Ecological Responses to Dam Removal in the Elwha River
By Matthew Thompson
Keywords: Historical Restoration, Dam, River Delta, Ecosystem Dynamics
Summary
The Elwha River in Washington State, historically a thriving salmon river, suffered significant ecological damage due to the construction of two large-scale dams in 1913. Decades of decreased salmon populations and concerns over dam structural integrity prompted their removal, mandated by congressional action in 1992 (Park, 2011). The removal of the dams, the Glines Canyon Dam and the Elwha Dam, led to significant changes in sediment flow, physical geography, and ecological dynamics within the river basin (Shaffer et al, 2017).
Following the dam removal, there was a rapid influx of sediment downstream, altering the river's physical characteristics. The estuary transitioned from a tidal-dominated system to a freshwater river system, impacting water quality and temperature fluctuations (Foley et al, 2015). Anadromous fish species, including several types of salmon, experienced increased habitat range and population growth post-dam removal (Duda et al, 2021). Additionally, native vegetation levels surged, contributing to ecosystem restoration (Brown et al, 2020). The success of the Elwha River restoration project highlights the potential for large-scale ecological recovery following dam removal. While full restoration to historical conditions may not be achievable, the project serves as a model for ecosystem rehabilitation efforts. Despite ongoing environmental challenges, such as declining fish populations and an unpredictable climate, the restoration of the Elwha River offers hope and inspiration for future conservation projects. It sets a precedent for the removal of aging dams elsewhere, emphasizing the importance of prioritizing ecosystem health and resilience. |
Credit: Ringman, S. (2016). The Elwha. The Seattle Times. https://projects.seattletimes.com/2016/elwha/
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Ecological Genealogy
The Elwha river is a 72-kilometer-long river located in the North West of the State of Washington, United States, with the mouth of the river flushing out into the Strait of Juan de Fuca (Parks, 2011). Historically it was one of the most productive salmon fisheries in the state reaching upwards of 300,000 fish a year (Parks, 2011). However, in 1913, the local population driven by the idea of creating a reliable and consistent source of electricity saw it fit to construct two large scale dams (Mauer, 2020). The hope was that with this power they would be able to attract paper, pulp and sawmills to the area rather than shipping their wood elsewhere. Not taken into account however was the local Indigenous tribe, the S’Kallam, opinions, nor the health of the ecosystem (Mauer, 2020). The dams led to the plummeting of salmon stocks in the rivers and by 2005 less than one percent of fish in pre dam time had returned to the river (Parks, 2011). This, along with concerns about structural integrity of the dams led to public pressure to remove the dams. In 1992, congressional action mandated the removal of both dams and to complete a restoration of the river (NOAA, n.d).
On the river there were two dams, the Glines Canyon Dam (64m high; located 21 kms from shore) and the Elwha Dam (33m high; located 8 kms from shore), both classified as large scale as they exceed 15m high (Duda et al, 2008). The reservoirs created by the dams differed in size and storage capacity, with Lake Aldwell, a product of the Elwha Dam, measuring 1.08 km^2 and storing 9.99 x 106 m^3 of water and Lake Mills, the reservoir created by the Glines Canyon Dam measured 1.68 km^2 and stored 5.12 x 107 m^3 of water (Duda et al, 2008). Combined, these reservoirs covered over 9 km of former riverine habitat, trapped sediments and woody debris which were transported down from the upper watershed, restricted transport of organic material and dissolved nutrients, and increased downstream water temperatures (Duda et al, 2008). It is estimated that prior to the removal of the two dams there was over 20 million cubic meters of impounded mud, sand, and gravel (Gelfenbaum et el, 2015). The trapping of riverbed sediments, especially in Lake Mills, shifted the river composition below the dams towards cobbles and small boulders (Duda et al, 2021). As well it created an unnaturally stable and less diverse riparian zone, reduced the diversity and size of the estuary by about 0.9 km^2, and changed the near shore beach and subtidal area (Dude et al, 2008). Not only did the dams physically restrict the passage of salmon upstream, but all these changes, especially in regards to the river compositions, limited their ability to spawn in the few sites along the river that were available to them (Shaffer et el, 2017). The majority of 72km river and subsequent 833km^2 watershed is mainly in the Olympic National Park, providing a perfect opportunity to study a removal without having to worry about other land use influences such as agriculture interfering with the restoration. (NOAA, n.d). Prior to the removal researchers, academics, non-profit organizations, the federal and state government, and the Lower Elwha Klallam Tribe all completed baseline assessments in the watershed, along with reference locations that established a before and after experimental design and a baseline to compare research with. (Duda et al, 2008). The Elwha River is unique in that it was the first large scale dam (<15m in height) removal in the United States. As such, the dam was closely study because scientists wanted to discover the impacts on freshwater ecosystems, in terms of the biotic, and abiotic factors, and if the system can be restored to the historical baselines that were recorded before construction (Foley et al, 2015). |
Credit: National Park Service. (2019) Restoration and Current Research. https://www.nps.gov/olym/learn/nature/restoration-and-current-research.htm
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Present Tense
Measurements within the basin of the river show that within two years of complete removal, in 2015, 2.5 million cubic meters of this sediment had traveled down the river to the estuary and basin of the river (NOAA, n.d). This rate of sediment deposition was roughly 100 times the normal amount measured prior to removal, signalling the massive changes that were associated with the removal (Gelfenbaum et al, 2015). These changes shifted physical aspects of the basin quite quickly. The reason why this is important to study is that the basin, or nearshore, can provide a wealth of ecosystem services, such as flood protection, water quality improvement, and species habitat (Shaffer et al, 2017). The size of the beach increased by an average of 40m, with a maximum of 95m in one spot, the active delta extended over two hundred meters offshore, and the front of the delta grew vertically by as much as 7.5m (Gelfenbaum et al, 2015). In addition, the amount of sediment, and the size of it affected change in the biological communities. By 2013, two years after the start removal had begun, there was not a singular channel exiting through the channel, but several bifurcated channels separated by sand bars, suggesting a more classic river morphology, along with the sediment in the river mouth became coarser, composed predominately of gravel and sand, and grew finer as the deposited thinned (Gelfenbaum et al, 2015).
