Study On Hydrodynamic Optimization Of Water Quality Improvement And Water Replenishment Project For Lakes With Scarce Water Resources In Platea

Lakes are extremely prone to water eutrophication due to their long-term closed or semi-closed status and poor hydrodynamic status under natural conditions.With the vigorous promotion of ecological civilization construction,many cities,in order to solve the problems of inequality in spatial distribution of water resources,insufficiency of water in lakes and poor hydrodynamic conditions,have built water diversion projects to replenish the water in lakes.At the same time,the water body with high pollutant concentration is replaced to improve the hydrodynamic conditions and improve the water quality.In this paper,we take Yilong Lake,a typical plateau water scarce lake in Yunnan Province,as the research object,and conduct water displacement simulation to investigate the spatial and temporal changes of pollutants in Yilong Lake.The paper also provides a reference for the precise restoration of the ecological and water environment of Yilong Lake.By comparing and analyzing the domestic and international research methods on the simulation of hydrodynamics and water displacement,the hydrodynamic module and convective diffusion module of MIKE21 software were selected,and the TN content in the lake was used as the water quality evaluation index.The simulation,comparison and optimization of water flow and pollutant dispersion in different water diversion conditions of Yilong Lake are carried out.In this study,four working conditions and 13 water diversion schemes were set up to analyze the spatial and temporal ranges and patterns of pollutant concentrations in Isorosaurus Lake,and the specific contents and conclusions of the study are as follows:(1)Based on the meteorological,hydrological and water quality information of Yilong Lake,the MIKE21 hydrodynamic-convective dispersion model of Yilong Lake was constructed by considering the water quantity and quality of the diverted water.The accuracy of the model was verified by using the mean absolute error and mean relative error between the measured data and the model simulated values.The results show that the model simulation errors are small and within a reasonable range.The results show that the model simulated error is small and within a reasonable range.The trends of water level and concentration are in good agreement with the measured values,and the model can better respond to the hydrodynamic change process and pollutant dilution and dispersion law in the water replacement process of Yilong Lake..(2)In this paper,we simulated the hydrodynamic conditions under different number of diversions and different flow diversion schemes and explored the improvement of TN concentration.The results show that the implementation of the water diversion project can significantly improve the hydrodynamic conditions of the lake and enhance the water quality of the lake.The scheme of separate diversion of the Cheng River has a longer residence time of the diverted clear water in the lake because the diversion outlet is far from the outlet.It can improve the utilization rate of clear water,and the overall effect is better than that of the two-port diversion and three-port diversion schemes.The water displacement rate increased by about 28% and the water quality compliance rate is increased by 17.84% by increasing the diversion volume under the scheme of separate diversion of the Cheng River,and the water replacement efficiency per unit of recharge volume is reduced.(3)In this paper,different installation positions of the thrusters with different power combination schemes are simulated and studied.The results showed that the water replacement rate in the middle and east areas of the lake was significantly increased after the installation of additional pushers,and the water replacement process in the lake as a whole was accelerated.By comparing the water quality improvement effect of four different installation locations,the installation location was determined.A comprehensive analysis of environmental and economic benefits was conducted to arrive at the optimal solution for thruster installation.(4)In order to improve water utilization,a method of diversion using intermittent diversion was proposed.The quantitative comparison between continuous and intermittent water diversions was conducted in terms of the amount of water used to achieve the same water quality objectives,the diversion time,and the water quality improvement effect using the same amount of water diversion.The most significant water savings were found in Option 13,which was adjusted for intermittent diversions,and was able to simultaneously improve the lake water replacement rate and reduce the stagnant water area.