Work to add a 7.5-MW hydroelectric powerhouse to the existing Dorena Lake Dam should be complete by April 2013. This project illustrates the success of a growing trend of adding hydropower at existing U.S. Army Corps of Engineers dams.
By John Douglas and Kuo-Bao Tong
In what is becoming a significant trend in hydroelectric project development in the U.S., Riverbank Power Corp. of Toronto, Ontario, Canada, is building the 7.5-MW Dorena Lake Dam Hydroelectric Project on a U.S. Army Corps of Engineers Dam in Lane County in western Oregon. According to the Corps' Portland District, this is the first non-federal hydropower development within the district for more than 20 years.
During its construction, this run-of-river facility on the Row River, a tributary of the Coast Fork Willamette River, will provide 30 to 40 jobs. When completed, this plant will generate 15 GWh of electricity annually (enough to power about 1,200 homes) and provide one or two full-time operating jobs. Environmental benefits include reduction of carbon dioxide generation of 15,486 tons per year and improvement of salmonid habitat in the upper and lower Row River.
Riverbank Power's total investment for this hydro facility is $25 million. The Dorena Lake project is expected to begin operating in April 2013.
Background on the dam
Dorena Lake Dam was completed in 1949 to provide flood control. It is also used for recreation, irrigation and improved downstream navigation.
The concrete and earthfilled gravel embankment structure is 145 feet high, with a crest length of 2,600 feet. Appurtenant features include a concrete spillway with a 200-foot crest length at elevation 835 feet that discharges into a stilling basin constructed with concrete retaining walls and located within the concrete tailrace channel. The dam impounds a 1,749-acre reservoir with 70,500 acre-feet of storage.
|Ground was broken in August on construction of the 7.5-MW Dorena Lake project at an existing U.S. Army Corps of Engineers dam.|
Modifying the dam to add a powerhouse
The design flow at this site is 812 cubic feet per second, and the net hydraulic head range is 42 to 105 feet.
Work to be performed to accommodate a water passageway to the powerhouse structure includes:
- Installing a submerged intake, protected by a trashrack;
- Adding a 10-foot-diameter penstock from the intake about 95 feet to a butterfly valve located immediately upstream of the dam face;
- Excavating a bore through the concrete dam to accommodate the penstock;
- Construction of a siphon house immediately downstream from the dam that will contain a 10-foot-diameter butterfly valve and vacuum equipment to initiate a siphon in the penstock when lake levels are below the siphon elevation; and
- Installation of a buried 10-foot-diameter penstock about 180 feet long from the siphon house to the powerhouse, including a bifurcation to 56 inches in diameter and about 130 feet of 56-inch-diameter penstock between the bifurcation and the powerhouse.
The two-unit powerhouse on the North bank of the river immediately downstream from the dam will contain one 4.4-MW vertical double-regulated Kaplan turbine-generator package and one 1.2-MW horizontal Francis turbine-generator package.
From a water quality perspective, existing dams that do not feature hydroelectric powerhouses often have reservoirs that are depleted of dissolved oxygen, but the existing flow-regulating structures create turbulent conditions that aerate the water downstream from the dam. Historically, DO concentrations in the water downstream from Dorena Lake Dam have met the Oregon Department of Environmental Quality's numerical criteria. Existing dam features added some aeration to water exiting the dam throughout the year and considerable aeration during the summer months.
A cost-effective three-tiered ap-proach to aeration was agreed on during the design of the hydro plant in order to maintain DO concentrations in the Row River below Dorena Lake Dam throughout all 12 months of the hydro project's operation.
First, during periods of limited oxygen deficit, DO will be maintained downstream via turbine runner casement aeration.
Second, as deficits increase, especially during the late months of summer or early fall, tailrace aeration also will be employed. This second feature consists of 390 high-capacity small bubble diffuser discs fed by PVC distribution manifolds. The aeration basin is divided into equal halves separated by a guide wall within the tailrace. This allows just half of the aeration facility to work while the Francis turbine is in use. Both halves of the basin would be used when the Kaplan turbine is operating.