During, and after, the dam removal there was also a large shift away from a tidal dominant system to a river system. Prior to the dam removal, factors such as salinity and temporary fluctuated multiple times a day as seawater was pushed in and out of the estuary (Foley et al, 2015). However, following the removal, the influence of the tide severely diminished, and there was much more limited fluctuation (Foley et al, 2015). Further, the estuary changed from a brackish and tidally influenced system to a perpetually freshwater system. The new configuration of the estuary also changed the seasonal pattern of tides being the driver of change, to river discharge and channel location as the dominant force and driver of water quality (Foley et al, 2015). The temperatures recorded on the river also reflect this shift from a tidal system to a river system drive. Prior to the removal the estuary exhibited daily temperature patterns that coincided with tidal fluctuations. However, beginning in the winter of 2013, a year after the deconstruction of the dam had begun, the daily temperature fluctuations were limited to a single cycle, and significant temperature jumps were correlated only with large river discharge events (Foley et al, 2015). Before the removal of the dam, anadromous fish (i.e spawning fish) were limited to a 7.9 km section of river downstream of the first dam (Duda et al, 2021). After dam removal there was almost an instantaneous passage of the following species into the upper reaches of the river: Oncorhynchus tshawytscha (Chinook), Oncorhynchus kisutch (Coho), Oncorhynchus nerka (Sockeye), Oncorhynchus gorbuscha (Pink), Oncorhynchus keta (Chum), Oncorhynchus mykiss (Steelhead), Entosphenus tridentatus (Pacific Lamprey) and Salvelinus confluentus (Bull Trout) (Duda et al, 2021). All these runs except for Chum Salmon were also observed in the upper Elwha sections within five years (Duda et al, 2021). Salmon and trout species had their possible habitat range increase by 60km (Duda et al, 2021). Undoubtably, the unblocking of the dams provided the opportunity for salmonid species to flourish again. Further, following the removal of the dam native vegetation levels increased. In measurements done per 100m^2 plots, from 2010 to 2017 native species richness increased by 31%, with the largest increase in the floodplains, followed by terraces and then bars (Brown et al, 2020). |
Credit: Gussman, J. (2018). Elwha Restoration. Olympic Park Advocates. https://olympicparkadvocates.org/elwha-restoration/
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Future trajectory
The removal of the Elwha dam has sparked the conversation around dam removal, and what happens to ecosystems after their removal. The reason for this is because in the United States there are over 2,000 of these large-scale dams that are nearing the end of their life span. Many of the dam’s owners, whether that be private power corporations, or the government have to make decisions about either restoring them or knocking them down. If the decision to knock a dam down is reached, the historical conditions to which the project managers and local people want the river to be restored to might not be entirely possible, yet that should not be the benchmark for success. As large scale pressures from the changing environment, along with declining fish numbers all over the Pacific Northwest, and more industrial activity in the area such as shipping, logging and resource extraction make the possibility of total restoration to historical conditions look unattainable.
