Swash-by-swash hydro-morphodynamics: crossing laboratory, in-situ and numerical modeling approaches
Collaborators: PI Laurent Lacaze (IMFT), Rafael Almar (LEGOS), Rachid Benshila (LEGOS), Francis Auclair (LA)
Support: Transversality programme of the IDEX-UNITI project of Toulouse university
Modeling the shoreline evolution is crucial to predict natural hazards and human-induced impacts. One of the main difficulties is the description of a complex coupling between hydrodynamics and sediment transport in the shoreline area, where hydrodynamics is mostly wave-driven. The present project is dedicated to a better understanding of these complex dynamics, with specific attention to the swash zone, which is the interface between land and sea. To that end, accurate field measurements are needed at wave timescale together with specifically designed laboratory experiments. The newly obtained data will also serve as a benchmark for the validation and use of a 3D numerical model (CROCO).
The laboratory experiments consist in single or paired incident bores on a sloping beach. Bores are generated using dam break devices at one side of a closed channel. In the case of the pair configuration, the lag time between two consecutive waves is a variable of the experiment in order to test different types of swash interactions. The beach will be made either of an inclined smooth plane, an inclined rough plane or an erodible beach made of solid particles. Such a simple set-up will allow us to explore a broad range of control parameter values for the dynamics of incident bores and the local grain motions at the surface of the beach. We will use PIV, shadowgraphy and Particle tracking techniques.
The field observations will be carried out at Nha Trang beach in Vietnam, a seasonally dominated environment, occasionally impacted by severe weather (e.g., cat-5 Typhoon Haiyan in 2013). This will be done within the framework of the ANR COASTVAR project (Multi-scale Coastal Variability), through 2 complementary observation strategies: seasonal scale monitoring which includes continuous LIDAR, Video and ADCP (wave and tide) monitoring and intensive short-term measurements (~ week) in May 2015 and December 2015. Emphasis will be given to the upper beach response to the forcing.
Finally, we will apply a 3D hydro-morphodynamic numerical model to simulate the laboratory experiments and push further the sensitivity studies and analyses. Its application to a real beach in Vietnam will present a further step in testing the ability of 3D models in representing swash zone hydro-morphodynamics and a mean to test available parameterizations of swash zone conditions in wave-averaged models.