[1] The process of formation of a rip channel/crescentic bar system on a straight, sandy coast is examined. A short review of earlier studies is presented. A morphodynamic stability model is then formulated. The resulting model includes a comprehensive treatment of shoaling and surf zone hydrodynamics, including wave refraction on depth and currents and waves. The sediment transport is modeled using a total load formula. This model is used to study the formation of rip currents and channels on a straight single-barred coast. It is found that this more comprehensive treatment of the dynamics reveals the basic rip cells predicted in earlier studies for normal incidence. Also as before, cell spacings (l) scale with shore-to-bar crest distance (X b ), while growth rates decrease. The l increases with offshore wave height (H) up to a saturation value; increasing H also increases instability. Experiments at off-normal wave incidence (q > 0) introduce obliquity into the evolving bed forms, as expected, and l increases approximately linearly. the e-folding times also increase with q. At normal incidence, l increases weakly with wave period, but at oblique angles, l decreases. Tests also reveal the presence of forced circulation cells nearer to the shoreline, which carve out bed forms there. The dynamics of these forced cells is illustrated and discussed along with the associated shoreline perturbation. Transverse bars are also discovered. Their dynamics are discussed. Model predictions are also compared with field observations. The relevance of the present approach to predictions of fully developed beach states is also discussed.Citation: Calvete, D., N. Dodd, A. Falqués, and S. M. van Leeuwen (2005), Morphological development of rip channel systems: Normal and near-normal wave incidence,

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[1] A nonlinear numerical model based on a wave-and depth-averaged shallow water equation solver with wave driver, sediment transport, and bed updating is used to investigate the long-term evolution of rip channel systems appearing from the deformation of a longshore bar. Linear and nonlinear regimes in the morphological evolution have been studied. In the linear regime, a crescentic bar system emerges as a free instability. In the nonlinear regime, merging/splitting in bars and saturation of the growth are obtained. In spite of excluding undertow and wave-asymmetry sediment transport, the initial crescentic bar system reorganizes to form a large-scale and shore-attached transverse or oblique bar system, which is found to be a dynamical equilibrium state of the beach system. Thus the basic morphological transitions ''Longshore Bar and Trough'' ! ''Rhythmic Bar and Beach'' ! ''Transverse Bar and Rip'' described by earlier conceptual models are here reproduced. The study of the physical mechanisms allows us to understand the role of the different transport modes: The advective part induces the formation of crescentic bars and megacusps, and the bedslope transport damps the instability. Both terms contribute to the attachment of the megacusps to the crescentic bars. Depending on the wave forcing, the bar wavelength ranges between 180 and 250 m (165 and 320 m) in the linear (nonlinear) regime.Citation: Garnier, R., D. Calvete, A. Falqués, and N. Dodd (2008), Modelling the formation and the long-term behavior of rip channel systems from the deformation of a longshore bar,

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