Translations:Versickerung und Retention/99/en

In the case of limited loading, in addition to the flood verification, the calculation of the required retention volume (Rain Retention Area (RRA)) must be carried out with the „simplest procedure“ in accordance with DWA-A 117. For simplicity’s sake, it is assumed that the yearly occurance T of the dimensioning rain (uniform in relation to the total effective property area) corresponds to the permissible exceedance frequency of the RRA. The loading restriction must include the throttle discharge, L/s and the yearly occurance T of the permitted excess. For the calculation of volume related dimensioning exercises, such as the dimensioning of precipitation water retention areas, the mean discharge coefficients C_m according to Table 9 are to be used to determine the effective area. The dimensioning of rain retention areas must considered according to DWA-A 117:2013 for the run-off entering the drainage system in relation to both the sealed area A_E,b as well as from the non-sealed area (Table 9, No. 3) from inlet to outlet in the drainage system. The determined surface types will be simply called A_FaG in this norm, with the mean run-off coefficients C_m multiplied and linked to the calculated value A_u. The required storage volume V_RRR will be determined according to the maximum difference between the rainfall amount and the discharge volume through the throttle in a specific time period.