Impact of Urbanization on Storm Runoff

by David Loh, Univ of Southern California, Los Angeles, United States,
Robert M. Ayer, Univ of Southern California, Los Angeles, United States,
Delores Taylor, Univ of Southern California, Los Angeles, United States,
Jiin-Jen Lee, Univ of Southern California, Los Angeles, United States,

Document Type: Proceeding Paper

Part of: Engineering Hydrology


The engineering design of hydraulic structures is directly associated with the estimation of design parameters connected with extreme events. Methods of estimating extreme events typically require a lengthy time history of selected parameters such as annual flood peaks, peak storm intensities, etc. A case study is performed for three watersheds in Ventura County, California, where adequate storm data is available for analysis. Using storm data from 1933 - 1991 which was made available by the Ventura County Flood Control District, three watersheds within Ventura County were investigated to determine the effect of urbanization on storm runoff. Two of these watersheds, Hopper Creek at Piru, California and North Fork Matilija Creek near Ojai, California have experienced virtually no urbanization during the entire period of storm record (1933 - 1991). The third watershed, Arroyo Simi at Simi Valley, California has experienced rapid urbanization associated with the population growth from 8,100 in 1960 to 103,220 in 1990. Using the undeveloped watersheds as controls, the ratio of peak flow at Simi Valley relative to Hopper Creek and North Fork Matilija Creek was considered. A preliminary study of these ratios proved to be inconclusive due to data scattering. Consequently, double mass curves were used to smooth out the scattering. The increase in storm runoff for an urbanized watershed was also correlated with various parameters characterizing the urbanization of the watershed such as population growth and land use.

Subject Headings: Storms | Urban areas | Runoff | Watersheds | Case studies | Municipal water | Urban and regional development | Rivers and streams | California | United States

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