of the amount before the project’s construction.

Flow monitoring continued through June 30, 2007. The last recorded discharge was on December 14, 2002. On and about October 20, 2003 the Seattle-Tacoma International Airport rain gauge registered its highest ever 24-hour rainfall total. The Viewlands rain station in the 2nd Avenue NW neighborhood recorded 4.22 inches (107 mm) of rain from late on October 19, 2003 to the morning of October 21 (a period of 32.5 hours). The next month a quantity of 3.86 inches (98 mm) fell at Viewlands over a 51.25-hour period from November 17 to 19, 2003. Then, in November 2006 Seattle experienced its largest ever monthly rainfall, 15.63 inches (397 mm) at the airport. Therefore, the SEA Streets drainage system ceased discharging runoff even with exposure to large short- and long-term precipitation quantities.

The 2nd Avenue NW SEA Streets site thus demonstrated a clear tendency to store and prevent surface runoff from even more rainfall than during its early years. The reason for this development can only be speculation. However, it is likely that the vegetation, as it matures, more effectively intercepts rainfall, after which it can evaporate; assimilates more water into its tissues, for storage and possible transpiration; and assists percolation through the soil by piping water along the root structures. In this condition the bioretention unit mimics a natural Pacific Northwest landscape, in which surface runoff is unusual.

The most complete performance study of a cascade was performed on the NW 110th Street system (Chapman and Horner 2010). It has 5-8 cm of 4-cm-diameter washed gravel over a minimum 20-cm-deep layer of soil mix containing 30 percent organic compost and 70 percent gravelly sand (by volume). These amended soils are underlain by a layer of 6-mm-diameter, bank-run gravel. Over three full wet seasons and two dry seasons, 235 storms delivered 2.23 meters (87.8 inches) of rain at the study location. There was no discharge recorded at the outlet in 79 percent of the events. During the full monitoring period 7635 m3 (2.69 x 105 ft3) of water entered at the inlet and 3982 m3 (1.40 x 105 ft3) left the system. Therefore, at least 48 percent of the incoming water never discharged from the 110th Cascade. However, the total impervious area draining to the system was carefully estimated to be approximately double that contributing to the inlet; therefore, the total runoff volume entering likely was also about double that measured at the monitored inlet. Given this, it would be more accurate to say that closer to 74 percent of the water entering the 110th Cascade was retained.

Table 6 presents estimated total pollutant mass loading reductions over the full monitoring period, both with and without the unmeasured inflows, with confidence limits for the latter set of estimates (Chapman and Horner 2010, NRC 2009). Including the estimated additional influent gives the most likely estimate of reductions. By either estimation technique, though, it is clear that the NW 110th Cascade attenuated the majority, or even the great majority, of the pollutant mass that would otherwise flow to Pipers Creek for most pollutants. This performance is chiefly a function of the great reduction of discharge volume. The low removal of dissolved phosphorus signifies the exception usually seen in vegetative treatment systems: vegetation decaying in the fall and winter appears to release in soluble form nutrients taken up in the growing season.

Table 7 gives the irreducible minimum and reliable maximum pollutant concentration values determined from the cascade discharge data, with volume-weighted average effluent concentrations for comparison (Chapman and Horner 2010). The reliable maximum is here defined as the event mean concentration (EMC) that was exceeded in only 10 percent of the runoff events, while the irreducible minimum is the EMC that was exceeded 90 percent of the time. These values were calculated as two-sided prediction intervals with α=0.10, using non-parametric (ranks) methods (Helsel and Hirsch, 1991). Volume-weighted averages were computed by multiplying concentrations times flow volumes for each monitored storm, summing, and dividing by total volume. While the minimums and averages show that pollutant concentrations in the discharge would usually be substantially less, the relative certainty of not surpassing the maximum concentrations is 90 percent.





Estimated Mass Loading Reduction Ignoring Unmeasured Inflows (%)

90% Confidence Limits on Estimate

Estimated Mass Loading Reduction Including Unmeasured Inflows (%)

Total suspended solids




Total nitrogen




Total phosphorus




Soluble reactive phosphorus

No significant decrease



Total copper




Total zinc




Total lead




Dissolved copper




Dissolved zinc




Dissolved lead

Usually not detected in inflow


Usually not detected in inflow

Total petroleum hydrocarbons (motor oil fraction)






Irreducible Minimum

Reliable Maximum

Volume-Weighted Average

Total suspended solids (mg/L)




Total nitrogen (mg/L)




Total phosphorus (µg/L)




Soluble reactive phosphorus (µg/L)




Total copper (µg/L)




Total zinc (µg/L)




Total lead (µg/L)­




Dissolved copper (µg/L)




Dissolved zinc (µg/L)




Dissolved lead (µg/L)

< 1

< 1

< 1

Total petroleum hydrocarbons (motor oil fraction, mg/L)

< 0.15



WDOE has set water quality standards for some of the pollutants in Table 7, particularly metals as dissolved quantities. Meeting the standards in the discharge could be a stormwater management objective. The metals standards are a function of water hardness, because the tendency of hardness producing minerals (mainly, calcium and magnesium) to reduce metal toxicity to aquatic life. Hardness tends to be relatively low in the Puget Sound area, making attainment of water quality standards sometimes difficult. The results for the NW 110th Street Cascade show that employing this strategy could meet the standards for zinc and lead under virtually all regional circumstances but would not necessarily meet the copper standard.

Bioretention Effectiveness and Relative Certainty

As pointed out earlier, performance comparisons among studies are difficult because of the many influencing variables, often undefined in reports, and always must be tempered accordingly. Bioretention facilities have been built and studied with and without impermeable liners and/or underdrains, either entirely eliminating (if lined) or reducing (if unlined but underdrained) infiltration. Obviously, this design feature would be expected to have a major influence on performance. Table 8 presents a comparison in surface runoff volume reduction with and without underdrains. Results for the unconstrained systems mirror those discussed above for Seattle’s natural drainage systems. Installing an underdrain but leaving the facility unlined appears to cut the hydrologic advantage by roughly one-third to one-half, while adding a liner diminishes that advantage by around two-thirds. Therefore, these design features should only be incorporated for a good reason (e.g., high groundwater table; very restricted infiltration rate that cannot be sufficiently increased by soil amendment; buried contaminants in the soil below, which could be mobilized by concentrated infiltration). Without such a reason, bioretention cells and other ARCD practices should be built without these features for maximum infiltration opportunity and minimum surface discharge.





Volume Reduction (%)



Unlined, no underdrain



Dietz and Clausen (2006)

Unlined, no underdrain



Ermilio and Traver (2006)

Unlined, no underdrain



Rushton (2002)

Unlined, no underdrain



Lloyd et al. (2002)

Unlined, with underdrain



Van Seters et al. (2002)

Unlined, with underdrain

North Carolina


Smith and Hunt (2007)

Unlined, with underdrain

North Carolina


Hunt et al. (2008)

Unlined, with underdrain



Davis et al. (2008)

Lined, with underdrain

North Carolina


Sharkey (2006)

The 20-29 percent of the inflow lost from the lined unit could only have departed via evapotranspiration. This result came from an installation in a location with the months of highest rainfall coinciding with the warmest months, maximizing evaporation, and the growing season, maximizing transpiration. Everything else being equal, this performance would not be expected in the Puget Sound region, with the highest rainfall in the coolest months outside the growing season. Nevertheless, design and, particularly, vegetation selection could increase ET in this climate; but research is necessary to determine that potential and how to optimize it.

Davis et al. (2009) summarized water quality performance registered by several bioretention studies in the eastern United States from New Hampshire to North Carolina. As shown in Table 9, the results were highly variable, most likely as a consequence of the many driving variables listed earlier. The results overall do not provide good indices of effectiveness and signify that relative certainty is quite poor. Along with the reports from the Seattle natural drainage systems, though, they do indicate the strong potential of bioretention to eliminate the discharge of almost all pollutant mass in the best applications and to meet or at least approach achievement of water quality standards at the point of release.




Effluent Concentration Range

Mass Loading Reduction Range (%)

Total suspended solids

13-20 mg/L


Total nitrogen

0.80-4.38 mg/L


Total phosphorus

58-560 µg/L

negative 240-79

Total zinc

17-48 µg/L


Permeable Pavement Effectiveness and Relative Certainty

Permeable pavements include porous asphalt and concrete and various modular concrete and plastic grid products. All have received some testing, but results are reported in many different ways. The tests have generally shown substantial reductions of both runoff quantity and measures of pollutants. Apparently, mechanisms operate within the porous matrices to capture the various classes of pollutants relatively effectively. Already generally relatively low, remaining contaminants exiting from the pervious pavement would receive additional opportunity for capture in underlying soil before reaching groundwater.

St. John and Horner (1997) investigated the performance of a King County, WA porous asphalt road shoulder relative runoff quantity and quality from the traveled lanes and in comparison to a conventional asphalt and a gravel shoulder. Over a wet season the porous asphalt shoulder prevented 85 percent of the incident runoff from flowing farther on the surface. Samples of the road runoff and shoulder infiltrate exhibited the water quality characteristics in Table 10. The results are roughly equivalent to or better than those from the NW 110th Street Cascade, with a relatively high degree of certainty. Notably and in contrast to the cascade, soluble orthophosphate-phosphorus was clearly reduced to low concentrations in the permeable pavement.

Struck, Rowney, and Pechacek (2009) summarized case studies on various kinds of concrete and plastic grid systems. Concrete blocks over four types of base materials in Germany reduced copper in the infiltrate to 16-51 µg/L, zinc to 18-178 µg/L, and lead to < 4 µg/L. A concrete-block system in North Carolina reduced runoff volume by 66 percent and held total suspended solids in water passed through the blocks to 12.4 mg/L, total nitrogen to 0.98-2.77 mg/L, TP to 70-400 µg/L, and zinc to 8 µg/L. Brattebo and Booth (2003) examined two concrete and two plastic grids over five years. There was almost no runoff at any time from any gridded area. Copper in the infiltrate ranged from below detection to 1.3 µg/L and zinc from less than detection to 8.2 µg/L. Oil was never detected.





