| In recent years,with accelerated urbanization,population growth and changes in land use patterns,the original hydrological regime has been destroyed.The heavy rainfall incident occurred frequently,and there were many problems with existing drainage systems,such as low design standards and poor drainage,which caused the original drainage system to be unable to match at this stage.Disaster losses caused by heavy rains have increased year by year,so it is urgent to use technology to predict the overall performance of the rainwater drainage system and optimize the rainwater drainage system.This paper takes part of Jingwei Town,Gaoling District,Xi’an City,Shaanxi Province as the research object,establishes the urban rainwater pipe network model and simulates the operation status of the pipe network under different rainfall conditions.The system surface runoff,node overload,rainwater pipe section load,and two-dimensional ground water accumulation range and depth of accumulation are analyzed under each rainfall condition to evaluate the drainage capacity of the current stormwater pipe network.Combined with the simulated problems of the current rainwater drainage system,the pipe network is reformed by changing the pipe diameter and zoning layout;Subsequently,based on the results of the renovation,and with the help of low-impact development facilities,surface runoff will be reduced,thus reducing the risk of flooding.The main conclusions are as follows:(1)Combined with the current situation information to establish a drainage model,the model parameters rate using the runoff coefficient method,the two fields of measured rainfall data were selected for rate determination,to obtain impervious area ground roughness coefficient 0.011,Horton maximum infiltration rate of 76 mm/h and other parameters.(2)According to the pipe network design standards and urban flood control requirements,the simulation set 1a,2a,5a,10 a,20a of the five rainfall conditions,analysis of the current rainwater system drainage capacity.In terms of node overload,the number of overloaded individuals accounted for 45%,71%,82%,85.9% and 89% respectively.In terms of pipeline overload,when the return period is 1 year,the pipeline overload rate reaches 73.2%,and more than half of the pipeline is overloaded and the drainage capacity is insufficient;In terms of ground water accumulation,with the increase of rainfall intensity,the scope of ground water accumulation has been continuously expanded,from 5.4% in 1a to 20% in 2a.all four drainage divisions have ponding conditions,especially drainage division two as a whole is more serious,all the pipes in its area do not meet the one-year recurrence period,and the ponding area also occupies a large proportion.(3)With the target of no more than 15 cm depth of water accumulation on the ground under the 2-year recurrence period,two transformation measures are proposed to increase drainage zoning and improve pipe drainage loading standards.Drainage zoning increased from 4 to 7,pipe loading standards increased to 2 years of a recurrence period for a comprehensive transformation of the stormwater drainage system.The modified system discharge volume increased,plus the overload rate of pipe sections and nodes decreased significantly,and the ground water depth was controlled within 15 cm to meet the set target.Based on the site conditions and the suitable construction conditions of low-impact development facilities,four kinds of facilities are selected to play a role,and three schemes are set up.With the annual total runoff control rate of 85% and the waterlogging prevention and control depth of no more than15 cm in 20 years as the control objectives,the water regulation effect,economic cost and environmental benefit are analyzed.Finally,Finally,using AHP for comprehensive benefit assessment,the comprehensive benefits of the three options were 0.5372、0.5471、0.5279,and the optimal option for comprehensive benefits was determined to be Option 2. |
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