The Geomorphic Response of Rivers to Dam Removal
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Presenter: Gordon Grant, USDA Forest Service, Pacific Northwest Research Station
Length: 3 parts, 63 min and 40 s
View: Part 1 | Part 2 | Part 3
Topics:
Part 1
- Big Dams / Little Dams
- Geomorphic Issues
- Geomorphic Issues: Upstream
- Geomorphic Issues: Downstream
- Coupled upstream downstream problem
- What do we want to know upstream of a dam removal
- Controls / Caveats
- Dam Removal Scenarios
- Examples of Geomorphic Effects
- Examples Matrix
- Let's Explore Maple Gulch: small dam removal
- Maple Gulch Dam Site - Aug 2002
- Sep 2002: sediment wedge
- Nov 2002: Knickpoint
- Dec 2002: Knickpoint marches backward
- New Years Eve 2002: sediment deposits left behind
- May 2003: revegitation
- Dinner Creek Dam- Aug 1 2003
- Aug 5 2003: shortly after removal
- Nov 2003: first storm of year
- Dec 11 2003: windthrow event
- Dec 15 2003: largest storm of the year
- Main point: Knickpoint migration
- Simple geometrical modelling of migration
- Reservoir Erosion Due to Knickpoint Retreat
- Cumulative Sediment Graph Post Dam Removal
Part 2
- Erosion Model for Filled Reservoir
- Upstream Effects: Episodic
- Upstream Effects: Knickpoint retreat
- Upstream Effects: Interaction with valley margins
- Upstream Effects: Channel may or may not find old bed
- Examples: Partially filled reservoirs
- Glines Canyon Dam
- Pictures of the Delta
- Drawdown Experiment
- After drawdown: Two main channels
- Cougar Reservoir Aerial
- Temperature Control Structure
- The delta
- Focus on delta mid-section
- Aerial of delta
- Area of focus
- Shortly after the drawdown, April 5 02
- Emergence of dominant channel, April 12 02
- Drawdown proceeded about 100 ft, April 29 02
- Drawdown continues, May 15 02
- The following winter, Jan 29 03
- Jan 30 03: Channel sweeps back
- Jan 31 03: Channel straightens
- Feb 15 03
- Channel and Stratigraphy
- Focus on this cross section
- Cougar Delta Stratigraphy
- Cougar Delta: Drawdown Incision
- Cougar Delta: Post-Storm Incision
- Modeling Glines Canyon Dam Removal
- Model Dam Notches
- Feeding Sediment In
- Empty Model
- Filled model during expirement
- Video of model during expirement
- Model: What is left behind after removal
- Erosion Model for Partially-filled Reservoir
- Upstream Erosion of Partially-filled Reservoirs
- Upstream Effects: Rate of dam removal drives rate of delta propogation
- Upstream Effects: Incision can be limited by armoring
- Upstream Effects: Complex response
- Upstream Effects: Interaction with valley walls
- Time since dam removal
- What do we want to know downstream of dam removal?
- Questions to ask
- Controls and Caveats
Part 3
- Downstream Sediment Storage Elements
- Types of Downstream Channel Response
- Examples: Small dam downstream
- Downstream Sediment Delivery
- Downstream from Maple Gulch Dam: pre-removal
- Downstream from Maple Gulch Dam: just after removal
- Downstream from Maple Gulch Dam: incision
- Cross-sectional representation of downstream deposition
- Dinner Creek - Pre-removal... looking downstream
- Dinner Creek: following first storm
- Examples: Cougar Reservoir Downstream of removal
- Downstream sediment delivery
- Longitudinal and Cross-section view
- The Cougar Reservoir Drawdown: A tale of woe
- The Cougar Reservoir Drawdown: Immediately following
- The Cougar Reservoir Drawdown: drawdown continued
- The Cougar Reservoir Drawdown: beautiful McKenzie into turbid waters
- Turbidity increased in reservoir during drawdown
- Did the sediment intrude into the gravels?
- Relative Abundance of Fines
- Marmot Dam Sandy River, Oregon
- Sand and gravel released in blow and go in 2007
- Where will it end up?
- Marmot Dam
- Below Marmot, Above Canyon ~13,000 cfs
- Channel response depends on channel morphology
- Steep Narrow Canyon
- Water Alluvial Channel
- Broad, unconfined Valley Bottom
- Predicted Sand Deposition
- Fine sediment survey in pools
- Scuba and probing
- Hydro-dynamic models
- Dog Pool: Erosivity as a Function of Discharge
- If you think geomorphic response is complex...
- Filled vs. partially-filled reservoirs
- What does it all mean?- O'Connor's Law
- Grant's Corollary
- Grant's Lemma
- We know more than we think
- Societal enthusiasm for dam removal
- Need for carefully planned and monitored removals
- Dam removals are great experiments!
- Dam Failure
- Apres Moi Le Deluge