Road Runoff Concentrationa

Porous Asphalt Infiltrate Concentrationa

Mass Loading Reduction by Porous Asphalt (%)

Total suspended solids (mg/L)

140 ± 22

17 ± 4


Total phosphorus (µg/L)

358 ± 35

101 ± 15


Orthophosphate- phosphorus (µg/L)

19.1 ± 5.2

5.8 ± 1.0


Total copper (µg/L)

16.2 ± 2.4

4.8 ± 1.0


Total zinc (µg/L)

105 ± 15

39 ± 11


Total lead (µg/L)­

39.7 ± 6.4

4.7 ± 0.8


Total petroleum hydrocarbons (motor oil fraction, mg/L)

2.5 ± 0.3

0.9 ± 0.1


a Given as mean ± 1 standard error

A coalition of public agencies and private professional associations and consultants has built an International Stormwater Best Management Practices Database11. The database is a reliable basis for characterizing effectiveness, because it incorporates only data collected using acceptable procedures and quality controls. Hence, this source is fully peer-reviewed. It is now primarily populated with conventional practices but will soon be supplemented with a range of ARCD methods. At this point, among those practices, only porous pavements are included. Table 11 summarizes the results from six studies on a variety of pavement types accepted into the database. Porous pavement technology requires further investigation on long-term sustainability, as well as stormwater management effectiveness; but the overall reports thus far are quite promising for greatly reducing runoff quantities and pollutant mass loadings and meeting or coming close to water quality standards.



95% Confidence Limits

Total suspended solids (mg/L)



Total Kjeldahl nitrogena (mg/L)



Total phosphorus (µg/L)



Total copper (µg/L)



Total zinc (µg/L)



Total lead (µg/L)­



a Ammonia plus organic nitrogen

Vegetated Roof Effectiveness and Relative Certainty

Dietz (2007) summarized retention without surface discharge of the precipitation falling on 10 vegetated roofs in Sweden, Michigan, North Carolina, and Oregon. The systems ranged from 2.0 to 12.7 cm in growth medium thickness and the roof slopes from 2.0 to 6.5 percent. Excluding one roof with a 2.0-cm medium, retention ranged from 58-71 percent. With infiltration not being a factor, ET had to be substantial. Because of the preponderance of precipitation in winter in the Pacific Northwest, it is generally thought that green roofs would not be very effective for stormwater management here. However, even the Portland, OR vegetated roof retained 69 percent of the rainfall (Dietz 2007). It also has the thickest medium, which might be one clue to boosting performance in this climate.

Pennsylvania State University has performed a large amount of green roof research (Berhage et al. 2009). The roofs tested retained over 50 percent of the total precipitation during the study period. During summer months nearly all the precipitation was retained. During the winter retention was smaller (< 20 percent). Seasonal effects appear to be a result of snow or freezing conditions; otherwise green roofs effectively retained up 0.4 inch (10 mm) of precipitation regardless of season. This result is encouraging for vegetated roof use in the Puget Sound region, where very cold conditions are much less frequent than in central Pennsylvania. The mean storm quantity in Seattle is 0.48 inch, meaning that the potential exists to achieve substantial retention of a fairly large number of storms. Water quality performance was not deemed good enough to discharge effluent without further treatment. This finding is discouraging to implementation of green roofs, since they are best suited to dense locations restricting use of other practices.

Benefits of Water Harvesting

To the extent that rain water can be harvested and directed to a use such as gray water supply or irrigation, the technique is 100 percent effective in reducing stormwater surface runoff and its contamination. Therefore, its effectiveness is expressed here in terms of water conservation potential. In downtown Seattle the King County Government Center collects enough roof runoff to supply over 60 percent of the toilet flushing and plant irrigation water requirements, saving approximately 1.4 million gallons of potable water per year (Puget Sound Action Team 2003). A much smaller public building in Seattle, the Carkeek Environmental Learning Center, drains roof runoff into a 3500-gallon cistern to supply toilets (Accetturo 2005).

ARCD costs

The USEPA (2007b) assembled a series of ARCD case studies, including costs. In general, the investigation concluded that:

... applying LID techniques can reduce project costs and improve environmental performance. In most cases, LID practices were shown to be both fiscally and environmentally beneficial to communities. In a few cases, LID project costs were higher than those for conventional stormwater management practices. However, in the vast majority of cases, significant savings were realized due to reduced costs for site grading and preparation, stormwater infrastructure, site paving, and landscaping. Total capital cost savings ranged from 15 to 80 percent when LID methods were used, with a few exceptions in which LID project costs were higher than conventional stormwater management costs (USEPA 2007b)

Among the Pacific Northwest case studies, Seattle’s 2nd Avenue NW SEA Streets project saved $217,255 of the expected $868,803 cost (25 percent) of upgrading the street’s previous “informal” drainage system to a conventional street curb-and-gutter configuration. Two parking lot rain garden retrofits in Bellingham saved 76 and 80 percent of the costs of the conventional stormwater management alternative of underground vaults. A design study for a Pierce County, WA subdivision using an integrated range of ARCD techniques estimated 20 percent savings compared to managing stormwater conventionally. On the other hand, in a design study for another subdivision in the same county maximizing ARCD opportunities, including home roof water collection, capital costs were estimated as about twice as high as for a conventional system. These costs were expected to be offset somewhat by operating savings over time. Portland’s residential roof downspout disconnection program has cost the city $8.5 million thus far in materials and incentive payments but is expected to save $250 million in construction costs for piping to store an extra 1 billion gallons per year to prevent combined sewer overflows. Case studies in USEPA (2007b) for other areas around North America illustrate the general savings that can accrue from replacing conventional approaches with ARCD.

Conventional Stormwater Management Strategies

Stormwater management on the conventional level is very well developed, especially in Washington State. King County and WDOE were among the first jurisdictions in the nation to write comprehensive stormwater manuals. The same two entities took continuous simulation hydrologic modeling into the mainstream of the profession, ahead of just about everywhere else. However, the conventional approach has been found wanting, contributing to the strong role of stormwater in compromising resources. The NRC (2009)study concluded that site-by-site specification of controls on stormwater discharges, the usual practice in the conventional approach to stormwater management, is inadequate and should be replaced by integrated implementation of controls, designed as a system. In particular, the committee found that the prevailing practices have not served well to manage runoff from the most frequent, relatively small storm events; and practices that harvest, infiltrate, and evapotranspire stormwater would be superior. This section examines the capabilities and limitations of conventional practices, what role they can still play, and how they can be enhanced for better performance.

WDOE’s (2005) Stormwater Management Manual for Western Washington provides a thorough catalog of the conventional practices at issue and can be consulted for full details about them. The practices under the infiltration and biofiltration categories can be recognized as identical in name to practices also in the ARCD category. The major differences as applied in that milieu versus conventionally come in the treatment of soils and vegetation. In ARCD applications soils are investigated for infiltration capability and amended if necessary to optimize it; whereas, conventionally, either the native soils are accepted as is or an infiltration BMP is rejected as a workable choice. In ARCD practices the vegetation palette generally has some diversity in more than one canopy layer, whereas conventional vegetated facilities tend more to be monocultures. In addition to the practices in Table 12, the manual has a volume (IV) of source controls, which have already been pointed out in the ARCD discussion.


Specific Practices

Manual Referencea

Quantity control:



Roof downspout controls

Downspout infiltration system



Downspout dispersion system



Perforated stub-out connection



Detention pond



Detention tank



Detention vault



Infiltration basin



Infiltration trench


Quality control:



Infiltration and bio-infiltration

Infiltration basin



Infiltration trench



Bio-infiltration swale


Sand filtration

Sand filter vault



Linear sand filter



Biofiltration swale



Filter strip


Wet pool facilities

Wet ponds



Wet vaults



Treatment wetlands


Oil/water separators




Coalescing plate


Emerging (generally, commercial) technologies

Media filters



Catch basin inserts



Hydrodynamic separators



High-efficiency sweeping


a Given as volume number (Roman numeral) and chapter section

Conventional Stormwater Management Strategies: Effectiveness and Relative Certainty in Water Quantity Control
As a consequence of the urban-induced runoff changes that cause flooding, erosion, and stream habitat damage, Puget Sound jurisdictions have long required some degree of stormwater runoff quantity mitigation for new developments. The most common approach has been to reduce flows through the use of detention ponds, which are intended to hold stormwater runoff from developed areas and release it at a slower rate than if undetained. Booth, Hartley, and Jackson (2002) reviewed the history and critiqued the effectiveness of the approach. The picture remains largely unchanged today, with the conventional practices described still prevailing and central to the approach of the Stormwater Management Manual for Western Washington (WDOE 2005).

Detention ponds can be designed to either of two levels of performance, depending on the desired balance between achieving downstream protection and the cost of providing that protection. A peak standard, the classic (and less costly) goal of detention facilities, seeks to maintain post-development peak discharges at their pre-development levels. Even if this goal is successfully achieved, the aggregate duration that such flows occupy the channel must increase, because the overall volume of runoff is greater. In contrast, a duration standard seeks to maintain the post-development duration of a wide range of peak discharges at pre-development levels. Yet, unless runoff is infiltrated, the total volume of runoff must still increase in the post-development condition. Thus, durations cannot be matched for all discharges because this excess water must also be released.

Applying these principles requires the use of some calculation procedure, a hydrologic model, to estimate pre- and post-development flows. Early protocols used the extremely simplistic “Rational Method,” succeeded about 20 years ago by the “Curve Number” method originally introduced by the Soil Conservation Service of the U.S. Department of Agriculture. Several flaws, resulting in detention ponds that did not meet desired performance criteria, were soon recognized in this method: (1) ponds were assumed to be empty at the beginning of storms, a condition often not the case in the Puget Sound winter climate; (2) the model commonly overestimated pre-development flows, giving the wrong targets for post-development design; (3) the method was still based on a peak standard, ignoring problems associated with increased flow durations.

