Simplified two-parameter gamma distribution for derivation of synthetic unit hydrograph

Abstract

Several methods for synthetic unit hydrographs are available in the literature. Most of them involve manual, subjective fitting of a hydrograph through few data points. Because it is difficult, the generated unit hydrograph is often left unadjusted for unit runoff volume. To circumvent this problem, a simplified version of the existing two-parameter gamma distribution is introduced to derive a synthetic hydrograph more conveniently and accurately than the popular Gray, Soil Conservation Service, and Synder methods. The revised version incorporates the approximate, but accurate, empirical relations developed for the estimation of β and λ (factors governing the shape of the dimensionless unit hydrograph) from the Nash parameter n (=number of reservoirs). The Marquardt algorithm was used to develop the nonlinear relationships. The applicability of the simplified version is tested on both text and field data.