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 mod els to use, as much for their simplicity of conception as for their fa st calculation times. One drawback, however, is that these general mod els consider each rainfall event to be perfectly homogeneous over the entire drainage surface of the watershed. Of course, such conditions a re practically non-existent given the short time steps used in urban h ydrology which tend to accentuate the heterogeneity of rainfall events . The main objective of this study was to verify whether the spatial h eterogeneity of rainfall does in fact influence the hydrologic respons e of an urban drainage basin. Upon observing the results obtained, dif ferences in the response of the drainage ba.sin for heterogeneous prec ipitation and homogeneous precipitation events of equal average intens ity 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 simul taneously upon the precipitation intensity, its duration, and also upo n which zone is favoured by strong precipitation intensities. These fa ctors aside, it was shown that the filling rate of the collectors also has an important effect.