Statistical Modelling of Sediment Supply in Torrent Catchments of the Northern French Alps.

The ability to understand and predict coarse sediment transport in torrent catchments is a key element for the protection and prevention against the associated hazards. In this study, we collected data describing sediment supply at 99 torrential catchments in the Northern French Alps. The sample covers a wide range of geomorphic activity: from torrents experiencing debris flows every few years to fully forested catchments exporting small bedload volumes every decade. These catchments have long records of past events and sediment supply to debris basins. The mean annual, the 10-year return period and the reference volume (i.e. the 100-year return level or the largest observed volume) of sediment supply were derived for studied torrents. We examined the relationships between specific sediment supply volumes and many explanatory variables using linear regression and random forest approaches. Results showed that the ratio of sediment contributing area (bare soil) to catchment area is the most important predictor of the sediment production specific volumes (m[sup 3]/km[sup 2]). Others variables such as the Metlon index or the indices of sediment connectivity have also an influence. Several predictive models were developed in order to estimate the sediment supply in torrents that are not equipped with debris basins. [ABSTRACT FROM AUTHOR]