Stephen D. Ellen

Real-Time Landslide Warning During Heavy Rainfall

A real-time system for issuing warnings of landslides during major storms is being developed for the San Francisco Bay region, California. The system is based on empirical and theoretical relations between rainfall and landslide initiation, geologic determination of areas susceptible to landslides, real-time monitoring of a regional network of telemetering rain gages, and National Weather Service precipitation forecasts. This system was used to issue warnings during the storms of 12 to 21 February 1986, which produced 800 millimeters of rainfall in the region. Although analysis after the storms suggests that modifications and additional development are needed, the system successfully predicted the times of major landslide events. It could be used as a prototype for systems in other landslide-prone regions.

Statistical and Simulation Models for Mapping Debris-Flow Hazard

We describe two different GIS-based approaches to the delineation of debris-flow hazard. The first is empirically based, and uses logistic regression to predict sites of rainfall-induced shallow landslides that initiate debris flows in San Mateo County, California. The second is both empirically and process based, and uses multiple physically-based simulations of debris flows to evaluate hazard downslope from initiation sites in Honolulu, Hawaii. The two approaches use fundamentally different data to delineate hazard in fundamentally different ways, and are described here as contrasting examples of approaches to hazard delineation.