- Public Works
- About Stormwater
- Stormwater Runoff
Stormwater runoff is unfiltered overland water flow that occurs when precipitation on snowmelt flows over the ground, especially over impervious surfaces - which includes roads, parking lots, driveways and roofs. This website page will help you understand the impacts that stormwater runoff has on all of us. But first, it's important to know how the water cycles works.
How does the water cycle work?
The water cycle is the basic process by which water is recycled. When water falls from the clouds as rain, snow, sleet or hail (precipitation) it takes one of the following paths:
- It seeps into the ground surface and becomes part of the groundwater, which feeds streams, wetlands, and aquifers.
- It is absorbed by vegetation and then transpires (evaporated from the plant tissues).
- It flows into rivers, lakes, reservoirs, etc.
- It remains in lakes or top soil and eventually evaporates back into the atmosphere.
What's the Problem?
In a natural setting, the majority of rainfall soaks into the forests and meadows and slowly flows underground, being naturally filtered before reaching streams, lakes, underground aquifers, and Puget Sound. When meadows and forested land is replaced by impervious surfaces (streets, driveways, rooftops, patios, etc.), stormwater runoff is produced. The natural process of the water cycle is modified and the rain water can no longer penetrate into the earth. As a result, the rain water (stormwater) flows directly into storm drains, ditches, and streams, all without the benefit of the natural filtration process.
To add to this problem, stormwater runoff from the urban areas often picks up pollutants along the way - carrying motor oils, fertilizers, pesticides, and even pet waste. These examples represent types of pollution called non-point source pollution. Non-point source pollution is a major problem, and is the primary contributing factor to water quality degradation nationwide. Regionally, non-point source pollution accounts for over half of the pollution reaching our creeks, streams, rivers, and the Puget Sound.
Stormwater pollution prevention is a community effort. Click here for tips on how you can help.
And always remember ~ Puget Sound Starts Here.