Chenier Formation Through Wave Winnowing and Tidal Transport

Cheniers are ridges consisting of coarse-grained sediments, resting on top of the fine sediment that forms the otherwise muddy coast. In this paper, we use Delft3D to explore how cheniers are formed through wave winnowing. We identify three phases of chenier development: (1) a winnowing phase, during which mud is washed out of the seabed initially consisting of a mixture of sand and mud, (2) a sand transport phase, when the sand in the upper layer is transported onshore, and (3) a crest formation phase, during which a chenier crest rapidly develops at the landward limit of onshore sediment transport. The main mechanism driving onshore sand transport is wave asymmetry. During calm conditions, sand transport takes place within a narrow band limiting the volume of sand delivered nearshore, and therefore no chenier develops. In contrast, average storm conditions mobilise sufficient sand for a crest to develop. Our results thus reveal that chenier formation through wave winnowing does not require extreme storm conditions. Furthermore, our study showed that chenier formation through wave winnowing is a relatively slow process, with the largest time scales associated with the winnowing and sand transport. Once sufficient sand is available nearshore, the crest develops rapidly.