Study On Sponge City Construction In Yangling Demonstration Zone Based On SWMM Model

With the accelerating process of urbanization in our country,various urbanization problems caused by the traditional urban development model have gradually emerged.In particular,the urban waterlogging has hindered the healthy development of the social economy.The proposal of the Sponge City concept has provided a new way of thinking and approach for the transformation of urban development in China.It also improved the ecological environment while optimizing the urban development so as to achieve a good development of the ecological environment and social economy.Based on the background of the construction of sponge city in China,this thesis explores the construction of sponge city in Yangling Demonstration Zone.The main research contents and achievements are as follows:(1)According to the conditions of the climatic conditions,hydrological characteristics,soil geology,current status of urban subsurface,historical waterlogging,and water and soil pollution in the Yangling Demonstration Zone.Considering the requirements for the dual development of urban agro-forestry and urban areas,the construction of the sponge city in the demonstration area is divided into urban construction area,ecological restoration area and agricultural protection area.(2)Sponge reconstruction in urban construction areas focuses on pollution prevention and waterlog relief;the ecological restoration area focuses on the construction of Yangling's eco-agricultural park and the restoration and treatment of urban water systems.The construction of park aims at improving the urban environment and promoting the multiple development of agriculture;the construction of agricultural reserve aims at the utilization of agricultural rainwater resources and related water-saving measures,for building green sponge agriculture.(3)Selecting urban construction area and the agricultural protection area as the research object,the former is Zone A and the latter is Zone B.Though generalizing the pipeline network,dividing the sub-water catchment areas,and designing rainfall data,the SWMM model is used as a platform to simulate and analyze the current status of the area.The result shows:Zone A system reaches the maximum infiltration rate of 5.61mm/h at P=3a;At P=50a,the amount of waterlogging in the system reaches 11324m~3,and the overload rate of the pipe segment reached 100%,which indicates severe waterlog.The total runoff coefficient of system B is 0.519 at P=0.65a and has increased to 0.889 at P=50a,which indicates that the system has large runoff and high risk of waterlog.(4)Based on the simulation results of the status quo in the study area and the suitability analysis of the sponge measures in the demonstration area,design and modify sponge measures in the study area.Zone A aims at waterlog prevention and absorption and utilization of rainwater,and comprehensively arranges different measures for individual sponges;In Zone B,rainwater reservoirs are set up with the goal of using rainwater resources.Comparative analysis of the model data before reconstruction and after the regional reconstruction,the result shows that the decline rate of system peak runoff rate is more than70%from P=0.65a to P=50a in Zone A;The system peak outflow rate reduction ratios are more than 50%,the highest reaching 82.19%;The reduction rate of the total discharge volume is more than 50%when P?5a,and the number of overloaded pipes and the overflow volume of the nodes also decreased sharply.When P?1a,the reduction rate of peak runoff is above 60%in Zone B,and the efficiency of rainwater collection and utilization reaches 100%,and the decline rate of the system's runoff coefficient after reconstruction is up to 60%.(5)Comparing and analyzing the simulation results before reconstruction and after the reconstruction of the study area,the effect of spongy measures in the small and medium-sized rainfall is more apparent,and the usage efficiency of rainwater is getting higher;with the recurrence period and the rainfall intensity gradually increasing,the detention storage effect of the sponge measures is gradually reduced.