Research On Hydrodynamic And Water Quality Simulation And Water Environmental Improvement Measures In A Shallow Reservoir

Shallow reservoir has the functions of flood control,water supply and ecological environment protection,which plays an important role in societal development and rational utilization of water resources.Due to the slow velocity or even static state of the water body,it is liable to induce sedimentation issues in shallow reservoir,and the water exchange capacity and self-purification ability is poor.In addition,with rapid socio–economic development and unceasing population growth,excessive external pollution load caused by human activities,such as domestic sewage,agricultural wastewater and industrial effluent has directly contaminated the water of shallow reservoir,and continuous pollution results in severe water quality deterioration.In order to alleviate serious water environmental pollution,a series of improvement measures are often adopted to improve the reservoir water environment.Therefore,it is a vital scientific basis for water environmental management of shallow reservoir to master the complex evolution of water environment and study the improvement effects of different measures.In this study,a three-dimensional numerical model of Suyahu Reservoir is developed to study the hydrodynamic and water quality patterns of the reservoir,so as to provide scientific and reliable decision-making support for water environment management of the reservoir.A series of improvement measures were proposed for the severe sedimentation and water quality deterioration of the reservoir,including sediment dredging,external load reduction and inflow regulation,and the effects of different improvement measures are quantitatively analyzed and evaluated.(1)A three-dimensional hydrodynamic and water quality numerical model of Suyahu Reservoir was conducted based on EFDC,and the main parameters of the model were confirmed.The model was calibrated and validated by comparing the simulation results with the measured data of the reservoir,which proved the validity and rationality of the model.(2)The hydrodynamic and water quality distribution patterns of the reservoir before and after implementing the expansion and sediment project were studied based on the reservoir numerical model.The water environment of the reservoir was analyzed and assessed from the aspects of flow field and water quality based on the simulation results,and the influence of the project was quantitatively analyzed.The results show that the water quality of the reservoir was not significantly improve and hardly meets the expected standard after expansion and sediment dredging project,indicating that the internal pollution load is not the root cause of water quality deterioration in the reservoir.(3)The inflow regulation was proposed in order to improve the hydrodynamic conditions in the reservoir,and the effects of inflow regulation on water environment were studied by using the reservoir numerical model.In addition,the proportion of stagnant water area and water exchange rate were used as the indicators for evaluating the influence of different inflow regulation scenarios on hydrodynamic conditions of the reservoir.The results suggest that inflow regulation can effectively improve hydrodynamic conditions of the reservoir,and the improvement effects of various regulation scenarios were quite different,but its positive effects on water quality were not obvious.The simulation results of various scenarios indicate that when the flows of Ru River's two inlets were evenly distributed,the hydrodynamics and water quality of the reservoir were best improved.(4)The external load reduction was proposed based on the anticipated water quality goals of the reservoir,and the load reduction ratios required for each tributary were confirmed.The water quality patterns of the reservoir after external load reduction were studied by using the numerical model,and the effects of external load reduction on water quality were analyzed quantitatively.The results indicate that the water quality of the reservoir would be significantly improved by reducing the external load,and the water quality in most areas could meet the water quality standards of Class IV.However,the TN and TP pollution in the northeastern part of the reservoir was still serious.(5)The inflow regulation was carried out based on the internal and external load reduction,the comprehensive impact of different measures on the water quality of the reservoir was studied by using the numerical model.The results show that the water quality of the reservoir was not significantly improved by inflow regulation after the internal and external load reduction,and the effect difference of different inflow condition was small.When the flows of Ru River's two inlets were evenly distributed,the water environment of the reservoir was best improved.