Effects of urbanization on storm-runoff volume and peak discharge of Valley Creek, eastern Chester County, Pennsylvania

Abstract

Peak discharge and runoff volume were simulated for 21 storms in the Valley Creek basin using the U.S. Geological Survey Distributed Routing Rainfall-Runoff Model (DR3M). Storm peak discharges ranged from 301 to 900 cubic feet per second. Rainfall was measured at three recording rain gages in the basin. Observed and simulated runoff volumes and peak discharges were compared for the upper 20.8 square miles of the basin. The average error for runoff volume was 29 percent. The average error for peak discharge was 19 percent for the 11 calibration storms and 32 percent for the 10 verification storms. Streamflow was routed to the Schuylkill River for the lower 2.6 square miles of the basin. Simulations were made to determine the effect on runoff volume and peak discharge of increasing impervious area from 9 percent to 15, 20, and 25 percent in the part of the basin most likely to be developed. For 25 percent impervious area, runoff volume would increase an average of 52 percent and peak discharge would increase an average of 55 percent for Valley Creek at the Pennsylvania Turnpike bridge. At the confluence of Valley Creek with the Schuylkill River, runoff volume would increase an average of 46 percent and peak discharge would increase an average of 50 percent.