| After the reservoir was built and impounded,the water flow pattern and water structure in the reservoir area changed.At the same time,it will also bring about some new environmental problems,especially for large-scale deep-water reservoirs.With the change of the season,there will be different degrees of water temperature stratification,resulting in greater physical and chemical indicators of water(dissolved oxygen,nitrogen,phosphorus,etc.).The impact makes the water body eutrophication.As the development of our country’s electricity market,there has been a great change in the demand and quality of power supply and people’s awareness of energy conservation and environmental protection.In order to improve the quality of power supply for the national grid and adjust peak power usage,a large number of pumped-storage power stations can be built.However,after the operation of pumped-storage power stations,the frequent exchange of water bodies breaks the relatively stable state of the water bodies in the reservoirs.The water ecological environment is obviously different from conventional reservoirs,especially for the upper dams.Panjiakou Reservoir is the largest drinking water source reservoir in North China.Panjiakou Hydropower Station is a typical hybrid pumped-storage power station.At present,the biggest problem of the reservoir is that the concentration of nitrogen and phosphorus is seriously exceeded,and the problem of eutrophication is serious.In particular,the concentration of nitrogen and phosphorus in front of the dam is always at a relatively high level.Based on the special engineering structure of the reservoir,the operation of the pumped-storage power station is likely to have a greater impact on the deterioration of water quality before the dam.Through the data collection and prototype data observation of the Panjiakou Reservoir,the main sources and distribution characteristics of nitrogen and phosphorus in the reservoir are analyzed,and the effects of the distribution characteristics of the physical factors(mainly water temperature,dissolved oxygen,p H,and conductivity)of the entire reservoir on the distribution characteristics of nitrogen and phosphorus were discussed.Through the establishment of a three-dimensional hydrodynamic-water quality model before the dam,the effects of different operation modes of the power station on the distribution of nitrogen and phosphorus in front of the dam of the Panjiakou reservoir were analyzed.At the same time,according to the different operating conditions and methods of the power station,the improvement plan of the water quality in front of the dam was proposed.The research results also provide important reference for the improvement of water quality in the late Panjiakou.The main conclusions of this study are as follows:(1)Analysis of the sources and distribution characteristics of nitrogen and phosphorus in Panjiakou Reservoir.The main pollution of the Panjiakou Reservoir comes from point source and surface source pollution in the upper reaches of the reservoir and its surrounding areas,as well as endogenous pollution caused by the fish cages in the reservoir itself.The main source of total nitrogen in the reservoir is due to point source and surface source pollution caused by industrial and agricultural production and domestic sewage in the upstream and surrounding areas of the reservoir,and the main source of total phosphorus in the reservoir is due to the endogenous pollution caused by the fish cages itself.In the period from July to September,the concentrations of total nitrogen and total phosphorus in the reservoir area basically showed the trend that the middle and bottom layers were larger than the surface layer,and the overall change trend was basically the same.In terms of spatial distribution,the total nitrogen concentration gradually decreased from the end of the reservoir to the front of the dam,and the total phosphorus concentration gradually increased.On the whole,total nitrogen and total phosphorus before the dam maintained a relatively high level from July to September.(2)The influence of distribution characteristics of water environment factors on nitrogen and phosphorus distribution in Panjiakou Reservoir.From July 2017 to January of the following year,the physical factors of each section showed a consistent and significant stratification in the vertical direction from July to October.The stratification gradually disappeared in November and the reservoir tends to mix vertically.In the absence of disturbance,the water temperature and dissolved oxygen in the reservoir are the main factors affecting the distribution of nitrogen and phosphorus;p H has little effect on total nitrogen,but affects the distribution of total phosphorus;conductivity affects the distribution of total nitrogen,but the total phosphorus distribution.