Debris flow network morphology and a new erosion rate proxy for steepland basins with application to the Oregon Coast Range

Abstract:

Channel reaches dominated by debris flow scour and incision tend to greatly influence landscape form in steepland basins as they can account for >80% of channel length as well as the vast majority of valley network relief. While hillslope and fluvial transport models have been combined with digital topography to develop proxies for erosion rates, debris flow networks, despite their ubiquity, have not been exploited for this purpose. This represents a major gap in our current ability to estimate landscape erosion from digital elevation models. In order to bridge this gap, we apply a previously proposed empirical function (Stock et al., 2003) that describes the variation of valley slope with drainage area in fluvial and debris flow reaches of steepland channel networks. We use high-resolution 1m airborne laser altimetry data for several catchments across the Oregon Coast Range to explore variation in the model parameters, chiefly the rate with which concavity decreases in the upstream direction. Our analysis documents variations in model parameters that result from differences in network geometry, scale, lithology, and the pace of base level lowering. Finally, we propose a function that relates these parameters to erosion rates acquired via cosmogenic nuclides for numerous catchments in the Oregon Coast Range.