| Due to the long history of construction,aging facilities,and dense population,the old urban area has a higher risk of waterlogging than other urban areas and is less resilient to waterlogging disasters.Urban green space plays an important role in reducing the total amount of runoff and reducing the peak value of runoff,and the landscape pattern of green space is an important factor affecting its runoff regulation function.In order to enhance the ability of stormwater runoff control in the old city,this paper takes the area inside the Ming-City-Wall of Xi’an as the research area,explores the response relationship between the green space landscape pattern and the overload of the pipe network,and proposes green space optimization strategies and sponge transformation measures.The simulation results show that the proposed measures can effectively reduce the total and peak value of runoff in the study area.(1)Construct the drainage system model of the study area and complete the rainfall runoff simulation with different return periods.The establishment of the topological relationship of the pipe network in the study area,the assignment of node ground elevations and the data processing of the underlying surface land use were completed,and the study area was divided into 19 drainage zones,374 stormwater pipes,374 nodes and 376 sub-catchments.The onedimensional pipe network model of the study area was constructed by using SWMM software,the model parameters were calibrated by the comprehensive runoff coefficient method,and the calibration results were tested according to the variation coefficient.The 180-min duration rainfall scenario design for each return period is carried out.The simulation results show that the runoff control ability in the study area is not strong,and the runoff control rate in the return period of 1 a is only 28.75%,and it gradually decreases with the increase of the return period.(2)The relationship between the landscape pattern of green space in the study area and the proportional response of node overloading was explored.Eight landscape pattern indexes representing the scale,shape and distribution characteristics of green space were selected,and Fragstats4.2 software was used to calculate the landscape pattern indexes of the whole study area and 19 drainage zones.The Pearson correlation analysis was carried out on the landscape pattern index value and node surcharge ratio of 19 drainage zones,and it was found that ED,PLAND,CONNECT,COHESION,PD and FRAC were significantly correlated with the node surcharge ratio.(3)According to the response relationship obtained in the research,the optimization strategy of the green space landscape pattern was formulated for the sample plot.At the same time,taking the 4# drainage zone as an example,select the green roof,rain garden,sunken green space and permeable pavement to formulate the LID renovation plan,and design the layout plan of the storage tank.The simulation results show that the scheme of LID transformation combined with deprivation storage tank has the best effect.In the return period of 3a,the runoff control rate can reach 59.92%,the peak reduction rate can reach 29.7%,and the reduction rate of the number of overloaded pipes and overloaded nodes can reach 66.7%.(4)Based on the research results,the runoff regulation strategy in the study area is given.In terms of green space landscape pattern optimization,it is proposed to increase the proportion of green space area,expand the scale of emission reduction facilities at the source,improve the connectivity of green space,and optimize the spatial layout of green space patches.In terms of sponge measures,the runoff control measures of LID + storage are proposed,low-impact development techniques are selected according to local conditions,and the layout of storage facilities is formulated. |
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