The present design of stormwater tanks is based on the creation of storage volume to retain stormwater and the prevention or reduction of stormwater overflows. The treatment of stormwater is often improved with mechanical equipment. The general layout rules do usually not include the appropriate choice of design inflow related to the chosen treatment equipment. In the following investigations it was the task to analyze the hydraulic efficiency and the overflow behaviour of a lamella particle separator inside a stormwater tank under different design approaches regarding the chosen design inflow. Therefore six scenarios with different precipitation yield approaches were chosen and applied to a given constant sized catchment to calculate the design inflows. For a given minimum particle size, the necessary number of lamellas were determined for the scenarios and standard stormwater tanks were dimensioned. These stormwater tanks were modelled in the hydrologic model SMUSI to investigate the overflow behaviour of the different tank sizes. The number of overflow events, their duration and maximum flow rates were the results of the modelling. Comparisons to the design inflows were carried out. The treated particles sizes at the overflow events were determined reversible and compared to the original chosen minimum particle sizes.
Ongoing and intensive land development over several decades has led to increasing imperviousness of urban areas. This is particularly true for town and city centres. Precipitation cannot infiltrate into the ground and this reduces groundwater renewaL Instead, stonnwater is conveyed by separate and combined sewer systems to the next treatment plant or receiving water. Frequently, problems occur when further development is planned in suburban areas to be connected to the main sewer system. According to traditional technology, existing parts of the sewer system become overloaded and must be replaced by larger diameter sewers to convey additional sewerage and storm water. In some cases some existing treatment plants become overloaded and must be rebuilt or modified to fulfil existing water quality standards. Investment costs for these modifications and extensions of the drainage system are distributed among the users connected to the system. Internationally a broad consensus exists that the rerouting of stonnwater back into the natural water cycle is compulsory from the ecological and economical point of view. It is well known that onsite infiltration of stonnwater can contribute to considerably reducing stonnwater peaks and volumes. Several infiltration technologies have been developed for this purpose, such as drainage wells, gravel trenches and pervious pipes that include subsurface storage, as well as depression and reservoir infiltration including surface storage. The BIRCO Company in Baden-Baden has developed a new drainage
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