Research On Hydrodynamic-water Quality Simulation And Endogenous Pollution Control System Of Daye Reservoir

Daye Reservoir is one of the important water sources in Jinan,and its water quality safety is directly related to people’s health and sustainable development of production and life.In order to ensure the safety of water quality,a series of control measures such as interception and restriction of discharge have been adopted for exogenous pollution,and the water quality of the surface water body has basically reached the standard,but insufficient attention has been paid to the prevention and control of endogenous pollution.Affected by water temperature stratification and seasonal incoming water,there are differences in the temporal and spatial distribution of pollutants in reservoirs,and there is a lack of monitoring and simulation research on the bottom water body.Moreover,the reservoir has little abandoned water,long water retention time,less dredging frequency,and continuous accumulation of endogenous pollutants in the reservoir,and there are potential risks to water supply security,for which there is no corresponding control measures.Therefore,in view of the above problems,the Daye Reservoir was arranged with monitoring sections and stratified sampling points that changed dynamically with water level,and the temporal and spatial variation characteristics of water quality and sedimentary physical and chemical indicators were analyzed.On this basis,a three-dimensional hydrodynamic-water quality model of Daye Reservoir is constructed,and the spatiotemporal changes of nitrogen and phosphorus in the bottom water body and sediments are numerically simulated,revealing the transport process of endogenous pollution.Based on the reservoir connection project,the model is used to optimize the hydraulic control position and water transmission flow scheme.Combined with a variety of ecological treatment technologies,an endogenous pollution control system is formed to provide technical support for water quality assurance.The main research contents and conclusions are as follows:(1)Water environment monitoring and spatiotemporal variation characteristics analysis of Daye ReservoirIn view of the difference in the temporal and spatial distribution of water quality in Daye Reservoir,the monitoring section was laid out on the principle of controlling the characteristic area of the reservoir,and stratified sampling points were set up according to the dynamic change of water level,and samples were taken for laboratory tests at the same time as on-site measurement to detect the physical and chemical indicators of water body and sedimentation.The stratification structure of reservoir water temperature and the temporal and spatial variation characteristics of water quality indexes were studied.The nutritional status of reservoirs was evaluated using the comprehensive nutrient status index method.The cumulative effect of sediment nitrogen and phosphorus nutrients was analyzed.The results show that there is a stable water temperature stratification structure in front of the dam in summer,and the maximum temperature gradient is 1.2℃/m.The water quality of the bottom layer was worse than that of the surface layer,and the corresponding average concentrations of total nitrogen and total phosphorus reached 6.03mg/L and 0.112mg/L,respectively,exceeding the limit of Class III.water quality standards.The comprehensive trophic status index of the reservoir exceeds 50,which is a eutrophic state;The average content of nitrogen and phosphorus in the overall sediment in the reservoir area was 1.368g/kg and 0.6084g/kg,respectively,and the soil nutrient grade was between advanced and intermediate.This shows that the risk of endogenous pollution in Daye water stocks needs to be controlled urgently.(2)Construction and simulation of three-dimensional hydrodynamic-water quality model of Daye ReservoirIn order to further study the release characteristics and accumulation process of endogenous pollutants,on the basis of fully considering the influence of water temperature stratification and endogenous release on water quality,the ECOlab water quality template was developed twice,and a three-dimensional hydrodynamic-water quality model of Daye Reservoir including water body and sediment system was constructed,which simulated the hydrodynamic conditions,water temperature structure,water nitrogen and phosphorus and sediment nitrogen and phosphorus from June 1,2022 to October 31,2022.The results show that the model errors are within the allowable range.The overall flow rate of the water body in front of the dam is about 0.01m/s,and the hydrodynamic conditions are poor.In summer,the upstream water temperature of the reservoir is 1～2℃ higher than that of other sections;Endogenous pollutants accumulate in the upstream retreat zone and diffuse to the front of the dam under the action of water flow.There was a significant negative correlation between nitrogen and phosphorus in the bottom water before the dam and nitrogen and phosphorus in sediment.It is further verified that endogenous pollution has a great impact on the water quality in front of the dam,threatening the safety of reservoir water supply.(3)Research on endogenous pollution control systemAiming at the water quality risk caused by endogenous pollution of Daye Reservoir,based on the reservoir connectivity project,the established three-dimensional hydrodynamic-water quality model is used to simulate different water transmission outlet locations and different typical water transmission flow schemes,and the results show that the optimal location of the water transmission outlet with endogenous pollution control as the goal is the south side of the spillway of Daye Reservoir.The average TN and TP contents of bottom water decreased by 36.00%and 29.10%,respectively,after the maximum water flow rate on the design day was adjusted.The water transmission flow rate in the range of 1.38～1.73 m3/s can reduce the concentration of TN and TP in the bottom layer before the dam by more than 25%.Combined with the actual situation,with a variety of ecological governance measures,a sub-regional regulation and control scheme was proposed,and a comprehensive control system of endogenous pollution of flow scheduling-endogenous treatment and exogenous prevention andcontrol was constructed to ensure the safety of water supply quality.