US 101 Hoh River Erosion

The Hoh River is located on the west side of the Olympic Peninsula in Washington State. U.S. Highway 101 runs parallel to a section of the Hoh River just prior to its emptying into the Pacific Ocean. The river can experience extreme differences in depth and water flow speeds throughout the year depending on precipitation, snowpack accumulation and snow runoff speed. Highway 101 is the only viable highway (North-South) in this remote area and the county was performing emergency erosion repairs frequently to protect the integrity of the highway. DelHur was hired to protect and improve a section of the highway against erosion by constructing engineered logjams in and along the river. Construction consisted of diverting the entire river to enable dewatering of the work area and fish handling procedures were implemented. Diversion of the river flow required excavation of a diversion channel, the installation of a river diversion dam at the upstream end of the work area, the installation of a backwater dam at the downstream end of the work area, and careful introduction of flow into the new channel to minimize bedload material deposition in the Hoh River downstream of the work area. Construction of the engineered logjams required excavating riverbed material and existing riprap armoring along the bank, installing and removing sheet pile, installing steel H piles, placing riprap and riverbed material, and grading excess excavated material on existing river bars.