An overview of Shoreline armoring in Puget Sound

More then 700 miles of Puget Sound shoreline is considered to be "armored," and as much as four miles of new armoring is added each year.

Shoreline armoring along railroad
Shoreline armoring along railroad. Photo: NOAA.

Much of Puget Sound's more than 2500 miles of shoreline is susceptible to erosion, depending both on its substrate type (e.g., whether it is bedrock or sandy bluff) and the hydrologic forces to which it is subject (e.g., wave action, runoff, or tides). 

Even in the recent past, shoreline erosion was thought solely a problem, rather than also a natural process that shaped the ecology of the Sound. In places where human development made both predictable and durable shores desirable, private property owners armored their shorelines to prevent them from eroding. They did this—and continue to do it—either by building a seawall or bulkhead, or covering a beach with riprap. According to a 2010 report by the Washington State Department of Ecology, more then 700 miles of Puget Sound shoreline is armored in one way or another, and as much as four miles of new armoring is added each year.

The extent of armoring can vary widely by region. More than 90% of the urban corridor between Tacoma and Everett is armored, while the number is 5% in far more lightly populated San Juan County. Two laws principally govern shoreline armoring in Washington State: the Shoreline Management Act of 1972, and the Hydraulics Code, which was first passed in 1943. Both dictate where and under what conditions armoring is allowed.

Shoreline armoring may prevent erosion above the structures, but it can also have profound impacts on nearshore ecosystem goods and services, as well as the ecology of marine organisms. The beaches in front of bulkheads may erode to the point of vanishing altogether. At the same time, nearby unarmored beaches may not be replenished with substrate from armored beaches. Also, armoring can lead to a loss of ecological connectivity between different beaches, due to the lack of shifting sands. The biotic community of Puget Sound shorelines is incredibly diverse, owing to the variety of coastal habitat types, from muddy beaches that support burrowing shrimp as well as clams and polychaetes, to the extensive eelgrass beds found on sandier beaches, which serve as refugia for salmonids, among other species.

Two species of special concern are surf smelt and Pacific sand lance. Both are forage fish that marine mammals, birds, and larger fish species depend upon. Both also spawn on sandy beaches throughout the region—sand lance in the winter, and surf smelt throughout the year, peaking in late summer and fall. A 2006 article in Estuaries and Coasts found that the proportion of surf smelt eggs with live embryos on a gravel-sand beach that was armored was half as high as on a nearby natural beach. Most likely, the difference was due to microclimate changes that hardening caused: the modified beach was a third again as warm, and had much greater sunlight intensity.


To protect existing shorelines and restore more compromised ones, the Puget Sound Partnership (PSP) has proposed three ways to mitigate the effects of armoring. By 2020, PSP aims to have the amount of armoring removed (primarily from public areas) greater than the amount of armoring added, for a net decrease in total shoreline armoring. The agency also wants to place new emphasis on so-called “soft shore” armoring techniques, for places where armoring must be replaced.

About the Author: 
The Encyclopedia of Puget Sound is published by the University of Washington’s Puget Sound Institute and represents the collective knowledge of leading experts from state and federal agencies, academic institutions and Puget Sound area tribes. It is intended as a primary source for synthesized and integrated scientific information on the Puget Sound and greater Salish Sea watersheds.