Analysis Of Overflow Characteristics And Optimization Control Of Combined Sewer Overflow In The Main Urban Area Of A Certain City

The rapid development of cities,an increase in impermeable areas,a surge in population,and the mismatch between old and damaged drainage systems and urban development have led to frequent occurrences of Combined Sewer Overflow(CSO),exacerbating urban water pollution problems,and making sponge city construction an important means of solving water problems.In order to study the pollution characteristics of confluence overflow in the main urban area of the City and the control effects of different overflow control strategies on CSO,and explore CSO control strategies for the main urban area of the City,a SWMM hydrological and water quality model was constructed based on pipeline network data,land use types,dry season sewage,and hydrological and meteorological data.Based on the SWMM model,the current situation and causes of confluence overflow in the region were simulated and analyzed,Study the control effects of different control measures on combined flow overflow.The main research conclusions are as follows:(1)The CSO phenomenon is frequent in the main urban area of a certain city.The proportion of pipe network drainage capacity less than once in a year is 55.20%;In 2016,the number of overflows was 28,and overflow occurred when the rainfall was greater than 4.4 mm.The annual overflow volume was 2.4038 million m~3,A total of 19 overflow outlets have experienced overflow,all distributed in the Shizi river and Heishui river,concentrated in the lower reaches of the Shizi River.The serious phenomenon of confluence overflow in the area fully demonstrates the necessity of adopting CSO transformation in this area.(2)Determine the total area of source control measures based on the proportion of green roofs,sunken green spaces,and permeable paving,and study the impact of different spatial layouts with a certain total area on CSO.Under the same Return period,when green facilities are distributed in 344 subcatchment areas(accounting for 4/5 of the total subcatchment),the control effect on CSO is the best.After the Return period is greater than 10 years,due to the limited capacity of green facilities to absorb rainwater,the control effect of different spatial layouts of green facilities on CSO in the same Return period is gradually similar.(3)Two locations and five volume comparison schemes were conducted for the CSO storage tank,taking into account the overflow flow rate,overflow load reduction rate,and economic benefits.The CSO storage tank was selected downstream of the south bank of the Shizi River,with a volume of 10000m~3 The reduction rate of overflow fluid volume is 52.97%.Taking into account the reduction effect of CSO and economic factors,the control effect on CSO is the best at this time.(4)On the basis of determining the layout plan of green facilities at the source and the end CSO storage tank plan,study the control effect of the combination of green facilities and CSO control measures on CSO.After adopting combined control measures,the frequency of overflow decreased to 10 times in 2016.When the rainfall was greater than 23.8 mm,a total of 8 overflow ports experienced overflow,and the overflow volume control rate reached 72.56%.(5)Study the control effect of different measures with different investment ratios on CSO under a certain total investment.Five different schemes for the proportion of green facilities and regulation pool investment were formulated.Under different Return period,the control effect on CSO fluctuated significantly with the change of cost proportion.The cost proportion of green facilities was 0.35,which was the best for CSO control,indicating that the combination of green facilities and CSO regulation pool should be considered to achieve the regulation of CSO,and the best control was to control the proportion of green facilities investment to 0.35.