Lower Saluda River Instream Flow Study

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Lower Saluda River Instream Flow Study

• TWC Study Team Workshop
• December 11, 2007

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PHABSIM Study

• Study Planning
• Locate reaches and transects
• Obtain channel profile and microhabitat data
• Develop hydraulic model
• Input suitability rating criteria
• 6. Output suitability available at each flow
  increment of interest

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Study Reaches
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Mesohabitat distribution
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TWC Site Reconnaissance

• November 2006 orientation
• May 2007 transect selection at 500 cfs

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Transect Selection
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Data Collection

• Site surveying
• Bed elevation
• Substrate mapping
• Water surface elevation
• Velocities
• Stream gaging

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Velocity and elevation data

• Standard optical survey
• Electronic flow meter
• Acoustic Doppler Profiler
• Trimble GPS
• Level logger

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Typical transect (looking downstream)
headpin
tailpin
Top of bank
Water surface
Toe of bank
Edge of water
Thalweg
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Verticals are located to capture key substrate
and profile features
headpin
tailpin
Top of bank
Toe of bank
Edge of water
Thalweg
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Verticals and cell boundaries act to divide each
segment into a mosaic of known areas
T-4
riffle
T-3
T-2
T-1
run
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Habitat is pixilated into a mosaic of known
dimensions
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Calibration data gathered across a spectrum of
flows
10,000 cfs (WSL only)
1,200 or 1,600 cfs (WSL and velocities)
500 cfs (WSL and some velocities)
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permits interpolation and extrapolation of
hydraulics at other flows
20,000 cfs
300 cfs
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Transect 2 at three calibration flows
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Model Calibration

• Establish stage-discharge relationship
• Calibrate velocities
• Simulate WSLs and velocities for other flows

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Depth, velocity and substrate are rated according
to SI Criteria
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Model output Habitat-flow relationships for
each river segment
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Traditional Problem-Solving Process

• Compare habitat under existing flow scenarios
• Assess extent to which all objectives are met
• Evaluate trade-offs
• Consider alternative flows as needed
• Compare project operation under existing and
  alternate flow scenarios
• Re-run alternative scenarios