Environmental Flow Instream Flow “Environmental flow” is the term for the amount of water needed in a watercourse to maintain healthy, natural ecosystems. It is used in the context of rivers which have been dammed, with most or all of the flow trapped by the dam - the failure to provide an environmental flow can have serious ecological consequences. The term "instream flow" is used to identify a specific stream flow (typically measured in cubic feet per second, or cfs) at a specific location for a defined time, and typically following seasonal variations. Instream flows are usually defined as the stream flows needed to protect and preserve instream resources and values, such as fish, wildlife and recreation. Instream flows are most often described and established in a formal legal document, typically an adopted state rule.

Environmental Flows Increasing states are defining standards for instream flow (NH, MI) and in the West some states allow requests for instream flow water rights (AZ) and require dam operators to consider instream flow needs in dam management (CA). Only a few countries, such as Australia, South Africa, and the UK have integrated the concept into water management.

Environmental Flows An ecologically sustainable water management program must always be built upon a foundation of knowledge about the river flows needed to sustain ecosystem health. When the water needs of a river ecosystem are clearly defined by scientists, water managers will be able to find ways of meeting human needs for water while maintaining adequate river flows for the ecosystem. A river ecosystem’s water needs are defined in an “environmental flow prescription.” This flow prescription describes the necessary seasonal and inter-annual variation needed in low flows, high flow pulses, and floods to support native species and critically important ecological functions.

Flow Related Values Recreation Use (swimming, boating, aesthetic enjoyment) Aquatic, riparian, and terrestrial flora and associated habitat –Basic Survival –Establishment –Competition –Rare and Endangered –90% of the AZ wildlife species use riparian/aquatic habitat in their lifetime Aquatic fauna (e.g. fish) –Spawning Period –Critical Periods (low flows) –Physical Habitat (pools and ripplies, banks) –Rare and Endangered Maintain channel characteristics (navigation, flood capacity, camping sites, habitat) Water quality (temperature, oxygen)

Flow Characteristics From presentation by Dr. Wendy Gordon, 2007

Assessment Process Physical Description: Collection and assessment of geomorphic, hydraulic and hydrologic data to predict a range of flow related conditions. –Type of conditions Channel shape Channel width and depth Extent of ripples, pools and bars Wetted perimeter Fish cover Water table levels –Hydrologic Analysis Statistical descriptions Frequency analysis (high and low flows) Flow durations Discharge/stage relationships –Model parameterization and calibration –Instream flow requests can be based on solely on hydrologic analysis Provide current flow conditions or determine an acceptable range of conditions. Example: Median month flows based on 5 year worth of data

Assessment Process Environmental Criteria Analysis – Relating important values to channel morphology or flow related variables. –Values/Flow relationships Behavioral response of fish to channel shape changes Response of vegetation to changes in high flows Water quality response to low flow changes –Determined by direct investigation or from literature. Models are also used.

Assessment Process Environmental Projections: predict the environmental responses as a function of flow. –Ex: Predict the available area and/or quality of habitat for fish species/life phase under investigation within the study area. Determine how water management affect flow characteristics. –Hydrology Models –How much has the natural flow regime been altered? Identify areas of potential conflicts.

Planning Foster collaborative dialogue with stakeholders to search for solutions Conduct water management experiments to resolve uncertainty –Experimental implementation of the “best” scenarios. Modeling Dam Release Monitoring (Case Studies)

Methods for Flow Assessment Hydrological - Primarily use hydrological data (historical monthly or daily flow records) for making e-flow recommendations for maintaining river health at designated level. Hydraulic rating - use changes in simple hydraulic variables (e.g. wetted perimeter) across single river cross-section as surrogate for habitat factors limiting to target biota. Habitat simulation - Assess e-flows on basis of modeling of quantity and suitability of physical habitat available to target species under different flow regimes (integrated hydrological, hydraulic and biological response data) Holistic – identify important flow events for all major components of river, model relationships between flow and ecological, geomorphological and social responses, and use in interdisciplinary team approach to establish recommended e-flow regime/implications of flow scenarios (bottom-up or top-down)

Hydrologic Analysis Matrices (Annual, Seasonal) Mean, Median Flow 25%, 75% Quartiles Q p Frequencies Low Flow Frequencies

Determine flow depended functions

Low Flows

Flow Duration Curves

San Pedro River Instream Flow Study