Study On Runoff Reduction And Control Effect Of Different LID Construction Schemes Under Different Rainfall Conditions

The construction of Sponge city is an effective way to solve the problem of urban waterlogging.The core is to change the natural properties of the underlying surface and reduce the site runoff discharge by constructing LID(Low Impact Development)in the catchment area.Taking a sponge building community in Beijing as an example,a refined SWMM numerical model is constructed,and four typical catchment units with different underlying surface characteristics are selected to simulate and analyze the runoff reduction and control rules of each catchment unit under different return period rainfall scenarios after LID construction.On this basis,a typical drainage unit of the building area is selected as the research object.Six LID construction schemes are obtained by changing the confluence path generalization,including four confluence relationships(The confluence relationship between road and LID and the connection relationship between LID are "series + series","series + parallel","parallel + series","parallel + parallel").Taking the design rainfall of Pilgrim&Cordery(P&C)with rainfall duration of 60 min,120min and 720 min and rainfall of 30 mm,50mm and 70 mm as the water source input of the model,the runoff reduction and control laws of different confluence relation schemes are simulated and analyzed,and the correlation between the average rainfall intensity and runoff coefficient,flood peak and flood reduction rate is established.The main results are as follows:(1)In the case of low recurrence rainfall,the runoff coefficient of catchment unit with large permeable proportion is the smallest,while in the case of high recurrence rainfall,the runoff coefficient of catchment unit with large permeable pavement proportion is the smallest;the effect of flood peak reduction by pervious pavement is better than that by vegetation ditch,biological detention facilities and other measures;the influence of the catchment area where LID receives more passenger water on runoff is more significant and the effect is more obvious;the contribution rate of LID to runoff at the outlet of the drainage basin can be reduced by arranging LID measures in the catchment unit.(2)The runoff coefficient,total flood volume and reduction rate of fully connected schemes are the lowest,but the peak value is the highest and the reduction rate is the lowest under high-intensity rainfall;with the increase of rainfall magnitude,the reduction rate index has the trend of "continuous increase","continuous decrease" and "first increase and then decrease",among which the reduction rate index of complete series scheme shows a single change trend of "continuous decrease" and the increase of peak discharge is the most obvious,reaching the maximum under the rainfall of 60 min and 70 mm,which is significantly higher than other reconstruction schemes;(3)Runoff coefficient and average rainfall intensity are logarithmic functions,and the reduction rate index is linear negative correlation or positive correlation;the peak and optimal reduction rate of flood volume of LID construction scheme with different confluence relationship do not necessarily correspond to the same rainfall,and the peak reduction effect of scheme with poor reduction effect of flood volume is not necessarily good.