| The construction of traditional urbanization has exacerbated hydrological cycle,resulted in frequent occurrence of waterlogging and urban water environment pollution.In order to solve the problem of urban stormwater,the concept of Sponge City is put forward in China,which is based on the concept of Low Impact Development(LID),and combined with the national conditions of our country.At present,the whole country is developing the sponge city construction in a raging way,and the control of total runoff volume is related to the realization of the goal of sponge city construction.Therefore,the simulation analysis of the rainwater runoff process in the process of construction of the sponge city helps to evaluate the construction effect and adjust the construction measures in time so as to ensure the realization of the construction goal.In this study,the area of the sponge city construction in Xiushan County is selected as the research area,based on the real-time rainfall and runoff monitoring,Storm Water Management Model was employed to simulates three different scenarios which is before and after the urbanization and LID retrofitted(Rainr Garden,Vegetative Swale,Permeable Pavement),and the hydrological change and drainage status after urbanization and the hydrological characteristics after LID retrofitted were analyzed.The main research contents include 5 aspects,(1)SWMM model was builded and the sensitivity of the parameters was analyzed.(2)The hydrological characteristics before and after urbanization was analyzed by SWMM.(3)The performance of the stormwater control of individual LID measures was studied in different return periods,and the performance evaluation method of individual LID measures was put forward.(4)The reliability of existing LID retrofitted scheme was verified by rainfall event capture ratio,and the optimization method of LID design scheme was put forward.(5)The best LID retrofitted scheme was applied to Xiushan County research area,and its impact on runoff was analyzed and evaluated.The main results of this paper are as follows:1)The sensitivity of SWMM model parameters is affected by rainfall conditions.In the light rain,the N-Imperv and Dstore-Imperv are both sensitive to the flood peak and the total runoff.Under the condition of heavy rain,only N-Perv is sensitive to the flood peak,in addition,in moderate rain and light rain,S-Imp is the most sensitive,under the heavy rain conditions,only N-Perv is sensitive to the flood peak,and under the condition of stormwater,S-P began to show sensitivity to runoff volume.In general,thesensitivity of SWMM parameters to flood peak is higher than that of runoff volume.2)After the urbanization,the impermeability of the underlying surface increased by50.3%,the flow capacity was enhanced,the curve of runoff flow was characterized by "high-thin",and the sensitivity of the rainfall intensity was strongly responsive.When P>2a,the runoff began to appear in some catchments,and the urban rainwater pipe network will overloaded and overflows,it is necessary to carry out LID retrofitted at the research area.3)The control effect of runoff would be different because of different types and size of LID measures.The control effect of the three kinds of LID measures on runoff was: Rain Garden>Vegetative Swale>Permeable Pavement,furthermore,Permeable Pavement is suitable for large-scale district-type retrofitted,Rain Garden and Vegetative Swale are more suitable for the small areas retrofitted.4)The existing LID retrofitted has not reach the target of 85% of the rainfall event capture ratio in Xiushan County.Four new LID retrofitted schemes have been specifically designed,and these schemes have been optimized by comprehensive performance evaluation system.The optimal LID retrofitted scheme:Rain Garden,Vegetative Swale and Permeable Pavement layout proportion accounted for 1.9%,0.9%and 22.8% of the research area.5)The hydrologic characteristics of the optimal LID retrofitted scheme were simulated and analyzed by SWMM.When the area ratio of LID retrofitted reached25.6%,the target that rainfall event capture ratio getting 85% in the research area could be achieved.However,under the short-term rainstorm intensity,the LID retrofitted measures mainly reduce the total runoff volume and peak runoff,but the total runoff volume and runoff peak value cannot be completely eliminated.In order to achieve a better effect of rainwater utilization,water storage facilities should also be combined.In this study,the hydrological characteristics and the reliability of LID retrofitted was analyzed and verfied by SWMM and rainfall event capture ratio,to provide a theoretical basis for evaluating the effect of stormwater control after LID retrofitted;and a comprehensive performance evaluation method on LID retrofitted was proposed,to provide a reference to select the optimizal LID retrofitted scheme. |
