Benjamin Dubarbier

Testing numerical hydrodynamic and morphodynamic models against BARDEX II Experiment data sets

ABSTRACT Castelle, B., Dubarbier, B., Tissier, M., Bonneton, P., Conley, D.C., Ruessink, B.G. and Masselink, G., 2013. Testing numerical hydrodynamic and morphodynamic models against BARDEX II Experiment data sets. The hydrodynamics on barred beaches and mechanics of sediment transport related to sandbar migration, berm formation/destruction, barrier crest dynamics and washover deposition are extremely complex. At this time, process-based models encompassing all these processes are non-existent. Among other shortcomings, the lack of existing intensive high-frequency full-scale data limits the range improvement and validation of nearshore process-based models. In June 2012, the large-scale Barrier Dynamics Experiment (BARDEX II) was performed in the Delta Flume, providing new datasets for rigorous testing of existing hydrodynamic, groundwater and morphodynamic models and further assisting their development. Three types of models are expected to be applied and further improved: (1) the short-wave averaged surfzone beach profile evolution models 1DBeach and UNIBEST-TC, (2) the short-wave averaged and infragravity-wave resolving XBeach model that addresses morphological changes of the nearshore area, beaches, dunes and backbarrier during storms including cross-barrier groundwater fluxes and (3) the short-wave resolving hydrodynamic models SURF-GN and SWASH. In this contribution, we present the application of three of the five models. 1DBeach is applied to a morphological sequence characterised by onshore and subsequent rapid offshore sandbar migration for time-invariant wave forcing and falling tide. XBeach model is applied to a rising tide sequence characterized by a rapid shoreline retreated and overtopping and overwash processes. SURF-GN is applied to a high tide run with occasional overtoppings. All these model applications are described and model skills are qualitatively assessed. Guidelines for future model improvements and validation on BARDEX II dataset are further discussed.

Mechanisms controlling the complete accretionary beach state sequence

Accretionary down-state beach sequence is a key element of observed nearshore morphological variability along sandy coasts. We present and analyze the first numerical simulation of such a sequence using a process-based morphodynamic model that solves the coupling between waves, depth-integrated currents, and sediment transport. The simulation evolves from an alongshore-uniform barred beach (storm profile) to an almost featureless shore-welded terrace (summer profile) through the highly alongshore-variable detached crescentic bar and transverse bar/rip system states. A global analysis of the full sequence allows determining the varying contributions of the different hydro-sedimentary processes. Sediment transport driven by orbital velocity skewness is critical to the overall onshore sandbar migration, while gravitational down-slope sediment transport acts as a damping term inhibiting further channel growth enforced by rip-flow circulation. Accurate morphological diffusivity and inclusion of orbital velocity skewness opens new perspectives in terms of morphodynamic modeling of real beaches.