Multiobjective Portfolio Analysis of Dam Removals Addressing Dam Safety, Fish Populations, and Cost

Abstract

Decisions concerning dam removal or retention are challenging because they involve tradeoffs, diverse stakeholders, and increasing public safety concerns. A multiobjective portfolio optimization approach, implemented as an integer linear program (ILP), identifies efficient portfolios of dam removals in terms of the objectives of public safety, fish population health, and cost. The ILP integrates judgments by dam safety experts with the results of ecosystem simulations and statistical analysis of empirical data, to explore tradeoffs among the three objectives when choosing a portfolio of dams to be removed in multiple watersheds. This methodology is applied to a case study including 139 dams in 10 watersheds of the Lake Erie basin. Significant tradeoffs are found between maximizing fish population health and minimizing safety risks under a given budget, with different dams recommended for removal in each case. Also, the way dam safety risk is quantified in the ILP affects the selected set, and therefore, deserves further research. Overall, the multiobjective portfolio analysis approach provides a simple, flexible, and useful tool for policy makers to explore the nature and magnitude of tradeoffs to screen potential dam removal projects.