Aug
11
2010

Last dam summer

A hard yank of the rusty metal door of the Acme Commercial Processing Facility outside of Port Angeles, Washington leads visitors down a white and green linoleum corridor to dark room dripping with condensation. Inside is a bank of twenty refrigerator-like machines whirring in unison day and night to preserve over 120 bushels of cones—Douglas-fir, grand fir, western red cedar, and western hemlock—for their eventual time the sun.

Seeds from one of the Elwha re-vegetation collection efforts
Seeds from one of the Elwha re-vegetation collection effortsCourtesy National Park Service
The cones, together with seeds and cuttings of more than 80 plant species native to Olympic National Park, have been collected over the course of several years as part of a plan to re-vegetate 268 square miles of land currently sitting beneath nearly sixteen billion gallons of water and 18 million cubic yards of sediment.

The land is located at the bottom of the Mills and Aldwell reservoirs, impoundments on the Elwha River that developed in the wake of the erection the Elwha and Glines Canyon Dams in the early 1900s. In a little less than one year, the process of removing the dams, and revealing land long drowned underneath billions of gallons of water, will begin.

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The Elwha and Glines Canyon Dams were built nearly 100 years ago when entrepreneur Thomas Aldwell saw the potential for power within the steep hills surrounding the Elwha River. Interested in harnessing that power, Aldwell formed the Olympic Power and Development Company and drew up plans to build the105-foot Elwha hydroelectric dam. Construction on the dam began in 1910 and by 1913 it was supplying energy to pulp mills in Port Angeles. By 1927,with the need for energy within Port Angeles continuing to increase, Aldwell’s company erected the 210-foot Glines Canyon dam eight miles upstream.

Elwha River watershed
Elwha River watershedCourtesy National Park Service
The Elwha is a rocky river that originates 4500 ft above sea level in the snowfields of the Olympic Mountains and cascades north through temperate forests to discharge its waters five miles west of Port Angeles into the Strait of Juan de Fuca. Before construction of the dams, the river’s 45-mile main channel and over 100 miles of tributaries had been host to runs of ten native anadromous salmon and trout. Potential range of salmonid fish on the Elwha River
Potential range of salmonid fish on the Elwha RiverCourtesy National Park Service

Today, changes to the river that developed in the wake of dam construction have conspired to reduce salmon populations by more than 100-fold. Since erection of the dams, migrating salmon have been confined to the lowermost 4.9 miles of river. Sediment that travels down river from the watershed’s mountains has been trapped behind the dams and available spawning habitat has decreased as a result. Diseases, parasites and fish mortality have increased concomitantly with river temperatures. In sum, native salmon populations have declined from approximately 400,000 to fewer than 3,000 individuals today. The diminished stocks are currently maintained primarily through hatchery production.

In the late 1960’s and early 1970’s the Elwha and Glines Canyon Dams were subject to licensing procedures by the Federal Energy Regulatory Commission (FERC). During the review, questions arose about the legal and philosophical conflicts involved in operating dams within a national park. Opposition to the dams mounted during the 70’s and 80’s and, in response to pressure from the Lower Elwha S’Klallam Tribe and sixteen area conservation groups, Congress considered the case of the Elwha River. In 1992 the Elwha River Ecosystem and Fisheries Restoration Act was passed.

The act mandated full restoration of the Elwha River ecosystem and its native anadromous fish, but did not specify the actions necessary to achieve “full restoration”. Instead, the Department of Interior was directed to study and evaluate alternative restoration scenarios, including the removal of one or both dams. By 1994, the National Park Service, the U.S. Fish and Wildlife Service, the U.S. Bureau of Reclamation, the Bureau of Indian Affairs, and the Lower Elwha S’Klallam Tribe released a joint study concluding that the best action for river and fish restoration would be removal of both dams.

Removing the dams from their place within the river involves more than simply eliminating the tons of concrete, enormous steel tubes, and spillway gates that comprise the dams’ structures. More than 80 years of restricted water and sediment flow in the river has resulted in the build-up of approximately 18 million cubic yards of sediment behind the dams. As easy as it might be to simply blast the dams out, releasing all the sediment in one pulse would devastate downstream and coastal habitats. Geomorphologists working on the project needed to find a way to control the downstream movement of sediment during and after dam removal.

Thirteen of the eighteen million cubic yards of sediment within the river lie behind the 210-foot Glines Canyon Dam. To study sediment movement in the wake of dam removal, researchers from the National Center for Earth-surface Dynamics constructed a physical model of the dam and surrounding watershed to test alternative removal scenarios.

Above are a series of stills from the sediment transport experiments conducted at NCED by Chris Bromely.

The agreed upon strategy, developed through analysis of the physical model studies in conjunction with mathematical models, involves gradually drawing-down the Mills reservoir using an outlet pipe to move water downstream. As the water level drops, demolition crews will cut and remove 7.5-foot sections of the dam starting from the top. Once the level of the dam has reached the level of the sediment layer sitting behind the dam, demolition crews will use controlled blasting to clear the remainder of the dam (see the really neat demolition illustration video from the National Park Service and Interactive Earth).

Removal of Elwha and Glines Canyon dams will be the largest dam removal project in U.S. history, one that is considered an unprecedented learning opportunity be scientists who study rivers and their associated ecosystems. Tim Randle, manager of the sedimentation and river-hydraulics group of the Bureau of Reclamation’s technical-service center in Denver, organized a recent trip to the site for engineers, fisheries scientists, biologists, geomorphologists, and a botanist to consider what can be learned from this extraordinary project. "It's the first time anyone has done a staged, step-by-step dam removal of this scale," Randle told the Seattle Times. “It's the largest controlled release of sediment ever in North America.”

The scientists plan to study what actually happens to all the mobile sediment once the dams are removed. They will investigate how salmon re-colonize the river once fish are again able to reach spawning grounds above the dams. They will research the re-vegetation of the hundreds of acres of exposed river banks and reservoir bottoms that will emerge as the Aldwell and Mills reservoirs drain, but they have nothing quite like this scenario upon which to base their expectations. Joshua Chenoweth, a botanist with Olympic National Park, likens the re-vegetation to that which occurred in the wake of the Mount St. Helens eruption of 1980. “At least there were buried roots at Mount St. Helens,” he told the Times, “We have nothing. This is the first time anyone has tried anything like this. The scale is unprecedented.”

The possibilities for renewal though, seem almost as vast as the wilderness itself. Bushel after bushel of those fir, cedar and hemlock cones still sit quiescent within the dark of cold storage at the Acme Commercial Processing Facility. In a matter of years the sun will shine upon the cones and on land long lost underneath billions of gallons of water. Native salmon and trout may be industriously swimming past.

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