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This video footage shows the Hoh River at flood stage on November 7, 2006, approximately 12 hours after the second-highest ever flow (58,000 cfs) was recorded on the Hoh River. The high flow peaked at about 7 feet above the water level shown in the video. Herrera Environmental Consultants assisted WSDOT in the design of engineered logjams at the site to deflect river flows away from the road, which had failed during previous, smaller floods. The structures were constructed in 2004. This event was the largest flood that these structures have endured and the road was not compromised. The footage was collected by staff biologist Josh Wozniak and project engineer Katie Jagt. |
The idea that engineered logjams could withstand the force of the Hoh, South Fork Nooksack, Mashel, and White rivers had many people rolling their eyes. After record rainfall and flooding (that washed away roads and homes) failed to dislodge these logjams, there are now fewer skeptics. There is also a growing awareness of this emerging technology that offers an ecologically restorative approach for protecting infrastructure against floods and erosion.
Flooding in recent weeks served as a powerful test of this new technology that combines engineering and river science to restore rivers and protect infrastructure. Over the last 4 years, Herrera has designed and constructed more than 40 engineered logjams in Washington and Oregon that have created new salmon habitat while protecting roads, pipelines, homes, and farmland.
After years of dumping large rock (riprap) into the Hoh River to protect U.S. Highway 101, the Washington State Department of Transportation called upon Herrera to design a series of engineered logjams to deflect the river away from the highway and create a haven of pools and side channels for salmon. The engineered logjams were designed to withstand the force of a 100-year flood event with a flow of 67,000 cubic feet per second (cfs). Constructed in 2004, these huge logjams each included more than 125 large logs stacked more than 30 feet high and 50 feet across. The November flood had a flow of 58,000 cfs and submerged the structures. After the floodwaters had receded, the logjams and highway were still intact and looked great. The logjams create not only the deep pools and cover sought by salmon but are a haven for otters, birds, and other wildlife.