Simulation of changes in storm-runoff characteristics, Perris Valley, California

The population of Perris Valley, California, has increased from about 20,000 in 1970 to more than 130,000 in 1992. Increased urbanization in Perris Valley since 1970 has produced appreciable changes in storm-runoff characteristics. Additional impervious area has resulted in increased storm-runoff volumes and peak discharges. Few studies have documented the effect of urbanization on runoff characteristics in the Perris Valley area. A study of runoff characteristics under the current level of development in Perris Valley was begun in 1989 to determine how recent urbanization changed runoff characteristics from 1970-75, a period for which rainfall and runoff data are available. This paper briefly describes the methods being used in a study to determine the effects of urbanization in Perris Valley and presents a few results of that study. Rainfall and runoff data collected in a previous study (1970-75) were used to calibrate a rainfall-runoff model. This model will be used to simulate the runoff in Perris Valley during the early development of the basin. Rainfall and runoff data currently (1990-93) being collected in Perris Valley will be used to calibrate and verify a rainfall-runoff model simulating the current runoff conditions. Two simulations of a long-term time series of runoff will be done using the rainfall-runoff models and historical rainfall. A duration analysis of the simulated runoff will be used to compare the storm-runoff characteristics of the two urban conditions.