And third, to resolve gas dissolution issues, a rubber dam and concrete training wall were added to increase bubble contact or resident time for aerated flows existing the powerhouse into the Row River. This final feature will be used for all aerated flows when the total dam and hydro project discharge is less than 2,700 cubic feet per second.
|Construction work on the 7.5-MW Dorena Lake powerhouse is progressing well. The facility is expected to begin operating in April 2013.|
Getting necessary clearances
Originally, Symbiotics LLC was planning to develop the Dorena Lake project. The company began state and federal licensing work on this project in 2002.
The water quality certification was issued in 2008. Licensing work was completed in October 2008, when the project received a 50-year operating license from the Federal Energy Regulatory Commission. The project received 408 certification from the Corps in 2011.
One component of the license is a resource protection and mitigation agreement to ensure the project will be a net benefit for local fish and wildlife. This agreement includes:
- Construction of a tailrace barrier to prevent fish injury and mortality resulting from operation of the powerhouse. Construction is to proceed as a joint effort with the Oregon Department of Fish and Wildlife, National Marine Fisheries Service and U.S. Fish and Wildlife Service; and
- Establishment of a fish habitat restoration and enhancement fund to finance salmonid projects on the Coast Fork Willamette River. The aim of these projects, designed by the local watershed council in conjunction with Oregon DFW, is to improve salmonid habitat in the upper and lower Row River.
Riverbank Power was founded in 2007, initially with a focus on developing utility scale pumped-storage project in North America. In 2010, the company expanded its capabilities to include run-of-river projects through its acquisition of Symbiotics Energy Corp.
Riverbank Power chose Mowat Construction Co. of Woodinville, Wash., as contractor for the project in March 2012. Engineering work on the project was completed in April 2012. In May 2012, Riverbank Power closed US$38 million in financing for a power of hydro projects in the U.S., one of which is Dorena Lake. The Dorena Lake project will assume $26 million in non-recourse debt arranged by Travelers Capital Corporation and funded by Industrial Alliance Insurance and Financial Services Inc.
On-site construction began in June 2012. The turbines and generator were delivered in August 2012. Riverbank Power officially broke ground on the facility on August 20 in a ceremony attended by U.S. Senator Ron Wyden and Congressman Peter DeFazio.
"I congratulate Riverbank Power on this historic groundbreaking at the Dorena Lake Hydroelectric Project in Lane County," Senator Wyden said at the event. "This project will provide 1,200 Oregon homes and businesses with renewable hydroelectric power, and do so while improving fish habitat and reducing CO2 emissions. I also want to commend the Corps of Engineers for working with Riverbank to expand the use of Dorena Lake Dam to include power production. I think this project can serve as an example for how other low-impact hydroelectric projects can be built and I look forward to its completion."
The tunnel and penstock are to be completed by December 2012. The project is expected to enter commercial operation in April 2013.
Scope of Riverbank Power's Development Work
Riverbank Power Corp. has projects in the pipeline of more than 276 MW of capacity at 15 run-of-river facilities and 2,000 MW of pumped-storage hydropower capacity at two sites in the U.S.
The run-of-river hydro facilities include 10-MW Applegate in Oregon, 4.7-MW Clark Canyon in Montana, 7.5-MW Dorena Lake in Oregon, 78-MW Overton in Louisiana, 6.8-MW Shelbyville in Illinois, 66.7-MW Uniontown in Kentucky, and 7.15-MW Wickiup in Oregon.
Another hydroelectric project under construction in the U.S. is Clark Canyon. This project was part of a US$38 million financing deal the company closed in May 2012. Clark Canyon will get $12 million in sub-debt financing provided by the Infrastructure Coalition Program. This facility is expected to be commissioned in 2013.
Riverbank Power and EDF Renewable Energy entered into a joint venture agreement in March 2012 to develop pumped-storage facilities, designed to provide energy storage that is necessary to integrate renewable energy and provide much-needed ancillary services. The joint venture's initial efforts are focused on large scale development in the northwestern U.S.
John Douglas is president and chief executive officer of Riverbank Power Corp., developer of the 7.5-MW Dorena Lake project. Kuo-Bao Tong is project manager for the company.