Study on the Changes of Flood Regulation Storage Capacity and Restoration Measures of Wanjiazhai Reservoir Since Its Operation
This paper systematically reviewed the inflow and outflow water and sediment,flushing and deposition rule,changes of flood regu-lation storage capacity and restoration measures of Wanjiazhai Reservoir.The results can provide scientific and technological support for the scientific reduction of sedimentation in the flood control capacity of Wanjiazhai Reservoir.The results show that a)the operating water level of Wanjiazhai Reservoir in non-flood season from 1999 to 2023 ranges from 952 m to 980 m.The operating water level ranges from 950.9 m to 967.2 m in the flood season from 1999 to 2010,and the lowest water level is 921.6 m after the operation of the reduced water level in the flood season from 2011 to 2023(except 2016).b)From 1999 to 2023,the average annual inflow of Wanjiazhai Reservoir is about 18.519 billion m3 and the average annual sediment volume is about 50.1 million tons,and the average annual discharge is about 18.070 billion m3 and the average annual sediment volume is about 36.3 million tons.c)The longitudinal profile of Wanjiazhai Reservoir after the 2010 flood basically reaches the designed equilibrium state of sedimentation.Since 2011,the reservoir has been used for sediment discharge.As of Octo-ber 2023,the total storage capacity has lost 285.9 million m3 due to sedimentation,and the siltation loss of the flood regulation storage capac-ity has reached 19.1 million m3.d)The long duration and high flow process of the Wanjiazhai Reservoir is beneficial for reducing water level and using open discharge for sediment discharge.When the water level in front of the dam is below 952.00 m,the sediment content in the sediment discharge increases rapidly,and when it drops below the sedimentation surface or when the discharge is open,the upstream erosion generated is beneficial for improving the sediment transport efficiency.It is advisable to implement open discharge and sand discharge during the flood season in normal and dry years,and to maintain it for 5 to 15 days as much as possible.e)Relying solely on hydraulic dredging is no longer effective in restoring the flood regulation storage capacity of Wanjiazhai Reservoir.A combination of hydraulic dredging and mechan-ical dredging can be used to reduce sedimentation.The dredged sediment can be transported to the main river channel for dynamic discharge or to the shore for comprehensive utilization of sediment.
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