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Dam Safety & Security

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TVA to conduct seismic evaluations at Pickwick Landing

Tennessee Valley Authority has accelerated its annual drawdown of the reservoir behind Pickwick Landing Dam in southern Tennessee for a dam safety seismic study.

TVA said in September that initial results from testing and core drilling suggest a remote chance that the earthen embankment south of the concrete portion of the dam could be damaged by a large earthquake. The dam is located a few hundred miles from the New Madrid Seismic Landing Zone along the Mississippi River.

Lower lake levels at Pickwick Landing will allow TVA to conduct analysis and testing over the next several months to determine what would be necessary to strengthen the south embankment against large seismic events. The agency said levels are expected to reach winter pool about six weeks earlier than normal, although water levels downstream of the dam on Kentucky Reservoir will not be affected.

The complex is also home to a 160-MW hydropower plant.

Corps announces rehabilitation work for four dams

The U.S. Army Corps of Engineers has announced contracts for infrastructure work on dams in Oklahoma, Nebraska, Oregon and Pennsylvania.

The Corps’ Tulsa District awarded a $26.99 million contract to Kiewit Infrastructure South Co. to perform the remaining excavation that will allow flows into a new auxiliary spillway at Canton Lake Dam on the North Canadian River in Oklahoma. This second phase will remove the remaining soil plug that prevents lake flows into the new spillway. Work includes reshaping some sections of the dam embankment, as well as construction of diaphragm walls and a cofferdam, and dewatering.

The Corps’ Kansas City District awarded a $25.7 million contract to OCCI Inc. to repair tainter gates at Harlan County Dam in Nebraska. The project includes the rehabilitation of two to three spillway tainter gates, with OCCI to strengthen structural steel components, replace trunnions and bearings, replace tainter gate chains, repair or replace electrical systems, and blast and paint gates.

The Corps’ Portland District has begun rehabilitation of one of two spillway gates at the 80-MW Green Peter project on Oregon’s South Santiam River. The work is intended to improve the dam’s ability to reduce flood damage on the South Santiam, with work to include strengthening the gate face; replacing the gate’s arms; replacing trunnion pins and wire ropes; and replacing or refurbishing electrical controls, gearboxes and other systems.

Last, Layne Christensen Co. was awarded a $132.5 million contract by for construction of a deep cutoff wall at East Branch Dam in Pennsylvania. The rolled earthfill dam, on the East Branch Clarion River, has experienced seepage problems that required repairs in 1957. The dam has been determined to be potentially unsafe, prompting the Corps to take precautionary measures pending implementation of a dam safety modification program. The concrete cutoff wall is to be constructed through the dam and abutments, reaching an expected maximum depth of 260 feet.

Grant PUD installs first anchor tendons at Wanapum Dam

Restoration of Wanapum Dam in Washington reached a milestone in September with the installation of the first steel anchor tendon. Grant County Public Utility District and its contractors will eventually install 35 of the tendons as part of the rehab project.

Each of the 200-foot-long anchor tendons will begin at the top of the spillway and end deep in the bedrock below the dam. Work is also being done to install more than 50 steel anchor bars to repair Wanapum Dam’s pier monolith No. 4, which was discovered as having a 65-foot-long by 2-inch-wide horizontal crack in May.

The repairs will allow Grant PUD to restore water levels upstream of the dam by the end of the year, pending Federal Energy Regulatory Commission approval. Grant PUD began a drawdown behind the dam after the crack was discovered, lowering levels by more than 25 feet.

The operational and repair costs of the project are estimated at US$69 million, with Grant PUD paying for the bulk of the work by using cash reserves and selling bonds.

FERC names consultant for geotechnical engineering

The Federal Energy Regulatory Commission has awarded a contract worth a maximum of $850,000 for a geotechnical engineering consultant to its Division of Dam Safety and Inspections.

Alfred J. Hendron of Savoy, Ill, received the contract to provide consulting services on a labor hour basis. The work is to include in-depth review of all factors leading to a determination that a dam requires remedial measures due to geotechnical deficiencies and review of proposed remediation and construction alternatives to ensure projects use best engineering practices.

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