Hydrological Effects Of Sponge City Based On The Coupling Of SWMM And MODFLOW

With the proposal of the construction of “sponge city” in China,the pilot cities and pilot areas of sponge cities have been built throughout the country to solve the problems of urban infighting,groundwater depletion and water pollution caused by the rapid development of the current city.The functions of various facilities in the construction of sponge cities are mainly reflected in the reduction of urban stormwater runoff,the collection and utilization of rainwater,and the infiltration of atmospheric rainfall to replenish groundwater.This paper proposes a method based on SWMM and MODFLOW coupling model simulation to study the hydrological effects of sponge city planning and construction.In order to couple the SWMM and MODFLOW models,by analyzing the simulation principle and structural characteristics of the SWMM model and the MODFLOW model,the coupling of the model is realized from two aspects: spatial scale and source and sink terms.The specific coupling method is: on the spatial scale,the SWMM model is divided into the catchment area based on the structured grid method,and the minimum computation unit of the SWMM model and the minimum calculation unit of the MODFLOW model are used as the basic exchange unit to realize the coupling of the model space unit;On the source and sink terms,from the hydrological cycle process of the hydrological model simulation principle,the time series data of the infiltration items in each sub-catchment area of the SWMM model simulation is transformed into the surface recharge item of atmospheric rainfall in the MODFLOW model to construct surface water.Interaction with groundwater,while coupling the two models on the source and sink terms.The model coupling method was applied to the Tianjin Airport Economic Development Zone for feasibility verification.The SWMM model based on structured grid is established,and the original SWMM model of natural sub-basin division(general division)is used as the benchmark.The simulation results are compared.The correlation coefficients of the water depth and total infiltration of the drain are both above 0.95.The Nash-Sutcliffe coefficient is 0.85 and above,and the estimated standard error is below 0.1.The results show that the SWMM model based on structured grid has little difference with the simulation results of general partition mode model.It is feasible to use structured grid to divide the catchment area.The SWMM and MODFLOW coupling models in the study area were constructed by analyzing the hydrogeological conditions of the study area and the SWMM model.The groundwater model was validated by the observation of the measured well water level and the simulated water level.The water level fitting effect was good.Taking the Tianjin Airport Economic Development Zone as an example,the SWMM model was used to simulate the surface hydrological effects of bio-retention facilities,permeable pavement,rain garden,rain bucket,green roof,and recessed green space under four impervious zones.Under the constraint of groundwater level,the applicability of rainwater buckets and green roofs is high,and the infiltration type LIDs such as bioretention facilities are less suitable.Comprehensive analysis of the hydrological effect of sponge city,based on the application examples,analyzes the hydrological effects of LID facilities before and after the addition of LID facilities,and analyzes the annual runoff total control rate,infiltration,evaporation,and groundwater level in the study area before and after the infiltration of LID facilities.Poor change.Taking the biological detention facility as an example,the hydrological effect under the historical rainfall scenario of the Tianjin Airport Economic Zone from 2000 to 2009 was analyzed.The research shows that the bioretention facilities have obvious effects on the reduction of runoff,and the effect of increasing the amount of infiltration is obvious when the centralized deployment is performed;the floating change of the groundwater level in the area before and after the deployment of the LID technology based on the following seepage function shows an increasing trend,in the case analysis The 10-year groundwater level difference is about 20 cm,and the increase trend is obvious.Therefore,in the high groundwater area,the local groundwater level limitation is considered in the construction of the specific sponge city,and the increase of the groundwater level after the addition of LID is below the water level of the groundwater confinement depth,thereby improving the applicability of the infiltration type LID facility.The research shows that the SWMM and MODFLOW coupling model is used to simulate urban rainfall-runoff hydrological system and sponge urban planning.The urban surface water and groundwater can be regarded as a whole to study urban hydrological effects,which can more accurately and reasonably plan the sponge city.Unified planning of local water resources during construction.