The planned removal of two dams that have been in place for over 95 years on the Elwha River provides a unique opportunity to study dam removal effects. Among the largest dams ever considered for removal, this project is compelling because 83% of the watershed lies undisturbed in Olympic National Park. Eighteen million cubic meters of sediment have accumulated in and will be released from the reservoirs, and there is potential for rehabilitating depressed Pacific salmon runs. Researchers from academia, non-profit organizations, federal and state governments, and the Lower Elwha Klallam Tribe are currently assessing baseline ecological conditions of the Elwha River as part of dam removal studies. We introduce dam removal topics, provide a brief history of the dams, and summarize the ecology of the Elwha River basin as an introduction to a special issue devoted to research in the watershed.

The decision to remove the Elwha and Glines Canyon dams on the Elwha River, Washington was preceded by the collection of substantial amounts of biological and physical data. Studies were conducted to identify existing water quality within the reservoirs and river, fish populations and habitat availability, fish passage mortality through the dams and reservoirs, effects of the hydro-power projects on wildlife habitat, and economics. Although this information was generally specific to the federal hydropower licensing process, it provides valuable information on baseline, or with-project, conditions that may allow for comparisons to the post-project river.

Removal of two hydroelectric dams on the Elwha River, Washington, one of the largest river restoration projects in the United States, represents a unique opportunity to assess the recovery of fish populations and aquatic ecosystems at the watershed scale. The current project implementation does not contain sufficient funding to support comprehensive monitoring of restoration effectiveness. As a result, current monitoring efforts are piecemeal and uncoordinated, creating the possibility that project managers will not be able to answer fundamental questions concerning salmonid and ecosystem response. We present the initial elements of a monitoring framework designed to assess the effectiveness of dam removal on the recovery of Elwha River salmonids, their aquatic habitats, and the food webs of which they are an integral component. The monitoring framework is linked to the Elwha Fisheries Restoration Plan, which outlines the restoration of native stocks of salmon and relies upon a process of adaptive management. The monitoring framework includes two areas of emphasis—salmonid population recovery and ecosystem response. We provide study design considerations and make recommendations for additional monitoring efforts prior to dam removal. Based on a power analysis, we determined that a minimum of 3–11 years and up to 50 years of monitoring will be required to capture potential ecosystem responses following dam removal. The development of a monitoring plan will be a significant step forward in objectively evaluating the success of Elwha River dam removal.

Removal of two dams from the Elwha River is a unique restoration opportunity. In place for over 95 years, the dams have contributed to changes in the river, its estuary, and marine areas off shore from the river mouth, largely through reductions in sediment supply and salmon populations. Impending removals of both dams will only restore part of the severely degraded Elwha nearshore, where additional large scale anthropogenic impacts will remain. The effects of lower river levees, marine bluff hardening including significant riprapping of the marine shoreline, among other lesser habitat alterations, will continue beyond dam removal. Understanding the relationship of dam removal to the adjacent nearshore area is critical to the design of additional work necessary for successful ecosystem recovery. We provide an overview of the Elwha nearshore and collaborative efforts underway to understand it, and the role it plays in ecosystem restoration. Dam removal is slated to begin in the next 3 to 5 years making timing of this sorely needed nearshore work critical.

Removal of two dams > 30 m from the Elwha River, on Washington State's Olympic Peninsula, can provide an unprecedented opportunity to study the geomorphic and biologic consequences of this activity. Resulting information can inform management decisions regarding Elwha resources, as well as future dam removal projects. Research and monitoring priorities for each river section (above, between, and below the dams) and nearshore depend on the location-specific effects of the dams, planned active restoration efforts, and conceptions of Elwha ecosystem dynamics. Several river section- or discipline-specific workshops were held 2001 to 2005 to describe impacts to the Elwha River, potential responses to dam removal and priorities for research and monitoring. We present conceptual models based on summaries of these workshops to provide a framework to integrate and relate studies that are currently planned or are underway. We identify the need for an organizational framework – including conceptual models, study designs, data management and integrated sample designs – for research and monitoring that will increase understanding of ecosystem response, and engender additional financial support.

