Sediment dynamics in flow-regulated streams and the impact on aquatic ecosystems

1
Sediment dynamics in flow-regulated streams and
the impact on aquatic ecosystems

• Nira L. Salant
• Dartmouth College
• 2005
• Advisors Carl Renshaw and Frank Magilligan

2
Impact of dams on ecosystems

• - Limited recruitment of riparian species
• - Reduced access to floodplain habitat
• - Reduced diversity and abundance of benthic
  fauna
• - Decreased productivity of algae and biofilm

3
O2
N
4

• Purpose
• Link the ecological impacts of dams to the
  geomorphic response resulting from hydrologic
  changes
• Primary questions
• What are the geomorphic responses of the
  streambed?
• How can we effectively quantify these responses?

5
Overview of methods

• Four metrics
• 1. Short-lived fallout radionuclides (7Be, 210Pb)
• 2. Embeddedness measurements
• 3. Long-term hydrologic and morphologic data
• 4. Benthic invertebrates
• Three rivers
• Regulated Ompompanoosuc, Black
• Unregulated White
• Year-long monitoring

6
Three inter-connected parts

• Use of fallout radionuclides to quantify
  sediment transport below dams
• Timescales of stream bed stabilization due to
  altered flow and sediment regimes below dams
• The effect of substrate stability and sediment
  deposition on benthic ecology downstream of a
  flood-control/run-of-the-river dam

7
water
sediment
DAM
Deposition and aggradation
Armoring and incision
Ecological changes
8
S vs. T
From Grant et al. 2003
9
DAM
Changes in sediment residence time and transport
velocity
Deposition and aggradation
Armoring and incision
10
Short-lived fallout radionuclides
Relative 7Be/210Pb activity High 7Be/210Pb
New Low 7Be/210Pb Old
7Be (t1/2 53.4 days)
Erosion
New
Old
11
Study sites
12
Union Village Dam
13
Level of flood-control gates compared to
hydrograph
14
Level of flood-control gates compared to
hydrograph
Highly regulated High flow
15
Level of flood-control gates compared to
hydrograph
Partially regulated High flow
16
Level of flood-control gates compared to
hydrograph
Unregulated Low flow
17
Bed sediment sampling Monthly sampling February
to July 2004
18
Samples dried, sieved and counted for 7Be activity
19
Highly regulated High flow
20
Highly regulated flow Early spring
21
Highly regulated flow Early spring
22
Partially regulated High flow
23
Study sites
24
Partially regulated flow Mid-spring
25
Entire time period
26
Measured transport velocities
Time period 7Be velocity (m/d)
Early spring 31 March 14 May 40 60
Mid-spring 31 March 28 May 40 60
Late spring 28 May 18 June below dam downstream 30 60 60 80
27
Comparisons to previous studiesSediment
transport rates
Material Velocity (m/d) Source
Bed load 0.3 4.5 m/d Beechie (2001)
Bed load 30 80 m/d This study
Suspended load 600 1500 m/d Bonniwell (1999)
28
Effect of grain size interactions on transport
29
Comparisons to previous studies Sediment
transport models
Dates 7Be velocity One-fraction velocity Two-fraction velocity Sand Gravel Two-fraction velocity Sand Gravel Sand fraction (Fs)
31 March 14 May 40 60 9200 39 59 0.62- 0.8 0.099 - 0.10
31 March 28 May 40 60 9000 36 62 0.62-0.8 0.099 - 0.10
28 May 18 June below dam downstream 30 60 60 80 5500 33 - 60 60 75 0.44 0.80 0.80 1.0 0.14 - 0.15 0.15
30
Timescales of stream bed stabilization due to
altered flow and sediment regimes below dams
Ompompanoosuc River - Sediment over-supply
Black River - Sediment limitation
31
Timescales of bed elevation stabilization
Bed elevation variance
32
Black RiverImmediate stabilization
33
Ompompanoosuc RiverGradual stabilization
34
Benthic ecology
Lack of disturbance Sediment deposition
35
Results
Family Date Regulated Unregulated P
Hydropsychidae July 39.8 10.9 0.008
Hydropsychidae September 57.8 14.2 lt 0.001
Ephemerellidae July 8.7 10.9 lt 0.001
Ephemerellidae September 16.8 22.9 lt 0.001
36
Conclusions

• Radionuclides offer a simple and effective method
  for directly measuring transport rates
• Dams and their specific operation control the
  geomorphic response of the streambed
• Geomorphic changes to the streambed drive changes
  to benthic ecology

37
Acknowledgements
Thank you Frank and Carl! Also thanks to Jim
Kaste, Keith Nislow, and Brian Dade for their
advice and assistance

• Biological assistance
• Jeffrey Veikko Ojala
• (USDA Forest Service)
• Scott Wixsom and Dan Mckinley
• (USFS Green Mountain National Forest)
• Craig Layne and Darren Ward
• (Dartmouth Department of Biology)
• Kaoru Itakura
• Rebecca Krystosek
• Julie Jo Walters
• Field assistance
• Kelly Sennatt and Alexandra Fleming
• (Dartmouth Department of Earth Sciences).

• Funding
• National Science Foundation
• Arthur D. Howard Award
• (GSA QGG)
• Vermont Geological Society
• Dartmouth College Earth Sciences
• Hydrologic records/ dam information
• Greg Hanlon and Thomas Snow
• (U.S. Army Corps of Engineers)
• Ken Toppin (USGS)