| With the rapid growth of urban population in China,the construction process of urbanization has been accelerated gradually,which has greatly promoted the development of China’s social economy,but it has also brought about a bad impact on the ecological environment of urban hydrology in China.The development and construction of cities has caused changes in the underlying surface structure,increased the proportion of the surface impermeable area,destroyed the natural hydrological cycle process,resulting in the continuous reduction of the water seepage,the surface runoff collection time is shortened,the runoff flood peak is advanced,the urban flood and water accumulation events occur frequently,the urban water circulation process is no longer in line with the requirements of sustainable urban development.Low Impact Development(LOW Impact Development,LID)technology is a"source control,decentralized treatment"rainwater management measures that can alleviate urban flooding to some extent.In recent years,the domestic research on it began,and in China’s sponge city construction has been pilot application,but in the facility planning layout is still lack of in-depth study.This paper consults many relevant literatures,analyzes the progress of the research on LID at home and abroad,and puts forward the main contents and technical routes of this study.The applicability and principle of storm water management model(SWMM)used in the study are then analyzed.Finally,the layout optimization design for low-impact development is studied,aiming at the economic cost of total annual runoff control rate,runoff peak flow and LID measures,and constructing a multi-objective optimization model,simplifying multi-objective functions into monocular functions through standardized methods,and in the MATLAB programming environment,The SWMM program is called to realize the export of the model run results after modifying the model parameters and parameter modifications,and finally solve the optimization model.Taking a district in Qingshan District of Wuhan As an example,the LID optimization method is used to obtain the proportion of the optimal layout of the study area,and further research is carried out on the effect of rain and flood control of LID measures.Through the auxiliary combination of GIS software and SWMM model,the simulation model of rain and flood in the study area is constructed,the design rainfall data are obtained by the method of the rainfall process line in Chicago,the model parameters are calibrated with runoff coefficient as the goal,the hydrologic and hydraulic parameters of the model are determined,and the reliability of the model is increased.The following conclusions were drawn by applying THE LID optimization model in the study area:(1)Under the local design rainfall conditions,the LID optimization method was applied to optimize the total runoff control rate of 40%and the runoff peak was 1.4m~3/s.After optimization,the total runoff control rate was 84.6%and the runoff peak was0.09m~3/s.After optimization,the total runoff control rate increased by 44.6%,runoff peak decreased by 1.31 m~3/s,the effect of optimization is remarkable,the annual runoff total control rate meets the requirements of national norms.It is proved that LID optimization method is feasible and has reference value in solving the problem of urban rainwater management in China.(2)Simulating the different reproducibility periods of p=1a,p=3a,p=5a,p=10a,p=20a,surface runoff changes and pipe network carrying capacity before and after the LID optimization measures were added to the study area.The infiltration before and after the LID optimization measures added under each reproduction period increased by 5.932mm,12.36mm,15.492mm,19.606mm,28.448mm,and the peak reductions were 1.31m~3/s,1.59m~3/s,1.23m~3/s,1.18m~3/s,1.4m~3/s,overflow nodes reduced by 0,16,20,8,9,and overloaded pipes reduced by 18,70,49,19,12.The results show that LID optimization measures can increase surface infiltration,reduce surface runoff,reduce peak flow,delay peak occurrence,reduce the average discharge flow of discharge ports,reduce the drainage pressure of pipe network,reduce the risk of urban flooding,and so on,and are more suitable for dealing with rainfall events of small and medium rainfall intensity. |