The Elwha River dams have disconnected the upper and lower Elwha watershed for over 94 years. This has disrupted salmon migration and reduced salmon habitat by 90%. Several historical salmonid populations have been extirpated, and remaining populations are dramatically smaller than estimated historical population size. Dam removal will reconnect upstream habitats which will increase salmonid carrying capacity, and allow the downstream movement of sediment and wood leading to long-term aquatic habitat improvements. We hypothesize that salmonids will respond to the dam removal by establishing persistent, self-sustaining populations above the dams within one to two generations. We collected data on the impacts of the Elwha River dams on salmonid populations and developed predictions of species-specific response dam removal. Coho (Oncorhynchus kisutch), Chinook (O. tshawytscha), and steelhead (O. mykiss) will exhibit the greatest spatial extent due to their initial population size, timing, ability to maneuver past natural barriers, and propensity to utilize the reopened alluvial valleys. Populations of pink (O. gorbuscha), chum (O. keta), and sockeye (O. nerka) salmon will follow in extent and timing because of smaller extant populations below the dams. The initially high sediment loads will increase stray rates from the Elwha and cause deleterious effects in the egg to outmigrant fry stage for all species. Dam removal impacts will likely cause a lag in recolonization and population rebuilding. These negative sediment effects will be locally buffered by the extent of functioning floodplain, and management attempts to minimize sediment impacts. Resident life forms of char (Salvelinus confluentus), rainbow trout (O. mykiss), and cutthroat (O. clarki) will positively interact with their anadromous counterparts resulting in a positive population level response.

The restoration of salmonids in the Elwha River following dam removal will cause interactions between anadromous and potamodromous forms as recolonization occurs in upstream and downstream directions. Anadromous salmonids are expected to recolonize historic habitats, and rainbow trout (Oncorhynchus mykiss) and bull trout (Salvelinus confluentus) isolated above the dams for 90 years are expected to reestablish anadromy. We summarized the distribution and abundance of potamodromous salmonids, determined locations of spawning areas, and mapped natural barriers to fish migration at the watershed scale based on data collected from 1993 to 2006. Rainbow trout were far more abundant than bull trout throughout the watershed and both species were distributed up to river km 71. Spawning locations for bull trout and rainbow trout occurred in areas where we anticipate returning anadromous fish to spawn. Nonnative brook trout were confined to areas between and below the dams, and seasonal velocity barriers are expected to prevent their upstream movements. We hypothesize that the extent of interaction between potamodromous and anadromous salmonids will vary spatially due to natural barriers that will limit upstream-directed recolonization for some species of salmonids. Consequently, most competitive interactions will occur in the main stem and floodplain downstream of river km 25 and in larger tributaries. Understanding future responses of Pacific salmonids after dam removal in the Elwha River depends upon an understanding of existing conditions of the salmonid community upstream of the dams prior to dam removal.

We characterized seasonal fish assemblage, relative density, and growth in river margins above and between two Elwha River dams scheduled for removal. Fish assemblage and relative density differed in the lateral habitats of the middle-regulated and upper-unregulated sections of the Elwha River. Rainbow trout was the numerically dominant salmonid in both sections, with bull trout present in low numbers. Sculpin were common in the middle section, but not detected in the upper section. In 2004, mean length and biomass of age-0 rainbow trout were significantly smaller in the middle section than in the upper section by the end of the growing season (September). In 2005, an earlier emergence of rainbow trout in the middle section (July) compared to the upper section (August) corresponded with warmer water temperatures in the middle section. Despite lower growth, the margins of mainstem units in the middle section supported higher mean areal densities and biomass of age-0 rainbow trout than the upper section. These results suggest that growth performance of age-0 rainbow trout was lower in the middle section than in the upper section, which could have been a density-dependent response, or a result of poor food production in the sediment-starved regulated section, or both. Based on our findings, we believe that seasonal sampling of river margins within reference reaches is a cost effective and repeatable method for detection of biologically important short- and long-term changes in emergence timing, density, and growth of rainbow trout before and after dam removals in the Elwha River.

