On tridimensional rip current modeling

Abstract

Low-frequency variability generated by lateral shear instabilities of the coastal circulation may promote stirring and mixing of coastal waters. The question remains open to whether tridimensional transient processes are important for the generation of these instabilities and for surf-shelf exchanges in general. An innovative modeling system with tridimensional wave-current interactions (McWilliams et al., 2004) was designed to investigate transient nearshore currents and interaction between nearshore and innershelf circulations. We present here some validation of rip current modeling in the French coastal zone (Bruneau et al., 2011) using in-situ and remote video sensing. We then proceed to show the benefits of 3D versus 2D modeling for the simulation of mean rip currents and their low-frequency variability. It is concluded that tridimensional nearshore models may provide a valuable and cost-effective alternative to more usual 2D approaches, which miss the vertical flow structure and its nonlinear interaction with the 2D flow.

Three‐dimensional transient rip currents: Bathymetric excitation of low‐frequency intrinsic variability

“…The ROMS‐WEC model has been adapted to 3‐D coastal applications with prevailing wave‐driven currents, showing quite good agreements with measurements [cf. Marchesiello et al ., ; Kumar et al ., ]. We show here that time‐invariant and spatially homogeneous offshore incident waves, which are not expected to induce the forced VLFs, excite 3‐D turbulent rip currents on timescales of O (1–10) minutes on an immobile beach with realistic spatial bathymetric variability ubiquitous in nature.…”

“…Marchesiello et al . [] applied the two‐way coupled WKB spectral peak wave model with the 3‐D circulation model developed in UMS10 to transient rip currents on Biscarrosse Beach, France. They successfully reproduced energetic intrinsic VLFs at O (10) minutes, mainly driven by slowly modulating waves on timescales of O (1–2) hours due to tides and wind.…”

On Eddy-Mixed Longshore Currents: Video Observation and 3D Modeling off Grand Popo Beach, Benin

“…The profile of breaker dissipation can be assessed as in Flores et al (2013) by estimating roller wavelength rather than light intensity. This method relying on energy conservation provides a safer means of calibrating the model wave forcing (Marchesiello et al, 2015). Recently, a new method was also proposed for estimating longshore currents from video images (Larnier et al, 2014).…”

“…Uchiyama et al (2010) implemented a modeling approach for 3D wave-current interactions based on vortex-force formalism (McWilliams et al, 2004) in the Regional Oceanic Modeling System (ROMS; Shchepetkin and McWilliams, 2005). Marchesiello et al (2015) followed with the same approach within ROMS-AGRIF (Debreu et al, 2012), allowing nesting and wetting/drying.…”

Swash hydrodynamic modelling using a tri-dimensional model: CROCO

“…It has the particularity of having nesting capabilities and a nonhydrostatic option (not used here). Initially developed for basin scale modelling (O10 km), its use has recently been extended and assessed to nearshore processes resolutions (O10 m, MARCHESIELLO et al, 2015) with phase averaged wave forcing. We propose here to go one range further in resolving decimetre scales processes and solving explicit waves.…”