Case Study - Restoration of the Elwha River Ecosystem
The construction of numerous hydropower projects fueled the economic growth of the Pacific Northwest during the early 1900s. With the seemingly inexhaustible supply of anadromous salmonids, little care was taken to reduce or mitigate the consequent impacts to these fish (Hoffman and Winter 1996). Two hydropower dams built on the Elwha River, on Washington’s Olympic Peninsula, were no exception.
Figure 1: Elwha Dam.
Fish passages were not constructed when the dam was built in 1910-1913.
The 108 ft. high Elwha Dam (Figure 1) was built from 1910-13 about five miles from the river mouth. Although state law required a fishway, one was not built. As a result, salmon and steelhead populations immediately declined, some to extinction, and remaining populations have been confined to the lower five miles ever since. The 210 ft. high Glines Canyon Dam (Figures 2 and 3) was built from 1925-27 about eight miles upstream of the first dam, also without fish passage facilities. Glines was licensed for a period of 50 years in 1925 while the Elwha Dam has never been licensed.
Glines Canyon Dam before removal Glines Canyon Dam simulation for post-removal
Figure 2: Glines Canyon Dam.
Figure 3: Glines Canyon Dam.
Simulation after removal.
In 1968, the project owner filed a license application for Elwha Dam and filed a relicense application for the Glines Canyon Dam in 1973. The Federal Energy Regulatory Commission (FERC) did not actively pursue the licensing of these two projects until the early 1980s when federal and state agencies, the Lower Elwha Klallam Tribe (Tribe), and environmental groups filed petitions with FERC to intervene in the licensing proceeding. The option of dam removal to restore the decimated fish runs was raised in most of these petitions, and FERC addressed dam removal in a draft environmental impact statement (EIS). Nonetheless, it was apparent that disagreements remained over numerous issues, and that litigation could take a decade or more.
Congressional representatives offered to broker a solution. In October 1992, President George Bush signed Public Law 102-495 (the Elwha River Ecosystem and Fisheries Restoration Act; the Elwha Act), which is a negotiated settlement involving all parties to the FERC proceeding. The Elwha Act voids FERC’s authority to issue long-term licenses for either dam, and it confers upon the Secretary of the Interior the authority to remove both dams if that action is needed to fully restore the Elwha River ecosystem and native anadromous fisheries. In a report to the Congress (DOI et al. 1994), the Secretary concluded that dam removal was necessary to meet the goal of the Elwha Act. Subsequently, Interior completed the EIS process FERC had begun but using the new standard of full ecosystem restoration rather than “balancing” competing uses as FERC is required to do (NPS 1995).
Interior analyzed various ways to remove the dams and manage the 18 million cubic yards (mcy) of sediments that have accumulated in the two reservoirs since dam construction. The preferred alternative for the Glines Canyon Dam is to spill the reservoir water over successive notches constructed in the concrete gravity-arch section, allowing layers of the dam to be removed with a crane under dry conditions (NPS 1996). Standard diamond wire-saw cutting and blasting techniques are planned. Much of the dam, including the left and right side concrete abutments and spillway, will be retained to allow for the interpretation of this historic structure.
The foundation of the Elwha Dam failed during reservoir filling in 1912, flooding downstream areas such as the Tribe’s reservation at the mouth of the river. A combination of blasted rock, fir mattresses, and other fill was used to plug the leak (NPS 1996). To avoid a similar failure during removal, the reservoir will be partially drained and the river diverted into a channel constructed through the bedrock footing of the left abutment. This will allow the fill material and original dam structure to be removed under dry conditions. Following removal of this material, the river will be diverted back to its historic location and the bedrock channel refilled. Since the Elwha Dam was built in an area that is religiously and culturally important to the Tribe, all structures will be removed.
The 18 million cubic yards of accumulated sediment consists of about 9.2 mcy of silt and clay (<0.075 mm), 6.2 mcy of sand (0.075-<5 mm), 2.0 mcy of gravel (5-<75 mm), and .25 mcy of cobbles (75-,300 mm). The coarse material (i.e., sand and larger) is considered a resource that is lacking in the river below the dams, the release of which will help restore the size and function of a more natural and dynamic river channel, estuary, and nearshore marine areas. The silt- and clay-sized particles are also reduced in the lower river, but resuspension of this material may cause the loss of aquatic life and adversely affect water users downstream for the approximately two to three years this process is expected to last (NPS 1996). Nevertheless, the preferred alternative incorporates the natural erosive and transport capacity of the river to move this material downstream, although roughly half of the fine and coarse materials will remain in the newly dewatered reservoir areas. Water quality and fisheries mitigation actions are planned to reduce the impacts of sediment releases during and following dam removal. Revegetation actions will be implemented on the previously logged slopes for stabilization purposes and to accelerate the achievement of old-growth characteristics. The old reservoir bottoms will be allowed to revegetate naturally; “greenup” should occur within three to five years.
Following the removal of both dams, the salmon and steelhead runs are expected to total about 390,000 fish, compared to about 12,000 to 20,000 (primarily hatchery) fish. These fish will provide over 800,000 pounds of carcass biomass (NPS 1995). About 13,000 pounds of this biomass is marine-derived nitrogen and phosphorous, the benefits of which will cascade throughout the aquatic and terrestrial ecosystem. The vast majority of wildlife species are expected to benefit from the restoration of this food resource and the recovery of over 700 acres of important lowland habitat. Restoration of the fish runs will also support the federal government’s trust responsibility to the Tribe for its treaty-reserved harvest rights. More wetlands will be recovered than will be lost from draining the reservoirs.