Study On The Simulation And Regulation Of Rainfall Runoff In Zhu Paichong Drainage Basin Of Nanning Based On LID Layout Optimization

In recent years,with the rapid development of urbanization,the impermeable area of cities has been increasing,the corresponding rain-island effect and extreme rainfall phenomenon are obvious,and urban waterlogging disasters are becoming more and more serious.At present,the theoretical basis of sponge city construction with stormwater and flood management as the core needs to consider the shortcomings of urban hydrology mechanism understanding of urban micrometeorological cycle,underlying surface and pipe network factors.Nanning,as the first batch of pilot construction cities of sponge city,has frequent rainstorm and flood waterlogging over the years.It is an urgent need to support the city to cope with storm and flood waterlogging to carry out the study of rainfall and runoff simulation and runoff regulation with optimal layout of LID facilities on the underlying surface.Firstly,the paper analyzes the spatial and temporal distribution characteristics of design rainfall in Nanning and the spatial evolution pattern of land use on the underlying surface.Secondly,based on the simulation of runoff process of different rainfall design scenarios in the zhupaichong drainage basin of Nanning sponge city,the evolution characteristics of runoff volume and runoff coefficient are analyzed.Finally,the scenario optimization of multi-dimensional LID facility layout in the watershed scale of the study area was carried out to realize the coordinated evolution mechanism of underlying surface regulation and runoff reduction,which laid a foundation for the construction of the runoff control index system for the sponge city construction in Nanning.The main conclusions of this paper are as follows:(1)In Nanning,there is significant spatial heterogeneity in the spatial distribution of design rainstorms under different recurrence periods.The mean value of Moran’s I index is greater than 0.5,showing a significant positive autocorrelation between overall and local space,and the local aggregation is dominated by"high"and"low"types.And the rainstorm center mostly appears in the transitional zone between the central urban area and the surrounding area.(2)Period from 1990 to 2015,the scope of Nanning basin evolution of land utilization rate will tend to slow down,FLUS model forecasts suggest that Nanning future land use remained in farmland circulation evolution characteristics of forest land,construction land is given priority to,the phenomenon of Nanning mainly presents the southward expansion,urban impervious area increased but the increase rate is slow.(3)The rainfall runoff simulation of bamboo drainage basin under different rainfall scenarios shows that the proportion of runoff volume in the system increases with the increase of rainfall,and there is a strong positive correlation between the runoff coefficient and the percentage of impervious area.The R~2 of the regression equation is close to 1,and the impervious surface in space is consistent with the spatial distribution of runoff coefficient.In addition,the total runoff control rate of Nanning sponge city is 75%-95%under the design rainfall condition,and the total runoff control rate of Nanning sponge city is58.5%～83.7%under the current condition of bamboo drainage and flushing,which fails to meet the sponge city construction index standard.(4)LID measures are adopted to regulate runoff in the study area.Single LID measures are used to set permeable pavement(60%of the roads and squares in the study area),green roofs(20%of the residences in the study area),biological retention ponds(10%of the water catchment area)and rainwater gardens(10%of the water catchment area).The runoff reduction rate is within15%.Multidimensional LID facilities,the combination of three single measure is a combination of surface runoff regulation,combination LID measures of runoff reduction rate of single LID measures are around two times,the permeable pavement,rain garden,biological stranded pool under the combination of the most significant effect of rainfall runoff regulation and control in the study area,the runoff reduction rate up to 34.84%.