Guests arrive at the Elwha Dam for the ceremony commemorating the official start of the dam decommissioning and river restoration project on the Elwha River in Washington state.

Over the last decade, the strategic decommissioning of obsolete or unsafe dams has become more common, with dam removal benefiting aquatic and streamside – or riparian – ecosystems. When natural river flow and sediment delivery regimes are restored, the result is a revitalization of degraded river channels and floodplains.  At the same time, migratory pathways of commercially valuable or threatened species, such as Pacific salmon or American eels, are reestablished. In these cases, the benefits and ecological effects of decommissioning span upstream and downstream of the dam site, as well as into surrounding watersheds.

The USGS, working with partners across the country, has been studying how the river’s shape and form and ecological outcomes of dam decommissioning.  USGS’s multi-disciplinary science helps decision makers answer fundamental questions about the downstream effects of dams and whether restoration targets are being achieved with dam removal.

Elwha River Restoration: Rebirth of a River

The USGS is an important science partner in the country’s largest dam decommissioning project, now under way in Olympic National Park in northwest Washington state. On September 17, 2011, the National Park Service began the simultaneous removal of the 108-foot tall Elwha Dam and the 210-foot tall Glines Canyon Dam on the Elwha River. For years previous to this day, the USGS worked with a number of partners, including the NPS, NOAA, the Lower Elwha Klallam Tribe, and others to conduct research and monitoring studies throughout the watershed. After establishing the baseline conditions for ecosystem components such as fish, wildlife, and riparian or streamside communities, scientists are continuing to monitor the rebirth of this river (for a slideshow showing marine sea life near the Elwha River’s mouth, click here.

Photo from a webcam showing the decommissioning of the Glines Canyon Dam, built in 1927 inside of Olympic National Park. Photo courtesy of the National Park Service.

The removal of the dams and restoration of habitat will reconnect salmon to their historical spawning grounds inside of Olympic National Park. For nearly 100 years, salmon were limited to the lowest 5 miles of the river below the dams, where their population numbers declined and their spawning habitat diminished as gravels were captured and stored in the upstream reservoirs.

Over time, nearly 24 million cubic yards of sediment accumulated in the two reservoirs, enough to fill a NFL football stadium eight times. Sediment transportation is a complicated process, with a variety of potential outcomes for river and marine habitats depending on the timing and pattern of sediment movement. In the short term, the massive amounts of sediments eroded during dam decommissioning will affect the clarity of the water and the downstream river bed. Some possible negative effects are loss of salmon habitat and some of their food supplies. In the long term, a natural sediment supply should increase habitat for salmon, shellfish, eel grass, and other forms of life in the river and the marine waters into which the river flows. The controlled release of this sediment is playing a major role in the dam-removal methods and schedule. For a fact sheet about the project, click here, and for a video of an Elwha River fish weir, click here.

Return of the American Eels: Dam Removal in Shenandoah National Park

Young American eels, such as the one pictured here, are beginning to recolonize streams in Shenandoah National Park after the removal of a dam more than 90 miles downstream.

The American eel, which lives in major rivers, streams, and some lakes all along the Atlantic coast from Greenland to northern South America, is under consideration by the U.S. Fish and Wildlife Service for federal listing as a threatened species under the Endangered Species Act. New research co-authored by USGS researcher Nathaniel (Than) Hitt and DOI partners reveals the benefits of dam removal for American eel conservation.  The research shows that removal of a large dam increased American eel migrations into Shenandoah National Park streams more than 90 miles away. This research evaluated eel abundances in the headwater streams of Shenandoah National Park and compared sites before and after the removal of a large downstream dam in 2004 on the Rappahannock River. Results of the study show that the immigration of small eels was primarily responsible for the observed increases in eel numbers. Although the dam did not prevent eel passage, the results indicate that it lowered eel abundances and altered eel populations within distant headwater streams. The benefits of dam removal may therefore extend far into headwater areas.

American eel numbers increased in Shenandoah National Park following the removal of a dam more than 90 miles downstream. Photo courtesy of Gary Tyson, Tiadaghton Audubon Society

Elwha River in Olympic National Park in Northwest Washington. Courtesy: John McMillan, NOAA

A new analysis of streams in the western United States has found that despite a general increase in air temperatures over the past several decades, western streams are not necessarily warming at the same rate. Several factors may influence the discrepancy, including snowmelt, interaction with groundwater, water flow and discharge rates, solar radiation, wind, and humidity. But even after factoring out those elements, the scientists detected cooler-than-expected maximum, mean, and minimum stream temperatures. Looking at streams individually, they found that some seemed to be getting warmer, some cooler, and others showed little change at all.

