Barred-beach morphological control on infragravity motion

A conceptual analysis of the coupling between bars and infragravity waves is performed combining laboratory experiments and numerical modeling. Experiments are carried out in a wave flume with a barred profile. The Boussinesq fully-nonlinear model SERR1D is validated with the laboratory data and a sensitivity analysis is performed next to study the influence on the infragravity wave dynamics of bar amplitude and location, and swash zone slope. A novel technique of incident and reflected motions separation that conserves temporal characteristics is applied. We observe that changing bar characteristics induces substantial variations in trapped energy. Interestingly, a modification of swash zone slope has a large influence on the reflected component, controlling amplitude and phase time-lag, and consequently on the resonant pattern. Variations of trapped infragravity energy induced by changes of swash zone slope reach 25 %. These changes in infragravity pattern consequently affect short-wave dynamics by modifying the breakpoint location and the breaking intensity. Our conceptual investigation suggests the existence of a morphological feedback through the action of evolving morphology on infragravity structures which modulates the action of short-waves on the morphology itself

International Conference on Coastal Engineering (ICCE)

Transparent exopolymer particles (TEP) are widely recognized to promote sediment aggregation in eutrophic environments. Flocculation in presence of TEP of various suspended sediment concentrations of material sampled on the bank of the Cam River was quantified at the laboratory for turbulence level consistent with slack water and mid ebb conditions measured in the Cam River estuary during dry season of 2009. Stickiness and concentrations of TEP were let to naturally fluctuate by incubation (aging in the dark) for up to nine days. We found that the impact of turbulence on overall buoyancy of TEP-governed aggregation was always opposite between slack water and mid ebb conditions for any duration of incubation; always negative for slack water conditions but for 126 hours of incubation and significantly negative for mid ebb conditions but for 126 hours of incubation. Suspended sediment concentration (SSC) consistently limited aggregates buoyancy, negative or positive. We propose a conceptual model that relates measured and inferred parameters to observed hydrosedimentary processes

International Conference on Coastal Engineering (ICCE)

This paper presents a 11-day experiment conducted at the high-energy dissipative beach of Mataquito, Maule Region, Chile. During the experiment, offshore significant wave height ranged 1-4 m, with persistent long period up to 18 s and oblique incidence. Wave energy reflection value ranged from 1 to 4 %, and results show that it is highly linked to both incoming wave characteristics and swash zone beach slope, and is well correlated to a swash-slope based Iribarren number. The swash acting as a low-pass filter in the reflection mechanism, our results show that the cut-off period is better determined by swash slope rather than incoming wave's period. A new low cost technique for observing high-frequency swash hydro-morphodynamics is introduced and validated using LIDAR measurements. A good agreement is found. Separation of uprush and backswash components using the Radon Transform illustrates the low-frequency filtering effect. These results show the key role played by swash mechanism in the reflection rate and frequency selection. More investigation is needed to describe the reflection process and its link with shoreface evolution, moving toward a swash-by-swash approach

International Conference on Coastal Engineering (ICCE)

A new remote sensing video-based method for measuring rapid variations of the bed elevation and free-surface in the swash zone is tested on a steep reflective beach at Grand Popo. The key assumption is that the free-surface has a distinguishable optical signature with respect to the bed level. This new set up enables a high frequency description of the wave transformation, dissipation and reflection in the swash zone as well as the variations of the bed evolution at the wave-by-wave scale. At a more integrated scale, a good correlation is found between the offshore reflected energy measured by an ADCP, the incident offshore wave characteristics and the swash local morphology, suggesting the importance of the swash dynamics on the energy reflection mechanism