Tech Briefs

Corps explores flow rates in short-intake Kaplan turbines

The U.S. Army Corps of Engineers issued a notice of interest in studies of measuring flow rates in short-intake Kaplan turbines. The Corps’ Hydroelectric Design Center says the notice is not a request for proposals or quotes. The Corps is interested in methods to accurately measure absolute water flow rates in its short-intake Kaplan turbines.

Traditionally, it has been sufficient to measure just relative flows in order to optimize the performance of individual generating units, the Corps says. However, computer programs recently have been developed that calculate the optimum manner to share load among individual generating units in a powerhouse. To fully use such programs, the amount of actual flow passing through the turbines must be known, the Corps says.

The cross sectional dimensions of the areas accessible for flow measurements are on the order of 20 by 40 feet. Flow velocities are in the range of 2 to 10 feet per second, with varying degrees of turbulence. Measurement accuracies of +2 percent or better are required.

– Contact Lee H. Sheldon, (1) 503-808-4298; E-mail: lee.h.sheldon@

Evaluating fish passage alternatives at Rocky Reach

Chelan County Public Utility District (PUD) is using a computational fluid dynamics (CFD) model of the reservoir upstream of its 1,287-MW Rocky Reach Dam to determine the most cost-effective way to improve guidance and survival of juvenile sockeye salmon passing the project.

Current fish passage tools in place at the project, which is on the Columbia River in Washington, consist of a surface-oriented bypass system and bar screens in two units near the heaviest fish passage area. A conduit conveys fish to the tailrace.

Now, Chelan County PUD is looking at finding ways to further improve fish passage via changes to powerhouse operations and/or physical structures at Rocky Reach Dam. The CFD model covers an area extending 5,000 feet upstream of the project.

A team of fish passage, hydrodynamics, and fish behavior experts are reviewing the alternatives developed via CFD. The work is to be completed by August 2007.

Preliminary results of model testing indicate that modifying the loading of the powerhouse during the outmigration of sockeye may increase the number of sockeye using an existing turbine bypass route.

The U.S. Army Corps of Engineers issued a notice of interest in studies of measuring flow rates in short-intake Kaplan turbines. Click here to enlarge image


Development of the CFD model and assessment of the alternatives is estimated to cost about $185,000. The Iowa Institute of Hydraulic Research developed the model.

Using seismic tomography to map concrete deterioration in a dam

The Bureau of Reclamation, U.S. Department of the Interior, recently used seismic tomography to image concrete deterioration within a 90-meter-high concrete arch dam suffering from alkali-aggregate reactivity.

The method works in the following way: Specialized equipment sends sound waves through the structure and records them on the other side. High-frequency accelerometers are used to record signals above the water, and hydrophones record underwater signals. The resulting tomograms map the variations in the velocity of the sound waves. The areas with the lowest velocities are interpreted as having the most severely deteriorated concrete. (See Figure 1.)

Reclamation recently developed specialized equipment for conducting seismic tomography on large dams. This consists of two sources of seismic signals: a two-pound sledgehammer hit directly on the concrete and a modified nail gun where the piston hits a metal plate held against the concrete. The accelerometers that record signals above the water are enclosed in plastic cases and mounted on concrete anchors. A custom-designed 16-receiver hydrophone string, hung vertically from the crest immediately upstream from the dam, records underwater signals.

Figure 1: Seismic tomography surveys performed at a concrete arch dam indicate significant deterioration on the crest and downstream face. The areas with the lowest p-wave velocities are interpreted as having the most severely deteriorated concrete. Click here to enlarge image

This method, although not new, has not been used much on dams in the U.S. because of the expense and time required to develop, construct, and maintain the equipment, says Lisa Block, geophysicist with Reclamation. However, Block says the method provides several benefits.

First, it is nondestructive because it does not require drilling of coreholes into the dam.

Second, the resulting image provides a cross section through the entire structure. This gives information about the spatial variation of conditions within the structure that is not provided using other methods.

Third, this method shows the condition of the concrete in-situ, under the exact physical conditions it experiences within the dam. This allows Reclamation to determine in which areas concrete is too deteriorated to be recovered as a core. It also allows analysis of the effects of extensive fracturing and variations in stress conditions across the structure.

Fourth, this method is valuable to use in conjunction with traditional investigational methods. For example, measurements of concrete properties obtained from laboratory measurements of core samples can be extrapolated away from the coreholes using seismic tomography images.

Block says Reclamation finds the costs to use the method varies by site, depending on water level (the higher the level, the less time required to acquire data – it is much faster to record data below the water level using a hydrophone string than it is to manually place receivers on the dam face); set-up time (setting up the equipment typically requires one to two days, and recording data for each cross section requires about two days); and recording time (typically, one day is required to measure and survey the shape of the dam along the cross-sectional lines for the purpose of computing precise source and receiver locations).

Repeating these surveys over the course of several years could help Reclamation monitor changes in a dam’s concrete condition.

Book released on big dams constructed in the 1930s

University of Oklahoma Press announces publication of Big Dams of the New Deal Era: A Confluence of Engineering and Politics. Authors are David P. Billington, a professor of engineering at Princeton University, and Donald C. Jackson, a history professor at Lafayette College in Easton, Pa.

The 416-page softcover book discusses how major water storage structures were erected in four western river basins in the 1930s. These massive dams were designed to serve multiple purposes: generating hydroelectricity, improving navigation, irrigating crops, storing water, and controlling floods.

The authors reveal how engineering science, regional and national politics, perceived public needs, and a river’s natural features intertwined to create distinctive dams within each region. In particular, the authors describe how two federal agencies – the U.S. Army Corps of Engineers and the U.S. Department of the Interior’s Bureau of Reclamation – became key players in the creation of these important public works.

By illuminating the mathematical analysis that supported large-scale dam construction, the authors also describe how and why engineers in the 1930s most often opted for massive gravity dams.

– To buy a copy of this book for US$36.95, visit the Internet: www. 0-8061-3795-9.

NPCC releases DVD on energy in the Pacific Northwest

The Northwest Power and Conservation Council (NPCC) announces a new DVD set, Place and Power: The Evolution of the Northwest’s Energy System. This free video outlines the history of power generation in the Pacific Northwest, with significant focus on the development of major hydroelectric projects.

The DVD covers a period starting with the construction of major dams along the Columbia River and ends at the present day. The video provides a comprehensive overview of the intersection between electricity and the environment and the role of NPCC to reach a sustainable balance between the needs of fish and wildlife and the human demand for electricity.

The second disc in the set contains interviews with eight key individuals who have unique perspectives on Northwest energy issues. Examples include:

    – Ralph Cavanagh, director of the Natural Resources Defense Council’s Northwest Energy Project;
    – Dan Evans, the first NPCC chair and a former Washington governor and senator;
    – James McClure, a retired Idaho senator; and
    – Daniel M. Ogden Jr., PhD, former manager of the Public Power Council, which represents the interests of consumer-owned electric utilities in the Northwest.

– For information on obtaining a copy of the DVD, visit www.nwcouncil. org/video/power.htm.

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