Study On Ecological Water Demand Of Urban Sluice Controlled River Under Flood Control And Drainage System

With the increasing demand of urbanization and urban flood control and drainage safety,problems such as insufficient hydrodynamic force,decreased self-purification capacity and reduced aquatic biodiversity have occurred frequently in urban watercourses.Therefore,it is necessary to carry out research on ecological flow of urban sluit-controlled watercourses under the flood control and drainage system.Based on the study of ecological water demand of urban sluit-controlled watercourses,this article studys ecological water diversion by using numerical simulation and prototype test techniques in Huai’an city of Huaihe River Basin.The main results are as follows:(1)The current operation situation of gates in Huai’an is all closed.Under this scenario,the watercourses are basically in a state of stagnation,and the velocity distribution is generally 0.001～0.01m/s.The water quality of the inland river is poor.Under the control of the safe water level fortification,the inbound flow in the northern part of the canal can be safely diverted to 57.77 m~3/s,and that in the southern part of the canal can be safely diverted to 104.40 m~3/s.The distribution of inbound flow is extremely uneven,with fewer high areas and more low areas,and the river hydrodynamics is poor.(2)Based on the indoor annular flume experiment and related literature references,the objective system of ecological water diversion in the study area is constructed by the river senses,algae growth inhibition and landscape entertainment needs.According to the transparency requirements of urban black and odorous river treatment,the experimental results of raw water sediment settlement under the flow velocity of the river without sediment disturbance is 0.09 m/s.Considering the requirements of algae growth inhibition,it is suggested that the ecological flow rate should reach 0.08 m/s and not lower than 0.05 m/s.The landscape water level of river course is restricted by the security fortification water level for flood control and drainage,which is generally4.4-9.5m.(3)According to the hydrological division of the study area and based on the MIKE 11 model,the hydrodynamic and water quality models of the northern and southern areas in Huai’an are established.There are 160 river channels,120 sluice gates and 27 drainage pumping stations.The roughness of the hydrodynamic model is0.02～0.025.The average relative error of water level verification is 0.28%-0.37%,and the average relative error of flow verification is 5.58%.For Ecolab water quality model,the relative errors of ammonia nitrogen and dissolved oxygen were 0.26%-13.33%and1.65%-7.19%respectively.(4)To improve water environmental carrying capacity,ensure water ecosystem health and balance inbound water flow,four water diversion dispatching conditions are designed in consideration of flood control safety and water resources saving.Through the model simulation and optimization choice,the article chooses the most optimal scenario,which satisfys the requirements of the ecological water diversion target system,high water diversion balance in the area,and the water conservation.Under this scenario,the designed ecological diversion volume is 17m~3/s.The north part of area deverses to 12.00 m~3/s,and the average velocity of 78%rivers reaches0.08m/s,.In the southern part of area deverses to 12.00 m~3/s,and the average velocity of 80%rivers reaches 0.05m/s.Compared with the scenario of flood control and drainage security,the total diversion of the inbound water decreased by 89.5%(the flow in the north and south of the area decreased by 78.42%and 95.21%respectively),and the variation coefficient of the diversion water per unit river length in each area decreased from 0.43 to 0.06,which balanced the transit water volume in the area,and the degree of landscape water level was about 55%.