Study On The Water Supplement Scheme Of Water Quality Improvement In Liedeyong River Projects

With the vigorous promotion of water ecological civilization,the water environment and water landscape of urban rivers have attracted widespread attention of the whole society.Water diversion and recharge is a common and effective engineering measure to improve the water environment and water landscape of urban rivers under the premise of pollution control and pollution interception.Lide river is the only non-man-made river in guangzhou that flows through the central business district of guangzhou zhujiang new town.After pollution control,the water diversion and replenishment in the dry season are pumped from the front channel of the zhujiang river to the changhong regulation and storage lake,and then pumped from the changhong regulation and storage lake to Lide river.Due to the limited storage capacity of the Changhong lake and the plan to take some of the water out to replenish the other urban rivers,Therefore,it is necessary to study the improvement effect of the low flow--long duration recharge mode on the water quality in Liede river,so as to provide a basis for the revision of the scheme.In this paper,water quality investigation and evaluation analysis and water quality simulation are studied respectively,the main research contents and results are as follows:First,in order to find out the present situation of water environment in Liedeyong River,this paper conducts a field survey on the water quality of Liedeyong River（transparency,ammonia nitrogen,total phosphorus,dissolved oxygen）.By establishing the comprehensive fuzzy optimization model for water quality evaluation,the water quality of current non-recharge schemes and several possible recharge flow schemes are evaluated,and the water quality improvement effects of each possible recharge flow scheme are compared.It is found that except for tidal reach,the water quality of supplementary water in Liedeyong is obviously better than that of non-supplementary water,and the water quality of supplementary water with large flow rate is obviously better than that of small flow rate.At the same time,the amount of sewage and pollutant concentration into the river were estimated,in order to further grasp the current situation of the water environment of Liedeyong River.Secondly,a one-dimensional hydrodynamic water quality model of Liedeyong River"MIKE 11"was constructed according to the river network,generalized section diagram and calculated boundary conditions.Considering the actual conditions and relevant specifications of river bottom,water-blocking buildings and other structures in each section,the roughness of the river was between 0.025 and 0.05,the diffusion coefficient was 5m²/s,the ammonia nitrogen attenuation coefficient was 0.1d^-1,the attenuation coefficient of total phosphorus was0.07d^-1,and then the parameters of the hydrodynamic water quality model were determined by the measured sampling data.The result shows that the water quality model can reflect the pollutant diffusion and attenuation law of Liedeyong River,and can provide a model basis for the simulation of rehydration scheme,and can more accurately simulate the water quality of Liedeyong River.Finally,according to the actual situation of the reservoir capacity of Changhong lake in the three stream water replenishment project and the change of tide level,different water replenishment conditions are designed,with 0.8m³/s,1.0m³/s and 1.2m³/s three water replenishment flows,and the three water replenishment starting times are 6:00,7:00 and 8:00every morning.Through the established hydrodynamic water quality model,the water quality in each working condition is simulated and analyzed,so as to evaluate the water replenishment scheme that is more in line with the actual daily needs of the project.After calculation and analysis,the following conclusions are obtained:the low-flow and long-duration water replenishment model has a significant effect on the improvement of water quality in the upstream section close to the water replenishment gap,while there is no improvement effect or deterioration of water quality in the middle and lower reaches.Considering the overall water quality of the Liedeyong River and Changhong Lake has limited reservoir capacity,etc.,it is recommended to refill at 1.0 m³/s starting from 6 am in the dry season.