| After the impounding of Three Gorges Reservoir(TGR), the tributaries flow velocity of TGR decreased and eutrophication is increasing due to the rising water level.This situation caused serious algal bloom which occurred part of the bay of tributaries in spring and summer. Some scholars believe that one of cause for eutrophication is the slow water flow, and they believe the water flow conditions will be improved through reservoir operation, restraining euthrophication in turn. These have been approved by many experts, but the ecological regulation for prevention and control of reservoir tributary algal bloom was not definite up to now.This paper selects the typical tributaries of the TGR area, Xiangxi River and Daning River. In this paper, we constructed the hydrodynamic and water quality model in the Delft3 d model platform.The Delft3 D software draws the hydrodynamic model of orthogonal curvilinear grid for Xiangxi River and Daning River based on the waterfront line, and constructs the model of 3D underwater topographic map. Based on the hydrodynamic model of hydrological verification of Xiangxi River and Daning river construction, the results show the calculated values of the water level are in good agreement, and the model has a high reliability as well. Hydrological characteristics and water quality pollution characteristics were calculated, and analyzed of relationship between hydrodynamic change and tributaries of the water quality. Then the work can put forward the ecological protection measures, and provide a reference for the scheduling of the TGR operation and management.Main research conclusions include:1.Xiangxi River were simulated, and the hydrodynamic characteristics were under different water levels. The results showed that in the flood season, Xiangxi River presented typical "River", the flow rate is larger. In the storage period, the Xiangxi River showed obvious lake trend, water level slowed uplift and flow tends to be stationary, increasing the risk of pollution to a great extent.2.In the water quality simulation of Xiangxi River, the pollution of backwater area was hard to spread and had the potential to accumulate, the result showed the hydrodynamic conditions in the water quality played a decisive impact.Once a large quantity of pollutants discharged into the Xiangxi River,the pollutants readily stayed in the backwater area,sparking other environmental problems to threat the quality and safety of Xiangxi River.3.The simulation results show that the water flow is slow in Daning River at low stage, and the typical features of lake reservoir. In the high water period, river is a typical lake facies reservoir.We can think Daning River flow has been dormant in high water level. Bay areas has become stagnant water, than make water self purification capacity greatly weakened. Once the pollutant emissions, water environmental accidents will happen.4. The simulation on Daning River results show that the total nitrogen and total phosphorus’ effect is good,but the chlorophyll a simulation is bad. The reason is that the chlorophyll a is an indicator of the growth of algae,and its affecting factors are so many,such as light,water temperature,nutrients and water power process,resulting in a large deviation between the simulation results and the measured results5.Finally,the use of hydrodynamic control method,constructed wetlands,and the use of the pollution load.All the improvements puted forward a set of water quality protection technology for typical tributaries to reduce the grass ditch technology. |
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