A deterministic gamma‐type geomorphologic instantaneous unit hydrograph based on path types

A geomorphological instantaneous unit hydrograph is obtained by dividing the whole catchment into subcatchments, according to the different “path types” which water follows to the outlet of catchment. Each subcatchment produces, at its own outlet, an impulse response which is described by a two‐parameter ( n , K ) gamma function. In traveling to the outlet of whole catchment, each impulse response undergoes a further pure translation with delay time τ, thus producing at the outlet of the catchment a partial impulse response described by three parameters ( n , K , and τ). Summation of these partial impulse responses with area weights W forms the impulse response of whole catchment. The parameters K and τ are estimated from catchment characteristics and the flow velocity of each flood event. Area weights W can be calculated from maps after defining the subcatchments. The parameter n is estimated by optimization. The proposed model is tested in two catchments in China and shows encouraging results.