DAMS

1
DAMS THE AQUATIC ENVIRONMENTSEDIMENT,
HYDROLOGY, GEOMORPHOLOGY HABITAT

• Joe Rathbun
• Michigan Dept. Environmental Quality
• Water Division

2
Outline

• Impoundments sediment traps
• Contaminated sediments
• Impoundments ? real lakes
• Physical effects of dams
• Hydrology
• Geomorphology (hungry water)
• Physical effects of dam removal

3
Basic Concept

• Rivers do two things very well
• Move water
• Move sediment

4
Reservoirs are Sediment Traps

• Trap up to 95 of the sediment that enters from
  upstream
• Large sediment particles form deltas at upstream
  end
• Small sediment particles transported farther into
  reservoir
• Most sediment transported during floods

5
Issues with Contaminated Sediments

• Direct toxicity to organisms
• Acute
• Chronic
• Bioaccumulation in organisms
• Alter benthic community
• Contaminate overlying water
• Affect disposal of dredged material

6
Sediment Contamination Sources

• Direct discharges to impoundment
• Upstream point or nonpoint sources
• Industries, mines, ag runoff, urban runoff
• Atmospheric deposition
• Mercury
• PCBs

7
Hard to assess without a survey
Dam
Gravel Bar
Silt Bar
8
Ponar grab sampler
9
Hand-coring
Core Tube
Plastic tube drive in with fence post driver or
sledge
Cant drive in farther than can be pulled out by
hand, or with small winch
10
Vibrocoring from the R.V. Mudpuppy
11
Vibrocoring from the R.V. Mudpuppy
12
Vibrocoring from john boats
13
Cores lots of information
14
Chemical Sediment Quality Guidelines
Presumed Toxic
PEC
Possibly Toxic
Increasing Concentration
TEC
Presumed Nontoxic
15
Freshwater Bioassay OrganismsMidge larvae
Amphipod
16
Bioaccumulation Testing

• Caged organisms
• Ideally expose until equilibrium
• More often, 28 days
• Organism choice important
• Benthic?
• Pelagic?

17
Almost always have to sample

• Because of potential for unexpected historic
  contaminant sources
• Orchards tobacco fields As, Hg
• Tanneries Cd, As, Hg
• Coal gasification plants PAHs, metals
• Glass factories As, other metals
• Cemeteries Pb, As
• Dye manufacturers metals

18
Impoundments ? Real Lakes

• Greater surface area/volume ratio
• Greater sediment deposition rates
• Further downstream in WS
• Lower hydraulic retention times

19
Impoundments ? Real Lakes

• Lateral gradients like rivers
• Vertical gradients like lakes
• Deepest at downstream end
• Shorelines can be more irregular

20
Impoundments ? Real Lakes

• Water levels often quite variable
• Discharge often from hypolimnion
• Flow patterns often reverse of natural lake
  discharges
• Discharges less variable disconnects river
  channel from floodplain

21
(Nislow et. al., 2002)
22
Impoundment Limnology

• Temperature stratification in warm months

23
Impoundment Limnology

• Hypolimnion
• Low dissolved oxygen
• High(er) phosphorus ammonia
• High(er) dissolved metals
• Water discharged from impoundment
• Colder or warmer
• Low or high dissolved oxygen
• Higher nutrients (?)
• Lower sediment content (hungry water)

24
Hungry Water

• Impoundments can trap up to 95 of the incoming
  sediment
• 80 of sediment load suspended
• Bedload sediment gravel, cobble
• Water exiting impoundment seeks to regain its
  sediment load

25
Effects of Hungry Water

• Stream bank erosion
• Stream bed erosion (incision)
• Channel slope decreases
• Bed material coarsens

26
(Hadley and Emmett, 1998)
27
Meadowbrook Lake dam, Rouge River, MI
28
Original bank toe
Downstream of Meadowbrook Lake dam, Rouge River,
MI
29
(Hadley and Emmett, 1998)
30
(Hadley and Emmett, 1998)
31
But not always

• In cohesive soils, downstream channel can become
  shallower hungry water offset by lower peak
  flows
• Yegua Creek, TX, after 35 years
• Depth decreased by 61
• Capacity decreased by 65
• Other studies 20 to 70 decrease

32
Physical Effects of Dam Removal

• Restore stream flow variability
• Re-form channel features
• Decreasing channel size u/s of dam
• Re-form gravel/cobble riffles
• Re-form riffle/pool sequences
• Reconnect river to floodplain (?)

33
Physical Effects of Dam Removal

• Temporary increase in sediment transport
• Silt in pools, riffles
• Start to reconnect river to floodplain
• But, not all impounded sediment will be
  transported downstream

34
Sediment Transport after Dam Removal

• Dam Result
• Chagrin R., OH 9 13 moved
• Hudson R., NY 33
• Muskegon R., MI 40
• White Salmon R., WA 65
• North Poudre R., CO 70 80
• (Doyle et al., 2002)

35
Response Rates after Removal

• Outcome Days/Weeks Months gt 1 Yr.
• Sed movement X X X
• Stable channel X
• Bed armoring X X X
• Reverse incision X
• Increase sedimentation downstream rapid, but
  temporary
• Reconnect to
• floodplain X
• Riparian veg.
• return X

36
Summary

• Contaminated sediment always a potential problem
  usually need a sampling survey
• Impoundments not real lakes
• Biology
• Chemistry
• Morphology and hydrology

37
Summary

• Dam installation
• Change in hydrologic regime
• Hungry water
• Channel capacity changes ( or -)
• Dam removal restoration of many, but not all,
  prior conditions
• Biology
• Chemistry
• Morphology and hydrology

38

• Still glides the stream,
• and shall forever glide
• the form remains
• the function never dies.
• William Wordsworth, 1820
• Unless you put a dam on it