Study on modelling the morphology of torrents on volcano slopes

An exploratory study is done to modelling of rivers on volcano slopes. Beside the occurrence of mud flows or lahars these rivers are characterised by unsteady supercritical flow and large suspended-sediment concentrations. A fully coupled 1D model is presented for the rivers, provided that lahars do not occur. It can simulate unsteady supercritical flow (Froude numbers between about 1 and 1.8) with volumetric sediment concentrations less than about 10%. The redistribution of the suspended-sediment concentration (i.e., the lag between concentration and transport capacity due to sediment relaxation) causes instabilities of the bed conformable to antidunes. Calculations with a numerical model using Preissmann's implicit scheme, and applied to a river on the Kelud Volcano in Indonesia, show the rapidity of bed-level variations and the upstream propagation and growth of bed disturbances. These results offer a deeper understanding in the problems of the rivers on the Kelud. Furthermore it yields a base for inve...