Kiewit Pacific Co., a subsidiary of Kiewit Corporation, was awarded this $15.3 million project to replace the top portion of the 128-ft.-high dam, damaged from more than 40 voids in the earthen embankment increasing the possibility of dam failure that would interrupt the water supply critical to farmers and jeopardize safety to downstream residents.
Located on the headwaters of the Yakima River, the dam was rebuilt on its existing footprint of both recycled and borrowed materials consisting of highly compacted fine-grained soils armored with large rock riprap. Of the 640,000 cu. yd. of material presently contained in the embankment, roughly half was reused in the new dam. Approximately 500 truckloads of material were moved on-site each day, hauling either excavated materials to stockpiles, or stockpiled and borrow material for placement into the new embankment.
The project incorporated several conservation measures and best management practices to minimize impacts on the surrounding environment. Approximately 1.5 acres of natural and 2.3 acres of manmade wetland was constructed downstream of the existing dam at the Meadow Creek alluvium. In addition, piezometers were installed throughout the embankment, foundation and tow drain to monitor water quality and quantity, and dam integrity.