Predicting Debris Flow Initiation Zone Using Statistical And Rock Kinematic Analyses, A Case Study From West Prong Little Pigeon River, TN

Nandi, A; Shakoor, A

ABSTRACT: Debris flows are a dominant form of slope movement in the southern Appalachian Mountains of the United States. These slope failures damage roadways, dam streams, and, occasionally, injure people. This study presents debris flow initiation zone susceptibility analysis of the West Prong Little Pigeon River (WPLPR) watershed in the southern Appalachian Mountains, using spatial statistics. Debris flow locations were identified from aerial photographs, satellite imagery, Light Detection and Ranging (LiDAR), and field surveys. Topographical, geological, hydrological, and structural data were collected, processed, and constructed into a spatial database of debris flow initiation zone using geographic information system (GIS) and image processing. Logistic regression model was used to evaluate the role of these data (i.e. factors) in controlling debris flow susceptibility. The area under the curve method was used to validate the results, showing 82.7% accuracy of the prediction model. A debris flow initiation zone susceptibility map was generated and compared with the spatial distribution of several debris flow initiation scars in the field, originating during extreme rainfall events. Additionally rock kinematic analysis was used to characterize the failure modes for selected slopes in the study area. The study pointed out that most debris flows initiated as wedge failures in weathered and weak phyllitic bedrock, with abundant discontinuities, which became unstable with the addition of water from spring thaw and summer storm events. In summary, the GIS based spatial statistical model provided a powerful tool for debris flow initiation zone susceptibility mapping, and the rock kinematic analysis provided a good evaluation of the associated failure mechanism that provided initial material for debris flows.