To counter these problems King County and WDOE introduced continuous simulation hydrologic models based on the HSPF (Hydrologic Simulation Program-Fortran) model, respectively, KCRTS (King County Runoff Time Series) and WWHM (Western Washington Hydrologic Model). These and other jurisdictions also converted to duration control standards, intended to match pre- and post-development flow durations for all discharges above a chosen threshold. From the standpoint of developers these changes were controversial, because they led to substantially larger detention ponds, consuming more land and costing more than before.

From the environmental protection standpoint, the use of a threshold (on development size and, hence, runoff production) ignores cumulative effects of numerous sub-threshold actions summing to a considerable hydrologic alteration. Booth and Jackson (1997) had earlier discovered that one-quarter of impervious area added to King County watersheds from 1987 to 1992 fell below the threshold. Horner et al. (2002) assessed various aspects of water quantity and quality control BMP application in four King County watersheds and found that only 12-31 percent of the developed area was served by any quantity control practices. This dearth appeared to be associated with vesting under old regulations and some development predating any regulations, in addition to the threshold.

Booth and Jackson (1997) performed an analysis to determine how much detention volume would be required to prevent the urban stream channel damage, which they and others had demonstrated, based on a duration-based standard based and KCRTS modeling and assuming no infiltration. They concluded that effective runoff mitigation in the Pacific Northwest requires pond volumes of 3 to as much as 14 cm-ha per ha of developed land (0.10-0.46 acre-ft/acre). With associated berms, control structures, and maintenance access roads, such a facility could occupy more than 10 percent of the total area of a development. Ponds of that size have never been built, and probably never will for economic and political reasons. If half of the runoff production could be avoided by ARCD mechanisms, ponds could shrink to around the sizes being built under current standards and still protect streams. The possibility certainly exists to achieve greater attenuation in the contributing catchment, to apply ARCD-type soils amendment and vegetation to the pond to increase infiltration and ET, or both.

Conventional Stormwater Management Strategies: Effectiveness and Relative Certainty in Water Quality Control

The optimal stormwater management practice can provide needed quantity control, substantially reduce pollutant mass loadings, and produce an effluent concentration within acceptable limits, as gauged by water quality standards in the receiving water. The effectiveness of conventional infiltrative practices in providing any or all of these benefits depends on the extent of infiltration that occurs, just as with their ARCD counterparts. Basin-type conventional water quality control practices can be designed to provide detention for quantity control. Ground-based practices that drain fully, such as detention ponds, biofilters, and media filters constructed in earth, generally have some incidental infiltration, although it is not usually accounted for in design. If that incidental infiltration is considerable, mass loading reduction will benefit both from volume decrease and pollutant capture in the device. Otherwise, cumulative mass of contaminants will not be reduced much or at all over what the pollutant capture mechanisms provide. Wet ponds and treatment wetlands hold water because they do not infiltrate much, a condition developing through soil structural changes with saturation if not the case at construction. Of course, any practice built in a hard structure will not infiltrate at all.

For practices not designed for infiltration, their effectiveness in reducing pollutant concentrations depends on a variety of pollutant removal mechanisms, the chief one being filtration and settling of suspended solids, which captures any other contaminants associated with the particles. The longer the residence time in the device, the more sedimentation will occur, because of the inverse relationship of settling velocity and particle size. Mechanisms removing dissolved pollutants (e.g., adsorption, ion exchange, precipitation) also depend on time to function effectively. Conventional BMPs are usually designed to treat runoff from the relatively frequent, small storms (e.g., 6-month frequency, 24-hour duration) and pass larger flows through rapidly or bypass them. The grounds for this practice are that these storms convey the great majority of the pollutant loadings, and targeting bigger storms requires increasingly larger treatment systems for diminishing benefits. The effectiveness reports here are a function of this design philosophy.

The International Stormwater Best Management Practices Database, introduced above, is the best basis for characterizing conventional BMP effluent quality in terms of pollutant concentrations. For supporting material on intertational stormwater BMP, see Appendix 4F. In an exercise to compare conventional to ARCD treatment in lowering pollutant concentrations, this author compared the medians and 95 percent confidence intervals in Table F1 with the volume-weighted averages, irreducible minimums, and reliable maximums in Table 7 summarizing the Seattle NW 110th Street Cascade’s performance, which is fairly typical in relation to other ARCD data cited above. These various statistics are, of course, not strictly comparable but do provide similar indicators of effectiveness and relative certainty. Table 13 shows the comparison in terms of when the conventional BMP concentrations were generally “higher,” “comparable,” or “lower” in relation to those in the natural drainage system effluent. There is no statistically quantitative basis underlying or implied in these ratings, simply a general overlap or deviation in one direction or another. Dissolved lead is not included because the influent to the cascade was generally below detection, differing from any entry in the database.

The results provide a convenient means of comparing the conventional BMPs to one another and to a typical ARCD installation. Wet ponds and treatment wetlands are quite comparable to one another and the natural drainage system cascade in exhibiting the highest effluent quality. Somewhat less effective overall are media filters and conventional biofilters, with detention ponds and hydrodynamic devices showing the lowest performance.

While this analysis indicated that it is possible to produce effluents with conventional practices of comparable quality to ARCD alternatives, the two comparable conventional types are essentially non-infiltrative. While they would provide an uncertain amount of evapotranspiration, they are unlikely to be comparable in mass loading reduction to a system that extracts the great majority of the surface runoff. Most media filters and all hydrodynamic devices use hard structural containments and offer no infiltration or transpiration and little evaporation.

Table 13.



Detention Ponds


Wet Ponds

Treatment Wetlands



Media Filters

Hydrodyn. Devices





























T Cu







T Zn







T Pb







D Cu



No data




D Zn



No data




% of cases C or L







a H—measures of central tendency and dispersion generally higher in conventional BMP than cascade effluent; L— measures of central tendency and dispersion generally lower in conventional BMP than cascade effluent; C—measures of central tendency and dispersion generally comparable

b TSS—total suspended solids, T—total, N—nitrogen, P—phosphorus, D—dissolved, Cu—copper, Zn—zinc, Pb—lead, Cd—cadmium

The California Department of Transportation (Caltrans 2004, Barrett 2005) performed an extensive study of conventional BMPs for highway applications. It was discovered that extended-detention ponds and biofiltration swales and filter strips infiltrated 30-50 percent of the influent, depending on soils and storm characteristics, giving an unanticipated boost to mass loading reduction, the statistical ranges of which are shown in Table 14. It should be noted that these facilities were not designed to provide for water quantity control, nor were they evaluated for that function.

These data can be compared with the mass loading performance of the NW 110th Street Cascade as shown in Table 6. All BMPs but the hydrodynamic device were fairly effective in cutting mass emissions of TSS and particulate metals. The wet pond and sand filters were at least the equals of the cascade in this regard. It should be noted that the Caltrans detention pond was designed for a 3-day holding time for the target storm, the longest generally used for this device; and it performed better than often reported elsewhere. The advantage of the greater flow volume reduction afforded by the cascade showed up more with respect to the dissolved metals and, especially, the nutrients, for which the cascade was estimated to remove 82-83 percent of the total nitrogen and phosphorus. Nevertheless, the generally better than expected performance of the Caltrans BMPs shows the way on how the most can be gained from conventional BMPs, a subject discussed below.

Table 14.



Detention Pond


Wet Pond

Biofiltration Swales

Biofiltration Filter Strips

Sand Filters

Hydrodyn. Device















Part. P














Part. Cu







Part. Zn







Part. Pb







D Cu







D Zn







D Pb







a Expressed as 90 percent confidence limits of percentage reductions from inlet to outlet rounded to nearest 5 percent; there were different numbers of BMPs in each category, and two different designs of sand filters; neg.—negative.

b TSS—total suspended solids, TKN—total Kjeldahl nitrogen (ammonia plus organic nitrogen), Part.—particulate (total minus dissolved), P—phosphorus, D—dissolved, Cu—copper, Zn—zinc, Pb—lead, Cd—cadmium

Potential Advances in Conventional Practices

The often limited or nonexistent infiltration and evapotranspiration occurring in non-infiltrative conventional stormwater practices limits their ability to achieve effective control over runoff quantity and pollutant mass loadings, even if they can be designed and built to attain relatively high contaminant concentration reductions. While sand and other media filters are often constructed with concrete vaults, they can also be established in earth or without a hard bottom. Indeed, Austin, TX, which pioneered one type of stormwater sand filter, promotes such a design (City of Austin 1988) and has many such open-bedded filters. There are no technical limitations to amending soils to promote infiltration, a technique institutionalized in ARCD practice, in otherwise conventional detention basins, biofiltration swales and filter strips, and open-bedded media filters. Likewise, vegetation could be converted from the often monocultural (usually, grass) stand to more diverse forms in several canopy layers in detention ponds and biofiltration swales and filter strips. Such plantings are thought to give a boost to water storage, infiltration and ET. Treatment wetlands already often have such diversity, but the fringe of wet ponds could be planted in this way too.

Advances in Industrial Stormwater Treatment

As discussed above under the topic Special Considerations for Industrial Land Use, industries have source control and other ARCD options but will still sometimes have to treat runoff to meet water quality objectives. There have been recent advances in technology for these applications, documented in a peer-reviewed study growing out of a Puget Sound-area challenge by environmental groups to the general stormwater permit for boatyards. In settlement the contending parties and their technical representatives designed a study to determine the effectiveness of three treatment technologies in removing total suspended solids (TSS) and total and dissolved copper, lead, and zinc from boatyard runoff. Taylor Associates, Inc. (2008) conducted the study under contract to the parties, who managed it and reviewed and approved its results (Box 9).

