Flow alterations are a significant driver of species population declines and biodiversity loss in California and globally. When stream flows are altered by human intervention, a wide range of physical and biological processes can be affected, triggering fundamental changes to habitat condition, and the distribution, diversity, and abundance of species. Ensuring the preservation of key flow components can improve riparian and freshwater ecosystem health by restoring physical processes and habitat conditions.
Multiple state and local agencies across California share responsibility for setting flow criteria that protect and improve the ecological health of California’s water resources. These approaches historically have not been coordinated at the statewide level, resulting in fragmented and siloed flow management programs. Consequently:
There is no overall framework or guidance for estimating flow criteria
Agencies tend to focus on site-specific solutions, instead of holistically managing the health of California watersheds
Environmental flow data are not readily available or comparable across the state
Improving coordination across California is a challenge. Environmental conditions and pressures vary widely, as do the priorities and capacities of agencies responsible for water resource management.
In 2016, a group of experts self-organized to pool knowledge and data, evaluate methods, and ultimately develop a statewide framework for determining environmental flow criteria for California. The strategy is organized into a two-tiered approach that varies in scale and detail.
The two-tiered framework will provide a set of functional flow criteria for all streams in California (Tier 1) and a technical guidance document for estimating refined flow criteria at regional to site-specific scales (Tier 2).
Tier 2: Provide guidelines for estimating refined flow criteria depending on the regional, local or site-specific context
» A tailored approach that incorporates specific environmental and water management factors and priorities