Dam removal: the Marmot Dam on the Sandy River in Oregon was demolished in 2007 using dynamite
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Keywords dam removal, engineering
SDG Sustainable Development Goals SDG11 Sustainable cities and communities
Authors DilchandNauth
Published 2021
License CC-BY-SA-4.0
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Dams are engineered to be installed in locations that would benefit the surrounding population on a long-term basis with minimal adverse environmental impacts. In modern times, dams are used for a variety of reasons including hydropower generation, inland navigation, flood control, recreation, water supply, and irrigation. However, dams may also be removed due to impedance of a river's natural flow of water, effects of fish population and other aquatic species, and damage to natural ecosystems such as wetlands that help maintain equilibrium. Four common dam removal methods used include the notch-release approach, the rapid release approach, the dig and dewater approach, and the retained sediment approach. Considering only the notch-release and rapid release dam removal methods, this paper will examine from a quantitative and qualitative perspective, the immediate short-term impacts and long-term effects of the implementation of these two dam removal techniques. The notch-release approach used for the removal of the Elwha Dam and Glines Canyon Dam in the Elwha River Restoration Project (ERRP) and the rapid release approach used for the removal of the Condit Dam in the Condit Hydroelectric Project (CHP), are used as illustrations of the techniques practiced and as a foundation of comparison. A risk assessment analysis and simplified cost-benefit analysis, based on the Proposed Action in the ERRP and Surrender Alternative in the CHP, focused on comparable sustainability variables for each dam removal project including water quality, fish population, wildlife impact, vegetation, and wetlands. These analyses, as well as an author opinionated ranking table and the actual outcomes of the projects, have supported the notion that notch-release approach is a more favorable method in terms of sustainability, relative to its immediate and long-term effects on the comparable sustainable variables, then the rapid-release dam removal method.

Methods[edit | edit source]

Both qualitative and quantitative methods are used as a basis of comparison between the notch and release approach used to remove the Glines Canyon Dam and rapid release approach used to remove the Condit Dam. Qualitative methods include extensive literature review of academic papers and documentations regarding each method. Quantitative methods include a cost-benefit analysis based on estimated costs of each technique and a risk assessment relative to the effects on the environment and public after dam removal.

Elwha River ecosystem restoration[edit | edit source]

The Elwha and Glines Canyon Dams were located on the Elwha River, in Olympic National Park, Clallam County, Washington, and became a part of the Elwha River Ecosystem Restoration Project. The purpose of this project was to remove two dams that severely affected the habitat of the river and its valley. The purpose and need for the removal of the dams included (NPS, n.d.):

  • Affected migration of native anadromous fish throughout the Elwha River and tributaries
  • Trapped sediments and other particles needed for the development and maintaining of the anadromous fish habitat and other ecosystems
  • Limited nutrients needed as a food source of many aquatic and terrestrial species
  • Increased water temperature resulting in habitat change for different species
  • Inundated riverine and terrestrial habitats, and lands of cultural and religious significance
  • Conflicted with Olympic National Park policy to restore fisheries and aquatic habitats
  • Inconsistent with federal responsibility toward different tribes in the area
  • Resulted in beach erosion in different locations of the park

Removal of these dams would assist in achieving the objects of the U.S. Department of Interior (DOI), which included (NPS, n.d.):

  • Fully restoring all the routes of native anadromous fish in the river
  • Restore the river ecosystem with respect to time

To achieve the goals of the project, four main alternatives were proposed:

Proposed Solutions Brief Descriptions
No Action Alternative No measures would have been taken to restore the river ecosystem and runs. This solution would be a basis for comparison to the environmental impacts of the other proposed alternatives.
Dam Retention Alternative In an attempt to achieve the fullest possible restoration of the river, alternate routes and passages would be adapted to the dams such as a fish ladder on the Elwha Dam, modified spillways and screens, a bypass pipe and vertical screen facility, an open channel flume, and a concrete pool and weir structure. This solution also included enhancing roughly 900 acres of land outside the park for wildlife benefits.
Proposed Action The Glines Canyon Dam would be completely decommissioned, the reservoir would be drained, and necessary structures would be removed for the safe travel of aquatic species. Certain features of the Elwha Dam would be removed relative to the safe travel of aquatic species.