Box 9. Technologies investigated for the Boatyard stormwater treatment technology study.

  • StormwateRx® Aquip™—an enhanced filtration device consisting of a pretreatment chamber followed by a series of inert media that filter particulates and adsorb dissolved substances;
  • Siemens Water Technologies, Inc. Wastewater Ion Exchange System—a device consisting of an activated carbon chamber to remove organics followed by tanks containing ion exchange resins to remove specific ionic contaminants; and
  • Water Techtonics, Inc. Wave Ionics™ Electro-Coagulation System—a device applying electric current to coagulate particles so that they either sediment, if more dense than water, or rise to the top of the water column, if buoyant, for capture.

Table 15 presents results for the first two technologies in Box 9, omitting those for the third, which was much less effective. Mass loading reductions would be similar to the concentration reductions in the table; because inflow and outflow quantities were essentially the same without infiltration and very little ET. The ion exchange unit was the more effective of the two treatments, especially in capturing zinc. Performance for copper was similar, but neither technology would guarantee meeting the water quality standard for that metal in Puget Sound or most of its freshwater tributaries at the discharge. After completion of the study StormwateRx® reached an agreement with Siemens to market their two systems together as a “treatment train” to gain the advantage of zinc capture and, probably, also somewhat reduce copper.







Average Concentration Reductionc (%)

Irreducible Minimum Concentration

Reliable Maximum Concentration


Enhanced. filt.


< 1



Ion exch.


< 1


Total copper

Enhanced filt.





Ion exch.




Total zinc

Enhanced filt.





Ion exch.




Total lead

Enhanced filt.


< 1

< 1


Ion exch.


< 1

< 1

Dissolved copper

Enhanced filt.





Ion exch.




Dissolved zinc

Enhanced filt.





Ion exch.




Dissolved lead

Enhanced filt.





Ion exch.


< 1

< 1

a TSS—total suspended solids; all concentration units µg/L, except TSS (mg/L)

b Enhanced filt.—enhanced filtration (Aquip); ion exch.—ion exchange (Siemens)

c Reported for composite samples (one grab sample also collected early in each storm)

d ND—not detected in influent and thus could not calculate

Strategies for Ubiquitous, Bioaccumulative, and/or Persistent Pollutants (BPT)
Certain toxicants found in stormwater are very widespread (ubiquitous) and persist in the same or related toxic forms over an extended period in the environment. In some cases these contaminants concentrate in the tissues of living organisms (bioaccumulation). In others they persist because of being in chemical elemental form (e.g., metals), and hence are not degradable, or are organic but degrade slowly. Some ubiquitous, persistent pollutants are relatively soluble (e.g., copper, zinc) and are, consequently, difficult to remove from runoff by conventional or even advanced treatment techniques to a level protective of aquatic life.

Box 10. BPT substances in stormwater identified by the NRC (2009) report.

  • Coal tar-based asphalt sealants, a common source of polycyclic aromatic hydrocarbons (PAHs), a group including carcinogens, mutagens, and otherwise toxicants;
  • Creosote- and chromated copper arsenate (CCA)-treated wood;
  • Zinc in tires, roof shingles, and downspouts;
  • Copper in brake pads and boat hull antifouling paints;
  • Various heavy metals in fertilizers; and
  • Road deicers, principally sodium chloride.

The NRC (2009) report pointed out that potentially less harmful substitutes exist or could likely be developed for many of these products, and also that federal legislation exists under with USEPA could restrict or ban them. Generally, this action is not happening, although the committee cited the bans on leaded gasoline and the pesticide diazanon as leading to documented large decreases in the environment. In the absence of federal action, some jurisdictions are taking action on the local level. For example, Austin, TX and Dane County, WI have banned coal tar-based asphalt sealants. These actions suggest possible strategies for the Puget Sound region to consider in advancing the product-substitution source control under a broad ARCD program. Washington got a strong start in implementing this strategy in March 2010 by becoming the first state to phase out and eventually ban copper and other metal toxicants in brake pads, pending the governor’s signing the legislation11.

These measures would address the threat of acute and chronic toxicity effects on aquatic organisms from metal and organic pollutants. They would contribute to Results Chain strategies RC6 (Stormwater) C2 generally and RC 7 (Wastewater) C1, specifically C1(2) (support Persistent Bioaccumulative Toxic program implementation)(Neuman et al. 2009).

Construction Site Stormwater Management

Land cleared of vegetation and not otherwise stabilized yields much more sediment compared to the original area well covered with plants and to the same area restablized with vegetative cover following construction. Both measurements and estimates using a mathematical model (Revised Universal Soil Loss Equation) indicate 30 to more than 1000 times as much soil loss after compared to before clearing (Novotny and Chesters 1981). Sediment discharge to receiving water bodies presents numerous threats, the delineation of which is beyond the scope of this chapter.

Effective controls are availableto prevent erosion and sediment movement and cut soil loss to a very small fraction of the maximum potential. WDOE’s (2005) Volume II is a thorough compendium of those practices. However, these techniques are often not applied effectively. The NRC (2009) committee diagnosed the problem, at least in part, as a failure to recognize the most effective practices and apply them first if appropriate to the construction site’s circumstances. To address this problem the committee outlined a recommended approach that puts the numerous types of practices in a hierarchy (Box 11). The first priorities are practices that avoid erosion, followed by those that do not entirely prevent it but limit it greatly. Sediment trapping practices are the lowest priority, because they are not nearly as effective as the erosion prevention and limiting options, although they still should be considered as backups where risk of damaging sediment release still exists.

These improvements to construction site stormwater management would likely addressthreats to salmon spawning and rearing habitat, aquatic food webs, and water quality in all downstream waters, including Puget Sound arising from the negative effects of eroded sediments and toxicants from construction materials, processes, and wastes. They would also contribute to Results Chain identified by Neumann et al. (2009).

Box 11 Recommended Construction Site Stormwater Control Measures (after NRC (2009))

1. As the top priority, emphasize construction management practices as follows:

  • Maintain existing vegetation cover, if it exists, as long as possible.
  • Perform ground-disturbing work in the season with smaller risk of erosion, and work off disturbed ground in the higher risk season.
  • Limit ground disturbance to the amount that can be effectively controlled in the event of rain.
  • Use natural depressions and plan excavation to drain runoff internally and isolate areas of potential sediment and other pollutant generation from draining off the site, so long as safe in large storms.
  • Schedule and coordinate rough grading, finish grading, and final site stabilization to be completed in the shortest possible time overall and with the shortest possible lag between these work activities.

2. Stabilize with cover appropriate to site conditions, season, and future work plans. For example:

  • Rapidly stabilize disturbed areas that could drain off the site, and that will not be worked again, with permanent vegetation supplemented with highly effective temporary erosion controls until achievement of at least 90 percent vegetative soil cover.
  • Rapidly stabilize disturbed areas that could drain off the site, and that will not be worked again for more than three days, with highly effective temporary erosion controls.
  • If at least 0.1 inch of rain is predicted with a probability of 40 percent or more, before rain falls stabilize or isolate disturbed areas that could drain off the site, and that are being actively worked or will be within three days, with measures that will prevent or minimize transport of sediment off the property.

3. As backup for cases where all of the above measures are used to the maximum extent possible but sediments still could be released from the site, consider the need for sediment collection systems including, but not limited to, conventional settling ponds and advanced sediment collection devices such as polymer-assisted sedimentation and advanced sand filtration.

4. Specify emergency stabilization and/or runoff collection (e.g., using temporary depressions) procedures for areas of active work when rain is forecast.

5. If runoff can enter storm drains, use a perimeter control strategy as backup where some soil exposure will still occur, even with the best possible erosion control (above measures) or when there is discharge to a sensitive waterbody.

6. Specify flow control SCMs to prevent or minimize to the extent possible:

  • Flow of relatively clean off-site water over bare soil or potentially contaminated areas;
  • Flow of relatively clean intercepted groundwater over bare soil or potentially contaminated areas;
  • High velocities of flow over relatively steep and/or long slopes, in excess of what erosion control coverings can withstand; and
  • Erosion of channels by concentrated flows, by using channel lining, velocity control, or both.

7. Specify stabilization of construction entrance and exit areas, provision of a nearby tire and chassis wash for dirty vehicles leaving the site with a wash water sediment trap, and a sweeping plan.

8. Specify construction road stabilization.

9. Specify wind erosion control.

10. Prevent contact between rainfall or runoff and potentially polluting construction materials, processes, wastes, and vehicle and equipment fluids by such measures as enclosures, covers, and containments, as well as berming to direct runoff.

Strategies for management of bacteria in stormwater

The following are the conclusions from a review by (Horner and Osborne 2005) that is available as supporting information to this update (Appendix 4G).

Two general methods exist to prevent or reduce shellfish bed contamination by urban stormwater: pollution source controls and runoff treatment. Source controls separate the points of pollution origin from contact with rainfall or runoff; if the separation is complete, they are 100 percent effective in preventing contamination. Runoff treatments attempt to remove pollutants already in runoff; they can reduce but cannot entirely prevent contamination, unless all runoff infiltrates the soil and only emerges to surface water after full pathogen die-off.

The literature review investigated commonly used urban stormwater treatment techniques: constructed wetlands, ponds, media filters, vegetated filter strips and swales, and hydrodynamic devices. It also covered the small amount of information available on stormwater disinfection.

Excluding disinfection, constructed wetlands yielded the best performance in terms of fecal coliform reduction efficiency and effluent quality. All other options reviewed, except disinfection, generally produced effluents with FC concentrations two to three orders of magnitude higher than the presumed target of ~101/100 mL. Ultraviolet disinfection has been shown, as would be expected, to lower concentrations below detection. However, it is the most logistically difficult and expensive option.

Even with constructed wetlands, effluent FC concentrations were still generally an order of magnitude above the ~101/100 mL target. The major exception to this observation was the StormTreat system, a modular, manufactured constructed wetland on the commercial market, which reduced influent concentrations ranging 102-104/100 mL to a mean below detection.

