Balancing Unit Efficiency and Fish Passage

 

Photo (above): The new turbine runners are designed to minimize the gap between the blade and hub, as well as the blade tip and discharge ring. The new runner design is fully spherical, which reduces harmful wedge-shaped gaps.


All 10 fish-friendly turbines have been installed in the powerhouse at the 1,092-MW Wanapum Dam project in Washington. The new design boosts salmon survival rates while also increasing generation by an average of 3.3%.

By Thomas Stredwick

In a win-win for fish protection and power generation, Grant County Public Utility District recently completed work to install 10 new turbines at its 1,092-MW Wanapum Dam hydroelectric facility. The new turbines slightly boost juvenile salmon survival rates and increase renewable energy generation by an average of 3.3%.

This article discusses the work already accomplished, ongoing work to complete rehabilitation of the powerhouse, and results to date.

Understanding the situation

Built in 1963, the Wanapum Dam project on the Columbia River in Washington has delivered clean energy throughout the Pacific Northwest for more than 50 years. Power from the project, as well as the downstream 956-MW Priest Rapids Dam project, serves the needs of Grant County, Wash., residents, farms, and industry, as well as millions of electric consumers throughout the Pacific Northwest under long-term power sales contracts.

After decades of operation, in the mid-1990s, the turbine-generator units in the Wanapum powerhouse began to show accelerated signs of wear and deterioration. Vibrations within the original 10 adjustable Kaplan turbines, as well as cavitation on the rotating blades, required frequent maintenance and repair by hydro mechanics, resulting in unit outages. The continued reliability of the units concerned plant operators.

Operational concerns coupled with the need to meet biological stewardship responsibilities provided a unique opportunity. Personnel at Grant County PUD set out to investigate turbine design solutions that would increase energy generation, reduce maintenance costs and allow for safer fish passage alternatives.

This led to a decade of research and collaboration among fishery scientists, engineers, utility operators and the U.S. Department of Energy to design a replacement turbine that would meet all of these needs. Grant County PUD participated in efforts jointly funded by the DOE and several hydro operating utilities to incorporate known turbine design improvements into an all-new, advanced turbine design. The goals of the project were to address the mechanical and hydraulic issues, reduce maintenance, increase generation efficiency, and solve fish survival concerns.

Grant County PUD operates with the belief that power generation and fish protection are both compatible and sustainable – the focus on the advanced design turbine is a tribute to this belief. Installation of this new design represented the first commercial application of this technology in the world.

The new advanced turbine design was finalized in 2002. Voith Hydro Inc. was awarded a US$120 million contract in 2002 to manufacture and install the advanced turbine components for all units at Wanapum Dam. The turbine replacement program is notably among the most extensive modifications carried out by Grant County PUD since construction of the dam.

Installation of the first unit was completed in early 2005. Following installation of this unit, the Federal Energy Regulatory Commission required a fish passage study prior to proceeding with the remaining nine units. After extensive testing and favorable results in 2008 (>97% survival for yearling chinook), the PUD received final approval from FERC to replace the remaining nine turbines at Wanapum Dam with the new design. The final turbine was operational in the fall of 2013. Between the research, design and installation process, the entire project spanned more than two decades.

Project challenges

Beyond the expected logistical and manufacturing challenges involved in a project of this scale, biological considerations were a significant portion of the work.

Over the past 20 years, Columbia River hydropower operators have managed projects with increasing regulatory requirements and laws requiring operators to improve the survival of any Endangered Species Act (ESA) listed species, such as the spring run of chinook salmon. Grant County PUD’s mission of generating energy cannot be accomplished without mitigation for environmental impacts.

Every design modification to the turbines and the structure of the dam had to take ESA-listed and non-listed salmon into consideration before the solution could be implemented. These biological challenges required more than 150 different research studies related to salmon behavior and survival. Studies focused on the areas of passage through the Wanapum and Priest Rapids fish bypasses, balloon tag evaluations to assess turbine survival at Wanapum and Priest Rapids dams, predator control and removal programs, and avian predation.

The results of this effort demonstrate that Grant County PUD met or exceeded survival standards for yearling chinook and sockeye, with observed survival through the dams at greater than 95% for yearling chinook, steelhead and sockeye. An area where survival is depressed is within the reservoirs and is association with Caspian tern predation. Recent avian predation evaluations have indicated that Caspian terns annually consume an average of 15.7% of ESA-listed steelhead smolts and 2.5% of ESA-listed yearling chinook salmon smolts out-migrating from the upper Columbia River through the Priest Rapids Project area. The utility is actively involved in solving the ongoing predation challenges.

