Tech Briefs

ASCE publishes guidelines for civil works for hydro facilities

The American Society of Civil Engineers (ASCE) announces the availability of Civil Works for Hydroelectric Facilities: Guidelines for Life Extension and Upgrade.

This 391-page book describes rehabilitation engineering methodologies and techniques for upgrading and extending the life of aging hydro infrastructure.

One feature of the book is case studies that illustrate solutions for improving the performance and extending the service life of civil works of dams and hydroelectric plants.

The Hydropower Task Committee of the ASCE Energy Division wrote the book for owners, operators, regulators, and engineers considering infrastructure rehabilitation or replacement.

– To purchase the book for $71.25 (ASCE members) or $95 (non-members), visit the Internet: bookstore/book.cfm?book=7762.

Hydraulic system allows more precise gate control

A water supply company in Pennsylvania is using hydraulically operated gate valves with programmable logic controllers (PLC) to control the transfer of water between reservoirs. Prior to installation of this system, the company had been using a valve from the early 1900s. Despite many attempted repairs, the valve did not function properly.

The company turned to a new hydraulically operated gate valve system for its high-hazard water supply dam. The new valve system allows the water company to reliably transfer a specified quantity of water between reservoirs.

The system, developed by Watershed Services Inc., employs a knife valve rather than a traditional sluice gate. This type of valve is frequently used in the paper and pulp industry.

The system consists of a valve-cylinder assembly, a controller cabinet containing a hydraulic pump, and a PLC. The unit is powered by 12-volt gel cell batteries, charged using solar panels. The pump, battery, and accessories are housed in a weather-proof enclosure on shore.

The PLC can open and close the valve based on a wide range of data, including rate of rise, water level, rainfall, inflow, outflow, time of year, and remote command. The controller can act on its own or receive signals from watershed modeling software, supervisory control and data acquisition (SCADA) systems, or other control systems.

The programmable gate control system allows operation from the shore, rather than from directly above the valve. This often requires operating the valve from a boat.

Communication to and from the system can occur by telephone, cellular phone, satellite, Internet, or radio.

Hydropower Generation Report
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Using GIS, aerial photography to analyze project effects

Combining geographic information system (GIS) technology with aerial photography is an effective method for qualitatively assessing how potential changes in water level will affect a reservoir’s habitat, says PPL Holtwood. The hydro project owner used the method to analyze the effects of a proposed 2.5-foot operational drawdown at its 107.2-MW Holtwood project on the Susquehanna River in Pennsylvania.

PPL Holtwood proposed the drawdown to allow greater generation during summer months (May 15 to September 15). The minimum level restriction for the project’s forebay, Lake Aldred, for this time period is 167.5 feet. PPL Holtwood proposed to change this restriction to 165 feet. The increased generation allowed by use of this water would bolster PPL Holtwood’s plan to increase capacity of the project by 125 MW (see “Industry News,” September 2006).

PPL Holtwood hired Kleinschmidt Associates to develop a GIS database of Lake Aldred, using ArcGIS software from ESRI. The database contained spatial information such as local hydrology and infrastructure; topography and bathymetry; and environmental parameters (i.e., location of threatened and endangered species, results of wetland surveys, etc.). Information in the database came from the Pennsylvania Spatial Data Access, the public access geospatial data clearinghouse for the state. To further populate the database, Kleinschmidt performed field surveys using a Pathfinder XRS differential global positioning system (GPS) from Trimble.

Subcontractor Kimball then took aerial photographs using GPS-integrated equipment and ground control surveys to produce precise topographic measurements of the lake during a temporary drawdown to about 163.3 feet. Kimball then computed topography from the photographs and ground control surveys. The resulting data was plotted at 1-foot intervals.

Kleinschmidt also used the GIS database to create a three-dimensional model of the bathymetry and topography of the lake.

During the temporary drawdown, Kleinschmidt surveyed the lake shoreline, identifying substrate transitions and plotting them using the differential GPS. Thirty-one sites along the shore were chosen to best represent the habitat throughout Lake Aldred. These characteristics then were extrapolated to the lake reaches between the transects. From this extrapolated data, the GIS created a “shape file” representing the entire lake. Using the shape file and the three-dimensional bathymetry model, researchers determined the area (in square feet) of each type of aquatic habitat available. At each lake elevation of interest (current maximum, current minimum, and proposed minimum), technicians calculated the amount of each habitat type.

Fisheries biologists then identified fish species composition, abundance, and spatial distribution in the lake. They also identified species requirements, such as preferred flow, depth, substrate, and vegetative cover. Finally, they gathered data on water quality and temperature requirements, response to turbidity, and effects of water level fluctuations (hourly and seasonal).

GIS analysis indicated that 50 to 60 percent of the habitat in Lake Aldred is deep water habitat that would be largely unaffected by the proposed project operations. The remaining habitat – a combination of shallow and deep littoral habitat – provides spawning, rearing, and foraging areas for the majority of the important resident fish. A 2.25-foot decrease from the maximum elevation would result in a slight decrease (about 4 percent) in overall aquatic habitat but would increase shallow littoral habitat by 24.4 percent. An additional 2.5-foot reduction in elevation temporarily would reduce habitat in the lake by an additional 4 percent. It also would result in a temporary relative gain in shallow littoral habitat of an additional 12.7 percent.

Due in part to the results of this GIS investigation, PPL dropped the proposed increased lake level fluctuations. However, PPL used the GIS/aerial photography method to analyze additional resource issues related to the proposed redevelopment, such as siting infrastructure to avoid effects on wetlands.

Book provides guidance on developing RCC specifications

The Portland Cement Association offers Guide for Developing RCC Specifications and Commentary.

Inadequate spillway capacity is one of the major causes of stress for dams. Use of roller-compacted concrete (RCC) can be a cost-effective method to provide overtopping protection for embankment dams. This 78-page book provides a comprehensive reference for developing RCC specifications for embankment armoring and spillway projects.

The guide includes sections on materials, equipment, construction procedures, and quality control requirements.

This new edition updates information in the first guide, printed in 2000.

– To order an Adobe pdf of the guide for $7 or a printed version for $18, visit the Internet: and search for “RCC specifications.”

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