It may seem counterintuitive to remove a dam that impounds water for an operating powerhouse, but for Duke Energy this decision avoided significant costs at its other hydro projects and eliminated lost generation resulting from the installation of bypass flow facilities.
By Ty Ziegler, Steve Johnson and Jeff Lineberger
The 225-kW Dillsboro Hydroelectric Project on the Tuckasegee River was constructed in 1913 to provide power to a community in southwestern North Carolina. As part of the Federal Energy Regulatory Commission (FERC) relicensing process, owner Duke Energy and two stakeholder teams recommended removal of Dillsboro Dam and Powerhouse and restoration of the site as mitigation to help Duke Energy meet relicensing requirements at six of its larger, more efficient hydroelectric projects in the area. This would allow the utility to preserve the power generation benefits at these six more efficient projects.
Today, a section of the Tuckasegee River is free-flowing for the first time in a century, and there is no evidence of the dam or powerhouse. The removal of Dillsboro Dam and Powerhouse provided mitigation for flows in bypassed river reaches at three peaking projects and delayed fish passage requirements at three run-of-river projects owned and operated by Duke Energy. Removal of Dillsboro Dam and Powerhouse also enhanced recreation opportunities (fishing and paddling) on the river.
|The Dillsboro Dam site, shown here two years after its removal, now offers natural conditions and enhanced recreational opportunities.|
Because of the carbon-free power benefits of hydroelectricity, the removal of an operating FERC-regulated hydropower facility is unusual compared to the many small, low-head, non-powered dams that have been removed across the U.S. In the case of the Dillsboro Dam removal, Duke Energy successfully adapted to challenging regulatory and political climates throughout the FERC consultation process. HDR, Duke Energy’s consultant, performed numerous energy assessments and environmental studies associated with the Dillsboro Dam removal and drafted the license surrender application.
The Dillsboro Project originally supplied power to local industries when no other electrical energy source was available in the area. C.J. Harris, a local industrialist, built the Dillsboro Project in 1913 to power his Blue Ridge Locust Pin Factory. Harris later formed the Dillsboro and Sylva Electric Company, which provided electricity to his business and a few commercial customers in the town of Sylva, North Carolina. Nantahala Power and Light Company (NP&L) purchased the Dillsboro Project in 1957. That year, NP&L increased the height of the dam by 2 feet (from 10 feet to 12 feet) and rehabilitated the power plant. FERC issued the initial operating license for the Dillsboro Project on July 17, 1980.
Duke Energy acquired NP&L in 1988 and assumed operational control of NP&L’s hydro stations in August 2000, just as the FERC relicensing process was getting under way. Duke Energy operated the Dillsboro Project in a run-of-river mode, maintaining the 15-acre headpond within 6 inches of full pond elevation. Project operations depended on available water flow in the Tuckasegee River, which is regulated by Duke Energy’s upstream 23.88-MW East Fork and 19.25-MW West Fork hydroelectric projects. But the electric energy provided by the Dillsboro Project had become a very small portion of the power needs of the region by 2000.
The original FERC license for the project expired on July 31, 2005. Duke Energy filed an application for license renewal on July 22, 2003, and about six months later filed two settlement agreements on behalf of Duke Energy and 26 other stakeholders on two stakeholder teams. The Tuckasegee and Nantahala Cooperative Stakeholder Team Settlement Agreements addressed FERC relicensing issues for six of Duke Energy’s other hydroelectric facilities in the Nantahala Area. Together, the two settlement agreements were intended to resolve bypass flow issues at the 42-MW Nantahala, East Fork and West Fork projects and fish passage issues at the 1.04-MW Franklin, 980-kW Bryson and 1.8-MW Mission projects. The settlement agreements were consistent and proposed a surrender of the Dillsboro Project license, including removal of Dillsboro Dam and Powerhouse.
Although many non-powered dams have been removed in the U.S. in recent years, at the time of the application for license surrender, the Dillsboro Project represented one of only a few FERC-regulated hydropower facilities to be removed. The removal faced challenges by local opposition and ultimately litigation, complex permitting requirements (several of which were required by resource agencies that supported the project) and Endangered Species Act compliance considerations.
In accordance with the settlement agreements, Duke Energy filed an application for license surrender for the Dillsboro Project on May 28, 2004. Between July 2004 and March 2005, federal and state regulatory agencies, local governments, non-governmental organizations, local businesses and private citizens filed interventions to the surrender application. Not all of these filings opposed dam removal, as parties had to file to remain a part of the FERC process. Those opposed to dam removal were mostly local groups wanting to retain the dam and pond, primarily for aesthetic reasons.