From these proposed alternatives and the Final Environmental Impact Statement (FEIS), it was decided that the proposed action by the DOI to decommission the Elwha and Glines Canyon Dams and remove all necessary structures to achieve its objectives, would be the best solution to implement (NPS, n.d.). Prior to the removal of the Elwha and Glines Canyon Dams, two water treatment facilities were built to protect municipal and industrial water supplies, specifically against sediments and other particles that could affect the quality of the water (NPS, 2019).

Elwha Dam removal[edit | edit source]

The following steps were taken to deconstruct the Elwha Dam (NPS, 2019):

  1. Using the existing water intakes and spillways built with the dam, the water level in the reservoir was lowered by approximately 15 feet. A diversion channel was dug to allow the lake to drain to a workable level.
  2. Cofferdams, which are temporary structures that act as dams, were installed which assisted in directing the outflow of the reservoir to the diversion channel. By doing this, the water immediately behind the dam was accessible and pumped out. Fill material behind the dam was then removed after the remaining water behind the dam was pumped out.
  3. The dam was removed, all remaining structures were demolished, and the diversion channel was refilled. At this point, efforts were done to rejuvenate and restore the area to resemble conditions before the dam was installed.

Glines Canyon Dam Removal[edit | edit source]

The following steps were taken to deconstruct the Glines Canyon Dam (NPS, 2019):

  1. Using the existing spillways, the water level in the reservoir was lowered to the bottom of the spillway gates. Hydraulic hammers mounted on barges were used to remove 17 feet of the dam, to align with the waterline.
  2. The remaining 173 feet were removed using the notch release removal process. This technique involved slowly notching down the sides of the dam, which created temporary spillways that helped drain the reservoir further. Doing this allowed the water to gradually lower at a controllable rate.
  3. In between notching, the structures associated with the dam were deconstructed which allowed sediments loads downstream to decrease.
  4. The notches varied in size depending on the flows necessary to maintain or lower the water level in the reservoir. Each new notch allowed the additional layers of the dam to be removed. Notching and releasing of water and sediments continued until the sediments in the upstream delta were resting against the walls of the dam.
  5. Once this had occurred to an acceptable level, the remaining portions of the dam were removed. Efforts were done to restore the river channel to pre-dam conditions.

Condit Hydroelectric Project[edit | edit source]

The Condit Dam was located on the White Salmon River, in Klickitat and Skamania Counties, Washington, and became part of the CHP. The purpose of this project was to provide electricity to local industrials. The discontinuation of the project was ultimately considered since the dam adversely affected several fish species in the rivers and surrounding ecosystems. The purpose and need for the removal of the dam included (Oey, 2015; Wallace, 2014; Wellner, 2007):

  • Affected populations and migration of different fish species in the White Salmon River
  • Trapped sediments behind the dams that are necessary for the natural maintenance of ecosystems in the river
  • Limited the number of nutrients available in the river
  • Significantly changed environmental conditions for aquatic and terrestrial habitats

Modification of the dam would assist in achieving the objects of PacifiCorp, an electric power company that provides utilities to territories throughout Oregon, and portions of California and Washington, which included (Wellner, 2007):

  • Enabling the White Salmon River and watershed to return to natural conditions of a free-flowing river
  • Restore connectivity to fish habitats and increase fish production potential
  • Restore natural ecosystems and sediment movement processes in the river

To achieve the goals of the project, the following alternatives were proposed:

Proposed Solutions Brief Descriptions
No Action Alternative No measures would have been taken to help or restore the ecosystem and aquatic species of the river, resulting in continuous operation of the CHP with no changes in the mitigation or enhancements to the river system.
Proposed Action

PacifiCorp's Proposal

The modification of the CHP, which would enable the river and watershed to gradually return to the conditions of a free-flowing river.
Proposed Action Alternative This alternative was suggested by the Federal Energy Regulatory Commission (FERC) staff to modify the original proposal by PacifiCorp to include fish passage facilities and other benefits that would help fish populations rejuvenate and be able to survive in the river.
FEIS Dam Removal Alternative This alternative would involve the FERC staff and retire the CHP completely. It also involved the removal of the dam entirely.
Partial Dam Removal Alternative In an attempt to conserve some of the benefits of having the Condit Dam, this FERC staff solution proposed removing part of the dam with a new upstream diversion that would assist in fish migration and population, as well as restoration efforts.
Surrender Alternative This alternative upheld the application that was filed by PacifiCorp to surrender their existing license to operate the dam.

