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MASSACHUSETTS | COLORADO | WASHINGTON | OREGON
Passing Gas Science & Management of TDG at Hydro Facilities
Modeling TDG Abatement Measures
MASSACHUSETTS | COLORADO | WASHINGTON | OREGON
TDG: A Primer
• TDG supersaturation can cause gas
bubble trauma in fish
– Bubbles form in fish blood and tissues
– The bubbles can block blood flow – likened
to divers getting “the bends”
• TDG production in spillway discharge is
related to
– the depth of air entrainment
– the residence time of bubbles at depth
• Abatement measures typically try to
reduce the depth of air entrainment or
residence time of air at depth
Gorham, F. P. (1901) Gas-Bubble
Disease of Fish and Its Cause, Bulletin
of the United States Fish Commission,
vol. 19, 1899 (!!)
MASSACHUSETTS | COLORADO | WASHINGTON | OREGON
TDG Abatement: Modeling
• Range of modeling/analysis options for abatement
measures screening, selection and design
– Spreadsheet-based calculations
• Example: Mystery project, undisclosed location
– CFD model of proxy characteristic (plunge depth)
• Example: Cabinet Gorge Dam, Idaho
– Multi-model (physical + CFD) coupled with gas-transfer equations
• Example: Boundary Dam, Washington
MASSACHUSETTS | COLORADO | WASHINGTON | OREGON
TDG Abatement: Modeling
• Outlets
– 4 spillway bays; 8 LLOs
• Abatement measures considered
– Block loading the LLOs/increasing
operating head
– Adding hydro power
– Spillway deflectors
• Tools
– MS Excel-based calculations
• Method
– Estimate the reduction in spillway use
as a proxy for TDG improvement
Mystery Project, Undisclosed Location
?
MASSACHUSETTS | COLORADO | WASHINGTON | OREGON
TDG Abatement: Modeling
Cabinet Gorge Dam, Clark Fork River, Avista
Before and After Modifications
• Outlets
– 8 spillway bays; 4 unit powerplant
• Abatement measures considered
– Original concept – re-open
construction diversion tunnels as an
alternative outlet to spill
– Final concept – add “roughness
elements” to break up jet to reduce air
entrainment depth
• Tools – Original concept: Physical and CFD
modeling, spreadsheet based gas-
transfer model
– Final concept: Single-bay CFD
MASSACHUSETTS | COLORADO | WASHINGTON | OREGON
TDG Abatement: Modeling
Cabinet Gorge Dam, Clark Fork River, Avista
Proof of Concept Field Testing
• Staged approach
– Step 1: Use a single bay “prototype test” as a full-scale
model for proof of concept for roughness elements
– Step 2: Use CFD model to estimate relative difference in
plunge depth from a single bay for different designs
– Step 3: Modify additional bays and monitor performance
MASSACHUSETTS | COLORADO | WASHINGTON | OREGON
TDG Abatement: Modeling
• CFD as a design development tool ‒ Compare relative TDG performance of different roughness
element geometries using air entrainment depth as a proxy
‒ Determine effect on spillway capacity during passage of the PMF
‒ Obtain hydrodynamic loads for structure design
• Did not attempt to quantify TDG or interaction of flow
released from multiple bays
Compare Jet Impact Area Compare Air Content with Depth Plunge Pool Geometry
Cabinet Gorge Dam, Clark Fork River, Avista
MASSACHUSETTS | COLORADO | WASHINGTON | OREGON
TDG Abatement: Modeling
Cabinet Gorge Dam, Clark Fork River, Avista
Proof of Concept Field Testing
MASSACHUSETTS | COLORADO | WASHINGTON | OREGON
TDG Abatement: Modeling
Boundary Dam, Pend Oreille River, Seattle City Light
• Outlets
– 2 spillway bays; 7 sluices, 6 unit
powerplant
• Abatement measures considered
– Throttle sluice gates
– Roughen sluice flow
– Spillway flow splitter/aerator
• Tools – Physical model
– Full project CFD
– Spreadsheet-based gas transfer
model (TDG predictive tool)
– Field data collection and analysis
Modeling and analysis by:
Alden Research Laboratory, Hatch, and Dr. John Gulliver
MASSACHUSETTS | COLORADO | WASHINGTON | OREGON
TDG Abatement: Modeling
Boundary Dam, Pend Oreille River, Seattle City Light
• Staged Approach
– Physical model for design development – simulate numerous
potential designs
– CFD model with particle tracking from upstream end of spillway to
point of particle exhaustion in tailrace
– Spreadsheet-based TDG predictive tool to convert particle histories
into estimated downstream TDG
– Field data for CFD model validation and performance verification
MASSACHUSETTS | COLORADO | WASHINGTON | OREGON
TDG Abatement: Modeling
Boundary Dam, Pend Oreille River, Seattle City Light
MASSACHUSETTS | COLORADO | WASHINGTON | OREGON
TDG Abatement: Modeling
Challenges
• Changed conditions ‒ Power generation protocols
‒ Generating unit/spill bay outages
‒ Upstream TDG
• Data collection ‒ Low flow years
‒ Sonde failure
• Proof of performance ‒ Direct comparison pre- to post-modification can be challenging
due to the above factors
• Near-field spillway hydraulics ‒ Roughness element concept is based on supercavitating baffle
blocks (USBR); predicting potential areas at risk of cavitation
damage and designing to protect against it is challenging
MASSACHUSETTS | COLORADO | WASHINGTON | OREGON
TDG Abatement: Modeling
Questions and Discussion
(after the last presentation)