Landslides can be a significant source of sediment in watersheds. Landslide materials which enter stream channels can create unwanted responses such as blockage or diversion of the stream and significant degradation of the aquatic and riparian habitats. Estimates of amount of material delivered to a stream channel by a landslide would be of great value to watershed managers. In this study, current methodology was reviewed and new models were developed for estimating the delivery of landslide materials to a stream channel.

A mutually beneficial collaboration was developed with researchers at the University of Newcastle-upon-Tyne, Great Britain, regarding a review of the state-of-the-art and conceptualization of new approaches. A very important literature review was produced by the British group.

New models were developed from landslide measurements collected in Idaho between 1974 and 1976. Over 1300 observations were screened and utilized to produce a two-step approach for estimating delivery. In the first step, site characteristics of landslide length, distance of the landslide from the stream, and the slope gradient are entered in a logistic model. The logistic model defines whether the landslide will reach the stream. If landslide material does reach or “makes it” to the stream, a multivariate model is used to estimate the percent of delivery. The multivariate model is conditioned on the observation that a slide reaches the stream. Although the confidence intervals on the delivery estimates can be quite large, the models combine physically meaningful site characteristics accounting for spatially variable landslide delivery. The models developed in this study will be useful in suggesting directions for further research and watershed modeling approaches.