The Influence of Spatial Heterogeneity of Rainfall upon the Hydrologic Response of an Urban Drainage Basin

Hydrologic models of the black box type are the easiest simulation models to use, as much for their simplicity of conception as for their fast calculation times. One drawback, however, is that these general models consider each rainfall event to be perfectly homogeneous over the entire drainage surface of the watershed. Of course, such conditions are practically non-existent given the short time steps used in urban hydrology which tend to accentuate the heterogeneity of rainfall events. The main objective of this study was to verify whether the spatial heterogeneity of rainfall does in fact influence the hydrologic response of an urban drainage basin. Upon observing the results obtained, differences in the response of the drainage basin for heterogeneous precipitation and homogeneous precipitation events of equal average intensity may be considered significant. Differences of greater than 35% for peak flows and 15 minutes for peak flow response times were observed in certain cases. The influence of spatial heterogeneity depends simultaneously upon the precipitation intensity, its duration, and also upon which zone is favoured by strong precipitation intensities. These factors aside, it was shown that the filling rate of the collectors also has an important effect.