The California Environmental Flows Framework (hereafter the Framework) is a management approach that provides technical guidance to help managers efficiently develop scientifically defensible environmental flow recommendations. Environmental flow recommendations consist of instream flow criteria that balance human and ecological needs for water. The Framework was developed to help managers improve the speed, consistency, standardization, and technical rigor in establishing environmental flow recommendations statewide. There are 12 steps in the Framework, which are divided into three main sections and encompass multiple tools and standardized methodologies. The key objectives of the Framework are to:
- Standardize, streamline and improve transparency of environmental flow assessments
- Provide flexibility to accommodate diverse management goals and priorities
- Improve coordination and data sharing among management agencies
The first two Sections of the Framework support development of consistent, scientifically-supported ecological flow criteria – i.e., quantifiable metrics that describe ranges of flows that must be maintained within a stream and its margins to support the natural functions of healthy ecosystems. Upon this scientific foundation, users are then able to develop environmental flow recommendations that take human uses and other water management objectives into consideration. These environmental flow recommendations are expressed as a “rule set” of flow requirements that are informed by ecological flow criteria that satisfy ecosystem water needs, but also other water management objectives.
The expected user of the Framework is an individual or organization tasked with defining ecological flow criteria to inform environmental flow recommendations for a stream, watershed, or region. Thus, this Framework is intended to be used by scientists, agency personnel, non-governmental organizations and local stakeholders working to develop environmental flow recommendations for streams in California. It may also be helpful in planning and prioritizing stream flow enhancement projects and environmental flow recovery efforts.
Framework approach and organization
The technical approach of the Framework rests upon the scientific concept of functional flows – i.e., distinct aspects of a natural flow regime that sustain ecological, geomorphic, or biogeochemical functions, and that support the specific life history and habitat needs of native aquatic species (Yarnell et al. 2015). California streams have five functional flow components:
- Fall pulse flow: First major storm event at the end of dry season
- Wet-season peak flow: Coincides with the largest storms in winter
- Wet-season baseflow: Sustained by overland and shallow subsurface flows in the periods between winter storms
- Spring recession flow: Represents the transition from the wet to dry season and is characterized by a steady decline of flows over a period of weeks to months
- Dry-season baseflow: Sustained by groundwater inputs to rivers
Managing for these five functional flow components preserves essential patterns of flow variability within and among seasons, but it does not mandate either the restoration of full natural flows or maintenance of historical ecosystem conditions. Furthermore, this functional flows approach is not focused on the habitat needs of a particular species, but rather, is focused on identifying and preserving key ecosystem functions – such as sediment movement, water quality maintenance, and environmental cues for species migration and reproduction – that are necessary to maintain ecosystem health and that are broadly supportive of native freshwater plants and animals.
The Framework is divided into three main sections that guide users through multiple steps. The first two Sections lead to the identification of scientifically-defensible ecological flow criteria in support of user-defined ecological management goals. The third Section guides development of environmental flow recommendations using these flow criteria in combination with consideration of human water needs:
- SECTION A (Steps 1-4): Identify ecological flow criteria using natural functional flows
Key question: What are natural functional flows for my location of interest? What are the corresponding ecological flow criteria?
Section A provides ecological flow criteria for a study area (e.g., river, watershed, or region) based on predictions of the natural ranges of flow metrics for each of five functional flow components. It also provides guidance for determining if non-flow impairments – such as altered physical habitat, poor water quality, or invasive species – require further consideration because the natural range of flow metrics may fail to support desired functions
- SECTION B (Steps 5-7): Develop ecological flow criteria for each focal flow component requiring additional consideration
Key question (as applicable): How do I use additional information to develop ecological flow criteria that accommodate physical and biological constraints?
Section B provides guidance for determining ecological flow criteria for functional flow components that may be affected by non-flow impairments. This involves development of conceptual models, compiling data and information, and quantitative analyses to assess the relationship between functional flow components and ecosystem responses relevant to ecological management goals. The outcomes of the assessment are used to develop ecological flow criteria for functional flow components that were not addressed in Section A.
- SECTION C (Steps 8-12): Develop environmental flow recommendations
Key question: How do I reconcile my ecological flow criteria with non-ecological management objectives to create environmental flow recommendations?
Section C provides guidance on balancing ecological flow needs with competing management objectives to develop a final set of environmental flow recommendations. This involves assessing flow alteration to inform management strategies and balancing ecological and non-ecological management objectives through tradeoff analyses. Additional guidance is provided for adaptively managing environmental flows, monitoring outcomes, and implementing environmental flow recommendations.
An overview of three sections and 12 steps of the California Environmental Flows Framework, with the key questions that get answered by the end of each section.
The hypothesis underlying Section A is that natural ranges of flow metrics for each of the five functional flow components will support multiple ecosystem functions and satisfy the habitat needs of native freshwater species. Therefore, the natural ranges of flow metrics are used as the starting point for defining ecological flow criteria. However, certain forms of physical habitat alteration, water quality impairment and biological interactions may make natural ranges for these flow metrics less effective in supporting ecosystem functions. For example, natural peak flows may not inundate floodplains if the channel is deeply incised, and thus the functions associated with floodplain inundation (e.g., fish breeding and riparian seed dispersal) may not be supported. Similarly, high stream temperatures resulting from riparian vegetation loss may limit the functionality of a summer baseflow for fish rearing if the temperatures exceed suitability thresholds. In such cases, affected functional flow components are subject to further analysis in Section B, resulting in potential revisions to flow criteria that take into account the altered stream condition and thus may deviate from natural ranges of flow metrics. When these criteria from Section B are combined with the ecological flow criteria developed in Section A, the user obtains a full set of ecological flow criteria for all five functional flow components.
For planning applications, or where non-flow limiting factors are not a concern, the user may only need to implement the steps in Section A to obtain ecological flow criteria for their study area. The Section A ecological flow criteria can be readily translated into environmental flow recommendations in section C and, in many cases, will help avoid resource-intensive, site-specific flow studies. In areas with non-flow limiting factors, such as altered water quality and/or physical conditions, Section B of the Framework offers a structured approach for developing a consistent, scientifically defensible set of ecological flow criteria for translation into environmental flow recommendations in Section C. Section C then provides general guidelines for how to develop environmental flow recommendations and implementation strategies.
The Technical team will continue communicating and collaborating with diverse stakeholders and partners at the state and local level engaged in flow management via the Environmental Flows Workgroup, a sub-group of the California Water Quality Monitoring Council comprised of state and federal agencies with responsibility for environmental flows through their various programs and authorities.