Instantaneous unit hydrograph evaluation for rainfall-runoff modeling of small watersheds in North and South Central Texas

Data from over 1,600 storms at 91 stations in Texas are analyzed to evaluate an instantaneous unit hydrograph (IUH) model for rainfall-runoff models. The model is fit to observed data using two different merit functions: a sum of squared errors function, and an absolute error at the peak discharge time (QpMAX) function. The model is compared to two other models using several criteria. Analysis suggests that the Natural Resources Conservation Service Dimensionless Unit Hydrograph, Commons' Texas hydrograph, and the Rayleigh IUH perform similarly. As the NRCS and Commons' models are tabulations, the Rayleigh model is an adequate substitute when a continuous model is necessary. The adjustable shape parameter in the Rayleigh model does not make any dramatic improvement in overall performance for these data, thus fixed shape hydrographs are adequate for these watersheds. ?? 2006 ASCE.