The first of 35 steel anchor tendons has been installed on the Wanapum Dam spillway in Washington, US, paving the way to increase the river elevation behind the dam later this year.
The tendons begin at the top of the spillway and end deep into the bedrock below the dam, in a bid to ensure the long-term stability of the spillway. Along with the approximately 200ft-long anchor tendons throughout the spillway, work is also underway to install over 50 steel anchor bars to repair the one fractured spillway structure, discovered by divers earlier this year.
The work is expected to continue into the first quarter of 2015, with enough of the installations completed to partially raise the level of the reservoir behind the dam in the fourth quarter of 2014, pending the Federal Energy Regulatory Commission (FERC) approval. These repairs and the subsequent increase in river elevation, will allow the utility to restore public access to the shoreline, increase electric generation, improve public safety concerns and protect culturally-sensitive sites.
Operational and repair costs at the dam have now been estimated at $69 million, up from earlier estimates of $61 million. The dam continues to generate electricity and accommodate river flows in coordination with the other dam operators on the Columbia River.
A fracture was detected in the dam’s spillway pier monolith No. 4 by divers on February 27, three days after a worker noticed that the top of the spillway pier had shifted slightly downstream.
Grant County PUD has said that a mathematical error during the pre-construction design of the dam may be partly to blame for the fracture developing.
