Dorena Dam – Hydro Retrofit

Akana provided Construction Quality Control services during development of this $25M hydroelectric project located at an existing U.S. Army Corps of Engineers (USACE) dam approximately 25 miles southeast of Eugene, Oregon.  The hydroelectric plant will provide 7.5MW (15 GWh/year) using release of water from Dorena Lake and, according to the USACE Portland District, is the first non-federal hydropower development within the district in more than 20 years.

The project includes over 300 feet of 56- and 120-inch diameter penstock, a Siphon House containing the emergency close valve and vacuum equipment, a Valve Vault holding the Kaplan turbine shut-off valve, and the Powerhouse housing two turbine generators – a 4.4-MW vertical Francis and a 1.2-MW horizontal Kaplan.  Flow passes through the turbine generators into a concrete tailrace before discharge to the Row River.  The Powerhouse is slated to generate up to 6.8 MW of electricity, which will potentially supply electricity to 1,400 households.

Construction of the in-water upstream portion of the work included 5,000 sf of Flexifloat barge sections utilized for placement of the intake/trashrack structure, 120-inch diameter upstream closure valve on the lake side the side of the dam, and a 75,000-pound welded penstock section placed using a two-crane lift.  An 11-foot diameter, 60-foot-long tunnel was bored through Dorena Dam between the upstream closure valve and the Siphon House for penstock installation.  A gooseneck-shaped section of penstock connects the Siphon House to the Valve Vault.  Just prior to entry of the 120-inch penstock into the Valve Vault, a 56-inch diameter bifurcation splits off, routing flow to the Francis turbine generator.

Construction of the Powerhouse required a 45-foot deep excavation that was excavated from earth and rock.  The lower level of the Powerhouse stretches 42 feet below finished grade and is constructed of concrete and reinforcing steel.  The above-grade portion of the powerhouse is made up of 20-foot high CMU walls topped with standing seam metal roofing.  The Powerhouse tailrace required cast-in-place construction of battered, radius walls on a 20 percent slope ranging from 10 to 32 feet in height.  The electricity generated in the Powerhouse will pass out of the Dorena Hydro substation and switchyard, traveling through approximately 5 miles of transmission line constructed between the project site and PacifiCorp’s Village Green substation in Cottage Grove.  Roughly half the transmission line was routed under an bike path, which was then repaved.

Akana professional engineers served as Quality Control Inspection Program Project Manager (QCIP PM) and Resident Quality Control Engineer (RQCE) throughout project construction.  USACE and FERC approval was required for staff members prior to participation on the QC team.  Project construction included mass excavation and rock removal; backfill and compaction; tunnel boring through the existing concrete dam; welding, installation, and painting of large-diameter penstock pipe; construction concrete structures; installation and maintenance of upstream and downstream cofferdams during construction; installation of horizontal and vertical turbine generator units; and installation of electrical and controls systems, and transmission line installation.  Work monitored by the QC program using third-party inspection included complex reinforcing steel, concrete testing, penstock welding and painting, structural steel welding, proprietary anchors, bolt tension verification, compaction, and electrical testing.

Project construction is largely complete and moving into commissioning and startup phases.  Systems associated with operation and control of the dam’s regulating outlet (RO) gates, upstream closure valve, siphon equipment, and ancillary support are largely commissioned.  Commissioning of the horizontal Francis unit is also finished.  Complete installation of the Kaplan turbine generator is anticipated for late May, followed by startup and commissioning.