Tales of the Coast
Coastal Dynamics


Circulation and Barriers

A primary means of barrier formation is through longshore sediment transport and deposition of the sediment, either as a spit attached to the sediment source or as a barrier island. Sediment can be derived from eroding headlands or riverine deposits and moved by currents. Longshore currents can also erode barrier beaches themselves and transport the sand downdrift on the barrier or to another location.

Tidal currents also affect barriers by influencing inlets often found between barriers. These currents carry sediment that is deposited as flood- and ebb-tidal shoals. Flood-tidal shoals can become new substrate for marsh formation, which contributes to a barrier's landward migration. Ebb-tidal shoals can present problems for navigation at the inlet mouth.

Because of barriers' dynamic nature, they are strongly impacted by the circulation of currents and sediment transport.

Barrier island
Source: National Park Service

Circulation and Barriers

Sand Bypassing: Erosion mitigation measures at Assateague Island, Maryland, include bypassing sand around Ocean City Inlet and its jetties, which block sediment transport. This action replicates the longshore sediment transport that takes places naturally along this part of the Atlantic coast.p>