Study On Optimal Utilization Of Rainwater Resources In Manrong Economic Development Zone Of Shenyang

With the rapid urbanization development,the urban underlying surface conditions have changed greatly.The sponge city theory provides an effective way to solve the water problems such as urban waterlogging,water shortage,runoff pollution and so on.lt is of great significance to build a sponge city suitable for city to meet the increasing demand for water resources,prevent urban waterlogging,supplement the groundwater resources,and improve the urban ecological environment.The research has drawn lessons from the domestic and foreign research results of rainwater resources utilization,then taking Manrong Economic Development Zone as the study area.SWMM model is used to build rainwater resources model,and identify the functions of measures and water quantity.The multi-object optimization method is used to establish optimal utilization of rainwater resources,then the optimal measures are given.The paper includes the following aspects:(1)The paper analyses the land use in the study area with the help of ArcGIS.The area is divided into three parts which are the water landscape area,the old city area and the new city area.And the impervious surface ratios of the tree areas are calculated to be 2.97%,58.32%,and 60.00%.According to the natural conditions and the layout of drainage network,the SWMM model is used to calculate.There can be generalized into 230 sub catchments,230 junctions,230 links,and 2 outfalls in study area through the Tyson Polygon method.The Chicago rain type is used as the design storm rainfall pattern,and it takes 0.5a,1a,2a,5a,10a as the rainfall return periods.(2)SWMM model is used to calculate the influences of individual measures on water quantity and water quality under different rainfall return period-According to the content of the study,the utilizable rainwater is redefined,and then the linear relationships between the water quantity and the four measures are calculated which are green roof ratio,permeable pavement ratio,low elevation greenbelt ratio,and increased water surface ratio.The results show that there are good linear relationships between the individual measures and runoff coefficient,as well as utilizable rainwater.Taking 2a as an example,the effects of individual measures on water quantity are compared which the order of the influence degree from large to small is permeable pavement,increasing water surface,green roof,low elevation greenbelt.Finaly,it is verified that the effects of different measures on water quantity under different rainfall return periods.(3)The equations of combined measures and water quantity are formulated according to the principle of SWMM and the functions of individual measures.With the goals of economic benefit,social benefit and ecological benefit,the optimization model of rainfall resources is established,which is based on the ratio of green roof,permeable pavement,low elevation greenbelt and increased water surface.Then the constraints are the total runoff control,the maximum ratio,and the maximum land use.Analytic hierarchy process is used to solve the multi-object model.The optimal results of green roof ratio,permeable pavement ratio,low elevation greenbelt ratio,water surface ratio are 16.39%,90%,85.6%and 7.2%respectively.Finally,it is proved that the combined measures have a good effect on controlling the urban flood and drainage,improving the utilization rainwater and purifying the runoff pollution.And it is of great significance for the utilization and management of rainfall resources,even providing reference for planning the sponge city.