Floods and sediment dynamics in mountain rivers

Abstract

While floods in plain rivers are solely controlled by water flow, severe inundations in mountain rivers are always related to extremely large inputs of sediment from landslides and debris flow, followed by sudden deposition along the hydrographic network and consequent bank overflowing. To describe the space — and time — dependent process in relatively large and morphologically complex watersheds, an adequate model for water flow and sediment transport is proposed. Since a fundamental role in the overaggradation mechanism is played by the grain size distribution of sediment input, an approximate method is described how to estimate the composition of input material by the composition of material at the stream bottom.

A description is given of the flood of July 1987 in the Torrent Mallero (Italian Alps), related to large mass movements (landslides and debris flow), together with a simulation of the event by a mathematical model.