Protecting Aquatic Life from Effects of Streamflow Alteration

Protecting aquatic life from the effects of streamflow alteration involves maintaining multiple components of the flow regime within their typical range of variation. The U.S. Environmental Protection Agency (EPA) in collaboration with the U.S. Geological Survey have developed a draft report to serve as a source of information for states, tribes, and territories on: 1) the natural flow regime and potential impacts of flow alteration on aquatic life; 2) Clean Water Act programs that can be used to support the natural flow regime and maintain healthy aquatic ecosystems; and 3) a flexible, non-prescriptive framework to quantify targets of the flow regime that are protective of aquatic life. This flexible framework incorporates EPA guidelines for ecological risk assessment and relevant concepts from contemporary environmental flow science literature. The framework does not prescribe any particular analytical approach (e.g., statistical modeling), but rather, it focuses on the process, information, and data needed to evaluate relations between flow and aquatic life and to select appropriate numeric flow targets. While this paper deals primarily with streams and rivers, non-flowing systems (e.g., lakes and wetlands) are inextricably connected to flowing systems and can therefore benefit from measures to maintain hydrologic conditions in flowing water bodies.