Puget Sound Salmon - Importance of Using Low-impact Development Methods in The Built Environment

Importance of Using Low-impact Development Methods in The Built Environment

Paving large expanses of land increases runoff of pollutants into our streams and rivers that eventually wash into Puget Sound. This impact is evident in the fact that salmon have large quantities of PCBs in their bodies. In 2007 the Department of Health issued a consumption advisory warning against eating Puget Sound salmon.

Since 1991, there has been a marked increase in the amount of impervious surfaces in the Greater Puget Sound area. Impervious surfaces are man-made structures such as roads, house foundations and roofs that prevent water from being absorbed and filtered through the soil. Stormwater management systems have reached their capacity to catch and treat this runoff water. Sudden increases in stream flow that occur during high rainfall can be greatly exacerbated by urbanization that replaces natural vegetation with pavement or rooftops.

The Department of Ecology found that surface runoff is the largest source of toxic chemicals being deposited into Puget Sound. Streams drain directly into Puget Sound from roads, driveways and rooftops, without benefit of filtration.

It is possible to reduce pollution of streams and rivers by using Low Impact Development (LID) methods in construction projects. These low-impact development methods are environmentally friendly by reducing the amount of storm water runoff that reaches Puget Sound. These building methods not only help Puget Sound salmon, but also benefit humans through increasing property values, and enhancing aesthetic appeal.

Rain gardens

Salmon friendly gardens, also called rain gardens, would prevent overflow and surges and would absorb pollutants which would otherwise be washed directly into freshwater systems. When a storm causes rainwater to surge into rivers and streams via storm drains, the heavy flow of fast moving water commonly erodes the soil thus destroying precious salmon and steelhead habitat. Said storm drain surges are typically warmer in temperature than the water of the streams into which they are being deposited. This causes river and stream temperatures to rise and places further stress on growing and migrating salmon and steelhead. The salmon friendly gardens are planted as depressions in the ground, and work by absorbing much of the rainwater runoff which is redirected to first flow through the gardens before ultimately ending up in the rivers and streams. The gardens therefore slow and lessen the storm surges and filter out pollutants being washed out of the city. Planting rain gardens would result in less erosion, lower and stable water temperatures, and less pollutants entering freshwater systems.


Urbanization of the Puget Sound lowlands has had a primarily negative impact on the salmon species that spawn in the surrounding streams and rivers. One of the most noticeable changes in these urbanized areas is the increase in the traditional 10-year flood being reduced to occurring once every 1–4 years. As a result of this increase in flood waters the areas where salmon lay their eggs are being washed away; this is because salmon lay their eggs just far enough beneath the bedrock to accommodate for the traditional annual flood, but due to urbanization the annual flood waters have increased and the layer of bedrock where salmon lay their eggs is washed away. This leaves the salmon with less habitat to successfully spawn on as a result. As stated above the one way to fix this problem is to use LID methods to help with the filtration process which at the same time reduces the quantity of water being put into the streams and rivers.

Read more about this topic:  Puget Sound Salmon

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