Dams alter flow, sediment, and thermal regimes of rivers. Seasonal flow distortions(top) cause shifts in species compositions. Dammed rivers with hydropeaking cause daily distortions that can eliminate key species from food webs. Small changes to flow releases can counteract these distortions and provide ecological benefit.
Post-dam environmental flow management can only incrementally improve lost ecosystem functions, making predam environmental planning essential. Making hydropower greener and dams more sustainable generally requires not only better design and management of flow releases but also balancing economic gain against environmental degradation and human dislocations, all in an increasingly uncertain hydrologic future.