Risk Analysis Of Hydropower Construction Closure Under Impact Of Downstream Regulation

With the gradual development of cascade hydropower stations,the phenomenon that the construction of upstream power station actualizes later than the construction of downstream power station is more and more common.Under leveled construction conditions,the storage and retarding effect of the downstream hydropower station inevitably changes the natural attribute of the channel.When the upstream hydropower station under construction is located in the backwater range of the downstream reservoir,the discharge control scheduling of downstream hydropower station becomes one of the important factors affecting the river closure gap hydraulic conditions of the upstream.Therefore,the governing body of the process of construction closure extends from the unilateral constructors of the upstream station to both sides of upstream and downstream hydropower stations,bringing new problems and challenges to river closure work.Meanwhile,as an important milestone in the construction of water conservancy and hydropower projects,construction closure is the key content of construction organization design.The consequences of closure failure are so serious that it is necessary to conduct a comprehensive risk analysis before construction.Therefore,it is of great significance for the development and construction of cascade hydropower stations to carry out the research on the risk of construction closure considering the regulation of the downstream hydropower station.Taking the hydraulic connection between adjacent cascade hydropower stations and the closure risk analysis based on it as the core,this article establishes quantitative analysis model between the water level of the downstream hydropower station and gap hydraulic parameters of the upstream station,analyses the effects of different discharge manners of the downstream hydropower station on the gap hydraulic parameters,builds closure risk estimation model considering the regulation of the downstream hydropower station,and furthermore analyses the sensitivity of closure risk to the water level of the downstream hydropower station.The main researching contents are as follows:(1)Taking the gap of closure dike for research objectives,the relationship between the reservoir water level of the downstream hydropower station and gap hydraulic parameters of the upstream downstream hydropower station is analyzed,including the downstream water level of closure gap(downstream water level of closure dike’s toe,abbreviates as DWLT),water depth of gap axis,velocity,drop,and flow.Numerical calculation and hydraulic calculation methods are used to quantify the correlation between the downstream water level and each index.The results show that the correlation between downstream reservoir water level and DWLT is the highest,which creates conditions for reducing closure difficulty with help of the downstream hydropower station.(2)In allusion to the regulation process of the downstream hydropower station,regulation patterns under different engineering conditions are analyzed.Based on the design closure flow and predicted flow,the corresponding relationship model between multiple discharge manners and gap hydraulic parameter of the upstream station is established.The effect of the operation scheduling of the downstream hydropower station on the closure process of the upstream hydropower station is disclosed,which can provide references for design and planning of the closure project.(3)Uncertainty of prediction error is introduced in closure risk analysis,and the risk calculation model is erected by using the Monte-Carlo method.The sensitivity of closure risk to the water level of downstream reservoir is calculated with the participation of single factor analysis method.Results show that the sensitivity is relatively high in the calculation interval,which provides a theoretical basis for reducing the closure risk via controlling the regulations of the downstream hydropower station.