The effects of spatially distributed rainfall on catchment response

Abstract

It is commonly assumed in the application of many models of catchment behaviour that catchment rainfall is uniformly distributed over a catchment. This study examines the effects of non-uniform spatially distributed rainfall on the application of the unit hydrograph theory. A simple distributed linear catchment model is used to simulate the response of a catchment to stationary and moving storms and three different unit hydrograph derivation techniques have been applied to the responses obtained.

The model responses demonstrate that spatial distribution of rainfall can produce effects which might be mistakenly used as evidence of non-linear catchment behaviour. The unit hydrograph derivation techniques were least successful for slow moving storms and large catchments. Overall the gamma distribution method resulted in the best estimates of the unit hydrographs. However the least squares techniques achieved the best results for stationary storms. The spatially distributed rainfall resulted in the derivation of markedly different unit hydrographs for different storms on the same catchment. An examination of the lumped representation of distributed rainfall showed that an alternative to the catchment mean rainfall could allow significant improvements in the application of the unit hydrograph theory for the case of moving storms.