Evaluation of New Control Structures for Regulating the Great Lakes System: Multiscenario, Multireservoir Optimization Approach

Water levels in the Great Lakes–St. Lawrence system located in northeastern North America are critically important to the Canadian and U.S. economies. Water managers are concerned that this system, which is currently managed by control structures at the outlets of Lakes Superior and Ontario, is not able to cope with the highly uncertain impacts of climate change. In particular, the frequency of extreme water levels throughout the system might be substantially increased. This study provides an exploratory conceptual analysis to determine the extent that new control structures at the outlet of Lake Huron or Erie (or both) and corresponding excavation along the St. Clair or Niagara River (or both) might mitigate the risks posed by future extreme water supply scenarios. Multilake parametric rule curves were developed to regulate systems enabled with these new control structures as a whole. Multiple stochastic water supply sequences were adopted that represented different future extreme climate scenarios. A multiscenario, multireservoir (multilake), biobjective simulation-optimization methodology was developed to optimize the rule curve parameters in such a way that the risk of experiencing extreme water levels is robustly minimized and fairly distributed across the system. The biobjective setting was designed to embed the secondary objective function so that the cost of the new control structures and excavation generates trade-offs between the costs and the associated achievable risk reductions. The recently developed Pareto Archived Dynamically Dimensioned Search (PA-DDS) multiobjective optimization algorithm was enabled with the efficiency-increasing “deterministic model preemption” strategy and utilized to solve the optimization problem. Results demonstrate that although systemwide regulation with the new control structures could substantially reduce the risk (i.e., by 86% compared to the current or base level of regulation), it could not eliminate such events entirely and would cause adverse effects on the lower St. Lawrence River. Numerical results also suggest that implementing a single new control point at the outlet of Lake Huron would not be effective despite its high cost; however, a single new control point at the outlet of Lake Erie would be very effective, with considerably less associated cost.