A physically based model for the topographic control on shallow landsliding

TLDR

The study develops a model linking digital terrain data with hydrologic and slope‑stability components to assess how topography influences shallow landslide initiation. The model couples the TOPOG hydrologic model, which estimates soil saturation under steady rainfall, with a slope‑stability analysis for cohesionless soils, and evaluates the resulting critical rainfall thresholds against observed landslide locations in three high‑resolution basins. The model reproduces the spatial distribution of landslide scars in all three basins, but unmodeled hydrologic heterogeneity limits its ability to predict specific sites and timing.

Abstract

A model for the topographic influence on shallow landslide initiation is developed by coupling digital terrain data with near‐surface through flow and slope stability models. The hydrologic model TOPOG (O'Loughlin, 1986) predicts the degree of soil saturation in response to a steady state rainfall for topographic elements defined by the intersection of contours and flow tube boundaries. The slope stability component uses this relative soil saturation to analyze the stability of each topographic element for the case of cohesionless soils of spatially constant thickness and saturated conductivity. The steady state rainfall predicted to cause instability in each topographic element provides a measure of the relative potential for shallow landsliding. The spatial distribution of critical rainfall values is compared with landslide locations mapped from aerial photographs and in the field for three study basins where high‐resolution digital elevation data are available: Tennessee Valley in Marin County, California; Mettman Ridge in the Oregon Coast Range; and Split Creek on the Olympic Peninsula, Washington. Model predictions in each of these areas are consistent with spatial patterns of observed landslide scars, although hydrologic complexities not accounted for in the model (e.g., spatial variability of soil properties and bedrock flow) control specific sites and timing of debris flow initiation within areas of similar topographic control.