Chapter Summary and Anticipated Responses to Elwha River Dam Removal 9 By Guy Gelfenbaum, Jeffrey J. Duda, and Jonathan A. Warrick Abstract Starting in September 2011, the removal low nutrient concentrations in the river of two large dams on the Elwha River will waters, and coastal erosion that has begin an unprecedented river restoration accelerated markedly with time. During project because of the size of the dams, and after the removal of these dams, the volume of sediment released, the the Elwha River and its ecosystems will pristine watershed upstream of the dam be altered by a renewal of sediment sites, and the potential for renewing discharge downstream of the dams and salmon populations. Ecosystem studies a reintroduction of salmon spawning of the Elwha watershed indicate that the upstream of the dams. This chapter effects of almost 100 years of damming summarizes the pre-dam and current state are measurable and of consequence. of the river and its coastal ecosystems, These effects include smaller spawning and describes the likely outcomes of salmon populations, massive sediment river restoration on the Elwha River retention behind the dams, coarsening ecosystems. of the riverbed downstream of the dams, Chapter 19 250 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal Introduction A. 125° 123° 49° The removal of two large dams on the Elwha River presents an opportunity to restore Str ait o Salish Sea natural fluvial processes to a mostly pristine f Ju an deFuca watershed and rebuild iconic salmon runs. fig. B 48° Glines After removal of the dams, salmon populations Elwha Canyon Dam are expected to increase dramatically over PACIFIC Dam their present numbers (U.S. Department of OCEAN Elwha the Interior, 1995a; Ward and others, 2008), River restoring several important runs to this Pacific 47° Northwest river that once produced large Base modified from U.S. Geological Survey numbers of fish (U.S. Department of the Interior 1:100,000-scale digital data and others, 1994; Wunderlich and others, 1994). The removal of the Elwha and Glines Easting, in kilometers Canyon Dams also presents an opportunity B. 290 295 300 305 310 315 to restore beaches along the Strait of Juan de 138 0 Fuca with sediment that has been trapped for 136 -30 nearly a century by dam-impounding reservoirs 134 -60 (fig. 9.1). Coastal erosion of as much as 22 m Freshwater over the past 16 years east of the river mouth is 132 Figure C -90 Bay Ediz Hook encroaching on the Lower Elwha Klallam Tribal 130 -120 Northing, in kilometers Port Angeles reservation (Warrick and others, 2009), and on Elevation, in meters 128 Elwha River -150 vital wetlands and estuaries that provide critical -180 habitat for rearing juvenile salmon. Shaded relief from Puget Sound LIDAR Consortium Although expectations are high for returning salmon populations to the river, restoring river function, and restoring beach sediment supply, a number of uncertainties are C. associated with the restoration of the Elwha River ecosystem. The rebuilding of salmon Levee populations, for example, is of particular interest. The spatial and temporal patterns of reemerging life-history diversity and competition among natural- and hatchery-origin Levee fish are complex and not fully understood. However, these processes ultimately will affect salmon recolonization, future population status (Brenkman and others, 2008; Pess and others, 2008), and will be a large determinant Dudley of ecosystem restoration success. Similarly, Pond the supply of sediment to the lower river and beaches downstream of the dams is uncertain. It is not known how much of the sediment trapped behind the dams will be eroded and transported Aerial photography from 2006 U.S. Department of Agriculture NAIP downstream. Of the sediment that is transported downstream, it is not known how much will be Figure 9.1. The coastal setting of the Elwha River, Washington. transported all the way to the Strait of Juan de Fuca, and if that amount will be enough to slow or stop the coastal erosion. watac11-0558_fig9-01 Summary and Anticipated Responses to Elwha River DamIntroduction Removal 251 The return of fish populations and end of their constructed lifespan or following dam removal will be large restoration of sediment supply will economic productivity, the impetus enough to change the existing aquatic cause numerous changes to the Elwha for dam removal is accelerating and and terrestrial flood plain ecosystems River ecosystem. For example, large becoming much less controversial than into a new stable state. This is certainly amounts of silt and sand, along with in the past (Hart and others, 2002; Heinz the case for the former reservoir sections gravel and cobbles may be deposited in Center, 