Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

After dam removal, sediment muddies the water

24.10.2012
The largest dam-removal project in history has increased river water cloudiness caused by suspended particles, a process that could affect aquatic life.

The dismantling of two large dams on the Elwha River in Washington began in September of last year and has significantly increased this river cloudiness, known as turbidity, even though most of the sediment trapped behind the dams has yet to erode into the river.

"The construction of dams can cause major disruptions to natural processes on riverways, and we can expect their removal to also have anomalous effects for some time until rivers regain their equilibrium," said U.S. Geological Survey Director Marcia McNutt. "What we are learning from the response of the Elwha River ecology to increased sedimentation during dam removal will help guide other large dam removal and river restoration projects in the future."

The U.S. Geological Survey authors examined sediment and water-flow data from the first six months of dam removal and found that dam-removal activities and natural processes both affected the river's turbidity. Breaching of several temporary earthen dams built to assist with deconstruction caused sustained increases in downstream turbidity. High river flows associated with rainfall also increased turbidity, at measuring stations both above and below the dams.

"During the first six months of dam removal, most of the sediment released was silt and clay, which caused substantial-but not unexpected-turbidity in the river and coastal waters. As dam removal progresses we expect more and more sand and gravel to be released into the river, which will likely help build river bars and slow coastal erosion near the Elwha River mouth," said Jonathan Warrick, lead author of the report and research geologist for the USGS. "Although the river has been quite turbid since dam removal began, most of the sediment-transport action is yet to come."

This first published report on sediment response to the Department of Interior's Elwha River Restoration Project, is published today in Eos, the weekly newspaper of the American Geophysical Union.

High turbidity levels can reduce the amount of light penetrating river and coastal waters, which can inhibit aquatic plant growth and affect wildlife that rely on sight to find food and avoid predators.

Removal of the dams is exposing more than 24 million cubic yards of sediment stored in the reservoirs, enough to fill the Seattle Seahawks' football stadium eight times. Using a combination of measurements from a station downstream of the dams, the authors estimated that less than 1 percent of the 24 million cubic yards of sediment stored behind the dams had eroded and moved downstream.

Thus, the authors conclude that completion of dam removal in 2012- 2013 will expose much more sediment to erosion, resulting in continued turbidity downstream as well as changes in the shape and sedimentary makeup of the riverbed and the coastal landforms around the mouth of the river into the Strait of Juan de Fuca, which is only 5 miles below Elwha Dam.

"Tracking these changes will be important to assessing their effects on habitat for fish and other wildlife in what historically was one of the most productive salmon rivers in Puget Sound," Warrick said. Scientists expect dam removal to cause short-term adverse effects on aquatic life, followed by large-scale ecosystem resurgence once the river's sediment load returns to a more normal and natural state.

Dam decommissioning has become an important means for removing unsafe or obsolete dams and for restoring rivers to a more natural state. Two dams are being removed incrementally during this 2-year project: the 105-foot-high Elwha Dam impounding Lake Aldwell and the 210-foot- high Glines Canyon Dam impounding Lake Mills.

Only part of the total sediment stored behind the dams-9 to 10 million cubic yards-is expected to erode into the river and move downstream to coastal areas. The methods and schedule of dam deconstruction are largely governed by management of this sediment, with controlled drawdowns of the reservoir levels to prevent deleterious impacts of an abrupt release.

More information on the Elwha River Restoration can be found on web pages hosted by the USGS and the National Park Service. This research and monitoring was funded by both the USGS and the U.S. EPA.

Title:
"River turbidity and sediment loads during dam removal"
Authors:
Jonathan A. Warrick: Pacific Coastal and Marine Science Center, U.S. Geological Survey, Santa

Cruz, California;

Jeffrey J. Duda: Western Fisheries Research Center, U.S. Geological Survey, Seattle,

Washington;

Christopher S. Magirl and Chris A. Curran, Washington Water Science Center, U.S. Geological

Survey, Tacoma, Washington

Contact information for the authors:
Jon Warrick: Telephone: (831) 460-7569; Email: jwarrick@usgs.gov
AGU Contact:
Kate Ramsayer
+1 (202) 777-7524
kramsayer@agu.org
USGS Contact:
Paul Laustsen
+1 (650) 454-7264
plaustsen@usgs.gov

Kate Ramsayer | American Geophysical Union
Further information:
http://www.agu.org

More articles from Ecology, The Environment and Conservation:

nachricht Bioinvasion on the rise
15.02.2017 | Universität Konstanz

nachricht Litter Levels in the Depths of the Arctic are On the Rise
10.02.2017 | Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung

All articles from Ecology, The Environment and Conservation >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Stingless bees have their nests protected by soldiers

24.02.2017 | Life Sciences

New risk factors for anxiety disorders

24.02.2017 | Life Sciences

MWC 2017: 5G Capital Berlin

24.02.2017 | Trade Fair News

VideoLinks
B2B-VideoLinks
More VideoLinks >>>