Study On Water Residence Time And Connectivity Of Gangnan Reservoir

Water is an essential substance for all living things to sustain their life activities.In recent years,the problem of water environment pollution has attracted more and more public attention.Many measures have been taken to improve the water environment of reservoirs,lakes,bays and wetlands.The water exchange characteristics directly affect the water environment.The better the water exchange capacity,the better the water quality.Therefore,it is very important to study the hydrodynamics and water exchange to improve the water ecological environment of reservoirs and lakes.Gangnan Reservoir is one of the four major reservoirs in Hebei Province,and it is the drinking water source of Shijiazhuang.Therefore,mastering the water quality of Gangnan Reservoir and exploring the water exchange characteristics and pollutant diffusion law of the reservoir can provide theoretical basis for improving the water purification capacity and ecological environment of the reservoir.Based on the background of Gangnan Reservoir,a mathematical model of hydrodynamics and water exchange was established in this thesis,and taken the water residence time and connectivity as research indicators to study the overall and each area water exchange of Gangnan Reservoir under different flow rates and wind fields.At the same time,the connectivity matrix was constructed to study the migration and diffusion law of pollutants in the reservoir under different working conditions.The main research topics and conclusions are as follows:(1)A mathematical model was developed to study the hydrodynamics and water exchange of Gangnan Reservoir,The model’s parameters were calibrated by comparing the simulated and measured data.The results indicated that the model accurately reproduced the hydrodynamics and water body exchange of Gangnan Reservoir,making it suitable for numerical simulation studies.(2)The water residence time under different flow and wind fields was simulated,and the influence law of flow and wind fields on the residence time of Gangnan Reservoir was obtained through comparative analysis.It was found that the flow rate and wind field have different impacts on the residence time of Gangnan Reservoir.The residence time of overall and each area in reservoir decreased with the increase of the flow,and the rate of decrease varies in different reservoir areas,but when the flow rate increased to 100 m~3/s,increasing the flow rate had little impact on the residence time.The wind field shortened the residence time in the bay areas,while increased that in the main areas.The diversion of water under windy conditions could shorten the residence time of reservoir bay area,improved the purification capacity of water body in reservoir bay area and improved water quality,among which the diversion of water under west wind conditions had a greater effect on the improvement of water quality.(3)The water connectivity under different flow and wind fields was simulated,and the influence of flow rate and wind field on the connectivity of water bodies in Gangnan Reservoir was obtained through comparative analysis.It was found that the flow and wind fields have different effects on the connectivity of the water body in Gangnan Reservoir.With the increase of flow,the degree of pollution in the main reservoir area was reduced.Except for the X reservoir area,the degree of pollution in the bay area was aggravated,and most of the pollutants are still difficult to flow out of the reservoir area due to the influence of the topography of the bay area.The wind field had influence on the pollutant diffusion in both the main reservoir area and the bay area of Gangnan Reservoir.The wind field promoted the pollutant diffusion in the main reservoir area of Gangnan Reservoir and reduced the degree of pollution in the main reservoir area,and promoted the pollutant diffusion in the bay area to its adjacent main reservoir area and reduced the degree of pollution in the bay area.Under the action of wind fields with different wind directions,the overall pollutant diffusion effect of the reservoir was roughly the same,but the degree of pollution in each reservoir area was slightly different.