| In the process of urbanization development,with the construction of facilities such as squares,factories and commercial bodies,the ground is gradually hardened,which makes the permeable green areas,ponds and other green facilities with certain infiltration and stagnation effects reduce a lot.When larger intensity rainfall occurs,runoff cannot be effectively reduced,and a large amount of runoff sinks into the stormwater pipe network increasing the load of the gray drainage system.Since stormwater pipe networks,rivers,lakes,and pumping stations are organically integrated,they can affect each other.In the coupled large drainage system,the traditional calculation method is weak,and the water dynamics model assists in decision making more in line with the requirements of the times.In this paper,the main urban area of Maanshan City is used as the study area to investigate the specific effects of river and lake water levels on flood discharge and flood control.Firstly,the information of stormwater pipe network and river network was organized,then combined with satellite image map and digital elevation map,the sub-basin partition and the initial value of each parameter were selected under the analysis of Arc GIS.Then complete the work of outlining the rivers and lakes,adding pumps and weirs,writing pumping station control rules and other tasks.Finally,a coupled rainwater pipe network-river-lake model is developed in SWMM and calibrated with historical flood point information and integrated runoff coefficients.The analysis of the specific impacts on the rainwater pipe network under short-time rainfall conditions with 5a return period and long-time rainfall conditions with 20a return period after the water level of the current situation and river and lake drops by0.2m,0.3m and 0.5m provides ideas for solving urban flood control and drainage problems.The main findings of this paper are as follows:(1)The river is outlined as an open channel,the lake as a reservoir,and combined with the rainwater network,and the three are interconnected.Build the model by this way.The results show that the coupling of the rainwater pipe network with rivers and lakes is achievable,the method of building a coupled rainwater network-river-lake model is feasible.(2)If the stormwater network is analyzed in terms of its total overflow.The results show that the total overflow of the status quo will reach 119.66×10~3m~3.When the river and lake level dropped 0.2m,the overflow was 104.81×10~3m~3,a reduction of12.41%;when it dropped 0.3m,the overflow was 95.85×10~3m~3,a reduction of 19.90%;when it dropped 0.5m,the overflow was 79.67×10~3m~3,a reduction of 33.42%.(3)If the analysis of the stormwater network is based on the total overflow volume of various overflow points.It is found that lowering the water level can significantly reduce the total overflow volume of overflow points below the moderate level.If the water level is lowered by 0.2m,it will be reduced by 15.75%;if it is lowered by 0.3m,it will be reduced by 22.33%;if it is lowered by 0.5m,it will be reduced by 39.19%.And the reduction of the total overflow volume of moderate overflow points is relatively significant.If the water level is lowered by 0.2m,it will be reduced by 12.78%;if it is lowered by 0.3m,it will be reduced by 16.97%;if it is lowered by 0.5m,it will be reduced by 30.85%.And the ability to reduce the amount of overflow at a point above moderate is relatively weak.If the water level is lowered by 0.2m,it will be reduced by 7.82%;if it is lowered by 0.3m,it will be reduced by19.12%;if it is lowered by 0.5m,it will be reduced by 25.5%.Overflow points above the medium level are mainly caused by the imperfection of the rainwater pipe network system under the current situation and the lack of drainage capacity of the rainwater pipe network,and the impact of falling river and lake water levels on these overflow points is minimal.(4)In the analysis of the floodway,under the current situation,an overflow occurred in one of the middle reaches of the Yushan River as well as Yushan Lake,with a total overflow of 217.09×10~3m~3.The water level of the rivers and lakes was lowered by 0.2m,eliminating the flooding point on the Yushan River,but Yushan Lake still overflowed,with an overflow of 47.30×10~3m~3;by lowering 0.3m,no overflow point in the floodway,but the safety height is only about 0.03m,which cannot support the renovation of the rainwater pipe network;by lowering 0.5m,leaving a safety height of about 0.15m,which can support some optimization of the rainwater network system.Figure[69]Table[21]Reference[73]... |
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