Global approaches to estimating torrential erosion - inputs from sloping land and sediment production

Abstract

The mountain streams are characterized by an important solid transport during floods. The materials are provided by the erosion processes occurring within the whole catchment. The knowledge of these processes and their quantification is an important point for engeneers studying torrential risks. This paper is restrained to the field of low spatial scales, where someone can observe processes with naked eye; they are considered in a global and integrating way. The disciplinary field of torrential erosion is complementary for torrential hydraulics and hydrology. It may be shared in 2 sections: slope sediment supplies and sediment yield. This paper would aim at presenting basic knowledge and engeneering methods. Flood is the integrating phenomenon connecting material fluxes: sediment supplies provided by slopes may reach the channel and are available for transportation by immediate or differred flows. Solid transport may be carried out as bedload transport or debris-flow. Geomorphology allows to situate actual erosion on a time scale and to assess if the considered catchment knows equilibrium or crisis. It helps when listing relevant processes and factors in a given study. The data on torrential erosion are rare. On slopes, each erosion process have his own rythm and fluxes are intermittent. Processes take turns to carry materials. Quantify slope sediment supply is very difficult. Some methods are suggested. Sediment yield is not the sum of slope sediment supplies: the reason are explicited. Some empirical and conceptual models may help prediction. Validation is a critical point.