Description |
SHALSTAB is a digital terrain model for mapping shallow landslide potential. It is based on a simplification of the infinite slope analysis coupled to a hydrologic model. The model assumes that the resistance to movement along the sides and ends of the landslide are not significant and that the cohesion is zero. Furthermore, the model does not consider the effects of root strength on slope stability on the assumption that the model is capturing the condition of low root strength that would occur after cutting, disease, or a fire. To model the hydrologic controls the steady state shallow subsurface flow is calculated based on the work of O'Loughlin 1986. It is assumed that the steady state hydrologic model mimics the effect of transient rainstorms whose short term effective rainfall is greater than the steady state value. The coupled hydrologic-slope stability equation is solved by the program. The model has three topographic terms that are defined by the numerical surface used in the digital terrain model: drainage area, outflow boundary length and hillslope angle. There are potentially four parameters that need to be assigned to apply this model: the soil bulk density, the angle of internal friction, the soil transmissivity, and the effective precipitation. The program can be used as a parameter free model in which the only decision is how to rank the mapped pattern of relative stability into such categories as "high", "medium" and "low" for the practical purpose of prescribing some land management practice. This utility is accomplished by eliminating many processes or factors that do matter to slope instability but require too much local parameterization to be useful in a practical context for application over large areas. |