However, the Elwha River’s unique situation within the Olympic National Park ensures its protection from industrial pressures, along with an ecosystem that can support and provide to the river and vice versa. The restoration of the nearshore, and subsequent rapid return of spawning fish species shows that restoration is possible. The Elwha River, which once was dammed and an ecological eyesore, is now becoming a beacon of hope for what is possible through major restoration projects. Hopefully this restoration proves to be enough to motivate governments and energy companies to remove other aging dams, or not build them to begin with. |
Credit: Ringman, S. (2010). Elwha River Ecology Bursts with New Life Following Dam Removals in Washington. Revitalization; The Journal of Urban, Rural, and Environmental Resilience. https://revitalization.org/article/elwha-river-ecology-bursts-with-new-life-following-dam-removals-in-washington/
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Summery
Brown, R. L., Thomas, C. C., Cubley, E. S., Clausen, A. J., & Shafroth, P. B. (2022). Does large dam removal restore downstream riparian vegetation diversity? Testing predictions on the Elwha River, Washington, USA. Ecological Applications, 32(6), e2591-n/a. https://doi.org/10.1002/eap.2591
Duda, J., Frelich, J., and Schreiner E. (2008). Baseline Studies in the Elwha River Ecosystem prior to Dam Removal: Introduction to the Special Issue. Northwest Science. https://doi.org/10.3955/0029-344X-82.S.I.1
Duda, J. J., Torgersen, C. E., Brenkman, S. J., Peters, R. J., Sutton, K. T., Connor, H. A., Kennedy, P., Corbett, S. C., Welty, E. Z., Geffre, A., Geffre, J., Crain, P., Shreffler, D., McMillan, J. R., McHenry, M., & Pess, G. R. (2021). Reconnecting the Elwha River: Spatial Patterns of Fish Response to Dam Removal. Frontiers in Ecology and Evolution, 9. https://doi.org/10.3389/fevo.2021.765488
Foley, M. M., Duda, J. J., Beirne, M. M., Paradis, R., Ritchie, A., & Warrick, J. A. (2015). Rapid water quality change in the Elwha River estuary complex during dam removal. Limnology and Oceanography, 60(5), 1719–1732. https://doi.org/10.1002/lno.10129
Gelfenbaum, G., Stevens, A. W., Miller, I., Warrick, J. A., Ogston, A. S., & Eidam, E. (2015). Large-scale dam removal on the Elwha River, Washington, USA: Coastal geomorphic change. Geomorphology (Amsterdam, Netherlands), 246, 649–668. https://doi.org/10.1016/j.geomorph.2015.01.002
National Oceanic and Atmospheric Admistion. (n.d). Dam Removals on the Elwha River. Science and Data. https://www.fisheries.noaa.gov/west-coast/science-data/dam-removals-elwha-river
Mauer, K. Whitney. (2020). Undamming: The Elwha River. Contexts (Berkeley, Calif.), 19(3), 34–39. https://doi.org/10.1177/1536504220950399
Parks, N. (2011). Washington’s Elwha River to run free. Frontiers in Ecology and the Environment, 9(6), 313–313. http://www.jstor.org/stable/23034426
Shaffer, J. A., Higgs, E., Walls, C., & Juanes, F. (2017). Large-scale Dam Removals and Nearshore Ecological Restoration: Lessons Learned from the Elwha Dam Removals. Ecological Restoration, 35(2), 87–101. https://doi.org/10.3368/er.35.2.87
Duda, J., Frelich, J., and Schreiner E. (2008). Baseline Studies in the Elwha River Ecosystem prior to Dam Removal: Introduction to the Special Issue. Northwest Science. https://doi.org/10.3955/0029-344X-82.S.I.1
Duda, J. J., Torgersen, C. E., Brenkman, S. J., Peters, R. J., Sutton, K. T., Connor, H. A., Kennedy, P., Corbett, S. C., Welty, E. Z., Geffre, A., Geffre, J., Crain, P., Shreffler, D., McMillan, J. R., McHenry, M., & Pess, G. R. (2021). Reconnecting the Elwha River: Spatial Patterns of Fish Response to Dam Removal. Frontiers in Ecology and Evolution, 9. https://doi.org/10.3389/fevo.2021.765488
Foley, M. M., Duda, J. J., Beirne, M. M., Paradis, R., Ritchie, A., & Warrick, J. A. (2015). Rapid water quality change in the Elwha River estuary complex during dam removal. Limnology and Oceanography, 60(5), 1719–1732. https://doi.org/10.1002/lno.10129
Gelfenbaum, G., Stevens, A. W., Miller, I., Warrick, J. A., Ogston, A. S., & Eidam, E. (2015). Large-scale dam removal on the Elwha River, Washington, USA: Coastal geomorphic change. Geomorphology (Amsterdam, Netherlands), 246, 649–668. https://doi.org/10.1016/j.geomorph.2015.01.002
National Oceanic and Atmospheric Admistion. (n.d). Dam Removals on the Elwha River. Science and Data. https://www.fisheries.noaa.gov/west-coast/science-data/dam-removals-elwha-river
Mauer, K. Whitney. (2020). Undamming: The Elwha River. Contexts (Berkeley, Calif.), 19(3), 34–39. https://doi.org/10.1177/1536504220950399
Parks, N. (2011). Washington’s Elwha River to run free. Frontiers in Ecology and the Environment, 9(6), 313–313. http://www.jstor.org/stable/23034426
Shaffer, J. A., Higgs, E., Walls, C., & Juanes, F. (2017). Large-scale Dam Removals and Nearshore Ecological Restoration: Lessons Learned from the Elwha Dam Removals. Ecological Restoration, 35(2), 87–101. https://doi.org/10.3368/er.35.2.87