Radar long term event time series for hydrodynamic discharge modelling

The relevance of non-uniform rainfall for the results of urban drainage design is often insufficiently discussed and underestimated. Using the example of the combined sewer system model of the city of Basel, the influence of non-uniform rainfall on the discharge behaviour is investigated based on a highquality radar long-term event time series. The results are compared with a uniform rainfall from a single rain gauge observation. The radar rainfall analysis shows a clear pattern in the spatial rainfall distribution with lower rainfall heights in the heavily paved city centre compared to the neighbouring settlement areas in the transition area to natural, unsealed surfaces. The differences for the total rainfall height are about 10%; for statistical heavy rainfall heights of convective events, the differences are more pronounced and amount to 30% - 40%. The small-scale spatial rainfall distribution has also an effect on the results of the hydrodynamic pollution discharge modelling. In the overall view of the drainage system, the pollution discharge for ammonium (NH4 kg /a) is reduced by 15% compared to the uniform rainfall from the rain gauge; the number of discharge days is reduced by 11%.