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Tales of the Coast
Coastal Dynamics

Tides and Deltaic Coasts

Tidal currents are an important factor in the reworking of deltaic sediments. At the river mouths of tide-dominant deltas, significant mixing of water eliminates the effects of buoyancy. For part of the year, tidal currents may be responsible for a greater fraction of the sediment-transporting energy than the river. As a result, at tide-dominant deltas sediment transport in and near the river mouth is bidirectional over a tidal cycle.

The location of the land-sea interface and the zone of marine-riverine interactions are greatly extended at tide-dominant deltas. Characteristic features of river mouths in macrotidal environments are bell-shaped, sand-filled channels and linear tidal sand ridges. The crests of the ridges, which have relief of 10-20 meters, may be exposed at low tide. As the delta progrades over time, the ridges grow until they are permanently exposed, forming large, straight tidal channels.

 

Tides and Deltaic Coasts

Tide-Dominant Deltaic Coast: An example of a macrotidal delta is the Essex River Delta in Massachusetts.