Reservoir Reoperation for Fish Ecosystem Restoration Using Daily Inflows-Case Study of Lake Shelbyville

Ecosystem restoration calls for reservoir reoperation. Traditionally, a minimum water release is set as a constraint for downstream ecosystem flow requirement. Recently, research has been conducted for the purpose of recovering natural flow regimes to a practical degree. This paper examines the practicality of adding an ecological objective to the operation of Lake Shelbyville, a reservoir situated on the Kaskaskia River in east central Illinois, which has been used primarily for flood control. A multiobjective optimization model that minimizes flood damage (the dominating priority in the historical operation) and maximizes fish diversity for the downstream ecosystem is developed for daily operation of the reservoir. The challenges addressed in this paper include handling daily reservoir release for the ecological assessment and evaluating the practicality of changing the existing operation rules for the purpose of including an ecological objective. The model results in the reduction of the maximum allowable water release to avoid extreme flooding events and an increase of the minimum water release. Thus, adding an ecological objective to Lake Shelbyville's operation can improve downstream fish habitat without jeopardizing its original flood control objective. Furthermore, the effect of hydrologic variability on the results is explored with Monte Carlo simulations of reservoir inflows. The robustness analysis shows that the modified operation rules are sensitive to water levels; the biased representation of the role of water level in the reservoir release function can cause the bias of water release from its optimal value. Despite the limited data for the case study, this paper presents a method to improve conventional reservoir operation rules with consideration of both ecological and economic objectives.