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Water Quality Program

Polluted runoff: Why Washington also regulates flow

Stormdrain pipe empties into a streamWashington’s municipal stormwater regulations are well understood for the pollution problems they address, but our regulations are less understood for the flow standards they provide.

Washington’s flow standard helps protect our state’s salmon populations and stream health.

Since polluted runoff — or stormwater — was included in the federal Clean Water Act permit program in 1987, we have a greater understanding of the environmental problems it causes.

People now understand that runoff from hardened surfaces in populated areas picks up chemicals and bacteria and carries them downstream into our waters.

And most of the time, stormwater is not treated, even when it goes into a street drain.

Harm from flows

However, there is also harm from uncontrolled runoff flows. High flows can cause significant environmental damage, putting our state’s threatened and endangered salmon at risk.

Development vs. natural conditions

Under “natural” conditions, before land was developed, there was virtually no surface runoff from the land. Forests absorbed much of the rainfall and snowmelt and released it slowly to streams. The aquatic species living in the streams of Western Washington, in particular the Northwest’s iconic salmon, adapted to thrive in waters adjacent to forested lands.

When we develop the land and cut down trees without regard for controlling stormwater, we increase runoff. The runoff comes off the land much faster. The runoff meets hard surfaces, rushes downhill where it scours smaller creeks and streams and causes flooding. When this happens, creeks and streams become inhospitable to salmon and aquatic life.

Runoff: before and after development

Under the federal Clean Water Act, it’s the state’s job to write permits that protect and restore water quality. If we don’t address the higher flows, as well as the pollution, that occur as a result of development, we are not doing our job.

Flow-control standard is working in many areas

The state’s flow control standard for Western Washington has been used on many sites in King County for over a decade. As required by their municipal stormwater permits, more than 90 municipalities and the Washington Department of Transportation, have adopted the standard in their areas.

However, some communities struggle with the concept of a flow control standard, especially those that neighbor other states with less proactive flow standards.

The state has a mandate to control runoff flows

The state’s Pollution Control Hearings Board has upheld the flow control standard and also ruled that the Department of Ecology require local governments to do more to address other hydrologic changes caused by land development.

Many cities and counties are already using wise development and redevelopment practices that reduce runoff. Through wise development practices, they are saving money by preventing new runoff problems.

Low-impact development is an example of wise development. It attempts to mimic nature so water can be taken up by trees or soak into the ground.

Additional information

Environment Education Guide: Protecting Washington’s Waters from Stormwater Pollution

Municipal Stormwater Permits