The Elwha and Glines Canyon dams caused a dramatic decline in the numbers of all species of native Pacific salmonids (Oncorhynchus spp.) in the Elwha River. During the fall of 2005 and 2006, we radiotagged 49 adult coho salmon (O. kisutch) and tracked their movements between the Elwha River mouth and Elwha Dam (7.3 rkms). Half of all tagged fish were never relocated, likely due to emigration from the river. The remainder tended to migrate quickly and directly to one or two areas saturated with large woody debris and gravel, known to be high quality spawning habitat, and remain there. However, 7 of the 13 tagged fish in 2005 made multiple upstream and downstream movements prior to spawning. No tagged fish in either year migrated farther upstream than a rock weir approximately 4.9 km from the river mouth and 2.4 km downstream from the Elwha Dam, possibly indicating a migration barrier for coho salmon. We did not detect qualitative differences in migration behavior between hatchery and unknown-origin fish, but we did find that males moved slightly larger distances after tagging than females (average, 3.6 km for males, 2.5 km for females, t-test, P = 0.41). A large flow event on 6 November 2006 caused 8 of 11 tagged fish residing in the river to emigrate; none of these fish returned. Results both confirm ideas of coho salmon biology and raise concerns regarding environmental impacts on coho salmon recolonization following dam removal.

We genetically characterized seven species of Pacific salmonids in the Elwha River and in selected neighboring rivers prior to the impending removal of two dams. Monitoring the genetics of recolonization of the watershed by remnant native, hatchery, and/or adjacent watershed populations is a critical element to further our understanding of ecosystem restoration. By pooling data from independent studies, we assessed intraspecific diversity for pink salmon (Oncorhynchus gorbuscha), chum salmon (O. keta), coho salmon (O. kisutch), sockeye salmon (O. nerka), Chinook salmon (O. tshawytscha), rainbow trout (O. mykiss) and bull trout (Salvelinus confluentus). Levels and patterns of genetic variability within and among collections were evaluated at 6–15 microsatellite (mSAT) loci per species. Each species had 3–8 loci with 20 or more alleles. In all species, an Elwha collection was statistically different from one or more nearest-neighbor population. In addition, the native in-river collections of Chinook salmon and steelhead (anadromous rainbow trout) were distinguishable from existing in-river hatchery stocks. In most species, Elwha populations contained similar levels of genetic diversity as observed in neighboring river systems. In O. mykiss, variability at an evolutionarily adaptive major histocompatibility complex (MHC) gene paralleled the mSAT variation. Given the various levels of distinctiveness of Elwha populations, we discuss the use of these data as a genetic ruler to manage and monitor the genetic aspects of recolonization of the Elwha River, and the importance of tissue archives for new genetic techniques.

After the removal of two dams, wild, natural, and hatchery produced fish are expected to recolonize historic habitats in the Elwha River. Fish populations previously isolated by the dams will interact, and potentially transmit pathogens. Geomorphic changes caused by dam removal could disrupt the balance between host and pathogen, resulting in pathogen transmission and amplification, potentially leading to disease. We reviewed historic stocking records and conducted an initial survey to better understand the distribution of salmonid pathogens in the Elwha River before dam removal. Review of hatchery plantings revealed that seven salmonid species were released throughout the Elwha River Basin since 1914. Approximately 61 million Chinook salmon (Oncorhynchus tshawytscha) and 40 million chum salmon (O. keta), coho salmon (O. kisutch), and steelhead trout (O. mykiss) were released below Elwha Dam from various stock origins. Additionally, 19 million salmonids were planted above Elwha Dam beginning in 1930. From 2003 to 2006, five salmonid species from the lower, middle, and upper Elwha River and tributaries were tested for bacteria (n=684), viruses (n=943), and were screened for Myxobolus cerebralis (n=740). Renibacterium salmoninarum was the only target pathogen found, and was detected in five salmonid species in each segment of the river. In Elwha hatcheries, erythrocytic inclusion body syndrome, R. salmoninarum, and Flavobacterium psychrophilum were most commonly detected. Information from baseline surveys in the Elwha River highlight the benefit of including fish pathogen distribution as an important factor in risk assessment for future dam removals.

