A practical guide to environmental flows for policy and planning (with 9 case studies)

Environmental flows are gaining broad recognition across the United States, and the underlying science is sufficiently developed to support regional planning and policy applications. This report explores how six states and three interstate river basins are effectively developing and applying regionalized environmental flow criteria to water resource planning, water withdrawal permitting, and multi-dam re-operation.

The broad range of approaches they relate clearly demonstrates the feasibility of integrating science-based environmental flow needs into regional water management in the absence of site-specific assessments.

The case studies embrace the following principles:

• Regionalized environmental flow criteria apply to all the water bodies across a state or large river basin for which site-specific criteria have not yet been established.

• Flow criteria link explicitly to the health of the entire aquatic and riparian ecosystem, and are not limited to specific species.

• Flow regimes mimic natural inter- and intra-annual flow variability.

• The development of environmental flow criteria and the policies for their implementation are closely linked.  Defining a clear path to policy implementation from the onset ensures that the ensuing science answers the right management questions.

• Flow criteria are developed through a transparent, inclusive social process informed by sound science. A structured social process for identifying, understanding, and negotiating tradeoffs is critical.

To varying degrees, the Ecological Limits of Hydrologic Alteration (ELOHA) framework influenced each of the case studies. ELOHA is a flexible framework for determining and implementing environmental flows at the regional scale using existing hydrologic and biological information. Major components of ELOHA include a hydrologic foundation of streamflow data, classification of natural river types, flow-ecology relationships associated with each river type, and river condition goals.