Environmental Flow Instream Flow

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Environmental FlowInstream 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.

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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.

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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 ecosystems 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.

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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)

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Flow Characteristics
From presentation by Dr. Wendy Gordon, 2007
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From presentation by Dr. Wendy Gordon, 2007
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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

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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.

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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.

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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)

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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)

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Hydrologic Analysis
Matrices (Annual, Seasonal) Mean, Median
Flow 25, 75 Quartiles Qp
Frequencies Low Flow Frequencies
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Determine flow depended functions
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Low Flows
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Flow Duration Curves
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San Pedro River Instream Flow Study