Grant County PUD dealing with crack in Wanapum Dam spillway
Grant County Public Utility District is undertaking work to deal with a crack found in one spillway section at Wanapum Dam in late February.
The most recent work involved studying options to safely pass adult and juvenile salmon and steelhead past the dam if the drawdown of the reservoir continues into fish migration season. Adult upstream passage and juvenile salmon and steelhead begin to swim downstream in April, Grant County PUD says.
A drawdown of the water behind Washington’s Wanapum Dam began in early March as crews worked to stabilize a crack discovered on one of the spillway sections. A 65-foot-long by 2-inch-wide horizontal crack was found by divers Feb. 26 after a worker noticed a slight bend in a conduit that runs the length of the dam, indicating a shift in Wanapum’s structure.
The resulting discovery led Grant County PUD to coordinate with the Federal Energy Regulatory Commission and upstream dam operators, dropping the Columbia River forebay levels to the lowest they have been since the reservoir was filled in 1964.
The affected spillway is one of 12, which, combined, are capable of releasing 80,000 cubic feet of water per second based on current river conditions.
Even under a worst-case scenario, however, failure of one spillway would not cause immediate danger. “If one of the spillway sections failed, the remainder of the spillways and the main dam structure would remain intact,” the utility said in a release. “Under current conditions, the amount of water that would flow through this section of the dam would be within the range of normal river conditions.”
The dam is also home to the 1,038-MW Wanapum plant, which will continue generating power despite the drawdown.
Seepage barrier construction to occur at Bolivar Dam
The U.S. Army Corps of Engineers awarded a US$44.2 million contract to Treviicos South Inc. to construct a dam seepage barrier at Ohio’s Bolivar Dam.
Bolivar Dam is an 87-foot-tall, 6,300-foot-long embankment on Sandy Creek, a tributary of the Tuscarawas River.
Per the contract, Treviicos will construct a partial depth seepage barrier 4,500 feet in length and 145 feet deep through the upstream slope of the dam embankment, terminating in the left abutment, from the end of the seepage barrier to near the emergency spillway. The barrier is intended as a flood control structure.
Importance of emergency action plans reinforced
Big Bay Dam failed on March 12, 2004, in Purvis, Miss., leading to one of the largest releases of water due to a U.S. dam failure, according to the Association of State Dam Safety Officials (ASDSO). Nearly 4 billion gallons of water traveled 17 miles downstream as a result. The cause of the failure was deemed to be “internal erosion as a result of internal seepage.”
More than 100 homes and four other structures were damaged, but no lives were lost. This was attributed to the implementation of the dam’s emergency action plan.
“Emergency action plans are valuable tools that can help save lives by putting important safety and evacuation procedures in place before an emergency occurs. Everyone has a role to play in creating a future where all dams are safe, and the anniversary of the Big Bay Dam failure reminds us of the importance of understanding the risks associated with potential dam incidents and failures,” says Lori Spragens, executive director of ASDSO.
More information on staying safe near dams can be found in ASDSO’s informational guide, Living with Dams: Know Your Risks, which can be found at livingneardams.org.
Corps performing dam safety work at Chief Joseph Dam
The U.S. Army Corps of Engineers plans to hire companies to perform drilling needed to replace inclinometers monitoring what the Corps calls a “massive landslide” on the left bank of Chief Joseph Dam on the Columbia River in Washington.
The agency said the highest rate of movement is concentrated toward the toe at the southern end of the mass, nearest the dam, causing two critical inclinometers to move so much as to disable their ability to be read.
The company hired will drill two 6-inch-diameter holes, one 135 feet deep and another 195 feet deep, with an option for a third hole to 145 feet deep. Work is to include installation of 85-mm-diameter ABS plastic grooved inclinometer casings. Soil samples are to be recovered for geological characterization. Standard penetration tests of soil units are to be performed while drilling.