Establishing Environmental Flow Criteria for California Streams
Quantifying and protecting environmental flow is becoming a priority challenge for California water managers, with major implications for stormwater and wastewater management. Flow alterations from dams, diversions or artificial discharges are a significant driver of species population declines and biodiversity loss in California and globally. When streamflows are altered by human interventions, a wide range of physical and biological processes can be affected, triggering changes in habitat condition, and the distribution, diversity, and abundance of species. Water resources management must balance these effects with potentially competing demands. Development of environmental flow criteria in California has previously focused on the Bay-Delta and discharges from hydropower facilities. But emerging water management issues, including stormwater capture, wastewater reuse, Cannabis production, and new groundwater management regulations have expanded the scope and complexity of environmental flow determinations. Working with a team of technical experts, a coalition of state and federal agencies are developing the California Environmental Flows Framework (CEFF) – a set of methods and tools for establishing flow criteria to balance ecological and human uses. The CEFF is structured as a two-tiered approach. Tier 1 informs development of initial flow criteria for all stream reaches in the state (outside of the Bay-Delta) by defining the expected range of natural variability for a set of ecologically-relevant flow metrics. Tier 1 also includes the development of a hydrologic classification for California that assigns all streams to one of nine stream classes based on their natural hydrology, and the production of reference hydrologic expectations for each stream class based on key functional flow components. Tier 2 allows for the development of finer-resolution of flow criteria that account for unique management considerations and local context. Tier 2 products will provide guidance on the selection of methods depending on specific management objectives, desired ecological outcomes, local physical and/or social constraints, and available data and resources. This talk will summarize the draft Tier 1 criteria and provide examples of how Tier 2 will inform development of localized flow criteria.