Repairing the Wanapum Spillway Crack

Wanapum Dam is a hydroelectric project on the Columbia River owned and operated by Washington’s Grant County Public Utility District (District). On 27 February 2014, a two-inch wide crack was discovered on the upstream side of Wanapum Dam’s Monolith 4, one of twelve concrete monoliths that make up the spillway. The fracture ran the length of the 65-foot wide structure and was two inches at its widest point. Detailed discussions of the root cause investigation[1] and the design of remedial measures[2] that were implemented at Wanapum Dam are being presented in separate papers at the September 2015 ASDSO conference.
The District and its engineering consultants, MWH, worked together with Nicholson Construction Company to develop and implement an emergency repair plan for Monolith 4 and strengthening measures for the rest of the spillway structure. The restraining force necessary to stabilize the dam required thirty-five 61-strand tendon anchors with lengths up to 260 feet installed through the dam structure. An additional sixty-nine solid bar anchors were installed most of which were installed under water through the ogee spillway on the upstream side of the radial gates.