Study On Capability Of The Initial Rainwater Detention Tanks

Initial rainwater detention tank makes a very obvious effect on controllingnon-point source pollution, and it has a strong practicability. Initial rainwater detentiontank can collect initial dirty rainwater. Initial rainwater detention tank can reducepollution no matter for new drainage system or for transforming system, which canobtain good economic benefits at the same time.The paper ordered a study of capacity of initial rainwater detention tank, aroundingthe initial rainwater depth, volume of detention tank and efficiency of detention tank.First of all, study on the initial rainwater depth, and hold a view that the initial rainwaterdepth should be determined by different pollution controlling targets, by which way theinitial rainwater depth calculated is scientific. According to research in this paper, it isscientific to calculate initial rainwater depth of any proportion by “rainfall eventmethod”. It is calculated that the initial rainwater depth is9.7mm in Dianchi Lake whilethe target is to reduce half rainwater of the whole year.Secondly, order a study on volume of detention tank. In this study, study onvolume of detention tank is divided into two parts, one is studying in the condition ofcombined system, the other is that of separated system. In the condition of separatedsystem, the volume of detention tank is calculated by calculating initial rainwater depthwhich is calculated by“rainfall event method”. In the condition of combined system, thefunction of the detention tank is to reduce overflows of the system. As a result, it issuggested to build the relationship of interception ratio and overflow. The volume ofdetention tank is determined by the target interception ratio which is calculated by theoverflow reduction target.Thirdly, the paper introduce the the use of SWMM and application field of it. Then,introduce the method of it and the way of building SWMM model and the way ofanalysis.Finally, order a study on the efficiency of detention tank. Introduce how to buildthe SWMM model of combined system (area measured by108.4ha) by an example. Andsimulate it in the condition of1996rainfall, we can find that overflow of the whole yearif276.990thousand m3, and the whole COD is56.007t. When the detention tank issetted in the system, the overflow will be reduced by55.7%, the whole COD will bereduced by60.5%. Meanwhile, three rainfall events (p=0.25, p=0.5, p=1) are synthetized by “Chicago rain type”. In the condition rainfall event of P=0.25, theoverflow will be reduced by100%and the COD will be reduced by100%as well whendetention tank is setted in the system. And that is33.38%,35.49%respectively in thecondition of P=0.5, and21.32%,23.1%of P=1.