Beyond the $120 million contract awarded to Voith Hydro, tens of millions of dollars have been invested on structural modifications to Wanapum Dam to assist with enhanced fish passage. One example, the juvenile fish bypass, was installed in 2008 at a cost of $35 million. This project involved cutting a hole through the middle of the dam to install a 290-foot-long concrete chute, or slide, for downstream-migrating juvenile salmonids. Results from this project demonstrate a survival rate of 99%. This project also ensured the use of less water to pass a greater amount of juvenile fish. This equates to a more efficient use of water resources while achieving a greater survival outcome for juvenile fish. Changes like the fish bypass and advanced turbines are intended to improve salmon survival while also balancing the needs of customers’ energy demands along the Columbia River.

Innovative design

The advanced turbine innovation comes from a collaborative relationship between Grant County PUD, Voith Hydro and DOE. Every design solution had to balance the varied objectives of energy efficiency, cost effectiveness and biological concerns throughout the process.

Considerations were presented to stakeholders, including federal and state fish agencies and Indian tribes, in a technical working group forum. These discussions led to design improvements and ultimately a design supported by all stakeholders.

The design of the new runner (which includes the hub and blades) incorporates a number of features intended to improve the survival of juvenile salmon passing through the units, along with increased turbine efficiency. The new runners are designed to minimize the gap between the blade and hub, as well as the blade tip and discharge ring. The new runner design is fully spherical, which reduces harmful wedge-shaped gaps, allowing safer passage for fish by minimizing shear and pressure injuries.

Another key element of the design is the increase in the number of blades from five to six and lowering the blade elevation. These changes significantly reduce cavitation, which occurs when water passes by the turbine and undergoes pressure changes resulting in the formation of air bubbles. As the bubbles go by the blades, the pressure increases and the bubbles collapse. The continual forming and collapsing of bubbles against the blade causes the metal to erode. Cavitation reduces efficiency and creates an environment that may be harmful to salmon. Once the erosion starts, it tends to progress quickly, creating inefficiencies in water passage.

The new design encapsulated the entire hydraulic passageway at Wanapum Dam, not just the turbines. Engineers modified the stay vanes, wicket gates and draft tubes to achieve a smooth flow of water, which naturally improves fish passage. The new design also featured 32 wicket gates instead of 20, and every other wicket gate is now aligned with one of the 16 stay vanes to reduce potential strike points for fish passing through.

Significant modifications to the draft tubes required detailed engineering consideration. Through model testing, Voith Hydro developed a modified draft tube design to enlarge the flow section and reduce water flow velocities.

Points of success

The last of 10 turbines was set in place during the summer of 2013, ending the decade-long installation process. Work on generators is ongoing and will likely be complete in 2018. The new design slightly boosts juvenile salmon survival rates while also increasing renewable energy generation by an average of 3.3%. This could allow Grant County PUD to provide clean energy to more than 8,000 additional homes.

By FERC order, Grant County PUD’s advanced-design turbine testing needed to achieve a fish passage survival rate that was equal to or exceeded the survival through an existing turbine, which at the time was 97.7%. In addition to the improved turbine efficiency, a final report on the fish passage tests shows juvenile salmon survival rates slightly improved (97.8%) compared to the previous units, thus meeting the FERC-mandated goal. While the incremental improvement to fish passage might appear small, the water use efficiencies, coupled with other fish passage improvements to the dam, are a significant contributor to the project’s overall success.

All 10 new turbines have been installed in the 1,092-MW Wanapum Dam powerhouse, boosting overall energy production by 3.3%.

In recent years, the number of salmon and steelhead migrating through the mid-Columbia River to spawn in the upper basin has substantially increased. Based on fish count data collected at Priest Rapids Dam, the average steelhead and salmon count at the 20-year, 10-year and four-year intervals are 274,057 (1995-2014), 394,083 (2005-2014) and 585,958 (2011-2014), respectively. The lifecycle of the species is complex, and survival is affected by many contributing factors, but their population increase is undoubtedly due in part to the investments made in the hydropower system by projects like Grant County PUD’s advanced turbine design.

Successful installation of the new advanced turbines at Wanapum Dam marks a significant milestone in balancing fish passage and power generation. Ultimately, these improvements extend the life of the power plant by about 50 years and increase the domestic renewable energy supply without any greenhouse gas emissions.

Thomas Stredwick is manager of public and government affairs at Grant County Public Utility District.

 

Wanapum Dam repair update

In February 2014, Grant County Public Utility District discovered a 65-foot-long by 2-inch-wide horizontal crack in a section of the 850-foot-long spillway. This discovery prompted the utility, in consultation with the Federal Energy Regulatory Commission, to drop the water levels behind the dam by 26 feet to stabilize the spillway. This action led to other issues that would ultimately impact hydroelectric generation, fish passage, recreation, cultural resources, irrigation and public safety.

As of March 17, 2015, Grant County PUD had successfully completed necessary repairs to the dam to raise the river level back to normal operating conditions. This allowed Grant County PUD to return to standard operations with a spillway that is even more stable than the day it was built.

In just over a year, the utility has responded to one of the most unprecedented emergencies in its history. For more information, visit www.grantpud.org/your-pud/media-room/wanapum-dam- spillway-response.

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