Impact Of Typical Underlying Surface Spatial Distribution On Urban Rainfall Runoff

With the rapid development of urbanization and the intensive and excessive intervention of human beings,green space,rivers and other natural underlying surfaces have been seriously damaged,which has changed the water cycle process of the city and resulted in the increasingly serious waterlogging problem.In recent years,the control management of stormwater runoff has become an important subject of city hydrology research.It is still a hot spot of present research to explore the method of adapting to stormwater control management in China,and construct the Blue-green ecological network,so as to solve the redistribution of urban rainwater resources.In this paper,the relationship between the change of impervious surface spatial distribution and the runoff was explored,and the change of the underlying surface and different influential factors(such as rainfall intensity,slope,impermeable area rate,flow length)on the surface runoff process was revealed through the testing simulation method first.Secondly,with the center of Luohe City as the research object,the land use and land cover information of the city center was extracted based on0.09 m high-precision aerial image in March 2016 to analyze the runoff characteristics of the research area in different rainfall repetition periods and the factors affecting the rainfall runoff by using SWMM model,and make the quantitative analysis of the effects of different spatial distribution patterns of green space and buildings on the runoff reduction.Finally,the control and utilization strategies of rainfall resources by city green space and rivers were proposed.The main research results were as follows:1.The experimental simulation results of the influence of different layout on rainfall runoff:(1)With the increase of rainfall intensity,slope and impermeable area rate,the more the surface runoff was,the greater the runoff coefficient was.(2)Combined with two influential factors of slope and rainfall intensity,the influence of the slope on rainfall runoff under high rainfall intensity was weaker than that under low rainfall intensity.(3)Under the same rainfall and slope conditions,the reduction rate of runoff increased with the permeable area.When the rainfall condition was contant,the influence of the slope on the runoff reduction was weaker than that of the permeable area.When the rainfall intensity was high,the influence of the permeable area on the reduction of runoff was not significant.(4)There was a certain relationship between the flow length and runoff of the permeable area and the impermeable area.2.The status of land use and land cover in the center of Luohe: the green space and the construction area respectively accounted for 17.04% and 20.97% of the total area of the central city,and the rivers accounted for only 2.86% of the total area.The numbers of greenspace patches and building patches were 24517 and 27472,respectively.The patch area of green space patches in the range of 1 to 5000m2 accounted for 95.93% of the total green land patches,and the number of green space patches with the patch area greater than 5000m2 was small,accounting for 64.23% of the total green land area.Overall,the green rate was low,and the patches were small and scattered.The buildings were dense and concentrated,and most of them were residential and commercial office land,mainly concentrated in Yancheng District,Yuanhui district and Zhaoling District.3.The simulation results of urban rainfall runoff in the center of Luohe City: the catchment area with the building density higher than 0.2 was selected to change the spatial distribution of green land and buildings,in order to simulate the effect on urban rainfall runoff.(1)With the increase of the rainfall repetition period,both runoff volume and comprehensive runoff coefficient showed an upward trend.After the change of the distribution,the total runoff volume decreased by 14.62%,and the maximum runoff rate reached 45.48 mm.(2)When the rainfall repetition periods were 5a,10 a,50a,the green space and building areas ratio were significantly negatively correlated with the runoff coefficient,and the runoff coefficient of the sub-catchment area which green space near the outlet was smaller than building.When the rainfall repetition period was 5a,the runoff reduction rate of a sub-catchment reached 44.49%.(3)After the change of the spatial distribution of green space and building,the runoff reduction rate decreased with the decrease of the rainfall repetition period,and increased with the increase of the ratio of the green space area to the building area.In summary,combined with different spatial distributions,flow length,area ratio and other factors,the scales and distributions of green space and buildings could be reasonably arranged,and put forward the specific ways for the construction of ecological drainage network in Luohe,so as to realize the spatial redistribution of rainfall and thus achieve the purpose of runoff reduction.