(3)The influence of the operation mode of Panjiakou pumped-storage power station on the distribution of nitrogen and phosphorus before the dam.With the reduction of the operating water level,regardless of the conditions under which the power station operates,the impact on the flow velocity,water temperature,and water quality before the dam is relatively increased.When the power station is operated by conventional water-discharging power generation and storage-storage generating units,the temperature distribution in front of the dam does not change significantly.The flow velocity at the inlet of the power station is much greater than the flow velocity at the bottom of the reservoir,and the disturbance to the water body in front of the dam is small,and not enough to break the original layered state of the water body.Under strong stratification,the bottom water body caused the release of nitrogen and phosphorus from the sediment due to lack of oxygen,which caused the nitrogen and phosphorus concentrations in the bottom of the dam to slightly increase under the two different operating modes.(4)When the power station is pumped and stored with an energy storage unit,the bottom flow velocity at the front 50 m of the dam at the time of pumped storage of the storage unit is 0.54m/s and 0.63m/s,respectively,which is greater than the sediment start flow velocity at the reservoir bottom of 50.20cm/ s,bottom sediment sediments will occur in general movement phenomenon,to provide favorable conditions for the release of sediment pollutants.Therefore,under the conditions of pumped storage,the power station will not only result in full disturbance of the water in front of the dam,but also will promote the release of nitrogen and phosphorus in the sediment before the dam.As a result,when the water quality in the lower pool is better,the concentration in the middle layer of the table decreases and the bottom layer concentration remains unchanged.When the water quality of the lower pool is poor,the concentration of the lower pool itself is the same as the concentration of the middle water body before the dam.Under the combined conditions of convection and sediment release,the surface layer concentration is increased,the middle layer concentration is constant,and the bottom layer concentration is also relatively high.Under the 205 m operating water level condition,because its total nitrogen concentration distribution is that the bottom layer is larger than the surface layer than the middle layer,and the concentration of the lower pool is the same as that of the middle water layer before the dam,due to the strong convective mixing,the water quality of the current pool is poor,the pre-dam concentration table and the bottom level were reduced and the middle layer remained unchanged.(5)An improvement plan based on the pre-dam water quality of Panjiakou Reservoir.When the water quality of the lower pool is good,under the condition of 216 m operating water level,the power station is operated for six hours with pumped storage to make the distribution of nitrogen and phosphorus in front of the dam stable,and the minimum concentration value appears;at the water level of 205 m,the power station pumps water.The operation of the energy storage mode for 5 hours can stabilize the nitrogen and phosphorus distribution in front of the dam and cause a minimum concentration value.When the water temperature is 5°C,7°C and 10°C respectively,the corresponding settling time is 4.8h,4.7h,4.0h in the upstream 216m running condition;the corresponding settling time is 3.4h,3.3h,2.8h in the 205m running condition..The settling time for downstream conventional generating units is 2.7h,2.6h,and 2.2h,and the settling time for energy storage unit generation is 3.1h,3.1h,and 2.6h.According to the operating scheduling principle of the pumped-storage power station in Panjiakou,in order to optimize the water quality during the flood season and the water supply period and improve the water quality before the non-water supply period,the following suitable schemes are proposed:1)In the flood season and the water supply period of 216 m water level,the elevation of the water intake of the reservoir is 166 m.To optimize the water quality before the dam,water can be supplied through the conventional generating units and generate electricity,and then the power station can stop operation.After 3 hours,the pumped storage power station is pumped.6h,then the power station stops running,and after 5h,it will supply water through the conventional unit and generate electricity.The power generation time will be automatically adjusted according to the daily water supply.2)In the non-water supply period,ie 205 m water level,in order to improve the pre-dam water quality conditions and eliminate the internal pollution in front of the dam,pumped storage power station can be pumped and stored for 5 hours,then the pumped storage power station can be used to generate electricity to discharge The suspended sediment particles are discharged to the downstream,and then the power station stops operation.After 4 hours,the pumped storage power station is pumped and stored.The pumped storage power station power generation time can be automatically adjusted according to the daily power grid peak adjustment. |
PDF Full Text Request