Research On The Quantification Of The Low Elevation Greenbelt Area Based On Volume Capture Of Rainfall In High-density Urban Areas

Because of the rapid urbanization in China,land use/land cover changes dramatically and there is a large proportion of urban impervious surface,which results in stormwater problems becoming more serious.Volume capture of rainfall can largely alleviate the stormwater problems,and it is one of the main targets of the rain flood control for the sponge city and the green stormwater infrastructure,which is mainly through natural and artificial enhancement to make rainwater infiltration,detention storage,collection and reuse.Low elevation greenbelt is the natural green stormwater infrastructure with good runoff infiltration and storage effects.Its functions for Volume capture are outstanding,and the investments are low.Effective green space which can penetrate and store rainwater is insufficient in high-density urban areas,leading to the contradiction of annual rainfall volume capture more prominent as well as the stormwater risks.It based on high-density urban areas which are taken as the objects of study,emphasis the systematical study of the contribution by the low elevation greenbelt doing to the rainfall Volume capture as well as the corresponding scale of the low elevation greenbelt,which can provide the technical supports for relieving urban stormwater problems and has the significant meaning on both theories and the practice simultaneously.The concrete research contents and the conclusions are as follows:?1?Study the relative theories on domestic and overseas stormwater systems,the rain water runoff total quantity control as well as the successful cases.Analysis the relevance of rain water runoff total quantity control and the inferior fovea type green space,and the particularity of the rain water runoff total quantity control in high-density urbanization areas.?2?Take the low elevation greenbelt as a the approach and method for alleviating the stormwater problems and controlling stormwater runoff volume,it is necessary to calculate the low elevation greenbelt.The quantitative model includes rainfall balance model,runoff generation model and the model of the main design parameters'relevant relationship which affect infiltration and storage functions of the low elevation greenbelt.?3?Aim at achieving different levels of volume capture ratio of annual rainfall,it is necessary to calculate the contribution of low elevation greenbelt for controlling annual stormwater runoff volume and the suitable scale of low elevation greenbelt.This paper takes the typical high-density developed residential district in the New Town which is located at Meixi Lake of Changsha city as the research subject.Assuming the volume capture ratios of annual rainfall targets are 85%,80%,75%,70%and 55%respectively,and the homologous designed rainfalls are 31.6mm,26.0mm,21.8mm,18.5mm and 11.3mm,meanwhile,we supposed it that the runoff produced during 1 hour will be all infiltrated by the low elevation greenbelt without residuals.The results indicated that,when the different soil infiltration rates are between 1×10^-6m/s and 1×10^-4m/s and fovea inferior depths are between 0.1m and 0.3m,the proportions of the low elevation greenbelt area in catchment area are from 21.14%to0.93%.Moreover,when the combination of soil infiltration rate and inferior concave depth are appropriate,the goal that different levels of annual rainfalls'volume capture ratios in field scale can be achieved through a relatively small low elevation greenbelt area in high-density urban areas.?4?Discusse the layout form of the low elevation greenbelt preliminarily,and demostrate the feasibility of the low elevation greenbelt application from the space.?5?Summarize the current existing problems in the processes of plannig and design,concrete suggestions are put forward.Research shows that the use of small-scale low elevation greenbelt in high-density urban areas can control stormwater runoff on the field scale effectively.when the combination of soil infiltration rate and inferior concave depth are appropriate,the low elevation greenbelt area is relatively small.Besides,from the spatial distribution,the application of the low elevation greenbelt is feasible.The results of this study can provide references for the goal setting of volume capture of annual rainfall and the scale setting of the concave green space in high-density urban areas,and furthermore,it can make a contribution to urban floods alleviated,water pollution control and groundwater recharge.