Geomorphology and Kinematic-Wave–Based Hydrograph Derivation

Geomorphology-based instantaneous unit hydrographs have been proposed by several engineers as a tool to produce runoff hydrographs from rainfall for ungauged watersheds. A difficulty in applying the geomorphology-based unit hydrographs is the determination of travel time that is actually a hydraulic problem. In this paper, kinematic-wave theory is used to analytically determine the travel times for overland and channel flows in a stream-ordering subbasin system. The resultant instantaneous unit hydrograph is a function of the time rate of water input (intensity of rainfall excess in application); hence the linearity restriction of the unit hydrograph theory is relaxed. In applying the instantaneous unit hydrographs for hydrograph simulation, the model deals with temporally nonuniform rainfall through convolution integration of the instantaneous unit hydrographs applied to the rainfall excess of varying intensities with time. The proposed model is tested by comparing the simulated and observed hydrographs of an example watershed for several rainstorms with good results. Sensitivity of surface runoff unit hydrographs to the model parameters is also investigated.