Construction And Simulation Of Rainfall-Runoff Effect Of Urban Green Network System

With the constant expansion of the city,the impervious surface continues to increase,leading to urban green space area decrease and space fragmentation,which results in many urban problems of which urban stormwater is the most prominent.Constructing a complete urban green space network system in order to give full play to the ecological function of the open space of urban green space is a favorable guarantee for effectively harnessing the hazards of urban stormwater and promoting the healthy development of the city.Based on the sponge city and landscape ecology,firstly,basic data about study area has been collected aim to construct a suitable for the study area SWMM model using which the problems of urban rainstorm and flood disasters are analyzed by.Secondly,the landscape pattern characteristics and issues of current green space are studied by using Fragstats software.The potential corridors are extracted by using minimum consumption distance model in order to construct a three-level green space network.Finally,according to the goal of rain-flood management,by comparing the hydrological effects of the green network in different situations,the relationship between landscape pattern of the green network and urban stormwater is explored,and the green network is optimized in two ways: the construction of flowable green network and sponges layout.The main research results are as followings:(1)SWMM model which is suitable for the study area has been constructed by using comprehensive runoff coefficient method.The comprehensive runoff coefficient is between 0.65 and 0.75 when simulating the recurrence period of 1 to 50 years.Through the rainfall-runoff simulation of the current green space,it is concluded that the runoff coefficient of sub-catchment has a great correlation with its impermeability;the number of flood nodes accounts for 44-69% of the total nodes;the flood volume of node and overloaded pipline are related to the flood recurrence period,size of piplines and location of nodes.(2)By using Fragstats software,the analysis of landscape pattern which includes CA,NP,PLAND and ENN_MN indicators shows that the connectivity of current green patches is poor;the coverage rate is low,which is about 27%;the distribution of green patches is uneven,which mostly concentrated in the South and less in the north.(3)In order to construct a three-level green space network system: firstly,50 patches were selected quantitatively by Conefor,and its area accounts for 57.35% of the total green space;according to different underlying surface types,resistance surface is built by assigning weight;finally,first,second and third-level potential corridors(total area of corridors is 172.6 ha)are extracted by the minimum dissipative distance model,and the third-level green space network system is constructed.By analyzing the landscape pattern of the green space network system,it was found that the green space area and the number of patches increased significantly,the patch density decreased,the patch connectivity increased,the spread degree decreased.(4)By analyzing the rainfall-runoff effect of green space network,it was found that green network has an obvious and stable effect on reducing runoff and doesn't change with recurrence periods,but fail to reach the goal of rainwater management;the relationship between landscape and rainfall-runoff effect is that the reduction of node flood volume is proportional to NP,CONNECT and SHAPE_MN,inversely proportional to LPI,CONTAG and AI,and the correlation coefficient with CONNECT is 0.997.The optimization of the green network can be taken in two ways: construction of flowable green network and sponges layout.The reduction of runoff coefficient of the sponge layout achieves the goal but reduction reduces with the increase of the recurrence periods;the reduction of runoff by the flowable green network is less;the combination of the optimization of the sponge in the green network and the flowable green network can achieve the maximum reduction of runoff coefficient,and the runoff coefficient will decrease from 0.1 to 0.15.