J.S. Gulliver, B.N. Wilson, O. Mohseni, A.J. Erickson, and R.M. Hozalski
This section discusses the physical, biological, and chemical processes that alter the flow and quality of urban stormwater. Stormwater treatment processes are different from stormwater treatment practices.A stormwater treatment practice is something that improves stormwater runoff quality, reduces runoff volume, reduces runoff peak flow, or any combination thereof. Examples of stormwater treatment practices include source reduction, sand filters, infiltration basins and trenches, rain gardens (bioretention), dry ponds, wet ponds, constructed wetlands, filter strips, swales, wet vaults, and underground sedimentation practices.
A stormwater treatment process is the mechanism by which a stormwater treatment practiceimproves stormwater runoff quality, reduces runoff volume, reduces runoff peak flow, or any combination thereof. For example, a dry pond holds stormwater and releases it slowly (relative to uncontrolled conditions) to downstream receiving waters. The primary treatment process of a dry pond is sedimentation because most of the pollutants in stormwater that are retained by a dry pond are settled out while the stormwater runoff is held in the pond. Because the treatment process is important, stormwater treatment practices in this manual are organized by their primary treatment process. To understand stormwater processes, however, one must first examine the composition and impacts stormwater has on the environment.
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