| Shanghai,located in the Yangtze River Delta,is the center of national economy,trade and shipping,which has been playing a major role in the national economy.Hongkou District,located in the northeast of downtown in Shanghai,south to the confluence of Huangpu River and Suzou River,is an important part of Central Business District.This area is an economically advanced region with developed urbanization.In recent years,with the frequent occurrence of extreme weather,urban flooding brought by heavy rain has seriously damaged economic development and residents living.Thus,for the phenomenon where urban flooding happened frequently in a storm,this study investigated the affecting factors of urban flooding and treatment measures,and analyzed the varied curves of Huangpu River's water level and Hongkou's precipitation from 2006 to 2015.Meanwhile,the mechanism that area,quantity and depth of urban flooding vary with precipitation at different water level was established.In addition,treatment measures of urban flooding were illustrated with economic and technical analysis of engineering application after investigating amount of urban flooding and regional water quality.Finally,these results of the research could provide technical support for studies on causes of urban flooding and engineering treatments.On the basis of large-scale data acquisition,the drainage system of Hongkou district,even whole Shanghai was investigated and counted.The popularity of pipe network in Hongkou was 87.58 percent and the attainment rate was 82.80 percent.The popularity of pumping station is 83.28 percent.In total,there were 29 urban flooding spots.The mechanism that Hongkou's monthly precipitation firstly increased and then decreased and increased up to 382.1mm at most was established by investigating Huangpu River's hydrological data and Hongkou's precipitation data.The rains were more in flood season and less in winter.The total precipitation was basically above 100 mm in flood season,which increased up to 967.7mm at most and occupied 67.33 percent in a year.Meanwhile,the monthly precipitation had a trend of increase except February and March and the increase rate was up to 28.2mm/10 a after comparing every month's precipitation in different years.Generally,Huangpu River's water level was about 2 m or below in dry season and above 4 m in flood season.Its change rule was same as precipitation in a year.However,as the mechanism that area,quantity and depth of urban flooding vary with precipitation at different water level stated,urban flooding spots increased firstly and then decreased with the increase of precipitation,which increased up to 29 at most.The decreasing rate was lower than the increasing rate.In addition,the rate of change of area increased firstly and then decreased.When water level was 4.20 m and precipitation was 130 mm,area was up to 180250m2.In the typical area,the increasing rate of depth was lower in both ends and higher in middle.When water level was high,the increasing rate of area was same as depth,which was up to 91.1m2/mm(area/precipitation)at most.In this study,three ways including control of safe water level before rains,analysis of rainfall-runoff and river's hydrodynamic model were investigated.The results of drainage amount were 26.98m3/s,27.35m3/s and 30m3/s by calculation of three ways and the final design amount was 30m3/s.At same time,the project of water resources operation was established under river's hydrodynamic model.When the diversion flow of Hongkou's pumping station was 15m3/s,water transfer ability of Hongkou's river would obviously improve.When the diversion flow was up to 22.86m3/s,water quality would totally improve and every water-quality index would improve more than 60 percent.In the end,we decided that the diversion flow was 15m3/s.In the confluence area,the pollutants' concentration in traffic area was obviously much higher than other area and the rainfall intensity was main factor affecting primary scouring effect with using scouring concentration model.The water quality indexes of rainwater in pipe's outlet near the river were as follows:BOD5=7.08mg/L,NH3-N=2.34mg/L,DO=2.18mg/L,CODcr=33.29mg/L.In the calculation of water resources operation,the water quality indexes of Huangpu River were as follows by river's water quality model: BOD5=7.20mg/L,NH3-N=2.82mg/L,DO=2.70mg/L,CODcr=34.00mg/L.Meanwhile,we proposed to use "pump and gate" asymmetric form in the program of Hongkou's pumping station where there were 3 submersible pumps of which size was 1800QGS10-3.25 and flow was 10 m3/s.Two of them were two-way and another was one-way.The design drainage amount was 30 m3/s in the pumping station where the net lift of diversion was 0~2.21 m and the net lift of drainage was 0~3.98 m.In the recommended engineering program,it cost ?517,899,600.The annual running cost was ?4,640,000 in total including materials,fuels,powers,salaries and welfare benefits,management and maintenance cost,etc.The construction of this engineering program would release city's drainage pressure and improve water environment and boost the economic development.The economic benefit for these years was ?799,557,600 in cash(converted in reference period,early 2011).In addition,the economic benefit for years was 15,991,200 in average,which was more than it cost.This study's results could be applied to analyze factors and engineering treatment measures of urban flooding and provide technical support for guaranteeing the ability of city's drainage and improving water environment.In the research,we investigated Hongkou district.And the consequences would help the analysis of urban flooding factors in Shanghai and the engineering treatment.Not only could it lay the foundation for further research on the mechanism of urban flooding,but also provide technical engineering support for promoting city's normal development. |
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