Optimal Determination of Loss Rate Functions and Unit Hydrographs

An optimization model is presented that can be used in the determination of loss rate functions and unit hydrographs using observed rainfall and runoff data. Composite unit hydrographs and loss rate parameters can be determined by using several multiperiod storms simultaneously or using individual multiperiod storms. The model is a nonlinear programming problem so that a generalized reduced gradient method is used as the solution technique. Kostiakov's, Philip's, Horton's, and the ϕ index methods are used to illustrate the model for comparative purposes. An infiltration equation that includes rainfall intensity is also introduced and is compared with the others by using the optimization model. The model is applied to storms for a hypothetical example, Shoal Creek watershed in Austin, Texas, and Wills Creek watershed near Cumberland, Maryland. A comparison of the new model with earlier optimization procedures is also presented.