A. Nnafie1,2, L. Perk1
The performance of the new flexible mesh (FM) morphodynamic numerical model Delft3D-FM in simulating morphology on long time scales (order years to decades) is verified by running this model for the case of a tidal inlet system. Results from this model are compared with Delft3D, which has been proven successfully in simulating the morphology of tidal inlet systems. As a benchmark, the Delft3D-FM should be able to simulate a seaward located ebb-tidal delta that is connected to a complex branching pattern of tidal channels inside the basin (Figure 1). This test case is adopted from the work by Ridderinkhof et al., 2014, who studied effects of the length of the back-barrier basin on the sand volume and spatial symmetry of ebb-tidal deltas using Delft3D.
Simulations with Delft3D-FM and Delft3D are carried out for the same configuration as that used by Ridderinkhof et al., 2014. The model domain consists of a rectangular open sea and a back-barrier basin, which are connected to each other by a narrow tidal inlet. The model, which starts from an initially flat bed, is forced by a propagating tidal wave with three harmonic constituents (M2, M4 and M6). The used sediment transport equation is the Engelund-Hansen total load formulae.
The formation of an ebb-tidal delta seaward of the tidal inlet is well captured by the Delft3D-FM model (Figure 2). However, the simulated bottom pattern in the back-barrier basin does not feature a clear formation of a tidal channel network. Moreover, bottom patterns grow too fast (order weeks to months), which is likely due to a high numerical diffusion that is generated in the model.
Figure 1 Map of an ebb-tidal delta and a tidal channel network in the Wadden Sea.
Figure 2. Simulated bottom pattern with the Delft3D-FM.
Ridderinkhof, W.; Swart, H. E. de; Vegt, M. van der; Hoekstra, P. (2014). Influence of the back-barrier basin length on the geometry of ebb-tidal deltas. Ocean Dynamics 64: 1333–1348. DOI: 10.1007/s10236-014-0744-3.