Understanding and Managing Urbanization-Induced Stream Erosion in Southern California: Fid-Bau Portal

Understanding and Managing Urbanization-Induced Stream Erosion in Southern California

Yeager, Matt A. / Wise, Darla D. / Suffet, I. H. "Mel"

Conventional urbanization modifies the hydrology of developed areas, causing increased runoff volumes and peak runoff rates for a given storm event, and runoff events occur more frequently. Hydromodification and negative flow-related physical impacts to stream channels have been well documented, along with water quality degradation. Recently adopted municipal storm water regulations in southern California require mitigation of hydromodification impacts at the project planning and approval stages. Studies in rainier regions, including Maryland, Washington State, Surrey, British Columbia, and elsewhere have recommended strategies to reduce erosion and habitat degradation in natural channels by controlling peak runoff rates and flow duration for storm events of specific return periods. Local jurisdictions have adopted numeric design criteria for control of runoff rates and flow duration based upon these recommendations, and incorporated them into engineering guidance documents. Despite valuable work in these more-humid regions, very few data relevant to the Mediterranean climate (approximately 38cm (15in.) average annual precipitation, with a long dry season) of southern California are available to support local or regional technical guidance. To provide local/regional data to support technical criteria development, a study that combines hydrologic computer modeling with field verification studies is recommended. An effective study would evaluate and link the most applicable existing erosion and sediment transport models to measured and modeled flow rates, and validate with field data. The study should also assess variability in stream response to urbanization across the region, and develop an assessment methodology and long term monitoring strategy.