Philippe Larroudé

Comparison of sediment transport formulae for the coastal environment

Most existing sediment transport formulae to estimate transport rate in the coastal environment have a restricted range of applicability and are often used beyond this range. The aim of this paper is to investigate the limits of five of these formulae: the Bijker, Bailard, Van Rijn, Dibajnia and Watanabe, and Ribberink formulae. The sensitivity of these formulae to wave orbital velocity, wave period, wave asymmetry, sediment grain size, and steady current has been studied and tested against data for large velocities where significant errors can appear. The formulae behave in very different ways if one of the main parameters is slightly modified, particularly when fine sediments are present and phase-lag effect appears. But important discrepancies between formulae can also be observed for medium sand. At last, the wave-related sediment transport (due to wave asymmetry) has great importance for the morphodynamic and is only accounted for in the Bailard, Dibajnia and Watanabe, and Ribberink formulae.

Wave Scour Around Piles

This paper reports the results of an experimental study on the scour around a vertical pile and in groups of piles submitted to wave forcing. In particular, the influence of the wave non-linearity on local scour around single piles has been studied. In fact, as the characteristics of non-linear waves evolves in the domain the scour processes shall depend on the position of the piles, i.e., on the local characteristics of the waves. The scour processes around vertical piles located in the surf zone are also discussed in this paper.

Methodology of seasonal morphological modelisation for nourishment strategies on a Mediterranean beach

A modified 2DH morphodynamical model was employed to simulate the evolution of large-scale features with major implications for beach nourishment. The study was focused on modelling the evolution of material artificially placed in different parts of the profile, extracting or adding material to the natural bars, and quantifying how the profile responds to different wave climates and nourishment placements. The simulated results were compared with field data from a Mediterranean beach.

Un modèle morphologique côtier pour la création de barres rythmiques

ABSTRACT A hydrodynamic and morphodynamic model for sandy beaches is presented. One interesting point is that the effects of the undertow and the wave asymetry are computed, which are the main factors in the creation of the bar. A study of the position and the initial vertical growth of the bar has been made with varying wave conditions and beach slope. This model is integrated in a commercial 2DH software. And it has also been coupled with a model of linear stability which gives the initial bottom, perturbations be added to an initial plane beach. The complete model allows the creation of a rythmic bar.

Longshore Sediment Transport Measurements on Sandy Macrotidal Beaches Compared with Sediment Transport Formulae

In a context of global climate change, local sea level rise could affect the different coastal processes as erosion, transport and deposition which are responsible in maintaining the coastline. The study of sediment transport processes is one of the key for a better understanding of the coastal evolution which is needed for effective design of coastal engineering or to protect anthropogenic activities and population from marine submersion. One of the main processes that control coastal evolution is sediment transport. A number of studies have been focused on this topic, but they were mostly restricted to micro- to mesotidal beaches [1-3] and field investigations on sandy macrotidal beaches appear to be more limited, notably because these environments are less common along the worldwide coastline [4]. Only a few studies have been conducted for quantifying sediment flux on macrotidal beaches [5, 6] where sediment transport results from the complex interactions of tidal currents with longshore currents generated by obliquely incident breaking waves, this complexity being further increased by the large variations in water level that induce significant horizontal translations of the surf zone. Although a number of studies were recently conducted on the morphodynamics of the barred macrotidal beaches of Northern France [7-12], relatively little effort has been dedicated to measuring longshore sediment transport on these beaches, even though it is largely recognized that they are affected by significant longshore transport that plays a major role in the morphodynamics of the intertidal zone [10, 13]. Apart from some attempts to make estimates of longshore sediment transport from fluorescent tracers [10, 14-16] and to infer transport directions using grain-size trend analysis techniques...

Sensitivity of beach morphodynamics to climate variability. Application to truc vert beach (France)

Coastal systems should be vulnerable to climate change/variability. The present paper investigates the sensitivity of Truc Vert beach to present day climate conditions as well as possible climate change in the near future. A modeling approach is used, based on three numerical morphodynamic models (MORPHODYN, MARSOUIN, TELEMAC). The first results show an important sensitivity to present day wave classes. Some first indications on the potential influence of wave climate changes are also given, investigating variations of wave classes characteristics. The present work also illustrates the need to go on improving and developing these models.

Two numerical approaches: 2D and 3D SPH model to simulate extreme waves over a barrier island

ABSTRACT Oudart, T., Larroudé, Ph. and Bouchette, F., 2013. Two numerical approaches: 2D and 3D SPH model to simulate extreme waves over a barrier island The barrier islands usually erode seriously during the occurrence of typhoon, especially, when storm surge comes at the spring tide period. The high water level combined with typhoon wave run-up induces overwash on the barrier islands and pushes the barrier sand into the lagoon behind. . We tentatively characterize this natural phenomenon with numerical modeling of the propagation of water waves onto a barrier island. The modelling work is based upon 2D and 3D Smooth Particle Hydrodynamics (SPH) models. The barrier island response to typhoon waves is analyzed in two different ways: 1) comparing the results from an experimentation in a wave flume with those from SPH computations performed on exactely the same barrier island morphology and the same long wave forcings; b) performing SPH computations in a real case study, i.e. the Wan Lu Tziao barrier island, south-western Taiwan (ANR KUN-SHEN program), from the shoaling zone in the open sea to the lagoon.

Sediment Transport Formulae for Coastal Morphodynamic Simulation: Calculated Sediment Flux Against In Situ Data

The aim of this chapter is to show the influence of the choice of sediment transport formulae in morphodynamic simulations. These simulations were conducted in the nearshore zone for time scales on the order of individual storm events. In a part of the chapter, we also compare directly the sediment flux calculated in the sediment code with different formulae with in-situ sediment transport measurements obtained on several beaches of the north coast of France.

Mechanisms of the onset of Rayleigh-Benard instabilities for a near critical fluid

Abstract Phenomena in near critical fluids has recently led to important theoretical and experimental results, in particular the prediction and the evidence of a mode of heat equilibration called the Piston Effect (PE). The numerical method uses a finite volume approximation based on the SIMPLER algorithm and it considers an acoustic filtering on the Piston-Effect time-scale. In the case of a Rayleigh-Benard configuration (heated from below). different types of flows are shown to develop depending on the local Rayleigh numbers and on the proximity with the critical point. The types of flows at larger Rayleigh numbers than critical, exhibit plumes at the bottom while the cooled top layer gives rise to an unstable diffusive layer.