Areal rainfall intensity distribution over an urban area and its effect on a combined sewerage system

The application of 21 pluviometers over the whole area of Lodz, Poland, enabled an examination of areal distribution of intense rainfalls during 2010-2011. On the basis of collected data the distribution of rainfall intensity was analysed and a circular zone model with exponential shape in all directions has been proposed for describing rain storms. Also, the velocity of storm zone movement between 2 and 30 km/h was determined. Using the SWMM 5.0 software, adapted for non-standard use, runoff from three real catchments and combined storm overflow discharge was examined for selected measured rainfalls. An effect of storm zone range and movement was also studied for the same catchments using model storms. It was confirmed that using data from the city pluviometric network enables significantly better simulation results for CSO overflows to be obtained compared to an option based on a single pluviometric station, especially for large catchments greater than 200 hectares.