Fish passage facilities under construction at Soda Springs Dam will give salmon access to 6.6 miles of habitat, while allowing PacifiCorp to retain the North Umpqua Hydroelectric Project's peaking capability.
By Monte G. Garrett
PacifiCorp Energy is reintroducing Chinook salmon and steelhead to a 6-mile stretch of the North Umpqua River above Soda Springs Dam by 2012.
Anadromous fish were cut off from this reach of the river when the dam was built in the 1950s to impound water for a hydroelectric project.
PacifiCorp is building upstream and downstream fish passage facilities at the dam, enhancing fish habitat in the river, and monitoring predation levels to document the long-term effectiveness of this effort. Construction of the $60 million project began in June 2010. Todd Construction was awarded the construction services contract and Mackay & Sposito Inc. received the construction management contract.
About the North Umpqua Hydroelectric Project
PacifiCorp's North Umpqua Hydroelectric Project consists of eight diversion dams and associated hydroelectric generation facilities with a total capacity of 185 MW. These dams and power plants were built between 1948 and 1956 along the North Umpqua River, about 60 miles upstream of Roseburg, Ore., on land owned by the U.S. Department of Agriculture's Forest Service.
PacifiCorp operates the project in a "peaking" mode, storing and releasing water for generation at strategic times during the day to meet peak energy demands. Soda Springs Dam, the project's lowermost development on the North Umpqua, serves as a re-regulating facility, smoothing out bulges of water and providing a more natural hydrograph downstream, including the 34 miles immediately below the project designated in 1988 as a Wild and Scenic River.
This re-regulating function of Soda Springs Dam also ensures consistent habitat and dependable spawning conditions for fish species highly valued by anglers.
The North Umpqua project's original 50-year operating license issued by the Federal Power Commission expired in 1997. Five years prior to the expiration date, PacifiCorp began the process of applying for a new license, as required under the Federal Power Act.
This relicensing was particularly challenging for PacifiCorp. Not only is the project on federally owned land, it was the company's first large project to be relicensed under requirements of the Electric Consumer Protection Act of 1986.
This legislation requires equal consideration of electric generation with non-power resources that may be affected by project operation, such as fish and wildlife, water quality, cultural resources, and recreation. These requirements set into motion a level of consultation with state and federal agencies and other interested parties that had not previously been considered in relicensing processes for privately owned utility companies.
Soda Springs Dam quickly became the focal point of North Umpqua project relicensing, because the dam completely blocks access to about 6.6 miles of riverine habitat.
Following relicensing studies and just prior to PacifiCorp's filing of its license application, fish passage gained additional importance when, in April 1994, Congress issued the Northwest Forest Plan.
This new plan included an Aquatic Conservation Strategy that requires the U.S. Forest Service to "maintain and restore spatial and temporal connectivity within and between watersheds."
As a result, PacifiCorp initiated a collaborative watershed analysis, a step recommended in the forest plan for conformance with aquatic conservation strategy requirements, intended to address additional study requests raised by the North Umpqua National Forest.
The watershed analysis concluded that the best way to benefit native anadromous fish near the North Umpqua project was to remove Soda Springs Dam. Removing the dam, however, would require PacifiCorp to provide the dam's re-regulating function in another manner or discontinue the valuable peaking nature of the project.
Reaching a settlement
Choices were limited and compromises were necessary to move forward. Following two years of intense negotiations, PacifiCorp and seven state and federal agencies signed a comprehensive settlement agreement in 2001.
The cornerstone of the agreement is the construction of fish passage facilities at Soda Springs Dam by 2012. These facilities will provide anadromous fish access to spawning habitat upstream of the dam, while allowing PacifiCorp to retain the project's peaking capability.
Once the passage facilities are in place, Chinook salmon and steelhead making the 180-mile run up the North Umpqua River from the Pacific Ocean will have access to the lower 3.5 miles of the Fish Creek bypass reach, in addition to approximately 2.5 miles of habitat in the North Umpqua River. The agreement also required completion of several significant habitat enhancement actions both upstream and downstream of the dam.
|This barrier, in the tailrace of the Soda Springs power-house, prevents delay and injury of Chinook salmon and steelhead as they swim upriver by the powerhouse.|
Design and construction
The settlement agreement requires PacifiCorp to design and construct by 2012 both upstream and downstream fish passage at Soda Springs Dam. To aid adult salmonids and lamprey attempting to move upstream, the utility will install a vertical-slot fish ladder that meets federal and state design criteria. Passage facilities for downstream-migrating juvenile fish must meet specific performance standards articulated in the agreement, or conform to federal design criteria.
The company will also modify the dam's spillway, which is considered too rough and turbulent for safe passage of juveniles during spill conditions. PacifiCorp will incorporate a video fish-monitoring station in the fish ladder and a fish trap and evaluation facility for sampling of downstream migrants.
Building fish passage facilities at Soda Springs Dam presents a construction challenge, not only due to physical and geological factors unique to the site, but also because of conditions necessary for PacifiCorp's hydroelectric operations. As a re-regulation facility, Soda Springs Dam provides water storage and a stable release of flows which facilitates optimal performance by upstream hydroelectric developments during times when generation demand is at its highest. What's more, by controlled releases from the dam, PacifiCorp can ensure a relatively natural hydrograph in the wild and scenic-designated downstream reach of the North Umpqua River.
The settlement agreement prohibits fluctuations in river stage below the powerhouse due to project operations. Peaking operations -- coupled with ramping restrictions -- could cause the 31-acre reservoir behind the dam to fluctuate as much as 14 feet a day. A ladder to accommodate movement of adult fish up and over the dam must be able to provide egress into Soda Springs Reservoir throughout this range of elevations.