From these proposed alternatives and the Final Environmental Impact Statement (FEIS), the demolition of the Condit Dam began in October 2011 after the FERC accepted PacifiCorp's application to surrender its license to operate the dam in 2010 (Wallace, 2014; Wellner 2007).

Condit Dam removal[edit | edit source]

The following steps were taken to deconstruct the Condit Dam (PacifiCorp, 2021):

  1. Before dam removal began, the FERC and PacifiCorp suggested two plans of decommissioning regarding sediment removal behind the dam. FERC suggested to dredge or bypass the sediment while the PacifiCorp alternative was to quickly flush the sediments out in an attempt to minimize the impacts of the sediment plume on aquatic life downstream of the dam.
  2. It was ultimately decided that a rapid-release dam removal approach would be used for the deconstruction of the dam, in favor of PacifiCorp's decommission plan. A large 30-meter (m) tunnel measuring (12 ft x 18 ft x 100 ft) was dug into the base of the dam. This allowed the base of the dam to be connected to the bottom of the reservoir.
  3. The final 15 ft or 4.6 m of the tunnel was drilled and filled with explosives. Any sediments would be removed using a dredge.
  4. The entire body of water behind the dam was drained in approximately 30 minutes rather than the estimated six hours.
  5. The remaining sections of the dam were cut into blocks and removed for disposal or recycled.

Analyses and results[edit | edit source]

The following analyses and results are based upon the FEIS of the ERRP and the Final State Environmental Policy Act (SEPA) Final Supplemental Environmental Impact Statement (FSEIS), respectively.

Elwha Restoration Project Propose Action Assessment[edit | edit source]

Table 1. Predicted and likely impacts of the implemented proposed action. Green asterisks (*) indicates an impact that is related to the notch-release approach.
Elwha & Glines Canyon Dams
Category Variable Impact
Sediments Transport Impact to water quality and aquatic organisms*
Restoration and Deposition Erosion will continue to occur but at a reduced rate, some lost beach areas will be restored. Controlled rate of sediment release*
Water Quality Temperature Normal temperatures will sustain in the river*
Fisheries & Fish Population Fishery Restoration Good to the excellent recovery of all fisheries. Poor to fair recovery of the sockeye fishery
Population Impact to aquatic species. Reduced number of trout in the river*
Wildlife & Vegetation Terrestrial Wildlife & Habitat Restoration The habitat will fully recover allowing it to be more fully utilized by wildlife and prey will be fully restored
Recovery of Species Prey will return and be more readily available and the habitat will fully recover
Vegetated Areas Approximately 715 acres of the vegetated area could be recovered
Wetland Restoration Approximately 43 acres could be lost near the reservoir, 122 acres of wet channels can be restored, and possible 48 new acres could develop

Condit Hydroelectric Project Surrender Alternative Assessment[edit | edit source]

Table 2. Predicted and likely impacts of the surrender alternative and dam removal action. Orange asterisks (*) indicates an impact that is related to the rapid-release approach.
Condit Dam
Category Variable Impact
Sediments Transport Impact to water quality and aquatic organisms*
Deposition Much of the sediment would be deposited on the tribal in-lieu site*
Water Quality pH Concrete particles can get into the river possibly affecting pH*
Fisheries & Fish Population Population Recovery of several endangered and other fish populations
Wildlife & Vegetation Aquatic organisms Concrete particles, blasting, and spilled fuels and chemicals can potentially kill wildlife*
Death Most aquatic species will die due to transport of mass sediments*
Fish migration Temporary dams will block upstream migration of anadromous fish
Wetlands Roughly 2.8 acres of wetlands will be loss. Some wetlands will be restored in place
Terrestrial Habitats Natural habitats will be lost for access roads and staging areas for dam removal
Vegetation Loss of vegetation due to and flooding*

