Palhegyi, Gary, Peter Mangarella, Eric Strecker, Jill Bicknell, and Dipankar Sen, "Developing Management Plans To Address Impacts From Urbanization On Stream Channel Integrity."
It is well documented that urbanization modifies the natural watershed and stream hydrologic and geomorphic processes by altering the landscape, modifying vegetation and soil characteristics, and introducing impervious surfaces and drainage infrastructure. The resulting increases in the volume, frequency, and duration of runoff from development projects are known as hydromodification. Hydromodification of natural runoff processes intensifies sediment transport and often leads to stream bank erosion and channel incision. These types of changes have occurred in San Francisco Bay Area streams. Stormwater management programs in the Bay Area are being required to address the impacts from new and redevelopment projects on the beneficial uses of streams resulting from erosion caused by hydromodification. The Santa Clara Valley Urban Runoff Pollution Prevention Program (SCVURPPP) NPDES permit requires co-permittee agencies to develop a Hydromodification Management Plan (HMP) that describes how they plan to manage increases in runoff volume and peak flow from development projects and protect stream systems. The HMP will establish in-stream stability criteria and runoff control design criteria, and provide guidance on management measures, which include a combination of on-site, in-stream, and regional control strategies. The HMP will also consider water quality and habitat impacts in evaluating and recommending control measures. To date, the project team has conducted a literature review, developed a conceptual model and defined the assessment method. Characterization of streams and future development, field data collection, and hydrologic/hydraulic modeling is underway, and an HMP assessment report is scheduled for completion in June 2003.