Results of the research, which was supported by the U.S. Geological Survey, the U.S. Forest Service, and Oregon State University, are published in Geophysical Research Letters, a journal of the American Geophysical Union.

Cold, clean water is one of the most important ecosystem services in the western United States. Many species of economically and culturally important salmon, trout, and other species depend on these cold waters to thrive and survive, so naturally, the potential loss of cold water in the face of climate change is a concern.

These findings show that changes in stream temperatures will not simply parallel changes in warming air temperatures, as commonly assumed or

Cutthroat trout in the Middle Fork Salmon River, Idaho. Courtesy: Steve Jacobs

projected. They point to the likely importance of local factors, such as land form, land cover, and geology, in influencing climate sensitivity of stream temperatures. A second key finding is that the vast majority of streamgages in the region either lack long-term data or are too strongly influenced by local human activities to provide a clear evaluation of climate effects.

For this study, researchers used long-term records from USGS and U.S. Forest Service gaging stations. Of the more than 600 stations evaluated from California, Nevada, Oregon, Idaho, Washington, and Alaska, less than 20 were suitable for analyzing climate effects. This set included streams with minimal human influences and sufficiently long-term records of temperatures for an evaluation of trends.

Rogue River Canyon in southwestern Oregon. Courtesy, Ruth Jacobs, USGS

These results highlight the fact that stream temperature is one of the most important, yet least understood aspects of climate change. The researchers caution that the findings do not mean that climate change will not affect stream temperature, which is a fundamental driver of ecosystem processes in streams. However, the relationship between air temperatures and stream temperatures may be more complex than previously realized and require additional monitoring.

The paper, The paradox of cooling streams in a warming world: regional climate trends do not parallel variable local trends in stream temperature in the Pacific continental United States, was authored by Ivan Arismendi, Oregon State University; Sherri Johnson, U.S. Forest Service; Jason Dunham, USGS; Roy Haggerty, Oregon State University; and David Hockman-Wert, USGS.

Additional Links:

Reconstructing Thermal Regimes in Streams from Sclerochronology of Freshwater Mussels (link to a paper, a USGS podcast, and an Oregon Field Guide television episode about the research)

http://fresc.usgs.gov/research/StudyDetail.asp?Study_ID=558

Climate Impact on Streamflows, Thermal Regimes, and the Changing Distribution of Trout in the Great Basin

http://fresc.usgs.gov/research/StudyDetail.asp?Study_ID=734

USGS Forest and Rangeland Ecosystem Science Center Aquatic Ecology Laboratory

http://fresc.usgs.gov/AquaticEcologyLaboratory/

Mountains towering above the mouth of the Copper River from the coastal Gulf of Alaska.

As warming temperatures cause glaciers to melt, the flow of freshwater in the Gulf of Alaska changes and impacts are felt across coastal ecosystems. Increased water flow can flush higher levels of iron and nitrate into coastal waters, and these compounds can radically alter the production of phytoplankton and zooplankton (tiny, free floating organisms), which serve as food for seabirds and fish such as salmon. Glacier runoff is of particular concern in the Copper River, which is the Gulf’s largest freshwater source and a major salmon production area.

How will accelerated glacial melting over the next 50 years as a result of climate change affect the unique Gulf of Alaska and Copper River coastal ecosystems? USGS scientists are studying these processes and impacts.

Planktic Foraminifera collected from a sediment-trap moored in the northern Gulf of Mexico, magnified 255x.

An extensive field campaign in 2010 included three oceanographic cruises studying the Copper River plume and adjacent regions off of the coast, six monthly river-sampling trips, and stream flow monitoring of several rivers. Modeling of these systems is also underway, including a predictive ecosystem model of the Gulf of Alaska. In addition, a glacier component is being added to an existing and widely-used water model. Model results will be an important resource for resource managers, as will mapping of current glacial areas using high resolution satellite imagery. These results will help scientists and resource managers assess the potential impacts that future changes in glaciers may have on the environment.

You can learn more about this USGS research at : http://nccwsc.usgs.gov/documents/projectsummary/Summary_for_NCCWSC-Crusius.pdf

Contact: John Crusius                                    (206) 543-6978

Salmon swimming in a river.

The timing of animal migration and reproduction, and observing when plants send out new leaves and bear fruit, is increasingly important in understanding how climate change affects biological and hydrologic systems. Photo credit Copyright C Brandon Cole.

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