Study On Water Temperature Stratification And Water Quality Response Characteristics Of Daheiting Reservoir

Daheiting Reservoir is a large type II drinking water source reservoir on the Luanhe River system.It is jointly dispatched with the Panjiakou Reservoir to provide functions such as flood control,water supply and power generation.The water depth in front of the dam can reach more than 25 m,and there is a stable water temperature stratification in summer.In this paper,the Daheiting Reservoir was used as the research object,and the combination of numerical simulation,water quality in situ monitoring and laboratory was used to systematically study the seasonal stratification of water temperature and the evolution characteristics of water quality in Daheiting Reservoir.A three-dimensional hydrodynamic and water temperature model of the Daheiting Reservoir was built.On this basis,the response characteristics of water environment to water temperature stratification were discussed,and relevant improvement measures were proposed.The main research results and conclusions of the thesis are as follows:(1)Based on MIKE 3 software,a three-dimensional water temperature model suitable for the Daheiting Reservoir was built.The model takes into account the hydrometeorological data of the Daheiting Reservoir.The parameters of the water temperature model were determined and the results were verified based on the measured water temperature data from April to December 2018.The simulation results were in good agreement with the measured data.(2)There is a obvious characterized of seasonal water temperature stratification in Daheiting Reservoir.The stratification period is from May to September.Under the influence of water temperature stratification,dissolved oxygen,chlorophyll a and pH in the water body also show similar stratification phenomenon.And the dissolved oxygen in the surface water can reach saturation or even supersaturation,while the bottom water body is in anoxic state.The pH value of the bottom water body declines from May to June,but the water body of Daheiting Reservoir is alkaline.The content of Chlorophyll-a is lower below 10 m water depth,and there is almost no change in the whole year.The chlorophyll-a in the surface water has two peaks in June and September,And the highest in the whole year is 15.0?g/L in June,which exceeds the warning value of the bloom.This is due to the fact that phytoplankton can be stably present in the surface water suitable for its reproduction during the stratification of water temperature,which is the main cause of the sudden bloom in Daheiting Reservoir in summer.(3)Under the anoxic environment of the bottom water body,the sediment deposits release a large amount of enriched nitrogen,phosphorus and iron,manganese metal ions into the water body.Which will cause the water quality at the bottom of the water body to deteriorate.As the disappeared of water temperature stratified,these pollutants spread to the surface with the convection of the water body,which could caused the water quality to deteriorate and the water blooms one more.Based on the above research,the influence of water temperature stratification and extinction on the vertical distribution of water quality and phytoplankton is the main reason for the outbreak of algal blooms in Daheiting Reservoir.Therefore,human control and aeration technologies were proposed to prevent algal blooms by destroying the stratified structure of water temperature and supplying oxygen to the bottom water body.So as to destroying the suitable growth environment of phytoplankton and inhibiting the release of sediment pollutants,and preventing the occurrence of algal blooms.