Cost-Benefit Analysis[edit | edit source]

Table 3. Simplified cost-benefit analysis which highlights the cost and time of the removal of each of the dams, as well as the main benefits which were a likelier outcome of these projects.
Elwha & Glines Canyon Dams
Cost-Related Factors Main Benefits
Cost to remove both dams: $40 - $60 million (1) More than 5 miles of stream habitat and 70 miles of useable river has been restored

(2) Temperatures downstream has reduced allowing for natural adaptation of aquatic species in the river (3) Recovery of nearly all fish species in the river (4) Wetlands, marshes, and other vegetated areas expected to recover overtime

Time of removal: 4 years
Condit Dam
Cost-Related Factors Main Benefits
Cost to remove dam: $32 - $37 million (1) Approximately 18 miles of previously inaccessible habitat is expected to be available. Improved fish migration

(2) Recovery of native vegetation important to native tribe cultural and tradition is expected (3) Recovery of several fish species (4) Restoration of ecosystems overtime

Time of Removal: 1 year (draining the reservoir took less than 6 hours)

Classification table[edit | edit source]

Table 4. Overall classification of key variables relative to the Elwha and Glines Canyon Dam removal, and Condit Dam removal. The most damaging impacts are classified in red (adverse), moderate impacts are classified in yellow (neutral) and beneficial impacts are classified in green (beneficial). Cost-related factors are chosen based on the most preferred method. This table is strictly the opinion of the author and may not necessarily align with the opinions of the reader.
Project Impacts (Pre-Dam Removal)
Variable Elwha & Glines Canyon Dams Condit Dam Preferred Method Reason
Transport of Sediments Neutral Neutral Notch-Release Releases sediments and water at a controlled rated
Deposition of Sediments Beneficial Neutral Notch-Release
Water Quality Beneficial Adverse Notch-Release Less contamination into the river
Fisheries & Fish Population Neutral Adverse Notch-Release Less dramatic impact on fish population relative to sediment loads
Wildlife & Vegetation Beneficial Adverse Notch-Release Less effects on aquatic organisms, no dramatic loss of vegetation
Cost-Related Factors
Removal expenses Most Expensive Least Expensive Rapid-Release Cheaper in general
Time More Time Required Less Time Required Rapid-Release Less time

Actual Impacts and Outcomes[edit | edit source]

Table 5. The aftermath of the efforts of the ERRP and CHP projects relative to the removal of the dams (Burkhardt, 2020; Grabowski et al. 2017; Hill, 2020; NPS, 2019).
Variable Elwha & Glines Canyon Dams Condit Dam
Fish Population 1. More than 70 miles of spawning habitat for fish has been recovered.

2. Monitoring of salmon species has shown increase rates in give different Pacific salmon species. 3. Trout population has also increased. Pink and chum populations are still critically endangered.

1. Fish are recolonizing available and formerly inaccessible habitats. Natural processes have improved degraded habitats now used as spawning for fish.

2. Fish species including salmon and steelhead have now returned to upstream locations previously inaccessible. 3. The response of species such as the Pacific Lamprey and Bull Trout have is largely unknown or have yet to be determined.

Vegetation 1. A revegetation project was immediately implemented after the removal of these dams. Diverse species of native plants have been restored and have continued to prosper in the area. 1. Efforts have been done to rework and replant the former reservoir with thousands of trees. Native vegetation has been observed growing on previous submerged sediments.

2. Upland habitats which were affected by prolonged inundation have been slower to recover.

Sediment & Hydrology 1. Overall stabilization regarding sediment load, turbidity, and channel stabilization in flood plains have resulted.

2. Sediments have formed new beaches and wetlands, creating new habitats for numerous species.

1. Natural river processes are now capable of transporting large debris and sediments downstream.

2. Recreation of missing gravel bars in the lower river and a delta located the Columbia River confluence has occurred.

Wildlife 1. Numerous terrestrial and wetland species have been restored in the years following the removal of the dams 1. Efforts to rework sediments and restore native vegetation has shown notable improvement wildlife habitat.

