![]() It is also worth noting that these relationships have been produced from regression (i.e., mean trends) or envelope curve models (i.e., maximum potential). Several relationships have been established in the literature (Table 1) involving only one or multiple parameters with, for example, a surface area parameter (catchment area, sediment-contributing area also called effective catchment area or contributive catchment area Harvey, 2002 Fryirs, 2013) a slope parameter (stream slope, fan slope) a length parameter (length of the erodible channel) or a parameter relating to the geological/geomorphological context, reflecting the potential for erodible materials. If there are sufficient data, a frequency analysis can also be considered ( Jakob and Friele, 2010).Įmpirical methods are relatively simple approaches to estimate the material supply of a torrent and are commonly used in engineering projects ( Jakob, 2021). Four main groups of approaches are typically employed to predict the volumes produced by debris flows and/or floods: (1) empirical approaches relating volume to catchment-describing parameters (e.g., Takei, 1984 Marchi and D'Agostino, 2004), (2) hydrological approaches considering the link between volumes and water flows ( Rickenmann and Koschni, 2010), (3) geomorphological approaches estimating volumes from on-site recognition of sediment sources located along the channel network ( Hungr et al., 1984), and (4) historical approaches assessing volumes from data observed during previous events (e.g., test pits, topographic surveys of the deposited volumes, dredging of debris basin D'Agostino, 2013). In mountain areas, knowledge of the mean annual and event-driven sediment supply potential is important for the assessment of torrential hazards and the management of torrent catchments. Several predictive models were developed in order to estimate the sediment supply in torrents that are not equipped with debris basins. Other variables such as the Melton index or the indices of sediment connectivity also have an influence. Results showed that the ratio of sediment-contributing area (bare soil or rock) to catchment area is the most important predictor of the specific sediment production volumes (m 3 km −2). We examined the relationships between specific sediment supply volumes and many explanatory variables using linear regression and random forest approaches. 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 the studied torrents. These catchments have long records of past events and sediment supply to debris basins. The sample covers a wide range of geomorphic activity: from torrents experiencing debris flows every few years to fully forested catchments exporting small bed load volumes every decade. In this study, we collected data describing sediment supply at 99 torrential catchments in the northern French Alps. The ability to understand and predict coarse-sediment transport in torrent catchments is a key element for the protection against and prevention of the associated hazards.
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