Abstract
Abstract. A reservoir operator does not favor storage above a certain level in situations such as the pre-release operation prior to a flood; scheduled engineering construction; or mechanical excavation of sediment in the impoundments, drawdown, and empty flushing, etc. This paper selects empty flushing as the case study, and a method is presented to promote the feasibility of emptying the reservoir storage. The impact of emptying reservoir on water supply is minimized through appropriate joint operation in a multi-reservoir system, where drawdown and empty flushing is carried out in a primary reservoir, and the other reservoir provides backup water for supply. This method prioritizes allocating the storage in the primary reservoir for water supply during specific periods prior to its emptying. If the storage of every reservoir achieves its predefined conditions, drawdown of the primary reservoir is activated and followed by empty flushing. Previously preserved storage in the other reservoir ensures adequate water supply during the periods of emptying the primary reservoir. Flushing of the primary reservoir is continued until either the accumulative released water exceeds the specified volume, storage in the backup reservoir drops below the predefined threshold, or the inflow to the primary reservoir recedes from the flood peak to be below the releasing capacity of outlets. This behavior is simulated and linked with a nonlinear optimization algorithm to calibrate the optimal parameters defining the activation and termination of empty flushing. The optimized strategy limits the incremental water shortage within the acceptable threshold and maximizes the expected benefits of emptying reservoir.
Highlights
Reservoirs intercept watercourses to store excessive water and regulate natural flow patterns into expected releases for different purposes
Where dnI,m and dnR,m represent the water shortage increment and ratio during the mth month following the feasible period of empty flushing in the nth simulating year; Dm denotes the water demand during the mth month following empty flushing; and dn,m and dn0,m represent simulated water shortages under conditions with and without empty flushing operations. dn0,m is from simulating the default regular water supply process using the generalized water allocation simulation model (GWASIM), and dn,m is obtained by incorporating empty flushing operations according to the activating and terminating conditions defined by the decision variables. nm is the number of months within which the impact of empty flushing on water supply is carried over, and ny is the number of simulating years
The total available storage in a system is allocated from the primary reservoir to the other to create favorable initial conditions and prepare backup water to be supplied during empty flushing
Summary
Reservoirs intercept watercourses to store excessive water and regulate natural flow patterns into expected releases for different purposes. There are circumstances in which storage above certain levels in reservoirs is not favored These situations include when an imminent flood is anticipated, when engineering construction or mechanical excavation of sediments within the impoundments is scheduled, and during empty flushing operations. The drawdown of storage is usually carried out by releasing water through bottom outlets During this process, the accelerated flow near the inlet may partially reactivate and scour out the depositions to generate a flushing cone in the vicinity of the inlet. The formation of the flushing channel usually leads to hyper sediment concentration of the bottom release and effectively recovers partial deposited capacity of the reservoir. This operation has been used to pursue sustainable utilization by many reser-
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