Repairs continuing at Wanapum Dam

WANAPUM VILLAGE - Grant County PUD officials still plan to raise the Columbia River behind Wanapum Dam before the end of the year. No date has been set for raising the water level.

That's according to a construction update presented at the regular commission meeting this week. The water level was dropped after a crack was discovered in a spillway pillar in late February. The water has remained at the lower level throughout the spring and summer. The shoreline was closed to the public.

Utility district employees conducted an analysis of the crack, and discovered there had been a mathematical error during the design phase. That error was repeated across the entire dam, and as a result repairs are being made to every spillway pillar, 13 in all.

The goal is to raise the water to somewhere between 558 and 562 feet above sea level, which is how the water level is measured, according to information presented at the meeting. The current water level is between 541 and 545 feet above sea level.

Once the refill begins, it will take a minimum of two to three weeks to refill the pool to the target of 561.5 feet, according to the report. Utility district managers will be meeting with the board of consultants overseeing the project to submit a refill plan, as well as the continuing repair plans for the spillway pillars, including the cracked pillar. The consultant board must approve the plans before the repairs can be completed.

The plan calls for drilling multiple holes through the structure into the bedrock, then dropping cables, called tendons, into each hole and cementing them in place. The cracked spillway pillar will get extra reinforcement, 20 cables around the cracked area.

The cables are installed and then stretched, although there's some flex to reduce the possibility of damage in case of an earthquake. Four have been installed and one has been stretched into place; there are 35 in all.

Commissioners also received an update on an ongoing project to assess the risk to Wanapum and Priest Rapids dams because of earthquakes.

The project was put on hold during the repairs at Wanapum Dam, according to the report. Utility district engineers were, and are, analyzing the spillway pillars, spillway gates and turbine intakes at Wanapum Dam, and the right bank at Priest Rapids Dam, to determine how they would react in an earthquake.

The draft reports have been completed, and completion of the entire report is projected by the third quarter of 2015.