Synthetic Unit Hydrograph

Equations are developed for computing the unit hydrograph for ungaged watersheds. The two‐parameter gamma function unit hydrograph from the HYMO hydrologic model is used in the study and equations for estimating the time to peak and the recession constant are developed. The equations use physical characteristics of the drainage basin to predict the parameters for the unit hydrograph. Stepwise regression analysis is used to reduce the number of physical and hydrological variables to four, which are the basin area, height, length, and watershed slope. Records of 283 storm events from 85 watersheds in 13 states were studied to develop and verify the equations. Results of the study indicate that these equations can be used to more accurately estimate the runoff hydrograph than the SCS (Soil Conservation Service) dimensionless unit hydrograph procedure for mild and steep watershed slopes.