Tech Briefs

Issue 4 and Volume 27.

Techniques minimize effects of blasting on structures, fish

Using a combination of rock work pads and bubble curtains helped Columbia Power minimize effects on both existing structures and fish during construction of the 120-MW Brilliant Expansion project. As a result of these measures, no fish were killed and no damage to the existing dam occurred during blasting.

The Brilliant Expansion project is situated immediately downstream from the existing Brilliant Dam and its 145-MW generating station. The Kootenay River below Brilliant Dam is home to endangered white sturgeon.

Construction of a new powerhouse, intake channel, power tunnel, and access tunnel began in spring 2003. Much of this work involved blasting. To protect both the existing dam and fish in the river, Columbia Power used rock pads and bubble curtains.

The rock work pads involve placing clean rock in the river and drilling through the rock to place explosive charges. These work pads were used to physically exclude fish from areas where pressures from the blast exceeded guidelines for the protection of fish, issued by Fisheries and Oceans Canada. The rock work pads were the primary fish exclusion measure; bubble curtains were used in locations where it was not possible to use the work pads, such as removal of the intake rock plug.

The bubble curtains consist of polyvinyl chloride (PVC) pipes with holes drilled in them. The pipes are placed underwater and compressed air is pumped through the pipes. As the shockwaves from the blasting pass through the bubble curtain, they lose energy. Bubble curtains were used to protect the Brilliant Dam intake gates and to exclude fish from the area next to a blast.

Columbia Power plans to use these techniques during construction of the upcoming Waneta Expansion Project.

Tool available to assess cyber security at hydro plants

Owners of hydroelectric facilities can use the Control System Cyber Security Self-Assessment Tool (CS2SAT) to help assess the cyber security of their control system networks. CS2SAT is a desktop software program for evaluating industrial control system networks. The tool was developed under the direction of the U.S. Department of Homeland Security (DHS).

CS2SAT guides users through a step-by-step process to collect facility-specific control system information, then makes recommendations for improving the facility’s cyber security. The tool pulls its recommendations from a database of the best available cyber security practices, which have been adapted specifically for application to industry control system networks and components. Each recommendation is linked to a set of actions that can be applied to remediate specific security vulnerabilities.

Hydropower Generation Report
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In addition, CS2SAT provides:

    – A comprehensive evaluation and comparison to existing industry standards and regulations, including those issued by the North American Electric Reliability Corporation, the U.S. Department of Defense, and the National Institute of Standards and Technology;

    – Opportunity for discussions regarding security practices within the facility, particularly with regard to industrial control system cyber security;

    – Identification of potential vulnerabilities and recommended actions for improving the facility’s control system design or security policies; and

    – Guidelines for industrial control systems cyber-security solutions and/or mitigations.

CS2SAT can aid in identifying and mitigating vulnerabilities in a control system infrastructure, says Jeffrey L. Hahn, P.E., industry outreach coordinator with Idaho National Laboratory’s Control System Security Program. Asset owners can use the software in developing a systematic approach to secure their facilities against cyber attacks. The laboratory assisted in developing the tool.

– CS2SAT is free to federal government agencies by e-mail: [email protected] gov. For others, the tool is being distributed by ISA Automation Standards Compliance Institute (visit: www.isa.org/ asci/cs2sat) and Lofty Perch (e-mail: [email protected]).

Membrane barrier installed without sealing seams

A geomembrane on the upstream face of a weir at the 49-MW Ashlu Creek project in British Columbia limits seepage through the weir. In installing the geomembrane blanket, Ashlu Creek Investments Limited Partnership used an unconventional approach of overlapping, rather than sealing, the seams.

The Ashlu Creek project diverts flow from behind the earth/rockfill diversion weir. The intake, sluiceway, and spillway are attached to the weir, which is founded partially on rock and partially on fluvial sands and gravel. The weir has a central clay core, rockfill shells, and an impervious geomembrane blanket that extends about 60 meters upstream from the weir.

The membrane and filters/drains under the downstream shell of the weir are intended to limit the amount of underseepage. Because seepage through the membrane contributes to the minimum downstream flows required at the project, it was not necessary to seal the seams. To prevent the buildup of underpressures, the contractor overlapped the seams of the membrane by at least 1 meter. Underpressures could develop when the water in the reservoir is drawn down to minimum operating levels and groundwater seepage pressures from the slopes above the intake may be higher than the reservoir pressures.

