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

O2 N

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

water sediment

Deposition and aggradation Armoring and incision

Ecological changes

DAM

S* vs. T*

From Grant et al. 2003

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

Union Village Dam

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

Bed sediment samplingMonthly sampling February to July 2004

Samples dried, sieved and counted for 7Be activity

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)

Effect of grain size interactions on transport

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

Black RiverImmediate stabilization

Ompompanoosuc RiverGradual stabilization

Benthic ecology

Lack of disturbance Sediment deposition

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