Sustainable River-Basin Designs: Siting Hydropower to Benefit American Eels and Energy Production in the Roanoke River Basin

What is the best way to arrange dams within river basins to benefit society?  Hydropower development has never been planned with the goal of providing society with a portfolio of ecosystem services into the future. We synthesized a review of river basin design around four spatial decisions, Is it better to build fewer mainstem dams or more tributary dams?, Should dams be clustered or distributed among distant subbasins?, Where should dams be placed along a river?, and At what spatial scale should decisions be made?.  Four principles emerged from this review: 1) At the scale of large river basins, 2) concentrate dams within a few tributary watersheds and avoid downstream mainstems, 3) disperse freshwater reserves among the remaining tributary catchments, and 4) ensure that habitat provided between dams will support and retain production.  We developed a simple model for the American eel (Anguilla rostrata) in the Roanoke river basin and located dams to maximize two objectives: power generation and eel survival.  Results demonstrated trade-offs between designs favoring the two objectives. This analysis illustrates that we can do better as a society in deciding how to develop river basins for sustainable hydropower production.