Numerical Modeling of Geomorphic Processes in the presence of Slope Failures.

Stefania Evangelista, Massimo Greco, Angelo Leopardi

Friday 3 july 2015

14:30 - 14:45h at Antarctica (level 0)

Themes: (T) Sediment management and morphodynamics, (ST) Sediment transport mechanisms and modelling

Parallel session: 16A. Sediment - Coast

Unsteady flows in rivers with steep bedforms or banks are not only governed by flow-driven sediment transport but also by collapse mechanisms. As a consequence, slope failure mechanisms have been recently included in morphodynamic models in order to improve their descriptive capabilities. The objective of the paper is to test the performances of a two-phase model which includes a geo-failure operator through its application to some synthetic test cases. The resulting mathematical model is numerically solved through a mixed Cell-Centered and Node-Centered Finite-Volume discretization over unstructured triangular meshes. The two-phase model accounts for variable bed-load sediment concentration and for inter-particle collisional stresses. The geo-failure operator performs in a way that when in the cell the bed slope exceeds a critical angle, the corresponding bed material and pore water becomes available to flow, thus following the two-phase flow dynamics. The algorithm also permits the failure to propagate from the single cell to the entire domain, preserving both the continuity of the bottom surface and the mass conservation. The numerical simulations of some significant test-cases enlighten the effectiveness of the proposed model. The selected examples simulate key-conditions in which the slope failure and/or the interactions between phases have to be mandatorily accounted for. In all the presented tests, the initial slope, connecting two horizontal reaches, exceeds the material repose angle in saturated conditions. In detail, the following scenarios have been simulated: a) slope partially or completely submerged by still water (where the submerged part is not in equilibrium in the initial condition); b) slope invested by a dam-break wave eventually overtopping the upper horizontal part; c) filling of a reservoir by a constant discharge, which gradually submerges the barraging slope. Simulation results prove the reasonable capability of the considered model to deal with all these different conditions, reproducing the main features of the complex interaction between sediment and water.