It is uncommon to overlap the seams rather than sealing them, says Richard Blanchet, vice president, western region – hydroelectric energy for Innergex, which owns Ashlu Creek Investments. At Ashlu Creek, the objective was to limit and control seepage, not stop it completely. At this project, there is overburden pressure on the seams of the membrane from the filter and riprap cover to the blanket. In addition, under normal conditions, the water pressure from the reservoir on top of the membrane is greater than the seepage pressure under the blanket, thus holding the seams together and limiting the leakage.

The membrane was installed in the fall of 2007.

Using self-consolidating concrete to form an ogee spillway crest

During construction of Hickory Log Creek Dam, the city of Canton, Ga., chose self-consolidating concrete (SCC) to form the ogee spillway crest and training walls. This alternative to conventional concrete can be used in areas where consolidation using vibration or other means is difficult.

Hickory Log Creek Dam is a roller-compacted-concrete (RCC) dam on Hickory Log Creek in Georgia. The 180-foot-high dam, the highest RCC dam in Georgia, was completed in November 2007 to increase available water for the growing area northeast of Atlanta.

For Hickory Log Creek Dam, using SCC allowed forming of the entire curved ogee spillway crest shape. Had conventional concrete been used, the ogee shape of the spillway would have to be hand-trimmed using a profile to ensure the correct shape.

The training walls at this dam also were built using SCC. Although the training walls were not heavily reinforced, they were close to 20 feet high in places. Using SCC allowed the contractor – Thalle Construction Co. Inc. of Hillsborough, N.C. – to forego concrete consolidation when placing concrete in multiple lifts from difficult placement areas.

SCC is conventional concrete with an additive that creates a mixture offering a high slump, without the need to add much water. The aggregate gradation is slightly different than in a conventional concrete mix. SCC flows through the formwork and around the reinforcing steel, avoiding the need for internal consolidation in most cases.

This type of concrete was introduced in 1990 in Japan. Although self-consolidating concrete has been used in the U.S. for several years, it has not been used extensively to form hydraulic structures.

Results of testing after placement at Hickory Log Creek Dam showed that compressive strength of the SCC was as specified, says Randall P. Bass, P.E., senior associate with Schnabel Engineering Inc. Bass was the overall project manager for construction of the dam.

Replacing hydraulic conduits with FRP pipe

The use of fiberglass-reinforced plastic (FRP) pipe to replace a section of penstock at the 3.5-MW Jackman hydro facility on the Contoocook River in New Hampshire is an example of application of this product in large-diameter pipes. FRP pipe has been available for more than 40 years and has been installed at hydro facilities. However, its use typically has been limited to the chemical industry, with pipes less than 36 inches in diameter.

During replacement of a 2,400-foot-long section of wood stave penstock at Jackman, Public Service of New Hampshire chose to use FRP pipe. FRP consists of fibers embedded in a polymer matrix. The fibers reinforce the polymer, improving its tensile strength. The polymer protects the fibers and distributes load to them through shear stress.

Since the early 1980s, manufacturing methods have evolved to create large-diameter, high-stiffness, corrosion-resistant FRP pipe at prices comparable to other pipe materials (such as steel or concrete), says Keith A. Martin, project engineer with Kleinschmidt Associates, the company that designed the installation.

However, there are challenges to using FRP as a penstock material. These include: the possibility of ultraviolet degradation when exposed to sunlight over time; the challenge of manufacturing fittings (elbows, tees, etc.) that can withstand the stress of a high-pressure application; and the difficulty of monitoring the manufacturing quality of the FRP.

The wood stave penstock at Jackman was installed in 1926. By the mid-2000s, the penstock was showing signs of aging (i.e., crushed staves, broken saddles, and significant leakage).

Public Service of New Hampshire chose FRP pipe for three reasons.

First, the wood stave penstock was low to the ground, in relatively flat runs. Peak internal pressure was less than 50 pounds per square inch. At this pressure, FRP was cost-competitive with steel.

Second, FRP is corrosion-resistant, making it a good candidate for burial in the rough-graded shallow trench of the original penstock. The new penstock was half-buried, which costs seven times less than supporting it above ground on 30-foot spans.

Third, FRP pipe is not expected to require maintenance for 30 to 50 years.

Installation of the penstock was completed in the summer of 2006. The pipe has performed satisfactorily since this installation.

Based on the initial experience at Jackman, Public Service of New Hampshire chose to use FRP pipe for a second phase of the penstock replacement. This work was completed in the fall of 2007, and the pipe has performed satisfactorily.