geomorphic impacts of dam removal
DESCRIPTION
Geomorphic Impacts of Dam Removal. Rollin H. Hotchkiss Director, Albrook Hydraulics Laboratory Washington State University, Pullman, WA [email protected]. http://www.matilijadam.org/. Defined. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/1.jpg)
Geomorphic Impacts of Dam Removal
Rollin H. HotchkissDirector, Albrook Hydraulics Laboratory
Washington State University, Pullman, [email protected]
http://www.matilijadam.org/
![Page 2: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/2.jpg)
DefinedGeomorphic impacts: changes in
hydrology and hydraulics which affect stream shape, planform, slope, and sediment transport
![Page 3: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/3.jpg)
Introduction• Dams – geomorphic disruptors!• My purpose – provide a primer on what
happens when we tinker with a river by building or removing a dam
• Emphasize geomorphic processes and qualitative relationships
• What questions should you ask before you “pull the plug”
![Page 4: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/4.jpg)
Road Map• Sediment Transport Processes• Sediment Transport and Reservoirs• Geomorphic Balance• Regime Adjustment• What do you need to Know?
![Page 5: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/5.jpg)
Sediment Transport Process
• Sediment weighs more than water!• Forces required to move sediment
– “Shear” – tangential dragging force downstream
– “Lift” – upward-directed vertical velocity fluctuationV
![Page 6: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/6.jpg)
Modes of Sediment Transport
Suspended Load
Bedload
![Page 7: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/7.jpg)
Yes, It’s NonlinearShear stress designated as S (S is slope)
S V2 (V is velocity)Therefore, V2
Sediment Transport designated as Qs
Qs 1.5 Therefore, Qs V3 or higher!
![Page 8: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/8.jpg)
To Further Complicate Matters
Armor layer – coarser material on top, finer beneath
![Page 9: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/9.jpg)
Road Map• Sediment Transport Processes• Sediment Transport and Reservoirs• Geomorphic Balance• Regime Adjustment• What do you need to Know?
![Page 10: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/10.jpg)
Within the Reservoir
Delta Formation
![Page 11: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/11.jpg)
Delta Formation
![Page 12: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/12.jpg)
Reservoir: a Sorting Machine
Due to nature of reservoir, coarser material farthest upstream
![Page 13: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/13.jpg)
Vertical Sorting as Well
Don’t just sample on the surface….
Consider a section…
![Page 14: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/14.jpg)
Combining the Two Processes
Finest on bottom
Uniform delta
Eventually, surface is like u.s.
![Page 15: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/15.jpg)
Upstream from the Reservoir
Matilija Dam, So. CaliforniaSediment does not reach the beachDeposited u.s. from pool
http://www.matilijadam.org/
![Page 16: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/16.jpg)
Atbara River, Sudan: 12 m deposition u.s. from reservoir pool
![Page 17: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/17.jpg)
Downstream from the Reservoir
• Sediment load decreased• Smaller peak discharges• Unfulfilled sediment transport capacity• Excess energy erodes bed and banks• Bed eventually becomes armored
![Page 18: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/18.jpg)
Bank Instability
Small dam Lower Elkhorn River, NE
Top view: upstream from 5 ft-high dam
Lower view: downstream from dam
![Page 19: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/19.jpg)
Downstream Impacts
Now
North Platte River, NE; 7 u.s. dams for 50 years
Before Dams
![Page 20: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/20.jpg)
Secondary Impacts• All things biological adjust
– New upstream river type– New downstream river type
• How long does that take?• Eventually change reaches
equilibrium….
![Page 21: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/21.jpg)
Road Map• Sediment Transport Processes• Sediment Transport and
Reservoirs• Geomorphic Balance• Regime Adjustment• What do you need to Know?
![Page 22: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/22.jpg)
Lane, E.W. 1955. The importance of fluvial morphology in hydraulic engineering. ASCE Proceedings, 81, paper 745: 1 – 17.
Qs x ds Q x So
From Applied River Morphology by Dave Rosgen, Wildland Hydrology, Figure 2-1
![Page 23: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/23.jpg)
Implications of BalanceRivers constantly shifting
geomorphology to adjust balanceWhen in approximate balance:
“in regime”Dam in or Dam out is out of balance!
![Page 24: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/24.jpg)
Road Map• Sediment Transport Processes• Sediment Transport and
Reservoirs• Geomorphic Balance• Regime Adjustment• What do you need to Know?
![Page 25: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/25.jpg)
On the Day of the Ribbon Cutting
• These geomorphic shifts begin• River system begins to change• It all takes time…time…time..
![Page 26: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/26.jpg)
Downstream Adjustment Time
• For Dam Building OR Removal
River 1 and river 2 here
![Page 27: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/27.jpg)
Adjustments after Removal
Where on deposit curve are you now?
![Page 28: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/28.jpg)
Depends upon Future Runoff Sequence!
• Large flood – lots goes out early• No large flood – wait and wait,
and…
![Page 29: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/29.jpg)
Dam Notching
Matilija Dam – helps control rate of downstream transport
http://www.matilijadam.org/
![Page 30: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/30.jpg)
Road Map• Sediment Transport Processes• Sediment Transport and
Reservoirs• Geomorphic Balance• Regime Adjustment• What do you need to Know?
![Page 31: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/31.jpg)
Hydrologic History• Flooding sequence and history• Change in downstream flood
peaks, duration, and timing• Changes in water temperature,
turbidity, and quality downstream
![Page 32: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/32.jpg)
Sedimentation History• “Snapshots” of bathymetry over time• Qs coming in and going out• Downstream streambed profiles over
time• Location of downstream tributaries
![Page 33: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/33.jpg)
Sediment Particle Size Distribution
• Within reservoir– Spatial coverage– Collect cores!!!!– PSD inversion?
• Downstream– Armored?
![Page 34: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/34.jpg)
Downstream Habitat• Benthics• Fish compared to pre-dam• Condition of spawning gravels• Riparian vegetation
![Page 35: Geomorphic Impacts of Dam Removal](https://reader033.vdocuments.site/reader033/viewer/2022051623/56815b80550346895dc97e09/html5/thumbnails/35.jpg)
Summary• Know how hydrology, sediment
transport and size have changed• Understand how downstream reaches
have adjusted• Need to predict (can we do that?) spatial
and temporal scenarios of impact