Because the Tuckasegee River in the vicinity of Dillsboro Dam is home to a federally endangered freshwater mussel called the Appalachian elktoe and has been designated as the mussel’s critical habitat, in August 2006 the U.S. Fish and Wildlife Service (FWS) issued a biological opinion on expected project-related impacts to the aquatic environment. The biological opinion authorized Duke Energy to relocate the Appalachian elktoe mussel population from downstream of Dillsboro Dam to suitable habitat upstream in preparation for removal of the dam.
FERC issued a surrender order on July 19, 2007, which was immediately challenged by the same local groups. FERC ultimately upheld the surrender order because the benefits resulting from dam removal (i.e., restored aquatic and riparian habitat and improved recreation opportunities) outweighed the aquatic habitat benefits of providing bypass flows at three of the six other hydroelectric projects. In turn, Duke Energy was able to retain significant generation capacity and avoid fish passage challenges at the other three (run-of-river) projects for at least the first 20 years of the new licenses.
The final surrender order was issued April 22, 2008, marking a major milestone. However, the removal of the Dillsboro Project involved a complex process of studies, negotiation, additional litigation, permitting and engineering challenges. Before the dam and powerhouse could be removed, Duke Energy and HDR addressed several environmental concerns and obtained local, state and federal permit authorizations to proceed with the removal.
One of the objectives of dam removal was to enhance the Appalachian elktoe population. However, the process and timing of the removal, in conjunction with pre-removal activities deemed necessary to protect this species during the removal process, significantly impacted permitting activities and the schedule. During the fall months of 2008 and 2009, 1,137 Appalachian elktoe mussels were tagged and relocated to a suitable area upstream.
To address concerns that a large release of sediment from the project might impact freshwater mussel beds, benthic macroinvertebrates and fish spawning areas, the Section 401 Water Quality Certification for the Dillsboro Dam removal also required removal of sediment accumulations (primarily clean sand) behind the dam. Sediment removal required a mining permit from the North Carolina Department of Environment and Natural Resources, which required clearing land alongside the project reservoir and installation of settling basins to provide a suitable dredging and dewatering area. Jackson County initially denied permits necessary for the sediment dewatering area but ultimately issued them in April 2009 after a successful court challenge by Duke Energy. Removing 58,000 cubic yards of sediment took about four months during the summer and fall of 2009.
The FERC surrender order required many actions, including preparation of the following:
– Demolition plan;
– Sediment management plan;
– Fish protection plan;
– Mussel relocation plan;
– Bat relocation plan (estimated 500 little brown bats in the powerhouse);
– Public safety plan;
– River bank restoration and re-vegetation plan;
– A temporary emergency action plan; and
– A quality control and inspection program.
The Duke Energy and HDR team planned the powerhouse and dam removal in three stages. Stage one included dismantling and demolishing the powerhouse superstructure and machinery, removing the tailrace training wall, and removing the headgates to the powerhouse to allow maximum flow through the remaining powerhouse substructure during dam removal.
The second stage centered on demolition of the 310-foot-long dam and involved drawing down the reservoir, creating a notch in the right abutment of the dam adjacent to the powerhouse and excavating/removing the dam in 3- to 4-foot vertical sections. To facilitate removal of the dam during high winter flow conditions, HDR designed a temporary concrete rubble and riprap pad to allow access for an excavator on the upstream side of the dam. Working from the end of the pad, a hoe-ram excavated the dam in horizontal lifts until the assumed original bed elevation was reached.
The third stage encompassed removal of the powerhouse substructure, disposal of concrete rubble and sediment, and bank restoration with native vegetation along the reservoir shoreline to mitigate erosion potential.
Throughout the powerhouse and dam removal activities, the team developed sound engineering practices to preserve the structural integrity of the adjacent roadway to avoid impacting municipal waste pipelines and communication cables running alongside the roadway. Also, the team planned and conducted the work in a manner that would not require road closures or impact local residents.
FERC also required a three-year post-removal monitoring study (through early 2013) to assess specific physical, chemical and biological changes in the project area to determine when the river system returned to background ambient conditions or stabilized. This included a comprehensive sediment monitoring study to evaluate upstream and downstream variability in scour and deposition patterns, basic water quality monitoring, fish and macroinvertebrate sampling, monitoring of the Appalachian elktoe mussel population (including returning some of the relocated mussels to their original location immediately downstream of the dam), and monitoring of bank stability along the shoreline of the former impoundment.
