One year after crews began to take down two obsolete dams on Washington state’s Elwha River, the unprecedented restoration is already yielding such signs of life as fish hatchlings, tree saplings and the beginnings of beaches for ongoing study by US Geological Survey scientists and their state, federal and tribal partners.
The Elwha River runs through Olympic National Park and empties into the Strait of Juan de Fuca near Port Angeles, Wash. Its sand and gravel beds and swift currents historically combined to make the Elwha an unusually diverse and productive fishery — with 10 runs of anadromous (freshwater-to-sea migration) fish, including all five species of native Pacific salmon and steelhead — until two hydroelectric projects dammed its flow in 1913 and 1927. The Elwha and Glines Canyon dams collected not just water but the large amounts of sediment that would normally have been carried downstream, providing habitat for many species and counteracting coastal erosion. The dams thus changed the watershed’s physical and biological character and with it the kind of species that could thrive there, from microbes to black bears. By 2011, the Elwha’s fish population had dwindled to less than 5 percent of its historical levels; the now-outmoded power plants had long been closed; and 19 million cubic meters of sediment – enough to fill Seattle’s NFL stadium eight times – had accumulated behind Elwha and Glines Canyon dams.
In 1992, the U.S. Congress authorized for the Elwha what would become the largest river restoration through dam decommissioning ever attempted in the United States. The USGS and many partners were called in to study the entire process, beginning with establishing baseline conditions for hydrology, geomorphology, biology and ecology.
“We have had the opportunity to gather a lot of data and information as the Elwha story unfolds. Our job is to provide a technically accurate scientific narrative of the ecosystem response, which will provide a baseline to help us understand the changes that occur over the short- and long-term,” explained USGS research ecologist Jeff Duda.
In just a year, USGS and scientific partners including the National Park Service, the US Fish and Wildlife Service, The National Oceanic and Atmospheric Administration’s National Marine Fisheries Service, and the Lower Elwha Klallam Tribe have observed:
About half a million tons of sediment — about 50,000 dump-truck loads — have exited the project site from the natural flow of the river. Though seemingly a large number, this winter’s river flow conditions were relatively mild and much greater sediment releases are expected in the coming years. The sediment releases to date represent only about 2 percent of total sediment trapped behind both dams and only about 5 percent of the total expected to move downstream in the next three to six years.
The USGS and collaborators collected detailed beach topography and nearshore bathymetry around the Elwha River mouth in May and August 2012 to document the initial delivery of sediment down the river to the Strait. Sand has already made its way to the lower beach in some places, but not yet in enough volume to stop the shoreline erosion. Roughly 90,000 cubic meters of sand has accumulated offshore and directly east of the river mouth in areas that USGS models predicted.
The changes in sedimentation, in turn, have begun to change the ecology of the river and its estuary in ways USGS and partners will continue to observe. For example, three river otters have been equipped with radio telemetry transmitters by Lower Elwha Klallam Tribe and USGS and NPS cooperators, allowing researchers to monitor movements of otters and begin illustrating how otters will use the changing river.
Willow and cottonwood saplings five feet high have naturally sprung up on parts of the newly exposed riverbed. This was aided by the timing of the dams’ removal – in June, when these species release their seeds, the silt-rich beds were newly exposed. Most of these deposits and associated seedlings are situated at relatively low topographic positions and so may be vulnerable to erosion or potential winter and spring floods. The areas are also highly vulnerable to invasive species. Because parts of the watershed are remote, USGS is deploying unmanned aircraft carrying remote sensing equipment to cost-effectively plot how vegetation in these areas responds to natural processes as well as to the NPS’ and Lower Elwha Klallam Tribe’s extensive revegetation plan.
As river water and sediment mix into the coastal waters of the Strait of Juan de Fuca, a large, turbid river plume was created. The plume led to reduced light levels on the seafloor near the river’s mouth, in turn likely leading to negative effects on photosynthesizing organisms such as phytoplankton and kelp. Decreases in annual seaweeds were documented by ongoing USGS-led scuba dive studies, but nearshore invertebrates and fish were still abundant during the first season of post-dam removal monitoring.
In what Duda calls a pleasant development, Chinook, coho, and pink salmon, as well as native steelhead, have begun to swim through the turbid waters to search for mates in waters that have been blocked by the dams for 100 years, including stretches inside of Olympic National Park. This natural recolonization, in addition to the biologist-aided relocation of coho and steelhead from this past winter, has resulted in the first cohorts of juvenile salmon to emerge from the gravels above the Elwha Dam site.
The increased turbidity and sedimentation observed by the Lower Elwha Klallam Tribe and USGS scientists at the Elwha River estuary is renewing important habitat for juvenile salmon. The news of their first natural passage in nearly 100 years is just a first step in restoring the Elwha’s uniquely productive fisheries. It is also highly symbolic to the Lower Klallam people, who for years saw reduced salmon runs in the fisheries that had nourished their ancestors. In fact, tribal tradition holds that life itself began for the tribe from within the Elwha River, at a site that was submerged by the reservoir behind Elwha Dam and restored to view only this year.
“There’s a bowl in the rock. That’s where the Creator created the Elwha people,” Lower Elwha Klallam chair Frances Charles told filmmaker John Gussman as he pointed out the once-again-visible spot. “It was life. Life-giving water.”