Study On LID System Reconstruction Of High Groundwater Level Cities

With the global warming and the rapid increase of the number and scale of cities in China,the ecological problems caused by it have become increasingly prominent,such as urban water pollution,frequent urban water logging and lack of water resources,which have seriously affected the life and safety of residents.Therefore,China has proposed the sponge city construction with low impact development technology.In addition,the wide application of low-impact development technology in the world has provided valuable experience for China’s sponge city construction.However,the homogenization of sponge city construction in China and the practice of copying other cities often happens,the sponge city construction has not taken the local special background characteristics,such as high groundwater level into consideration.And still focusing on how to take measures such as "infiltration,stagnation,storage,purification,utilization and drainage" in the general background,so that rainfall can quickly penetrate into the underground to reduce surface runoff and replenish groundwater.In the end,the sponge city has a great discount in economic,social and ecological benefits.Therefore,the study on the construction and reconstruction of high groundwater level with low impact development technology is of great significance to the construction of sponge city in China.At present,there are few researches on the construction and reconstruction of sponge city in the area of high groundwater level,and there is no clear definition of the water level height of the city with high groundwater level.Therefore,taking qushuifang in Suining City as the research object,this paper analyzes the surface runoff and pipeline overload of the project when the groundwater level is 4m,2m,0.5m below the surface.In order to solve the problem of urban water logging caused by high groundwater level,two kinds of LID facilities reconstruction schemes under the most unfavorable conditions are designed,and the scheme comparison is carried out to determine which one is better.In the end,this paper evaluates the rainwater control capacity of Winding Streams under the better scheme reconstruction.The main research work and results of this paper are as follows:1.According to the modeling principle of SWMM,the underlying surface conditions and pipe network data of Winding Streams,this paper builds the SWMM model of the research area and the effect of the rainwater management of qushuifang is simulated when the groundwater level is 4m,2m and 0.5m below the surface.2.Under the most unfavorable condition that the groundwater level is 0.5m below the surface and P = 10 a,two kinds of LID transformation schemes with different emphases are designed.Scheme 1 is composed of semi permeable pavement,sunken green space and PP water storage module,scheme 2 is composed of semi permeable pavement,sunken green space,rainwater garden.3.This paper uses AHP to compare the two schemes and find out scheme 2 is the better one.And take environmental efficiency,economic efficiency and social efficiency as the evaluation criteria to seek the most comprehensive efficiency transformation scheme for Winding Streams.4.On the basis of scheme 2,this paper studies the control effect of rainwater runoff from the angle of four indexes,including rainwater infiltration and retention,surface runoff and peak flow,rainwater flow at discharge outlet and pipeline drainage.The results show that the transformed Winding Streams can increase the amount of retention,slow down the speed of rainwater infiltration,better control the rainwater runoff and peak flow,reduce the discharge of the outlet,alleviate water logging.The reconstruction scheme and ideas can provide reference for the construction and reconstruction of LID facilities in similar areas with high groundwater level.