Discussion[edit | edit source]

The risk assessments of the proposed actions taken in the removal of the Elwha and Glines Canyon Dams (Table 1) and the removal of the Condit Dam (Table 2), present the impacts due to the notch-release and rapid-release approach, respectively, on the comparable variables between the ERRP and CHP projects, regarding sustainability on a short- and long-term basis. Sediment transportation and deposition, water quality, fish population, and wildlife and vegetation were all impacted as a result of these approaches used to remove the dams. The key difference between the notch-release and rapid-release approaches were the impacts they had on aquatic organisms and fish population, as the more devastating impacts can be attributed to the rapid-release approach and removal of the Condit Dam.

The cost-benefit analysis (Table 3) used two key factors including the cost of dam removal and total time required relative to the removal of the dams. The rapid-release approach was a cheaper and less time-consuming method for removing the Condit Dam, and also resulted in sufficient benefits for the surrounding environment, including the primary objectives of the CHP project, restoring the connectivity to fish habitats and increase fish production potential and restoring natural ecosystems and sediment movement processes in the river.

Removal of the Elwha and Glines Canyon dams has resulted in more than five miles of stream habitat and 70 miles of useable river has been restored (NPS, n.d.). Temperatures have also reduced downstream allowing for the natural adaptation of aquatic species in the river. The restoration potential of nearly all fish population is expected to increase especially in the five Pacific salmon species which include the pink, chum, chinook, coho, and sockeye. Recovery of the pacific salmon and other anadromous fish is important in restoring fisheries and cultures of tribes who depend on the Elwha river (Wallace, L). The 108-year lifespan of the Elwha Dam and 94-year lifespan of the Glines Canyon Dam destroyed ecosystems including wetlands which were vital for aquatic plants and organisms who depends on it for survival. Removal of these dams has allowed for these critical ecosystems and other vegetated areas to rebuild overtime.

Removal of the Condit dam has resulted in different fish species being able to migrate to approximately 18 miles of previously inaccessible habitat. Supporting efforts by volunteers involved in the project have conducted restoration actions which include replanting 34 different species of plants and roughly 3 acres of native vegetation, important to native tribe cultural and tradition (Oey, 2015). These tribes have also regained access to recovering fish populations that are important to their culture. Vegetated area and wetlands lost to the dam and during explosion of the dam, have been revegetated in an effort to minimized long-term erosion of the surrounding area (Wellner, 2007). Removal of this dam has allowed for the restoration of ecosystems such as wetlands.

The sustainability of the Elwha River and White Salmon River ecosystems are directly dependent upon the relationship between key sustainability variables including water quality, fish population, wildlife impact, vegetation, and wetlands, listed in Table 4. Water quality is important in providing and maintaining diverse plants and aquatic organisms. Excess sediments in riverbeds can potentially disrupt the natural food changing by damaging habitats that fish depend on for food, resulting in reduced fish populations. Decline in fish populations directly impacts terrestrial animals including humans that may rely on fishing as a source of food or income. Riparian and aquatic vegetation play a key role in river hydromorphology. Plant biomass directly affect sediment transport in the river by changing flow resistance causing sediment deposition. Generally, plants can interact with the structure of the river by changing its topography and bed sediment composition (REFORM, 2018). Wetlands are important ecosystems as they act as natural absorption barriers, capturing and releasing surface water at a controlled rate. Wetland vegetation can potentially slow the speed of flood waters, allowing for gentler distribution over floodplains, resulting in reduced flood heights and erosion (USDEP, 2018). Having a natural sponge as a flood protection measure is valuable as it assists in preventing damages to the surrounding environment and developments further downstream such as crops or made-man structures.

Conclusion[edit | edit source]

Using variables that could easily be compared, the variables of the risk assessment supported the notion that the notch-release approach would have less adverse impacts on the environment. The most undesirable impact that the rapid-release approach had on the White Salmon River was the mass amount of sediment loads released during the removal of the Condit dam, which severely impacted aquatic species and more than likely caused the death of many fish. On the contrary, the most desirable outcomes of the Condit Dam was the expenses and time required for decommission. The most undesirable impact that the notch-release approach had on the Elwha River were the expenses and time required for decommission of the Elwha and Glines Canyon Dams. The most desirable impacts of utilizing the notch-release approach was the control the workers had relative to the rate at which the water and sediments could be released from behind the dam. Moreover, this likely minimized the impact on aquatic species and fish.

