Study On Investigation And Treatment Of Non-point Source Pollution In Small Watershed Into Water Source Reservoir

China has the largest number of reservoirs in the world.In recent years,with the pollution of rivers,many rivers cannot supply water,and reservoirs have become the main water source.Reservoir supplying water is one of the most important means of relieving water supply pressure.Biliuhe Reservoir is the most important water source reservoir in Dalian,so it is necessary to ensure the safety of water quality.However,the water pollution control in the small watershed upstream of the Biliuhe Reservoir has been rarely carried out.Dissolved or solid pollutants in small watersheds,such as nitrogen,phosphorus,livestock manure,agricultural plastics,domestic garbage,etc.,under the action of precipitation and runoff,cause a large amount of pollutants to enter the downstream water.In order to protect the water quality of the water source downstream of the small watershed,it is necessary to intercept the upstream pollutants and solve the pollution problem in the upstream small watershed.In this paper,the Mitun watershed is taken as the research object.The small watershed is located upstream of the Biliuhe Reservoir.Based on the output coefficient model,the non-point source pollution status of the small watershed is studied.The treatment technology for non-point source pollution is proposed,and the flood control impact after the construction of the submerged dam is analyzed.The main research results are:(1)The main sources of non-point source pollution in Mitun watershed are rural life,livestock and poultry breeding and planting.The pollution loads of TN and TP in Mitun watershed are 24289.22kg/a and 5043.03kg/a respectively.The water inflow load is2201.44kg/a and 374.24kg/a respectively.From the source,cultivation is the main source of pollution load and source of water load of TN,accounting for 35.82%and 39.52%respectively.Chicken breeding is the largest source of pollution load and source of water inflow,accounting for45.61%and 43.02%respectively.(2)The treatment needs of non-point source pollution in Mitun watershed are proposed,mainly to reduce TN,TP pollution,intercept solid waste and precipitate sporadic suspended matter and particulate matter.According to the demand of management,three schemes of horizontal subsurface flow constructed wetland,surface flow constructed wetland and submerged dam to expand natural wetland are proposed.Choose the dam to expand the natural wetland plan from the perspective of governance needs and engineering safety.The submerged dam expands the natural wetland to expand the natural wetland by constructing two-stage submerged dams.After the construction of the submerged dam,the wetland area is 48,900 m~2.The hydraulic retention time is 5.22 days.The submerged dam realizes the interception of the underground diving through the HDPE geomembrane to raise the water level,and the surface covering gabstone cage keeps the overall structure stable.(3)Using MIKE 21 model to calculate the flood control impact after the construction of the submerged dam.When the downstream water level is 64m,the maximum water level of the first stage dam is 0.41m,and the water level of the second stage dam is 0.60m.The water level does no exceed the reservoir range;the flow velocity near the downstream of the first-stage submerged dam increased by 0.61m/s,and near the second-stage dam increased by 0.86m/s.The water depth before the first stage dam is increased by 0.33m,and before the second stage dam is increased by 0.60m.The water depth after the dam is hardly changed.When the downstream water level is 68.1m,the water level of the first stage dam is 0.41m,the second stage dam does not change,the water level does not exceed the reservoir range.The flow velocity near the downstream of the first stage dam is increased by 0.63m/s.After the construction of the second-stage submerged dam,there is almost no impact on the flow rate.The water depth in front of the first-stage dam is increased by 0.30m,the water depth before the second-stage dam is hardly increased,and the water depth behind the two-stage dam is hardly changed.