Kadlec and Knight (1996), in evaluating results from municipal wastewater treatment in wetlands, offered an important clue regarding why the StormTreat system can out-perform large, more naturalistic constructed wetlands in FC reduction. They concluded that constructed wetland outflow concentrations cannot consistently be reduced to near zero, or even close, without disinfection, if the wetland is open to wildlife. This point was also illustrated in the research of Grant et al. (2001) on the man-made Talbert Marsh, concluding that the seagull droppings were a direct source of FCs emerging from the marsh to the surf zone along Huntington Beach, CA. The StormTreat units are not conducive to wildlife occupancy or access by domestic animals. The Caltrans (2004) experience with a constructed wetland in an urban freeway right of way adds evidence supporting this conclusion. This wetland was not easily accessible or attractive to wildlife and domestic animals. It exhibited the lowest bacterial effluent concentrations among the installations reviewed, although they were still considerably above the StormTreat levels.

The StormTreat system thus would deserve serious further consideration for application in the Puget Sound region from the performance standpoint.

Climate Change Relative to Stormwater Management

Rosenberg et al. (2009) assessed the impact of climate change on Puget Sound’s stormwater infrastructure with predicted precipitation distributions and the Hydrologic Simulation Program—FORTRAN (HSPF) to simulate stream flow in two urban watersheds. They found that the range of precipitation projections is too large to predict effects on engineering design, and actual changes could be hard to distinguish from natural variability. Nonetheless, they suspected that the rainfall records of the past will not be a reliable design basis. As reported earlier, a shift toward higher cool-season and lower warm-season storm runoff is expected for the Puget Sound region. This pattern would tend to necessitate enlarging stormwater management facilities, but the extent of that need is not clear at this point.

Synthesis of stormwater management strategies

A leading theme of the NRC (2009) committee, and this segment of Chapter 4-2, is a comprehensive approach to stormwater management. A manifestation of that approach, now formalized in some stormwater programs around the nation, is a five-factor framework (DeBarry 2004) built around management of:

  • A groundwater recharge volume;
  • A water quality volume;
  • A channel protection storage volume;
  • An overbank flood protection peak flow rate; and
  • An extreme flood protection peak flow rate.

WDOE’s (2005) approach implicitly incorporates much of the philosophy but lacks a groundwater recharge element and treats channel protection in terms of duration instead of volume explicitly. Requirements are hence not set here for recharge and are needed to fill out the region’s strategy.

DeBarry (2004) noted that the final two factors are easily managed using the traditional post- to pre-development peak rate match for the large, infrequent storms at issue. However, the first three, involving volume management, require a more innovative strategy, in particular one using ARCD methods. The strategies emerging from the assessment presented in this segment of the chapter can be approached from the five-factor model. Essentially, they boil down to making every attempt to meet the three volume (or duration) targets by selecting, as appropriate to the location being managed, ARCD practices from among those summarized in Table 5. The intention is to apply practices in a decentralized (i.e., close to the source), integrated fashion. If a full, scientifically based analysis shows that it is indeed impossible to meet the targets with these practices, then one can turn to in lieu fees, trading credits, and/or conventional techniques to make up the difference. It was pointed out earlier that advances can be brought to bear on those conventional practices to raise their effectiveness, in part by adopting ARCD elements like soil amendment and more diverse planting. Data presented in this chapter (e.g., from the 2nd Avenue NW SEA Streets project) showed that it may even be possible in some instances to contribute strongly to meeting overbank and extreme flood protection requirements with these strategies.

Three general key strategies arise from the review of ARCD and conventional stormwater management practices and the special topics:

Strategy 1: As the principal basis of urban stormwater management, apply Aquatic Resources Conservation Design practices in a decentralized (i.e., close to the source), integrated fashion to new developments, redevelopments, and as retrofits in existing developments as necessary to meet established protection and restoration objectives. If a full, scientifically based analysis shows that it is indeed impossible to meet objectives with these practices, employ, first, in lieu fees or trading credits or, as a second priority option, conventional stormwater management practices according to Strategy 2.

Strategy 2: Employ conventional stormwater management practices when Strategy 1 options do not fully meet objectives. Increase the effectiveness of conventional vegetation- and soil-based practices whenever possible by using ARCD landscaping techniques. Apply enhanced filtration, ion exchange, or a treatment train involving both in industrial situations when source controls and ARCD measures are insufficient to meet objectives.

Strategy 3: Address special stormwater problems as follows:

3A. Promote source control under a broad ARCD program by assessing ubiquitous, bioaccumulative, and/or persistent pollutants that can only be controlled well by substituting with non-polluting products and enact bans on the use of products containing those pollutants.

3B. Improve construction site stormwater control by prioritizing, first, construction management practices that prevent erosion and other construction pollutant problems; second, practices that minimize erosion; and, last, sediment collection after erosion has occurred.

3C. To counteract dispersed sources of pathogens that compromise shellfish production and other beneficial uses, implement strong source controls and treat remaining sources with subsurface-flow constructed wetlands, assuming additional research and development verifies the promise of that technique.

14. Domestic Wastewater Issues and Strategies


With municipal wastewater treatment plants now converted to a secondary level or treatment, the former problems associated with biodegradable organics in discharges are largely solved for collected wastewater (Box 12).

Box 12. Issues concerning wastewater treatment addressed by WDOE (2008)

  • Combined sewer overflow—discharge directly into a receiving water without treatment from a wastewater collection system designed to carry sanitary sewage and stormwater in a single pipe to a treatment facility, resulting from precipitation causing a high storm runoff quantity exceeding the plant’s capacity;
  • Sanitary sewer overflow—discharge onto the land surface or a water body when the capacity of a separate sanitary sewer is exceeded, normally during storm events due to unplanned inflow from the surface and infiltration from the subsurface;
  • Advanced municipal wastewater treatment—for constituents other than the solids, biodegradable organics, and pathogens, for which secondary treatment plants are designed, remaining as threats, principally nitrogen in the Puget Sound region but could also include phosphorus and toxic metals in some cases and may expand to include pharmaceuticals and other organic consumer products now emerging as concerns; and
  • On-site wastewater treatment— the general ineffectiveness of the conventional septic tank and drain field in preventing delivery of nitrogen and, to a lesser extent, phosphorus and pathogens to nearby receiving waters via subsurface flow.

WDOE (2008) addressed each of those issues in a document intended to establish a consistent basis for the design and review of plans and specifications for sewage treatment works. Each subject represents a specialized technical field with many complexities and references of varying level available to address them.

Combined Sewer Overflows

Because of state actions under federal mandates, combined sewer overflow (CSO) interdiction programs have been underway in the Puget Sound region for a number of years, but remain incomplete. WDOE (2008) covers numerous techniques to address CSOs, prominently including: 1) Institutional controls (e.g., sewer use ordinances, pollutant source pretreatment programs); 2) Source controls (e.g., ARCD water quantity and quality controls, conventional stormwater quantity and quality controls, construction site controls, catch basin cleaning); 3) Collection system controls (e.g., sewer separation, infiltration and inflow control, maximizing use of existing system, valves and other flow regulating devices, flow diversion); 4) Storage technologies(e.g., in-line storage, off-line near-surface storage. deep tunnel storage); 5) Centralized treatment technologies (e.g., use of excess primary treatment capacity during storms to obtain some treatment, addition of primary or secondary capacity); 6) On-site treatment (e.g., off-line near-surface storage and sedimentation, screening, vortex technologies, disinfection, dissolved air floatation, filtration).

There are many considerations in selecting among the profuse alternatives, with cost being a leading one. With the documented cost savings usually accruing to ARCD methods relative to highly structural ones, there is growing interest in applying these techniques as retrofits in cities with combined sewers. The Center for Low Impact Development engaged in a two-phase project under Water Environment Research Foundation sponsorship to identify strategies for implementing decentralized ARCD controls for urban retrofits in general and CSO reduction in particular. Phase 1 of the project (Weinstein et al. 2006) demonstrated the technical feasibility of the concept by drawing on the experience of a number of early adopters using decentralized controls to complement their existing municipal stormwater and wastewater infrastructure. However, institutional and programmatic issues required further study to broaden the use of a distributed, decentralized stormwater approach.

The second phase of the project (Weinstein et al. 2009) evaluated implementation strategies for incorporating decentralized controls into an infrastructure management system. The distributed nature and multiple environmental benefits of decentralized controls necessitate an integrated and inter-departmental management approach. The Phase 2 report emphasizes policy and financing strategies, along with guidance for using common stormwater models to analyze decentralized controls. Case studies and programmatic and regulatory examples detail alternatives to expedite the adoption of decentralized controls. This work can be put to work in the Puget Sound region through the following key strategy:

Key Strategy: Bolster incomplete combined sewer overflow reduction programs by using ARCD techniques identified for application in that setting to decrease stormwater flows.

Sanitary Sewer Overflows

Sanitary sewer overflows (SSO) are considered unauthorized discharges not covered by National Pollutant Discharge Elimination System (NPDES) permits, and must be reported as spills (WDOE 2008). SSOs are mostly a function of the condition of sewer lines and their ability to exclude infiltrating subsurface water at transition points in the system (e.g., pipe joints). While it can be expensive, the strategy for addressing this problem where it exists is relatively straightforward: trace the sources of excess water and repair leaks.

15. Advanced Municipal Wastewater Treatment


Starting with the removal of treatment plant effluents from Lake Washington about 50 years ago, the outfalls of all Puget Sound-area municipally operated plants discharging to fresh waters were moved to salt water. Over the past 30 years any plants with primary treatment (solids settling) only have been upgraded to a secondary level (adding biological decomposition of organics). These improvements have greatly reduced the problems associated with discharging relatively high solids and organics. However, secondary treatment leaves high concentrations of nitrogen (N) and phosphorus (P) present in the influent domestic wastewater and, if there are contributory sources, may also discharge metals and complex organic chemicals not well decomposed in the process.