The planned removal of two dams on the Elwha River, Washington, will likely increase river sediment flux to the coast, which may alter coastal habitats through sedimentation and turbidity. It is therefore important to characterize the current habitat conditions near the river mouth, so that future changes can be identified. Here we provide combined sonar and video mapping results of approximately 20 km² of seafloor offshore of the Elwha River collected with the purpose to characterize nearshore substrate type and distribution prior to dam removal. These combined data suggest that the nearshore of the western delta and Freshwater Bay are dominated by coarse sediment (sand, gravel, cobble, and boulders) and bedrock outcrops; no fine-grained sediment (mud or silt) was identified within the survey limits. The substrate is generally coarser in Freshwater Bay and on the western flank of the delta, where boulders and bedrock outcrops occur, than directly offshore and east of the river mouth. High variation in substrate was observed within much of the study area, however, and distinct boulder fields, gravel beds and sand waves were observed with spatial scales of 10–100 m. Gravel beds and sand waves suggest that sediment transport is active in the study area, presumably in response to tidal currents and waves. Both historic (1912) and recent (1989–2004) distributions of Bull Kelp (Nereocystis sp.) beds were preferentially located along the boulder and bedrock substrates of Freshwater Bay. Although kelp has also been mapped in areas dominated by gravel and sand substrate, it typically has smaller canopy areas and lower temporal persistence in these regions.

Dam removal and subsequent restoration of salmon to the Elwha River is expected to cause a shift in nutrient dynamics within the watershed. To document how this influx of nutrients and energy may affect black bear (Ursus americanus) ecology, we used radio-telemetry to record movements of 11 male and two female black bears in the Elwha Valley from 2002–06. Our objective was to collect baseline data on bear movements prior to dam removal. We calculated annual home ranges, described seasonal timing of den entry and emergence, and described seasonal patterns of distribution and habitat use. Adaptive kernel home ranges were larger for males (mean = 151.1 km², SE = 21.4) than females (mean = 38.8 km², SE = 13.0). Males ranged widely and frequently left the watershed during late summer. Further, they exhibited predictable and synchronous patterns of elevation change throughout each year. Bears entered their winter dens between 8 October and 15 December and emerged from dens between 10 March and 9 May. Male bears used low-elevation conifer and hardwood forests along the Elwha floodplain during spring, mid- to high-elevation forests and meadows during early summer, high-elevation forests, meadows and shrubs during late summer, and mid-elevation forests, shrubs and meadows during fall. Data acquired during this study provide important baseline information for comparison after dam removal, when bears may alter their late summer and fall movement and denning patterns to take advantage of energy-rich spawning salmon.

The impending removal of two dams on the Elwha River in Washington State offers a unique opportunity to study ecosystem restoration at a watershed scale. We examine how periphyton and benthic invertebrate assemblages vary across regulated and unregulated sections of the Elwha River and across different habitat types, and establish baseline data for tracking future changes following dam removal. We collected multiple years of data on physical habitat, water chemistry, periphyton, and benthic invertebrates from 52 sites on the Elwha River and a reference section on the Quinault River, a neighboring basin. We found that substrate in regulated river sections was coarser and less heterogeneous in size than in unregulated sections, and summer water temperature and specific conductivity higher. Periphyton biomass was also consistently higher in regulated than unregulated sections. Benthic invertebrate assemblage structure at sites above both dams was distinct from sites between and below the dams, due in large part to dominance of mayfly taxa compared to higher relative abundance of midges and non-insect taxa at downstream sites. Following dam removal, we anticipate that both periphyton and benthic invertebrate abundance and diversity will temporarily decrease between and below dams as a result of sediment released from behind the reservoirs. Over the long-term, increased floodplain heterogeneity and recolonization by anadromous fish will alter benthic invertebrate and periphyton assemblages via increases in niche diversity and inputs of marine-derived nutrients. The extended timeline predicted for Elwha River recovery and the complexities of forecasting ecological response highlights the need for more long-term assessments of dam removal and river restoration practices.

Hydrochory, the dispersal of seeds by water, is important for maintaining the diversity and genetic continuity of riparian plant communities. Dams may reduce levels of hydrochory to downstream reaches by trapping seeds within their impoundments. On Washington's Olympic Peninsula, we studied whether hydrochory in the Elwha River was affected by the Glines Canyon Dam. We also explored whether Lake Mills, the dam's impoundment, holds a hidden seed bank of trapped hydrochorous seeds, which may aid in revegetation after the dam is removed. Hydrochory levels were sampled during three time periods in July and August, 2005 using floating and submerged drift nets above and below Glines Canyon Dam. The Lake Mills seed bank was sampled along transects across Lake Mills. For all drift net samples there was a 90% reduction in seed abundance and 84% reduction in species richness below Glines Canyon Dam. The decline in seed abundance was seen at each of the three sampling times. Similar numbers of seeds were found in both floating and submerged nets, suggesting that buoyancy is not required for hydrochory in this system. Relatively few seeds germinated from the Lake Mills seed bank. There was no relationship between seed density and distance from the Lake Mills delta; however seed density declined with increasing water depth. Our results suggest that Glines Canyon Dam has reduced the rate of hydrochory in the Elwha River, which may cause fragmentation of the riparian flora and reduced diversity of riparian species below the dam.

