Stormwater

Sandwiched between the Olympic and Cascade mountain ranges, Puget Sound's urban areas receive up to 40 inches of rain each year. Historically, most of this water soaked into the ground or was taken up by plants. In forested areas in the Pacific Northwest, evergreen trees transport about 40% of rainfall back to the atmosphere through their needles. The remaining water filters through other plants and the soil. The ecosystem is driven by this water cycle, but over the past 100 years, human development has drastically altered this natural pattern.

Urban areas were originally designed to move stormwater quickly and efficiently downstream through a series of drains, pipes, and sewers. Flood prevention was the main reason for getting stormwater out of the city fast, but over the years municipalities have come to realize that speedy water removal is actually detrimental to the health of Puget Sound.

Without the filtering effect of plants and soil, surface runoff increases and stream flows become "flashier"—surges in runoff are more frequent and more intense. This means greater flooding, and more polluted water flowing into Puget Sound.

 

Source: "Stormwater fixes could cost billions"; Salish Sea Currents.

Stormwater flowing into catch basin carries contaminants to our waterways. Photo: Ben McLeod (CC BY-NC-SA 2.0) https://www.flickr.com/photos/benmcleod/420158390

OVERVIEW

Stormwater facts

Runoff from rain and melting snow is one of the leading causes of pollution in Puget Sound. Here are selected facts related to stormwater, its prevalence, how it affects the Puget Sound ecosystem, and its environmental and economic impacts.

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