Rodgers Dam Spillway is located near the end of the 300-mile long Humboldt River, which runs through northern Nevada. In 2006, due to an unusually wet spring, the river sustained a continuous high rate of flow for three full months and on July 17, the 55-year-old dam failed.
Initially, Dyer Engineering Consultants (DEC) considered gabion baskets to line the North spillway, but the gabions would be labor intensive. As an alternative, a concrete lined trapezoidal channel was suggested but the concern was that the soft sub-grade soils would settle, move and erode causing an inflexible structure to break.
ArmorFlex Class 70T articulating mats were presented as an option for the spillway. Using a hydraulic engineering center-river analysis system model of the channel provided by DEC, a solution that could withstand the 3,000 cubic feet per second discharge and handle sub-grade settlement without compromising the structure was determined.
As water transitioned from the spillway slope onto a flatter surface, original plans called for a concrete stilling basin to ease the flow of the water. However, site accessibility and logistics were challenging, and DEC sought to install 24-in. A-Jacks at the width of the spillway. The flow comes down the slope over the ArmorFlex and water transitions to the flatter surface where it runs into a field of A-Jacks forcing a hydraulic jump that brings the water down to a sub critical flow.
“By January 15, we had a revised set of plans ready to go and construction was underway. The entire structure was built by March 9,” commented Walter Slack, PE, project engineer for DEC. “We worked well with Contech and the Water District is very happy with the results and the speed of completion.”