Urban flood frequency and hydrograph analysis

A set of seven-parameter regression equations was developed for estimating flood discharges at ungaged areas. The regression equations can be used to estimate urban flood discharges throughout the United States for recurrence intervals from 2 through 500 years. The average standard errors of regression range from 37 percent for the 5-year flood to 49 percent for the 500-year flood. Flood hydrographs representing average, or typical, runoff conditions can be estimated by using a dimensionless hydrograph technique. The dimensionless hydrograph is used to simulate a flood hydrograph by using two parameters - the design peak discharge and the basin lagtime.