sediment dynamics in flow-regulated streams and the impact on aquatic ecosystems
DESCRIPTION
Sediment dynamics in flow-regulated streams and the impact on aquatic ecosystems. Nira L. Salant Dartmouth College 2005 Advisors: Carl Renshaw and Frank Magilligan. Impact of dams on ecosystems. - Limited recruitment of riparian species - Reduced access to floodplain habitat - PowerPoint PPT PresentationTRANSCRIPT
Sediment dynamics in flow-regulated streams and the impact
on aquatic ecosystems
Nira L. SalantDartmouth College
2005Advisors: Carl Renshaw and Frank Magilligan
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
Purpose
Link the ecological impacts of dams to the geomorphic response resulting from
hydrologic changes
Primary questionsWhat are the geomorphic responses of the
streambed?How can we effectively quantify these
responses?
Overview of methods
Four metrics1. Short-lived fallout radionuclides (7Be, 210Pb)2. Embeddedness measurements3. Long-term hydrologic and morphologic data4. Benthic invertebrates
Three rivers
Regulated: Ompompanoosuc, BlackUnregulated: White
Year-long monitoring
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
Deposition and aggradation Armoring and incision
Changes in sediment
residence time and transport
velocity
DAM
Short-lived fallout radionuclides
7Be (t1/2 = 53.4 days) Relative 7Be/210Pb activity
High 7Be/210Pb = “New”
Low 7Be/210Pb = “OldErosion“New”
“Old”
0 2 km
Ompompanoosuc River
ConnecticutRiver
UnionVillageDam
Site 3Site 2.2
Site 2
Site 1
Site 2.1
W. Branch
E . B ran ch
Ve rm on t
Study sites
0
5
1 0
1 5
2 0
2 5
3 0
3 5
0
0 . 2
0 . 4
0 . 6
0 . 8
1
1 . 2
5 0 1 0 0 15 0 2 0 0
Level of flood-control gates compared to hydrograph
0
5
1 0
1 5
2 0
2 5
3 0
3 5
0
0 . 2
0 . 4
0 . 6
0 . 8
1
1 . 2
5 0 1 0 0 15 0 2 0 0
Level of flood-control gates compared to hydrograph
Highly regulatedHigh flow
0
5
1 0
1 5
2 0
2 5
3 0
3 5
0
0 . 2
0 . 4
0 . 6
0 . 8
1
1 . 2
5 0 1 0 0 15 0 2 0 0
Level of flood-control gates compared to hydrograph
Partially regulatedHigh flow
0
5
1 0
1 5
2 0
2 5
3 0
3 5
0
0 . 2
0 . 4
0 . 6
0 . 8
1
1 . 2
5 0 1 0 0 15 0 2 0 0
Level of flood-control gates compared to hydrograph
UnregulatedLow flow
0
5
1 0
1 5
2 0
2 5
3 0
3 5
0
0 . 2
0 . 4
0 . 6
0 . 8
1
1 . 2
5 0 1 0 0 15 0 2 0 0
Highly regulatedHigh flow
Highly regulated flow: Early spring
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
50 60 70 80 90 100 110 120
Below dam (Site 3)
Midstream (Site 2)
Downstream (Site 1)
Julian day
Highly regulated flow: Early spring
80 90 100 110 120 130 1400
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Julian day
Below dam (Site 3)
Midstream (Site 2)
Downstream (Site 1)
0
5
1 0
1 5
2 0
2 5
3 0
3 5
0
0 . 2
0 . 4
0 . 6
0 . 8
1
1 . 2
5 0 1 0 0 15 0 2 0 0
Partially regulatedHigh flow
0 2 km
Ompompanoosuc River
ConnecticutRiver
UnionVillageDam
Site 3Site 2.2
Site 2
Site 1
Site 2.1
W. Branch
E . B ran ch
Ve rm on t
Study sites
Partially regulated flow: Mid-spring
130 135 140 145 150 155Julian day
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Below dam (Site 3)
Midstream (Site 2)
Downstream (Site 1)
Below dam (Site 2.2)Midstream (Site 2.1)
Entire time period
50 100 150 2000
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0
0.2
0.4
0.6
0.8
1
1.2
Below dam (Site 3)
Midstream (Site 2)Downstream (Site 1)
Below dam (Site 2.2)
Midstream (Site 2.1)
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 – 6060 – 80
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)
Dates 7Be velocity
One-fraction velocity
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 – 6060 – 80
5500 33 - 6060 – 75
0.44 – 0.800.80 – 1.0
0.14 - 0.150.15
Comparisons to previous studiesSediment transport models
Timescales of stream bed stabilization due to altered flow and sediment regimes below dams
Pre-dam Post-dam
-0 .2
0
0 .2
0 .4
0 .6
0 .8
1
1 .2
19 45 19 5 1 1 9 57 19 63 1 96 9 1 97 5 1 9 91
0
0 .2
0 .4
0 .6
0 .8
1
1 .2
1 94 5 1 954 196 3 19 82 1 99 1
Y ear1 9 36-0 .2
Ompompanoosuc River- Sediment over-
supply
Black River- Sediment limitation
0
0.2
0.4
0.6
0.8
1
1.2
Pre Post 1 Post 2 Post 3 Post 4
OmpompanoosucBlack
Decade
Timescales of bed elevation stabilization
Bed elevation variance
Family Date Regulated Unregulated P
Hydropsychidae July 39.8 10.9 0.008
Hydropsychidae September 57.8 14.2 < 0.001
Ephemerellidae July 8.7 10.9 < 0.001
Ephemerellidae September 16.8 22.9 < 0.001
Results
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
Acknowledgements
Funding
National Science Foundation
Arthur D. Howard Award
(GSA QG&G)
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)
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 ItakuraRebecca KrystosekJulie Jo Walters
Field assistance Kelly Sennatt and Alexandra Fleming
(Dartmouth Department of Earth Sciences).
Thank you Frank and Carl!
Also thanks to Jim Kaste, Keith Nislow, and Brian Dade for their advice and assistance