Nitrogen has become a particular concern in Puget Sound with the recognition of its role in reducing oxygen and stressing or killing fish. Secondary treatment reduces biochemical oxygen demand (BOD) from influent concentrations greatly but still leaves as much as 30 mg/L in the effluent. Material composing BOD also biodegrades and consumes oxygen. While N in the organic and ammonia or ammonium forms exerts an oxygen demand, the principal oxygen-depletion mechanism is through eutrophication, which is algal-growth-promoted, mainly by N in nitrate form, which is readily taken up and used by algae. The usual initial by-product of organic decomposition in the normally circumneutral pH of natural water is ammonium ion, with the ammonia form, toxic to aquatic life, very suppressed except at high pH. The ammonium converts, in the bacterial-mediated process called nitrification, first to nitrite-N and then, quickly in well aerated waters, to nitrate-N.

Treatment processes can enhance nitrification and make it more complete. Such processes must be aerobic, in the presence of oxygen. Once nitrate forms, though, it can only be further converted in a process mediated by anaerobic bacteria, capable of living only without oxygen, termed denitrification, where the end product is nitrogen gas. Full conversion of nitrogen from wastewater to an innocuous substance can only be performed through the sequence of nitrification-denitrification, thus requiring a sequence of opposite oxygen environments.

The growth of marine algae is generally limited by an insufficient supply of N in relation to available carbon and P. In other words, if that deficiency should be relieved by the inflow of nitrogen in wastewater, the limitation is relaxed, more primary production occurs, and algal biomass builds up in the eutrophication syndrome. If favorable growth conditions change (e.g., temperature and light decrease with the onset of autumn), cells die in large numbers and are decomposed by aerobic bacteria, taking dissolved oxygen from the water. The high P content of wastewater can reinforce eutrophication, by supplying P should it become limiting in the presence of very abundant N. P is also the limiting nutrient in fresh waters more often than N. While municipal treatment plants are no longer a concern in the eutrophication of Puget Sound’s fresh waters, on-site treatment systems and small packaged treatment plants are.

Municipal treatment plants impose pretreatment requirements on industrial dischargers to limit the influent heavy metals, which are toxic to aquatic life in varying degrees. While these plants generally have no particular processes designed to remove metals, particulate settling and incorporation in sludge reduce their concentrations. Municipal plants remain sources, but metals enter receiving waters in other important pathways, particularly via stormwater runoff and atmospheric deposition.

Domestic wastewater also contains a host of chemicals present in pharmaceuticals, cosmetics, cleaning products, industrial materials, etc. that are variably removed in secondary treatment. These chemicals are just emerging as concerns and not much is known yet about their quantities, environmental dynamics, and effects on organisms in the receiving water.

Advanced Municipal Treatment Options and Their Effectiveness and Relative Certainty

Advanced wastewater treatment, often termed tertiary treatment, can be accomplished by a number of technologies, which can be combined in different ways depending on treatment objectives, wastewater characteristics, plant configuration, and costs. This review concentrates on well developed methods that can potentially address major threats to Puget Sound and advance PSP Action Agenda and Results Chain strategies. We report primarily on nitrogen (N) and to a lesser extent, phosphorous (P) and heavy metals. While the most advanced technologies generally address all classes of pollutants, specific study of their effectiveness in removing emerging chemicals from waste streams is very sparse at this point.

According to the perhaps most authoritative textbook in the field, Metcalf and Eddy (2003), there are 12 recognized classes of physical and chemical processes for the removal of the general range of residual contaminants in treated wastewater effluents. There are also various biological techniques to reduce N and P, which are complicated by the alternating aerobic-anaerobic environments that must be produced for the initial nitrification step followed by denitrification. There are many permutations of the treatment system in both suspended- and attached-growth forms. The system can be set up in separate chambers, although it is possible for the processes to proceed in the same tank with different oxygen environments in different parts of it (Metcalf and Eddy 2003). Filtration can be added to improve nitrogen removal over what is possible with nitrification-denitrification. Depending on the process selection and operation, total N in the effluent can be reduced to a concentration of 3-10 mg/L (Metcalf and Eddy 2003).

The typical biological P removal system has an anaerobic reactor ahead of an activated-sludge aeration tank, with activated sludge recycling from the secondary clarifier to the head of the process and, in some designs, an intermediate reduced-oxygen chamber (Metcalf and Eddy 2003). Anaerobic organisms in the first vessel accumulate complex forms of P and release simplified, more directly usable forms like orthophosphate, which are incorporated into cell tissue in the aerobic reactor and subsequently settled out. A total P effluent concentration of ≤ 2 mg/L can be attained through biological treatment alone (Metcalf and Eddy, Inc. 2003). In a survey of 23 advanced municipal wastewater treatment plants nationwide, USEPA (2007c) found that a concentration as low as 0.3 mg/L was often attained. The same survey established that addition of aluminum- or iron-based coagulants to wastewater followed by tertiary filtration can reduce total P concentrations in the final effluent to near or below 0.01 mg/L. Combined systems can be designed to treat for both P and N.

Among the 12 classes of available physical and chemical treatment alternatives, membrane technologies represent the best combination of a relatively high state of development and treatment versatility, including removal of both N and P (Metcalf and Eddy 2003). The primary membrane applications and their abbreviations and filter pore sizes as designated by the Water Environmental Federation (WEF 2006) are: (1) low-pressure membranes- microfiltration (MF) and ultrafiltration (UF), (2) nanofiltration (NF), and (3) reverse osmosis (RO). A membrane bioreactor (MBR) is a combination of suspended-growth activated sludge secondary biological treatment with MF or UF replacing the conventional secondary clarifier, either submerged in the bioreactor or placed in a subsequent unit. The arrangement can precede discharge or serve as pretreatment for highly advanced NF or RO follow up (WEF 2006).

Table 16 gives a membrane technology performance summary for the contaminants of most concern in the Puget Sound ecosystem. MF following conventional secondary treatment does not improve overall performance as much as the MBR configuration. In comparison to the purely biological treatments covered above, capable of achieving total N and P concentrations of 3-10 and 0.3-2 mg/L, respectively, MBR is comparable or a slight improvement for N and somewhat better for P. Adding RO to MF or UF conveys major performance advantages at increased cost. Based on the data presented above, coagulant addition and filtration can improve P removal even more, although without nearly as much advantage for N reduction.





Conventional Activated Sludge

Conventional Activated Sludge + MF




Conventional Activated Sludge + MF or UF + RO

Biochemical oxygen demand

5 – 30


< 2 – 10

< 2 – < 5

< 2 – < 5


15 – 25

20 – 35

< 1

≤ 0.1


1 – 2

20 – 35

< 3 – < 10c

ND – < 2

Total nitrogen

15 – 35

5 – 30b

< 3 – < 10c

≤ 0.1

Total phosphorus

1 – 10

0.1 – 8d

< 0.2 – 1d

≤ 0.5

a MF—microfiltration; MBR—membrane bioreactor; UF—ultrafiltration; RO—reverse osmosis; ND—not detectable

b Total Kjeldahl nitrogen (nitrogen in organic plus ammonia or ammonium ion forms)

c< 3 mg/L with pre- and post-anoxic zones; < 10 mg/L with pre-anoxic zone only

d With chemical addition

The reverse osmosis system is also effective in metals removal. Reported effluent concentrations (all as total recoverable metals in µg/L) are: arsenic—< 2 – 5, cadmium—< 1 – < 10, chromium—< 10 – < 50, and mercury—< 0.2 – < 2 (WEF 2006). These concentrations would be sufficiently low to meet or approach fresh and marine water receiving water quality standards at the discharge point (i.e., without dilution).

Synthesis of Strategies

If nitrogen discharge from a municipal treatment plant is a serious threat, reverse osmosis tertiary treatment with highly efficient filtration as a pretreatment is the most effective and certain solution (Metcalf and Eddy 2008, WEF 2006). The same solution can apply to phosphorus and toxic metals. However, if phosphorus alone is the problem, then coagulation and tertiary filtration appears to offer an equivalent or possibly even better solution. That latter situation is not likely to occur in the Puget Sound region though.

Key Strategy: If nitrogen discharge from a municipal treatment plant must be reduced below 1 mg total nitrogen/L to remove a threat to marine dissolved oxygen resources, apply reverse osmosis tertiary treatment with highly efficient filtration as a pretreatment. If analysis demonstrates that a lesser reduction will suffice, apply membrane bioreactor treatment.

The nitrogen-reduction strategy supports Results Chain strategies RC 7 (Wastewater) C1, specifically C1(8) and C1(9) (remediation actions to address low dissolved oxygen); and C3, specifically C3(1) (advanced wastewater treatment), C3.1.1 (improved nitrogen removal at wastewater treatment plants), and C3.4 (technologies that reduce nutrients) (Neuman et al. 2009).

On-site Wastewater Treatment

On-site wastewater treatment refers to systems treating effluents, most often domestic, from a single building or a small cluster. A typical conventional on-site treatment system consists of a septic tank and a soil absorption field (drain field). The septic tank functions as an anaerobic bioreactor promoting partial digestion of organic matter and solids settlement. The drain field distributes septic tank effluent through perforated pipes into the soil for additional biological processes, adsorption, and filtration before infiltration of the water to groundwater.

These systems work well if they are installed in areas with appropriate soils, hydraulic capacities, and separation from groundwater; designed and installed properly; maintained in good operating condition; and replaced when necessary to maintain performance. These criteria are often not met, however. Only about one-third of the United States land area has soils suitable for conventional on-site systems (USEPA 2002). In addition, septic tanks and drain fields are frequently not large enough for the flows from modern houses, system densities sometimes exceed the capacity of even suitable soils to effectively process waste, and installations are too close to ground or surface waters. As a consequence failure rates are known to be high but are difficult to establish precisely for a number of reasons, including varying definitions of failure. The failure rate in Washington is estimated at 33 percent (USEPA 2002).

