US Army Corps of Engineers
Institute for Water Resources Website

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.