Ephemeral dams caused by landslides have been observed around the world, yet little is known about the effects of their failure on landforms and vegetation. In 1967, a landslide-dam-break flood in a pristine reach of the Elwha River valley filled the former channel and diverted the river. The reach is a reference site for restoration following the planned removal of dams on the river. We identified five surfaces on the 25 ha debris fan deposited by the flood. Based on tree ages and historic air photos, three of the surfaces formed in 1967, while two formed later. The surfaces varied in substrate (silt and sand, to boulders), and height above the river channel. Tree mortality resulted from tree removal and burial by sediment, the latter leaving snags and some surviving trees. Tree species composition was generally consistent within each surface. Dominant species included red alder (Alnus rubra) and Sitka willow (Salix sitchensis), alone or in combination, a combination of Douglas-fir (Pseudotsuga menziesii) and black cottonwood (Populus balsamifera ssp. trichocarpa), or a combination of alder and cottonwood. There were significant differences between surfaces in stem density, basal area, and rate of basal area growth. The large degree of heterogeneity in forest structure, composition, and productivity within a relatively small floodplain feature is in part due to spatial variability in the intensity of a single disturbance event, and in part due to the occurrence of subsequent, smaller events. To recreate natural diversity of riparian forests may require mimicking the variety of physical and biotic habitats that a single, complex disturbance event may create.

The Elwha dam removal project presents an ideal opportunity to study how historic reduction and subsequent restoration of sediment supply alter river-floodplain dynamics in a large, forested river floodplain. We used remote sensing and onsite data collection to establish a historical record of floodplain dynamics and a baseline of current conditions. Analysis was based on four river reaches, three from the Elwha River and the fourth from the East Fork of the Quinault River. We found that the percentage of floodplain surfaces between 25 and 75 years old decreased and the percentage of surfaces >75 years increased in reaches below the Elwha dams. We also found that particle size decreased as downstream distance from dams increased. This trend was evident in both mainstem and side channels. Previous studies have found that removal of the two Elwha dams will initially release fine sediment stored in the reservoirs, then in subsequent decades gravel bed load supply will increase and gradually return to natural levels, aggrading river beds up to 1 m in some areas. We predict the release of fine sediments will initially create bi-modal grain size distributions in reaches downstream of the dams, and eventual recovery of natural sediment supply will significantly increase lateral channel migration and erosion of floodplain surfaces, gradually shifting floodplain age distributions towards younger age classes.

In the early 1900s two hydroelectric dams were built along the Elwha River in northwestern Washington State. In order to restore the Elwha River ecosystem and native anadromous fish runs, the dams are scheduled to be removed. During and after removal, accumulated reservoir sediments are expected to erode downstream. The exposed sediments remaining after the dam removals and initial erosion will be prone to continuing secondary erosion and should be stabilized as quickly as possible. Experiments were performed on both fine and coarse sediment from underneath Lake Mills (formed by the Glines Canyon Dam) to determine strategies to stabilize the sediments under moderately high rainfall. Two slopes (5° and 15°) and two rainfall intensities (high and low) were examined along with mulch, plants, or polyacrylamide (PAM) stabilization treatments. The Revised Universal Soil Loss Equation (RUSLE) was used in comparison with experimental results to refine predictions. In both the experiments and as modeled with RUSLE, the coarse sediment was much less erosive than the fine sediment. Comparing the controls, the experiments had a similar erosion rate to the RUSLE model. For fine sediment, the mulch treatment was much more successful in preventing erosion in the experiments whereas the plant treatment was more successful as modeled with RUSLE at 5° slopes, but not 15° slopes. Mulch reduced erosion up to 99%, PAM up to 87% and plants by 33% in the experiments. A combination of stabilization treatments may be the most effective method of erosion reduction.