Efficient consolidation model for morphodynamic simulations in Low-SPM environments

Abstract

This paper presents a new model, using existing consolidation theory, suitable for long-term morphodynamic simulations; we refer to the dynamic equilibrium consolidation (DECON) model. This model is applicable for muddy systems at small suspended particulate matter (SPM) concentrations, where the sedimentation rates are smaller than the consolidation rates and small fractions of sand can be accounted for. Thus, the model assumes quasi-equilibrium of the consolidating bed. It is derived from the full consolidation (Gibson) equation and is implemented in a mixed Lagrangian-Eulerian bed model guaranteeing stable and non-negative solutions, while numeric diffusion remains small. The erosion and deposition of sand and mud is accounted for, whereas internal mixing (e.g., bioturbation) is modeled through diffusion. The parameter settings for the new consolidation model (the hydraulic conductivity, consolidation coefficient, and strength) can be obtained from consolidation experiments in the laboratory. The model reproduces one-dimensional consolidation experiments and the qualitative behavior of erosion and deposition in a tidal flume. The DECON model was also applied to more natural conditions, simulating fine sediment dynamics on a schematized mud flat and in a schematized tidal basin under tide and wave forcing. The computational results of the mudflat simulations compared well with the simulations with the full Gibson equation. For the tidal basin simulations, DECON predicted the expected landward tidal transport of fine sediment during tide-dominated conditions, while the tidal basin withstood erosion during the more energetic wave-dominated periods. Computational times for the morphodynamic simulations of the tidal basin example without waves increased by a factor of 5 when consolidation was included. For the simulations with waves, this increase in computational times was only a factor of 2, as simulations with waves are always expensive. Applying a complete consolidation model would be prohibitive. The DECON model therefore serves as a useful tool to simulate fine-sediment dynamics in complex wave- and tide-dominated conditions, as well as the effects of seasonal variations.