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Storm water discharges are generated by runoff from land and impervious areas such as paved streets, parking lots, and building rooftops during rainfall and snow events that often contain pollutants in quantities that could adversely affect water quality. Most storm water discharges are considered point sources and require coverage by an NPDES permit. The primary method to control storm water discharges is through the use of best management practices.

Learn about the science of stormwater

Get answers to common questions about Stormwater - What is it? Where does it come from? How is it polluted? What are the pollutants of concern? How is the pollution controlled? What are stormwater facilities?

And last but not least, what can you do (as a business or as a homeowner) to protect stormwater?

Flow control terminology

As we alter the land through development, we alter the lands ability to naturally handle stormwater. Earth that was once porous is now hardened with asphalt and buildings. This leads to a number or problems - flooding, aquatic habitat degradation in lakes and streams, and water quality problems. The King County Surface Water Design Manual contains the requirements that must be implemented during development to address these and related impacts.

With development, stormwater peak flows increase, and stormwater volumes change annually and seasonally. Groundwater recharge is also impacted by the loss of impervious soil. King County categorizes Flow Control based on the target of the control - peak flows, flow duration, or a combination of these two. Want to know more?

Stormwater legislation and regulations

The United States Environmental Protection Agency (EPA) develops the stormwater regulations, in accordance with the Clean Water Act (CWA).

The Washington State Department of Ecology (Ecology) develops stormwater regulations in Washington State, in accordance with Chapter 90.48 of the Revised Code of Washington, Water Pollution Control.

King County administers its Stormwater Management programs in accordance with King County Code Title 9, Surface Water Management. Note: Title 9 is being revised in early 2003 to incorporate a new Stormwater Ordinance.


Stormwater glossary of terms and abbreviations

For questions about the stormwater website, please contact Blair Scott, Water Quality Planner, King County Stormwater Services Section.