The main consequences of failure are contamination of groundwater, surface waters, or both by nitrates, phosphorus, and/or disease-causing bacteria and viruses. Table 17 summarizes the performance capabilities of a well-functioning conventional drain field. It is evident in the table that the conventional system can produce a BOD as low as or even lower than secondary treatment.



Typical Septic Tank Effluent Concentration

Soil Removal Efficiency (%)

Concentration Remaining in Water Exiting Drain Field

BOD (mg/L)




Total N (mg/L)




Total P (mg/L)




Fecal coliforms (CFU/100 mL)




a BOD—biochemical oxygen demand; N—nitrogen, P—phosphorus, CFU—colony forming units.

In contrast to P, soils do not have a similar capacity for N, which is mostly in the highly soluble ammonium form in a septic tank effluent. Nitrification is rapid in the aerobic environment of the soil, with the result that nitrate, also highly soluble and at a very elevated concentration, makes up most of the total N moving out from the drain field (USEPA 2002). The nitrate can penetrate to groundwater, where it can be a health risk if the water is drawn for potable supply. Methemoglobinemia, (“blue baby syndrome”) is the most well-established effect, but others are suspected (Washington State Department of Health 2005). As Table 17 shows, conventional systems are highly efficient in reducing disease-causing organisms, represented by fecal coliforms, an indicator organism present with numerous pathogens in sewage. However, the numbers are so high that even strong removal can leave counts in the many thousands for each 100 mL of water. Failed systems would do far worse yet. As with nitrogen, waters are threatened by pathogen-contaminated groundwater and surfacing effluent, especially from installations near the shore.

Advanced On-site Treatment Options and Their Effectiveness and Relative Certainty

Advanced treatment categories and specific examples put forth by Jantrania and Gross (2006) include aerobic treatment units, media filters using such substances as sand, peat foam and textiles, natural systems such as treatment wetlands and greenhouses, waterless toilets and disinfecting systems using UV light or chlorination.

Aerobic treatment units are essentially miniature versions of devices commonly used in municipal secondary treatment plants. Numerous packaged units are on the commercial market for small-scale applications. Given their process similarity to larger scale secondary treatment, their effluent quality is also similar: approximately 15-35 and 1-10 mg/L total N and P, respectively. Since they normally discharge to soil, additional reductions are possible there. However, since the reason to use such an option is often poor soils, further capture may not be much. Pathogens are not greatly reduced by secondary treatment, or the miniaturized aerobic treatment units, alone and require disinfection if soil or other conditions make pathogens a threat to receiving waters.

Media filters are normally placed between a septic tank and drain field. The most common are sand filters in single-pass or recirculating form. Packaged units with sand and other media are available on the market. Table 18 gives reported performance data (USEPA 2002).


Single-Pass Filters

Recirculating Filters

Biochemical oxygen demand (mg/L)



Total nitrogen (mg/L)



Fecal coliforms (No./100 mL)



There is a great deal of literature on treatment wetlands for municipal wastewater treatment, generally in relative small communities. These reports can give further insight on what might be possible to achieve in on-site treatment wetlands. The summary data (USEPA 2000) show that only systems with open water can achieve much nitrogen reduction, to < 10 mg total Kjeldahl N/L. With a long hydraulic retention time (up to 15 days), effluent can be maintained at < 1.5 mg total P/L. As discussed above, pathogen reduction is expected to be better with a submerged-bed wetland (without a free water surface), but this configuration would be disadvantageous for nitrogen removal. Nevertheless small treatment wetlands appear to offer promise of effluent quality roughly comparable to discharges from aerobic treatment units and media filters (USEPA 2000).

The Washington State Department of Health (WSDOH 2005) reviewed specific on-site nitrogen-reducing technologies for WDOE. The review concluded that biological nitrification-denitrification is the only process that has been demonstrated to be technically and economically feasible for on-site applications. The process must be structured to manage the alternating aerobic/anaerobic environments required for the two steps. The aerobic phase can be accomplished by a variety of aerobic treatment units or media filters. The anoxic phase requires addition of organic carbon to nourish the bacteria. One option is to recycle nitrified wastewater back through the septic tank, where the anaerobic, high carbon environment can facilitate denitrification. Another is to provide a separate denitrification chamber and external carbon source.

Numerous non-proprietary (public domain) and proprietary (patented) systems exist to provide these functions. USEPA and the National Sanitation Foundation have collaborated on an Environmental Technology Evaluation protocol to test and verify the performance of these systems (WSDOH 2005). Six technologies have completed the testing and exhibited total N effluent concentrations in the range 14-19 mg/L. An additional nine products have been tested in USEPA demonstration projects and reported a wide range of 2-83 mg total N/L in effluents. The NITREX™ system, a processed wood fiber media filter13, showed the best performance, discharging 2.0-2.4 mg/L, but was tested at only two installations (WSDOH 2005).

Synthesis of Strategies for Controlling Wastewater

The reported results show that a specialized solution must be sought if nitrogen is the threat to be countered. A reasonable strategy for the Puget Sound region would be to test further the available system(s) exhibiting the best results in limited assessments. It would not be appropriate to adopt any generic type of system, as different versions of a general technology type have exhibited varying performance. It would also not be appropriate to adopt a promising system that has not been thoroughly tested under regionally prevailing conditions.

If pathogens are a threat, it is highly likely that no system designed for nitrogen removal will reduce them sufficiently; and disinfection will be necessary. Since small-scale disinfection is not very well developed, additional research and development work will be necessary in this area.

Phosphorus is a threat to lakes with heavily inhabited shorelines using conventional on-site systems. The review did not reveal as much work to address P with advanced treatments as appeared for N. The limited results available do not indicate alternatives that can lower concentrations to the levels that affected lakes would need for substantial water quality improvement. Lake eutrophication from on-site systems is a localized problem in comparison to the more broadly distributed threats from nitrogen and pathogens discharged to marine waters with oxygen depletion and shellfish bed contamination.

As an alternative to the continuing on-site treatment, with presently developed advanced treatment options of only limited effectiveness relative to the treatment need to meet environmental objectives, would be to construct sewers and a municipal treatment plant where on-site systems are a leading threat. However, it would be essential to apply this strategy in such a way that it did not lead to additional development, the storm runoff from which could undo progress made from eliminating on-site wastewater discharges.

Key Strategy: If discharges from on-site wastewater treatment systems are a serious threat to: (1) marine dissolved oxygen resources as a result of nitrogen; or (2) shellfish production or contact recreation as a result of pathogens, assess as possible solutions: (1) construct sewers and a municipal treatment plant, with advanced treatment for nitrogen if that is the threat, to replace problem on-site systems; or (2) apply advanced on-site treatment, tested and verified to reduce the problem sufficiently to remove the threat (note: at this point more testing is required for both on-site nitrogen removal systems and small-scale disinfection).

16. Strategies to Manage Agricultural Activities for Water Quality Protection

Best Management Practice Guidance

Best management practices are available to serve virtually every agricultural function. The Natural Resources Conservation Service (NRCS) of the U.S. Department of Agriculture has codified them in the National Handbook of Conservation Practices (NHCP, NRCS 2007b), containing more than 165 practices. For each BMP the NHCP presents a standard and a conservation practice physical effects (CPPE) worksheet. The conservation practice standard contains information on why and where the practice is applied and sets forth the minimum quality criteria that must be met during its application for it to achieve its intended purpose(s). The CPPE worksheet provides guidance on how the application of the practice will affect the resources (soil, water, air, plants, animals and human) and the concerns associated with each of those resources. It reflects the best estimate of the effects, either positive or negative, of the practice on the resource concerns. For many practices there is also a conservation practice information sheet and a job sheet. The information sheet contains a photograph of the installed practice, a definition or description, where it is commonly used, and a brief, qualitative description of its conservation effects when it is properly applied. The job sheet provides detailed guidance on the application of the practice and has worksheets that can be used to document the practice plan and design for a specific site. The NHCP cautions that the standards themselves should not be used to plan, design, or install a conservation practice; instead the specific analogous standard developed by the state in which the agricultural site is located should be consulted to insure that all state and local criteria are met. The Washington State Department of Agriculture’s website14 provides some related guidance, but the department apparently has not comprehensively revised the NHCP practices.

Mostaghimi et al. (2001) summarized 18 commonly used practices from the NHCP and two other emerging ones (integrated pest management and precision farming). Each BMP is described and assessed for its impact on the physical, chemical, and biological processes that control the generation and transport of pollutants. Each practice is classified in two ways: (1) purpose (source reduction, transport interruption, or a combination), and (2) mechanism (managerial, structural). Next, each account covers the situations and pollutants for which the practice is appropriate. A third section discusses any negative effects and limitations. Finally, the presentation suggests combinations of practices that can synergize effectiveness. This book chapter is a useful adjunct to the NHCP.

Special Considerations for Nutrient Management Pertinent to Puget Sound

As pointed out earlier, N is generally the nutrient limiting, and therefore controlling, algal growth in marine waters; while P usually plays that role in fresh waters. However, relieving a limitation with excess supply of one nutrient can switch control to the other and stimulate algal growth further. This eutrophication process yielding high algal production results in a number of problems in the affected water. Oxygen depletion caused by the death and decay of marine algae stimulated by nitrogen supply is the issue of greatest prominence now in the Puget Sound region. Relative to the interplay between these two nutrients, some important considerations in selecting and applying agricultural BMPs have emerged in the research literature.

