Streamside Policies for Headwater Channels: An Example Considering Debris Flows in the Oregon Coastal Province

Abstract

Abstract Management policies are increasingly debated for headwater channels given their prevalence and ecological importance in many landscapes. Quantitative differences among headwater channels may offer an objective basis for prioritizing streamside protection. Here, we examine differences among headwater channels as potential transport corridors for debris flows. Specifically, we model differences among hill slopes and headwater channels in probabilities of initiating and being traversed by debris flows that deliver to fish-bearing channels. We develop an approach to rank these probabilities and apply the ranks in delineating alternative streamside management zones. Initiation and traversal probabilities are estimated from an empirically calibrated debris-flow model using regionally available 10-m digital elevation data. Alternatives are delineated by encompassing 25%, 50%, and 75% of debris-flow susceptible hill slopes and headwater channels. Highest initiation and traversal probabilities were contained in a relatively small percentage of the study area. Encompassing lower probabilities required disproportionately larger areas. Substituting delineated alternatives for currently prescribed headwater riparian management zones decreased the total area encompassed on federal lands but increased it on private and state lands. Our intent is not to advocate for any particular alternative but to demonstrate that knowledge about how headwater channels differ over large areas can help tailor riparian policies.