RESPONSE OF ROAD-STREAM CROSSINGS TO LARGE FLOOD EVENTS IN WASHINGTON, OREGON, AND NORTHERN CALIFORNIA

The relative importance of water, wood, and sediment in triggering road-stream crossing failures has not been adequately studied. Effects on downstream aquatic and riparian resources from road-stream crossing failures would be reduced if appropriate designs were incorporated into existing culvert-sizing techniques to facilitate the passage of organic debris and sediment. As part of a flood impact assessment project, the US Department of Agriculture Forest Service and US Department of the Interior Bureau of Land Management initiated a survey of failed road-stream crossings on public lands in areas of the Coastal, Klamath, and Blue Mountain Provinces of the Pacific Northwest. The objectives of the survey were to identify the mechanisms and on-site consequences of road-stream crossing failure and determine the degree to which specific failures could have been predicted by using watershed-scale screening methods currently under development. This report discusses the results of the survey.