Transcript Environmental Flow Instream Flow

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
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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)
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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
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
Qp Frequencies
Low Flow Frequencies
Determine flow depended functions
Low Flows
Flow Duration Curves
San Pedro River Instream Flow Study