Coasts, as land-sea interface, are among the most dynamic and fragile environments on Earth. Sandy coastlines are particularly vulnerable, a reason being coastal hazards, which impact sediment transport and sand budgets. Hydrodynamics forces play a critical role driving beach change, being increasingly responsible for major perturbations of coastal socio-ecosystems. Furthering research on the interactions between nearshore hydrodynamics and sediment transport is crucial to evaluate the future response of coastal systems Over the past two decades, significant research efforts have been dedicated to the understanding and modeling of sediment transport processes under realistic non-linear waves in the nearshore zone. The erosion mechanisms during extreme events being well described in the literature, the novelty of WEST is to initiate new research on sediment transport during accretive periods, leading to beach recovery. In fact, storm erosion can have short- to medium-term impacts on coasts, depending on the post-storm recovery mechanisms and timescales. To predict coastal evolution, both erosion and accretion mechanisms should be accurately defined. During beach recovery, several physical processes interplay with no predominant factor controlling the sediment transport. The overall aim of WEST is to evaluate the interactions between waves, hydrodynamics and bed slope leading to onshore net sediment transport under waves in the surf zone, during post-storm or seasonal recovery. The overall objectives are to clarify the relative contributions of physical processes leading to onshore net sediment transport and to evaluate the net transport over one wave cycle according to hydrodynamic and morphological factors. The first objectives of WEST will be to study the impact of free-surface deformation on water column hydrodynamics, especially in the Wave Boundary Layer (WBL). Then, the interaction between current and sediment transport (via bedload and suspension) will be investigated in a second objective, as well as, in a lesser extent, the possible influence of seabed micro-mechanics. The sediment transport will induce bed erosion or accretion and thus will modify the bed slope. The third objective of WEST addresses then the retroaction of the bed slope on the wave non-linearities and the breaking. The novelty of WEST lies also in the first attempt to obtain accurate time-resolved in situ measurements in unison of sediment transport and free-surface deformations at the critical zone: towards wave breaking. For the first time, the whole water column towards breaking will be monitored in the natural environment. Many research point out the lack and thus the need of fields observations to determine the relative importance of physical processes. Monitoring natural waves in their physical environment is very challenging yet crucial if we aim to make new advances in physic-based numerical modeling and improved predictions of future shoreline position. WEST will build on the most recent research in wave dynamics and sediment transport, implementing cutting-edge technology to produce the most comprehensive measurements of WBL under natural breaking waves, as well as using the most recent improvements in process-based numerical methods. At the time of project completion, WEST will provide the world first dataset allowing to address the influence of wave non-linearities across the water column down to the WBL and their influence on the bed shear stress variability. WEST will also make it possible to quantify the sediment transport in suspension as well as in bedload. These results will enhance our understanding of beach recovery mechanisms, leading to improvements in morphodynamic models commonly used by engineers and coastal practitioners for coastal zone management.
Madame France Floc'h (Université de Bretagne Occidentale (UBO), Laboratoire Géosciences Océan (LGO))
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
UBO-LGO Université de Bretagne Occidentale (UBO), Laboratoire Géosciences Océan (LGO)
Help of the ANR 289,440 euros
Beginning and duration of the scientific project: December 2020 - 48 Months