Dams and mitigation of their effects Ch' 9

1
Dams and mitigation of their effects(Ch. 9)

• Introduction (see Ch. 3, pp. 60-67)
• Effects of dams
• Blockage
• Mortality
• Time of travel
• III. Mitigation of dam effects
• Fish passage
• Predator control
• Transportation
• Spill
• Flow augmentation
• Reservoir drawdown
• Dam removal

2
Increase in dams in the PNW
Volume levels off does not
Hells Canyon 1961
Chief Joseph 1950
Grand Coulee 1941
Number of dams
Volume of dams
3
Dam utility

• Hydropower (first and foremost for major dams)
• Irrigation (first dams)
• Navigation
• Flood control

4
Major Dams in the Columbia River Basin
5
Habitat lost to dams
Complete fish blockage Columbia River Grand
Coulee Dam Chief Joseph Dam Snake River Hells
Canyon Dam
6
Many other dams
(602)
(3635)
Constitution of Oregon Territory (1848)
prohibits dams on salmon-bearing rivers unless
upstream and downstream fish passage allowed.
7
Plus, splash dams
Washington
Oregon
8
II. Effects of dams

• Blockage
• Complete
• 1/2 of former habitat in Columbia Basin is lost
• Difficult to assess in other systems because of
  lack of records
• Incomplete
• - Loss of spawning habitat (inundation)
• - Gain in rearing habitat?

9
B. Mortality

• Upstream
• Drop back from fish ladders (into spill-ways,
  turbines)
• Delayed spawning
• Interdam losses (up to 25 between Bonneville and
  John Day on lower Columbia)
• Average estimates 4-5 per project

10
B. Mortality

• 2. Downstream
• a. Direct contact (e.g., turbines, deflection
  screens)
• b. Delayed development
• c. Predation
• i. Stress/disorientation
• ii. Concentration of prey (e.g., in outfalls of
  bypasses)

11
Accounting of mortality

• Direct carcass counts mortality 1 for
  downstream migrants
• Including all bypass-related mortality 5-7

12
Cumulative mortality effects

• Downstream 5 per dam
• 9 mainstem Columbia dams (below impassable Chief
  Joseph dam)
• N1 N0 (1-m) 100 (1-0.5) 95
• N2 N1(1-m) 95 (0.95) 90.25
• Nx N0(1-m)x 100 (0.95)9 63

13
C. Time of travel

• Depends on life history (e.g., subyearling vs.
  yearling Chinook)
• Early data from 1970s unreliable
• We just dont know.

14
III. Mitigation of effects

• Most solutions aim to resolve all three major
  issues (blockage, mortality, time) to greater or
  lesser degrees.

15
Selection of alternatives

• Spill at Snake River
• Eliminate transportation
• Flow augmentation
• Drawdown Snake River resevoirs

16
(No Transcript)
17
(No Transcript)
18
(No Transcript)
19
(No Transcript)
20
(No Transcript)