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:
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, WashingtonContact information for the authors:
Kate Ramsayer | American Geophysical Union
New mathematical model can help save endangered species
14.01.2019 | University of Southern Denmark
Foxes in the city: citizen science helps researchers to study urban wildlife
14.12.2018 | Veterinärmedizinische Universität Wien
The scientific and political community alike stress the importance of German Antarctic research
Joint Press Release from the BMBF and AWI
The Antarctic is a frigid continent south of the Antarctic Circle, where researchers are the only inhabitants. Despite the hostile conditions, here the Alfred...
World first experiments on sensor that may revolutionise everything from medical devices to unmanned vehicles
The new sensor - capable of detecting vibrations of living cells - may revolutionise everything from medical devices to unmanned vehicles.
Dead and alive at the same time? Researchers at the Max Planck Institute of Quantum Optics have implemented Erwin Schrödinger’s paradoxical gedanken experiment employing an entangled atom-light state.
In 1935 Erwin Schrödinger formulated a thought experiment designed to capture the paradoxical nature of quantum physics. The crucial element of this gedanken...
Cellulose obtained from wood has amazing material properties. Empa researchers are now equipping the biodegradable material with additional functionalities to produce implants for cartilage diseases using 3D printing.
It all starts with an ear. Empa researcher Michael Hausmann removes the object shaped like a human ear from the 3D printer and explains:
The phenomenon of so-called superlubricity is known, but so far the explanation at the atomic level has been missing: for example, how does extremely low friction occur in bearings? Researchers from the Fraunhofer Institutes IWM and IWS jointly deciphered a universal mechanism of superlubricity for certain diamond-like carbon layers in combination with organic lubricants. Based on this knowledge, it is now possible to formulate design rules for supra lubricating layer-lubricant combinations. The results are presented in an article in Nature Communications, volume 10.
One of the most important prerequisites for sustainable and environmentally friendly mobility is minimizing friction. Research and industry have been dedicated...
16.01.2019 | Event News
14.01.2019 | Event News
12.12.2018 | Event News
18.01.2019 | Materials Sciences
18.01.2019 | Life Sciences
18.01.2019 | Health and Medicine