Tech Briefs

Water withdrawal tower acts as fish collector, intake structure

Portland General Electric (PGE) and the Confederated Tribes of the Warm Springs Reservation are installing a tower at the 366.8-MW Pelton Round Butte project that will both collect fish and act as an intake structure for the powerhouse. This 273-foot-tall tower, called the selective water withdrawal facility, should be complete and operational in the spring of 2009, says Stephen Quennoz, vice president of PGE.

The tower is located in the reservoir behind Round Butte Dam, the uppermost of the three dams in the Round Butte project. It is being built as part of an effort to renew fish passage and to reintroduce anadromous salmonid species upstream of the dam.

The tower consists of three sections being built on a barge behind the dam, Quennoz says. As each section is completed, it will be floated to the intake site. The bottom section of the tower – which draws water from the bottom of the reservoir as well as from the top section – directs water to the power intake for the generating facility. This section was anchored in August 2008. The middle section – a 40-foot-diameter steel pipe that connects the bottom section to the top section – was to be installed in October 2008. And the top section, to be installed in December 2008, features the fish collection facility and screens that will allow both collection of fish and intake of water for generation.

The tower being installed in the reservoir behind Round Butte Dam is designed to allow withdrawal of water from both the top and bottom of the reservoir and to collect fish that will be transported downstream of the dam. Click here to enlarge image

Once the entire structure is in place, a bridge will be used to anchor the facility to the shoreline and provide access to the fish collection and transfer facility. At the fish collection facility, fish will be sorted. Migrating salmon, steelhead, and bull trout will be transported by truck downstream of the dams.

The tower is designed to draw water from both the warmer surface layer (through the top section) and the cooler bottom layer (through the bottom section) of the lake, Quennoz says. It is intended to modify currents and temperatures to mimic natural conditions and to attract migrating fish to the collection facility. The tower is expected to:

    – Lower lake temperatures, providing healthier conditions for fish;
    – Modify the temperature of the lower Deschutes River to more closely match pre-dam conditions; and
    – Improve water quality in the project reservoirs and in the river.

CH2M Hill, EES Consulting, and ENSR/AECOM Technology Corp. designed the tower in collaboration with PGE Engineering. Barnard Construction Co., Dix Corp., and Thompson Metal Fab are constructing the facility.

Hydropower Generation Report Click here to enlarge image


Website provides access to Columbia River information

The new International Columbia River Center of Information website provides information designed to encourage dialogue and public awareness of the water, power, fish and wildlife, and related aspects of the Columbia River.

The Northwest Power and Conservation Council (NPCC) and the Columbia Basin Trust developed the site to serve as a comprehensive, publicly accessible repository of information about the river.

Content includes:

    – Data on the history of the region, Indian tribes and first nations, municipal and industrial water uses, and water policy;
    – Climate change information, including that released by the Climate Impacts Group at the University of Washington, Environment Canada, and the Intergovernmental Panel on Climate Change;
    – Links to hydropower websites, such as those hosted by BC Hydro, Bonneville Power Administration, the Canadian Electricity Association, the U.S. Department of the Interior’s Bureau of Reclamation, the U.S. Army Corps of Engineers, and public utility districts; and
    – Links to other websites of interest, including the Columbia Basin Biodiversity Atlas, the Selkirk Geospatial Research Center’s watershed planning and management work, the history of hydroelectric development in southeastern British Columbia, and more.

NPCC develops and maintains a regional power plan and a fish and wildlife program to balance environmental and energy needs in the Pacific Northwest. The Columbia Basin Trust is a corporation of the province of British Columbia created to deliver economic, social, and environmental benefits to the residents of the Columbia Basin.

– The URL address for the site is:, click on International Columbia River Center of Information at right.

Using ultrasonic inspections to monitor runner operating gaps

A few months after the first two Kaplan units were commissioned at Hydro-Québec’s 227-MW Rocher-de-Grand-Mere powerhouse, a visual inspection during a maintenance shutdown revealed a problem. The runner blades on one unit were coming into contact with the discharge ring on one side. This contact can damage the smooth hydraulic surface on the discharge ring and decrease unit efficiency, says Benoit Papillon, principal hydraulic design engineer for Alstom Hydro Canada. Alstom designed the units.