In addition, the FERC surrender order required Duke Energy to construct the C.J. Harris Recreation Area to provide a new boating access area (including parking, bathrooms and a boat ramp) adjacent to the former impoundment.
Many of the about 2,500 powered dams in the U.S. provide substantial electric generation and improve the reliability of transmission systems. However, some of these powered dams no longer meet their original purpose, and removing them may provide benefits that offset the costs of maintaining them. The decision to remove a dam is based on economic (e.g., energy production, capital costs, O&M costs) and environmental considerations, both positive and negative. For a FERC-licensed project, the application process for license surrender is the same as the license application process. However, at the time Dillsboro Dam and Powerhouse were being considered for removal, only a few FERC-regulated hydropower facilities had been removed. As a result, there were few projects to use as guideposts through the extensive FERC consultation process.
Perhaps the most innovative aspect of the Dillsboro Dam and Powerhouse removal project was the decision to remove the dam in the first place – and the science used as the basis for that decision. The Dillsboro Project generated only 912 MWh of electricity during an average year – enough to power 69 average-sized homes. The potential lost generation resulting from bypass flows at Duke Energy’s six other Nantahala Area hydroelectric plants was about 1,912 MWh per year per cubic foot per second (cfs) of bypass flow – enough to power 145 average-sized homes per cfs of bypass flow. From an energy perspective, maintaining the generating capability of the other hydroelectric plants and avoiding capital expenditures associated with the construction of bypass flow facilities greatly outweighed the loss of generating capability at the Dillsboro Project.
From a science perspective, restoring the aquatic environment to pre-project conditions outweighed the benefits associated with providing bypass flows or fish passage at the other six hydroelectric plants. From a recreation perspective, restoring the former impoundment to a free-flowing stretch of river and providing a new boating access area greatly enhanced angling and paddling opportunities on the Tuckasegee River.
Once FERC ordered the removal of Dillsboro Dam and Powerhouse, it took patience, perseverance, rapport with local stakeholders and sheer determination to finish the work. The Duke Energy team could not take the “blow and go” approach and instead were very deliberate in taking care of both the natural resources and many other stakeholder interests every step of the way. Many of the requirements were mandated by FERC and state regulatory agencies. Non-FERC-licensed facilities do not have to go through such a rigorous process.
The Dillsboro Dam removal helped Duke Energy meet its relicensing needs by striking a balance between power benefits within the region, returning aquatic habitat in the Tuckasegee River to its original condition and expanding whitewater boating and riverine angling opportunities.
Six years elapsed between filing the license surrender application in 2004 and removal of the dam and powerhouse in 2010. Including the three-year post-removal monitoring study, the removal process took nearly a decade to complete at an estimated cost of million. It is worth noting that the original cost estimate for the Dillsboro Dam and Powerhouse removal project was about $500,000. Some additional costs were associated with surrender order requirements, including environmental studies, mussel relocation and stream bank restoration. Other additional costs were created by unanticipated permitting activities, especially removing sediment from the impoundment, and by litigation. Actual demolition and removal of the Dillsboro Project was one of the more straightforward aspects of the effort, which was completed in just two months for less than $1 million.
Decommissioning the Dillsboro Project resulted in only a small loss of energy capacity (225 kW) to Duke Energy’s overall electric generating capability in the region (89 MW). The energy, environmental and recreational gains associated with project removal include:
– Preserving the generation capability at Duke Energy’s larger, more efficient hydro projects in the area greatly outweighed the loss of generation capability at the Dillsboro Project;
– Aquatic habitat was restored within a 0.8-mile-long segment of the river;
– Fish access was restored to 9.5 miles of river that previously were blocked to upstream movements;
– Endangered freshwater mussel species relying on the movement of host fish to distribute juvenile mussels have benefitted from the removal, thereby enhancing aquatic resource distribution within the Tuckasegee River system and species richness of upstream areas;
– The C.J. Harris Recreation Area was built adjacent to the former impoundment; and
– The free flow of the river improves recreational opportunities for riverine angling and other land-based recreation that was previously non-existent.
Ty Ziegler is an environmental and regulatory manager with HDR. Steve Johnson in a project manager II and Jeff Lineberger is director of water strategy and hydro licensing with Duke Energy.