Consolidation effects on morphodynamics modelling:application to the Gironde estuary

Abstract

This paper presents some on-going developments made jointly at Saint-Venant Laboratory for Hydraulics, in order to improve the numerical schemes, physical processes and accuracy of a 2D morphodynamic sand transport model. The final objective is to build an operational tool which can be applied by end users in complex estuarine environments. The 2D morphodynamic model (Sisyphe) of the finite element Telemac system has been applied to simulate the medium-term bed evolution in the central (40 km long) portion of the Gironde estuary, in the presence of sand-mud mixture and highly dynamical tidal forcing. Here, the main issue is to predict the sand bank migration and associated deposition rate around the outflow of the Blayais nuclear power plant. Up to now, the transport of non-cohesive particles has been treated separately from the cohesive material. Major effort has been conducted to optimise the numerical methods in order to reduce the computational time. The present 2D approach allows to predict the 10 year bed evolution within a couple of days. The influence of skin friction has been highlighted and the accuracy of numerical predictions can be improved by implementing a rippled bed rouhness predictor. However, the bank migration is overall underestimated, which probably comes from the neglected cohesive sediment properties. Further improvements are still in process to include cohesive sediment transport processes. Three different 1D vertical consolidation models have been developed using either finite elements, finite differences or a simple heuristic approach. Intercomparison of these 3 models shows that the second approach gives the best agreement with experimental data and needs to be integrated in Sisyphe.