Prioritizing Dams in California for Environmental Flow Recovery

There are thousands of dams in California, most of which were built and are operated with little consideration for their effects on fish. However, recent successful lawsuits relying on the Public Trust Doctrine and Fish and Game Code 5937 indicate that there is opportunity for broader implementation of environmental flow protections for California’s rivers and streams. The sheer number of dams and unique physical and biogeographic character of each site suggests that a systematic approach for selecting dams for environmental flow recovery is required. Here, we present an evaluation framework for identifying dams in California that have impaired downstream fish communities due to inadequate flow releases. We use a tiered approach to (1) evaluate whether fish downstream of dams are in good condition, (2) assess the degree of hydrologic alteration to the natural flow regime, and (3) identify potential constraints for selecting the subset of dams for which environmental flow protections should be implemented. Based on the screening framework, we expect that approximately one third of the 1,400 large dams in California are potential candidates for improved environmental flows.