Role of topography on the volume of material eroded by debris flows, The

Abstract

Prediction of sediment volume of debris flows is the most important factor for designing debris-flow control structures or estimating debris-flow prone area. It has been considered that debris-flow volume may increase due to erosion at the steep channel. So, clarifying erosion volume (in this study, erosion volume is sediment volume in the channel eroded by debris flow) due to debris flow is a key information to mitigate debris-flow disasters. This study hypothesized that erosion volume might be controlled by topography, because it can be thought that the transport capacity of debris flow increased with the increase of stream bed gradient and contributing area. In Recent field observations by Schürch et al. (2011) supported to this hypothesis and showed a correlation, showing the correlation between flow depth and magnitude of erosion. However, detailed information about spatial pattern of erosion depth due to debris flow is still limited. In this study, spatial pattern measurements of erosion volume due to debris flows for 16 debris flows in Japan. LiDAR data taken before and after the debris flow was used for the comparison. Then, examination of stream bed gradient and drainage area derived from the LiDAR dataset was performed. The study found that erosion volume of debris flow increases as slope of stream bed gradient and drainage area increases. The study proposed methods to predict erosion volume due to debris flow using stream bed gradient and drainage area based on the probabilistic relationship between measured erosion volume and topography. That is, it is considered that the topography derived from LiDAR can be used as one of the indicators used in estimating volume of future debris flow.