Based on up to 30 years of experimental and monitoring data from a Pennsylvania watershed, Pionke et al. (2000) found that most of the surface runoff and P export originated from areas near the stream. About 90 percent of the form of P most available to algae exported in outflow was generated during the largest seven annual storms. In contrast, nearly all N was exported in the nitrate form and originated as subsurface flow entering the

soil or groundwater some distance from the stream. These flows occurred during non-storm flow periods. Heathwaite et al. (2000) estimated the primary P-yielding zone to constitute < 20 percent of the total contributing area, while the upland N-generating areas were around 60 percent, in locations of well-draining soils and high fertilizer and manure application. The researchers concluded that strategies for managing P should focus on the few larger storms and relatively small critical source areas (Heathwaite et al. 2000). Conversely, strategies for N control depend more on balancing nitrogen application over the watershed. Without integrating strategies, solving one water quality problem can aggravate another. For example, practices applied to reduce surface runoff and P export by increasing infiltration will typically increase groundwater recharge and nitrate leaching.

Sharpley et al. (2001) took observed that the small areas disproportionately exporting phosphorus are located where high soil P, or P application in mineral fertilizer or manure, coincide with high runoff or erosion potential. They argued that the overall goal of efforts to reduce P loss to water should involve balancing P inputs and outputs at farm and watershed levels by optimizing animal feed rations and land application of P as mineral fertilizer and manure, targeted to relatively small but critical watershed areas for P export. These authors elaborated on the need to manage N and P together, citing more examples of how practices directed toward one can enlarge a problem with the other. For example, basing manure application on crop N requirements to minimize nitrate leaching to groundwater can increase soil P and its export. In contrast, reducing surface runoff losses of total P via conservation tillage can enhance N leaching and even increase algal-available P transport (Sharpley et al. 2001)

Sharpley et al. (2001) also advocated development of a technically sound framework that recognizes critical sources of P and N export so that optimal strategies at farm and watersheds scales can be implemented to manage both together in the best way. One approach is to employ a phosphorus index to target its management toward critical P-source areas and apply N-based management on all other areas. As reported by Sharpley et al. (2003), the P indexing approach has been adopted by 47 states. The index ranks site vulnerability to P loss by accounting for source (soil test P, fertilizer, and manure management) and transport factors (erosion, runoff, leaching, and connectivity to a stream channel). Some states have modified the index to reflect local conditions and policies. Careful consideration must be given to the potential long-term consequences of N management on P loss and vice versa.

Lowrance et al. (1984) provided early support, but also qualification, on the value of a riparian buffer between agricultural fields and streams. They studied a subwatershed of the Little River, Georgia, 1568 ha (3872 acres) in area, with 30 percent riparian forest; 41 percent row crops; 13 percent pasture; and 16 percent roads, residences, fallow land, and other uses. They estimated nitrogen and phosphorus retention by the riparian buffer at 68 and 30 percent, respectively, of the inputs. Soils of the riparian ecosystem presented ideal conditions for denitrification: high organic matter from input of forest litter; seasonal waterlogging leading to anaerobiasis; and large inputs of nitrate-N in subsurface flow. Denitrification outputs alone were enough to remove all of the N inputs from upland fields to the riparian zone. The lack of an analogous process limited P retention.

The results from Lowrance et al. (1984) point out the particular importance of tributary riparian buffers to interrupt nitrogen transport to N-limited marine waters. However, the findings regarding P export originating mainly near streams indicate that riparian buffers can also play a larger role in stemming discharge of that nutrient than indicated by the modest 30 percent retention, not from interrupting transport but from excluding agricultural operations where they have the greatest potential to yield P to the receiving water (Lowrance et al. 1984).

Strategy Effectiveness for Nutrient Management and Relative Certainty

The NRCS National Handbook of Conservation Practices (NHCP) gives qualitative indications of practice effectiveness but not the quantitative data needed for objective comparisons among options. USEPA’s (2003c) National Management Measures for the Control of Nonpoint Pollution from Agriculture partially fills this gap, drawing on the extensive but uncoordinated research on the performance of some of the many NHCP practices. The USEPA document covers BMPs for nutrient management, pesticide management, erosion and sediment control, animal feeding operations, grazing management, and irrigation water management.

Synthesis of Strategies

NRCS’s NHCP is an exhaustive compendium of practices available to prevent or reduce contamination of water, and the USEPA (2003c) manual is one source of quantitative effectiveness and relative certainty data. Relative to the particular concern with eutrophication, the research literature offers a clear and conclusive strategy for integrated management of nitrogen and phosphorus sources.

Key Strategy: Upgrade the implementation of established agricultural best management practices, especially where agricultural runoff is: (1) a eutrophication threat as a result of nitrogen (N) and/or phosphorus (P); or (2) a threat to shellfish production or contact recreation as a result of pathogens. Manage nitrogen and phosphorus in concert by: (1) employing a phosphorus index to target management of critical P source areas, generally near receiving waters; and (2) applying N-based management to all other areas. Maintenance of riparian buffers advances both facets of the strategy by keeping agricultural activities out of the potentially most critical P production area and providing a sink for N to capture the majority of it before it can enter the water.

Further work is needed to institutionalize this strategy in watersheds subject to the negative impacts of eutrophication and, in general, to provide more directed guidance on the full range of contaminant issues to Puget Sound agricultural concerns.

1. Forestry Water Pollution Sources and Control Strategies

The potential for sediment delivery to streams is a long-term concern from almost all forestry harvesting activities and from forest roads regardless of their level of use or age (i.e., for the life of the road). Other pollutants, generally of somewhat shorter concern, include nutrients, increased temperature, toxic chemicals and metals, organic matter, pathogens, herbicides, and pesticides (USEPA 2005). Forest harvesting can also affect the hydrology of a watershed, with potential to degrade aquatic ecosystems. Forestry activities can also affect the aquatic habitats through physical disturbances caused by construction of stream crossings, equipment use within stream corridors, and placement of slash or other debris generated by forestry activities within streams. Negative impacts and conditions vary with location and water body type, but in general the ecological conditions that management measures and BMPs are intended to protect include the following (USEPA 2005) (Box 11):

Box 11. Attributes of watersheds that best management practices put forth by the USEPA (2005) are intended to protect.

  • General water quality, by minimizing inputs of polluted runoff;
  • Water temperature, by ensuring an adequate (but not excessive) and appropriate amount of shade along shorelines and stream banks;
  • Nutrient balance, by providing for an adequate influx of carbon and nutrients that serve as the basis of aquatic food chains;
  • Habitat diversity, by ensuring that inputs of large organic debris to the aquatic system are appropriate for the system; and
  • Hydrologic processes, by limiting disturbances to stream flow patterns, both seasonal and annual.

As with the segment on agriculture, we present only a brief summary of strategies available to reduce water pollution from forestry activities. Again, numerous practices have been developed and well institutionalized to control the full range of activities. This review generally describes the system existing in Washington and sources of best management practice information. With no attempt at comprehensiveness here, further detailing could be a follow up in a future edition of the Puget Sound Science Update.

This account addresses PSP Results Chain strategies RC6 (Stormwater) C2, specifically C2.8 (private stewardship and incentives for pollution prevention). Forestry activities are both private and public, under the jurisdictions of the U.S. Forest Service and the Washington Department of Natural Resources.

Strategies to Manage Forestry Activities for Water Quality Protection: Best Management Practice Guidance

Modern management of forestry in relation to water resources in Washington stems from 1986, when Tribes, the timber industry, the state, and the environmental community decided to try to resolve contentious forest practices problems through negotiations as an alternative to competitive lobbying and court cases. This process resulted in the first Timber Fish Wildlife (TFW) agreement in 1987.

Over the years of TFW operation, regulation and management of forestry for the protection of water resources became well developed in Washington. Forest Practices Rules 15 , a compilation of 15 chapters of the Washington Administrative Code (WAC), establish standards for forest practices such as timber harvest, pre-commercial thinning, road construction, fertilization, and chemical application (Title 222 WAC). They give direction on how to implement the Forest Practices Act (chapter 76.09 Revised Code of Washington [RCW]) and Stewardship of Non-industrial Forests and Woodlands (chapter 76.13 RCW). The rules are designed to protect public resources such as water quality and fish habitat while maintaining a viable timber industry. They are under constant review through the adaptive management program. The Washington Department of Natural Resources’ (WDNR) Forest Practices Board Manual16 is an advisory technical supplement to the forest practices rules. It consists of 26 sections containing the BMPs for the full slate of forestry activities and detailed guidance for their proper implementation.

Listing of certain species of Pacific salmon as endangered or threatened resulted in a new round of TFW activity in the late 1990s. The interagency caucus formed issued the Forests and Fish Report17 to the Forest Practices Board and the Governor’s Salmon Recovery Office presenting recommendations for the development and implementation of rules, statutes, and programs for the protection and recovery of salmon. The general goal was to develop biologically sound and economically practical solutions to protect and improve riparian habitat on non-federal forest lands in the state, known as the “forestry module” for Washington’s Statewide Salmon Recovery Strategy. This report does not outline BMPs per se but has influenced their development and adoption.

Strategy Effectiveness and Relative Certainty

The Forest Practices Board Manual does not provide data on the effectiveness and relative certainty of the BMPs covered. However, substantial performance data have been compiled in federal and state reports. USEPA’s (2005) National Management Measures to Control Nonpoint Source Pollution from Forestry gives such data for many practices associated with pre-harvest planning, streamside management, road construction and subsequent management, harvesting, forest regeneration, fire management, revegetation, chemical application, and wetlands management. The TFW Cooperative Monitoring, Evaluation, and Research Committee sponsored three performance studies during the 1990s. Rashin and Grabin (1992) assessed riparian management zone regulations for protection of stream temperature. Rashin and Grabin (1993) covered BMPs for aerial application of forest pesticides. Finally, Rashin et al. (1999) reported on the performance of forest road and timber harvest practices. These works provide a basis for the following key strategy.

Key strategy: Upgrade the implementation of established forestry best management practices to protect stream water quality and hydrology in the vicinity of forestry activities and minimize the delivery of pollutants from those activities to downstream receiving waters, including Puget Sound.







6 Stormwater control measures, also known as best management practices (BMPs)

7 This account is adapted from NRC (2009) and was originally written for that report of the author of this section











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