Sandbars, submerged ridges of sand parallel to the shoreline, tend to develop crescentic patterns while migrating onshore. At straight coasts, these patterns form preferably under near‐normal waves through the generation of circulation cells in the flow field, whereas they decay under energetic oblique waves with associated intense alongshore currents. Recently, observations at a man‐made convex curved coast showed an alongshore variability in patterning that seems related to a spatiotemporal variability of the local wave angle (Sand Engine). Here, we aim to systematically explore how coastline curvature contributes to alongshore variability in crescentic pattern formation, by introducing local differences in wave angle and the resulting flow field. A nonlinear morphodynamic model was used to simulate the patterns in an initially alongshore uniform sandbar that migrates onshore along the imposed curved coast. The model was forced by a time‐invariant and time‐varying offshore wave angle. Simulations show that the presence of patterns and their growth rate relate to the local breaker angle, depending on the schematization of the offshore angle and the local coastline orientation. Growth rates decrease with increasing obliquity as both refraction‐induced reductions of the wave height as well as alongshore currents increase. Furthermore, simulations of variations in coastline curvature show that patterns may develop faster at strongly curved coasts if this curvature leads to an increase in near‐normal angles. This implies that beaches where the coastline orientation changes substantially, for example, due to km‐scale nourishments, become potentially more dangerous to swimmers due to strong currents that develop with pronounced bar patterns. Plain Language Summary: Surf zone sandbars front many sandy beaches worldwide. Their dynamics are crucial to the development of potentially hazardous rip currents and the movement of sand between sea and land. Breaking waves drive this sand movement and may organize the sand into a remarkable alternation of shallow sandbars and seaward‐directed rip channels along the beach. The mechanism driving this pattern formation is relatively well understood at straight coasts, but it is unknown how this translates to strongly curved coasts. Recently, this has become of particular interest with the increasing volumes of sand placed at the coast for coastal management purposes. Such meganourishments may locally change an otherwise straight coastline into a strongly curved coastline. We used a numerical model to study the sandbars along a strongly curved coast, inspired by the km‐scale Sand Engine nourishment. We found that the variable coastline orientation causes an alongshore variation in the angle of wave approach and resulting currents. Sandbars develop pronounced patterns and move landward where waves approach normal to the shoreline, whereas patterns remain absent where waves arrive at an angle. We also show that nourishment shape and wave climate are both crucial to the formation of sandbar patterns and associated hazardous rip currents. Key Points: Curved coasts impose an alongshore variation in wave incidence, provoking variability in the formation of crescentic sandbar patternsCrescentic sandbar patterns develop where alongshore currents and refraction‐induced wave height reduction are limitedImplementing a km‐scale coastline perturbation may increase local near‐normal wave incidence and thereby the presence of rip currents [ABSTRACT FROM AUTHOR]
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