The immediate aftermath of the implementation of the notch release approach and the rapid release approach to the removal of the Elwha and Glines Canyon Dams and the Condit Dam, respectively, is evident through the impacts on these sustainability. Through the notch release approach, the sediments behind the Elwha and Glines Canyon Dams were released at a fix rate that could be controlled, therefore, minimizing the impacts of the river system, aquatic species, and other ecosystems already established. Though this was a more time-consuming method, it ultimately reduced the impacts on water quality, fish population, the wildlife, and vegetation. Comparison of the notch release approach and rapid release approach through the ERRP and CHP has shown that the notch release approach had less harmful impacts on the river.

The rapid release approach will definitively result in more consequences on the environment and public resources. While the river and its environment has been able to recover from the removal of these dams, the notch release approach is a more favorable dam removal method in terms of sustainability, relative to its immediate and long-term effects on the comparable sustainable variables than the rapid release dam removal method.

References[edit | edit source]

1. Bonnet, M., Witt, A., Stewart, K., Hadjerioua, B., Mobley, M. (2015). The Economic Benefits of Multipurpose Reservoirs in the United States-Federal Hydropower Fleet. Report prepared for U.S. Department of Energy Wind and Water Program. Report prepared by Oak Ridge National Laboratory.

2. Burkhardt, J. (2020). Rewilding the White Salmon River: The view from nine years after the removal of Condit Dam. The International Journal of Salmon and Steelhead Conservation, (97). The Osprey.

3. Grabowski, Z. J., Denton, A., Rozance, M. A., Matsler, M., Kidd, S. (2017). Removing Dams, Constructing Science: Coproduction of Undammed Riverscapes by Politics, Finance, Environment, Society and Technology. Water Alternatives 10(3): 769-795

4. Hill, M. (2020). How a Dying River Came Roaring Back to Life. The Saturday Evening Post. https://www.saturdayeveningpost.com/2020/04/how-a-dying-river-came-roaring-back-to-life/

5. National Park Service. (2019). Dam Removal: Mechanics of Dam Removal. U.S. Department of the Interior. https://www.nps.gov/olym/learn/nature/dam-removal.htm

6. National Park Service. (2015). Elwha River Restoration Frequently Asked Questions. U.S. Department of the Interior. https://www.nps.gov/olym/learn/nature/elwha-faq.htm

7. National Park Service (NPS). (n.d.). Final Environmental Impact Statement Elwha River Ecosystem Restoration. U.S. Department of the Interior. https://www.nps.gov/olym/learn/nature/upload/elwhafinaleis1.pdf

8. National Park Service. (2019). Restoration and Current Research. U.S. Department of Interior. https://www.nps.gov/olym/learn/nature/restoration-and-current-research.htm

9. Oey, M. (2015). Effective Mitigation of Sedimentation on Riparian Riverbeds and Salmonid Populations After Dam Removal. The University of San Francisco. https://repository.usfca.edu/cgi/viewcontent.cgi?article=1137&context=capstone

10. PacifiCorp. (2021). Energy: Condit. https://www.pacificorp.com/energy/hydro/condit.html

11. REFORM (REstoring rivers FOR effective catchment Management). (2018). Role of Vegetation.

12. Robbins, J. (2017). Why the World's Rivers Are Losing Sediment and Why It Matters. YaleEnvironment360. Yale University. https://e360.yale.edu/features/why-the-worlds-rivers-are-losing-sediment-and-why-it-matters

13. Wallace, L. (2014). CONDIT DAM REMOVAL: A DECISION-MAKING COMPARISON WITH REMOVAL OF ELWHA RIVER DAMS. Kansas State University. Department of Geography College of Arts and Science. Approved by Major Professor Lisa M.B. Harrington.

14. Wellner, R., J. (2007). Condit Dam Removal Final SEPA Supplemental Environmental Impact Statement (FSEIS). Ecology Publication #07-06-012. Department of Ecology. State of Washington.