The contact occurred for two reasons, according to Papillon. First, seasonal movement of the powerhouse foundation was occurring. Second, in an effort to improve performance, the units had been designed to limit water losses at the turbine runner blade tips. Consequently, the gaps between the blade tips and the discharge ring were narrow. This reduced the tolerance for centering the turbine runners.

Alstom decided to use the non-conventional method of ultrasonic inspections to monitor the gap once a month for a year before re-centering the runner. Ultrasonic inspections – an alternative to direct radial clearance measurements in the hydraulic passageway – can be performed for any unit where the outside surface of the discharge ring is accessible.

The advantages of this technique include the fact that personnel do not need to stop the unit for a long time or enter the turbine hydraulic passage to perform the measurements, Papillon says. In addition, by using this technique, it is possible to perform frequent measurements, which can lead to an increased understanding of the movements of the embedded components over time.

The one-year time frame was chosen to obtain a good idea of the relative foundation movements over the course of a year, taking into consideration all the effects of seasonal temperatures on the powerhouse foundation.

To perform ultrasonic inspections, Alstom personnel stop the unit but do not dewater it. Personnel use scans from an ultrasonic sensor to determine the blade position, then to draw a representation of the blade profile on the surface of the discharge ring. Personnel use this drawing to approximate the location of the runner blade and perform the ultrasonic measurements.

For each reading performed, two measurements are necessary. The first is to determine the thickness of the discharge ring at that particular location, and the second is to determine the distance between the blade tip and the ultrasonic sensor. Subtracting the discharge ring thickness from the distance between the blade tip and the sensor gives the thickness of the water wall. This equates to the radial clearance between the blade tip and the discharge ring.

Personnel then take into account a calibration factor determined using two steel blocks in a receptacle filled with water. Dividing the water wall thickness by the calibration factor provides the actual radial clearance.

Results of the monitoring showed that the position of the runner relative to the discharge ring varied by as much as 1.2 millimeters. These results were similar for all three units. To solve the problem, Alstom modified the shaft alignment.

Biologist questions limits on total dissolved gas

The incidence and severity of gas bubble disease in fish at hydroelectric projects may be much lower than previously thought, says Don E. Weitkamp, PhD, fish biologist for Parametrix Inc. He is asking regulators in the Pacific Northwest to consider whether the supersaturation limits of total dissolved gas – which can lead to gas bubble disease – are too conservative.

The federal water quality standard for total dissolved gas states that levels cannot exceed 110 percent of saturation. This criterion, established in the early 1970s, was based primarily on laboratory investigations and not investigations in natural waters. However, hydrostatic pressure is a major factor in determining the biological outcome of total dissolved gas supersaturation and lab studies generally restrict fish to water less than 1 meter deep. Because of these two factors, Weitkamp says it is important to consider natural water conditions where the criterion is applied. For example, for a total dissolved gas level of 120 percent, a fish at 2 meters deep only experiences 100 percent of saturation, which would not cause gas bubble disease, Weitkamp says. Gas bubble disease can lead to impaired movement in fish and even death, as a result of gas emboli in the gills and tissues.

To prove his point, Weitkamp conducted an extensive review of literature published between 1980 and 2008. The review showed an absence of fish deaths in field conditions with water depths of 2 meters and greater. Weitkamp says this result could indicate the criterion of 110 percent of saturation is too conservative.

Weitkamp is providing the results of his review to state regulators in Oregon and Washington and is encouraging them to reconsider the total dissolved gas criterion. Given the impracticality of maintaining total dissolved gas levels within 110 percent in many situations (such as high spring runoff), combined with the absence of lethal or other long-term effects, Weitkamp suggests a criterion of 120 percent would be more appropriate for general river conditions where depths are at least 2 meters.

Weitkamp plans to publish a report detailing results of the literature review.

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