SPACE-TIME HETEROGENEITIES OF RAINFALLS ON RUNOFF OVER URBAN CATCHMENTS

Simulated outlet flow series are compared downstream of a 14 sq.km. ur ban watershed. They are generated either with design rainfall, with lo ng-term point rainfall series, or with long-term space distributed rai nfall series (measured with 3 raingauges or with radar). The use of th e double-triangle shaped hyetograph as design rainfall provides the sa me T-year flow as the long term 3 raingauge series, if it is used with a areal reduction factor and uniformly applied to the watershed. For the same T-year mean areal precipitation depth during the time of conc entration, the rainfall spatial and temporal heterogenities may induce differences up to +/- 30% on the peak now, compared to the T-year pea k flow.