2002). Moreover, relicensing that will change from lentic (lake-like) the bed of the lower river, which would efforts for existing dams have a critical to lotic (river-like) water bodies. In the alter the grain-size distribution in the need for the best available sediment- years following dam removal, as more riverbed, the structure of pools and and river-response data to assess the coarse-grained sediments arrive from the riffles, and the suitability of spawning costs and benefits of dam removal former reservoirs, this lower intensity habitat. The return of large numbers of compared with continued operation. stressor may or may not change the fish to the lower river and estuary may Meaningful monitoring efforts are ecosystem. It is not known if multiple alter nutrient concentrations, thereby needed to document ecosystem recovery phase shifts will arise in the Elwha River changing the chemistry, and ultimately and to assess the benefits of restoration after dam removal, or if the ecosystem the productivity, of these systems. The expenditures (Duda and others, 2008). will settle into a new equilibrium fining of bed sediments may alter the As noted in the previous chapters following the high intensity changes suitability of the ecosystem for kelp of this report, as well as numerous shortly after dam removal. species if large amounts of fine sediment other reports documenting scientific Additionally, the large numbers are delivered offshore. The response investigations of the Elwha River of salmon anticipated to return to the of ecosystem processes, structure, basin, the Elwha River ecosystem river and the large volume of sediment habitat, and the biological resources they has been affected by the Elwha and expected to be mobilized after dam support will be complex, and are largely Glines Canyon Dams, and removal removal, will create a system response unpredictable. The scientific knowledge of those dams will affect it further. with large “signals” relative to the of many of these ecosystem linkages However, it is also likely that dam “noise” of natural background changes. is limited and the results of this large- removal and ecosystem restoration For these reasons, a comprehensive scale restoration project are uncertain, may not simply restore the ecosystem research and monitoring program such which highlights the need for ongoing to its pre-dam state, but may instead as that described in this report will multidisciplinary scientific research. result in something new. The concept have a high likelihood of successfully The scale of the Elwha River of “alternative stable states” proposes documenting ecological changes caused Restoration Project is unprecedented. that there are suites of abiotic and by dam removal. The Elwha and Glines Canyon Dams biotic conditions in an ecosystem A comprehensive description of will be the largest dams removed in the that lead to particular assemblages of the ecosystem response to dam removal United States, and to our knowledge, uniquely adapted species. As the system will require the monitoring of multiple the world. Moreover, the removal is perturbed with small changes, the interrelated variables across a varied of these dams will cause the largest density or species composition of the geographic domain that will depend controlled release of sediment into system may temporarily change, but on the sediment grain size mobilized a river and adjacent marine waters. will drift back into the equilibrium (Woodward and others, 2008). For This project represents one of the state when the perturbation ceases. example, ecosystem responses will vary best remaining opportunities in the Larger perturbations that exceed a across the different sections of the river conterminous United States to restore given threshold, on the other hand, can (upstream of, between, and downstream salmon in large portions of a watershed lead to a phase shift in the system that of the dams), the reservoirs, beaches, that are protected as wilderness. gives rise to a new stable state (Holling, and the adjacent nearshore zone of the The Elwha River dam-removal and 1973; Bender and others, 1984; Beisner Strait of Juan de Fuca. The response ecosystem-restoration project also is and others, 2003). Due in part to the in each of these domains will depend an opportunity for increasing scientific steepness of the basin, and the proximity on the grain size of the sediment that understanding (Gelfenbaum and others, between the upper reaches of the accumulates there, which may include 2006). Billions of dollars are spent river and the coast, the dam removal very fine-grained (silt and clay) to very on ecosystem restoration around the project will create short duration, high coarse-grained (cobble and gravel)