The dam is in a highly incised canyon. The settlement agreement requires the facilities to be constructed in 2010, yet the Oregon Department of Fish and Wildlife (ODFW) stipulates an in-water work "window" of only three months a year -- mid-June until October. To make possible the construction of such massive facilities in the constrained work area, the parties requested, and were granted from FERC, a three-year construction period of 2009 through 2011. Additionally, ODFW is providing latitude for the in-water work window.
In early 2007, a fish passage design technical work group convened to begin analyzing a variety of design alternatives. Ladder alternatives included left bank and right bank options, a spiral staircase at the base of the dam, and various ladder exit types, including fixed, articulating, and false weir exits. Screen alternatives included a forebay criteria screen, a forebay high-speed screen, a forebay modified inclined-plate screen, a criteria screen off the penstock, and non-criteria Eicher-type screens. Geotechnical evaluations indicated the proposed area was highly unstable. The proposed screen location presented difficulties with respect to ongoing access for operations, maintenance, and inspection, and could potentially limit access for construction.
The final design includes a fish ladder consisting of 8-foot-wide by 10-foot-long pools with 1-foot steps. The ladder entrance at the base of the dam will rise 60 feet from the tailwater pool below the dam, pass under the spillway, meet the left bank of the river where it will rise further, penetrate the gravity portion of the dam, and exit into the reservoir.
The ladder exit will consist of 14 gated exit pools that will open and close to track the fluctuating reservoir water surface elevation.
The spillway modification will involve construction of an ogee-type crest, extending the existing spillway and providing a smooth flow pattern to the deep tailwater pool at the base of the dam. This design is expected to reduce fish mortality on the rock outcrop below the spillway.
The fish screen will replace one of the dam's spillways, extending over the top of the fish ladder and spillway modification. The screen will provide water intake for hydroelectric generation, downstream-migrating juvenile fish, and the minimum flow requirement for the Soda Springs bypass reach.
The settlement agreement calls for completion of several habitat enhancement actions to ensure adequate conditions are present when fish passage facilities at the dam are completed in 2012. These actions include: enhancing gravels downstream of the dam, experimenting with the creation of spawning habitat in the Slide Creek bypass reach upstream of the dam, restoring habitat in the Soda Springs bypass reach, and constructing tailrace barriers at the Soda Springs and Slide Creek powerhouses.
In addition, PacifiCorp has increased flow in other bypass reaches where, traditionally, water releases were minimized to the benefit of hydroelectric generation. Increased flows in these bypass reaches are expected to improve the quality and availability of fish habitat.
Soda Springs Dam historically prevented free movement of gravels downstream, thus affecting the quality of instream fish habitat.
To mitigate this, a technical work group appointed by the settlement agreement's Resource Coordination Committee began a process of experimental releases of gravel downstream of the Soda Springs powerhouse.
In August 2004, about 2,600 cubic yards of spawning gravel was placed below the powerhouse and another 400 cubic yards in the bypass reach. The group's hypothesis was that the gravel would be naturally distributed during high flow events.
Creating spawning habitat
The settlement agreement specified the creation of spawning habitat in a 0.6-mile stretch of the North Umpqua River for use by salmon and steelhead once the fish passage facilities are in place.
This stretch of the river, the Slide Creek bypass reach, is in a steep canyon. To create this habitat, PacifiCorp placed large boulder structures in the river.
These structures are comprised of hundreds of boulders, from three to six feet in diameter.
The structures are being monitored to gauge their effectiveness in trapping gravel and forming spawning habitat.
Constructing the tailrace barriers
The settlement agreement required PacifiCorp to construct barriers in the tailraces of the Soda Springs and Slide Creek powerhouses. The purpose of the barriers is to reduce the amount of turbulence in the flow coming out of the powerhouses through the draft tubes. Turbulent water attracts salmon and steelhead and they risk injury in attempting to swim up into the draft tubes.
Construction of the Soda Springs tailrace barrier was completed in 2007, and the Slide Creek barrier is expected to be fully functional by 2012.
These tailrace barriers baffle turbulent tailrace discharges into slower laminar flows spread over a wide cross section of river. Water from the powerhouse is diffused through an underwater fence of pickets, preventing adult fish from entering the tailrace area.
Increasing flow in bypass reaches
In the Soda Springs bypass reach, where anadromous fish already exist, PacifiCorp has increased the amount of flow released from the dam to 275 cubic feet per second (cfs) from 25 cfs.
In the Slide bypass reach, located immediately upstream of Soda Springs Reservoir, the company has increased flow releases to 80 cfs from 25 cfs, and will increase flows to 240 cfs when the fish passage facilities are completed by 2012. In total, PacifiCorp has increased flows as much as 10-fold in all project bypass reaches.
Effects on hydropower
A major management goal of the settlement agreement was to maintain ecological processes and habitat in a condition sufficient to support interconnected and well-distributed fish and wildlife populations in the North Umpqua River watershed, including the restoration of native anadromous fish populations in historically-accessible habitat. Accomplishing this goal while maintaining the viability of the project for hydroelectric generation was a significant challenge.
Over the 35-year tenure of the FERC license for the project, PacifiCorp will forego an estimated $370 million in lost generation due to increased bypass flows, as well as $125 million in capital construction projects. However, this hydroelectric project continues to provide cost-effective electric service for PacifiCorp customers, while balancing conservation of natural resources with generation of clean, renewable energy.
Monte Garrett is the Implementation Program Manager for PacifiCorp Energy. Garrett oversees the fish passage project at Soda Springs Dam, making sure it complies with requirements of the settlement agreement and license with the Federal Energy Regulatory Commission.