Optimizing multiple dam removals under multiple objectives: Linking tributary habitat and the Lake Erie ecosystem

A model is proposed for optimizing the net benefits of removing multiple dams in U. S. watersheds of Lake Erie by quantifying impacts upon social, ecological, and economic objectives of importance to managers and stakeholders. Explicit consideration is given to the linkages between newly accessible tributary habitat and the lake's ecosystem. The model is a mixed integer linear program (MILP) that selects a portfolio of potential dam removals that could achieve the best possible value of a weighted sum of the objective(s), while still satisfying the constraints. Using response functions extracted from the Lake Erie Ecological Model and an empirical cost model, the MILP accounts for ecological and economic effects of habitat changes for both desirable native walleye and undesirable sea lamprey. The solutions show the effect on removal decisions of alternative prioritizations among cost and environmental objectives and the resulting trade-offs among those objectives. The MILP can be used as a screening model to identify portfolios of dam removals that are potentially cost-effective enhancements of habitat and the Lake Erie ecosystem; subsequent site-specific studies would be needed prior to actually removing dams.