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Sand deposited at the mouth of a delta or crevasse distributaries is subject to wave or tidal reworking. The interaction of the fluvial deposition, wave action, and tidal action will determine how much rework will occur. In fluvially dominated deltas, prograding mouth bars will be prevalent. In wave dominated deltas, breaking waves will create the turbulence to mobilize the sand which can then be transported by longshore currents. In regions with strong tidal action, the deltas will exhibit many estuary features with the detrital material being reworked in and out of the channel by the tides.

If most of the sand is reworked, beach ridges or coastal barriers will develop. Although somewhat similar to nondeltaic wave-dominated barrier bars or islands, deltaic barrier sands exhibit a strike orientation parallel to the coast near the shore, but farther inland, where the sand is actually part of a mouth bar, the orientation is perpendicular to the shore.

Friction-Dominated River Mouth
Friction-Dominated River Mouth
After Reading, H. G. (editor), Sedimentary Environments and Facies.
Blackwell Scientific Publications, Boston, 1986.
Friction-Dominated River Mouth  Buoyancy-Dominated River Mouth 

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