Micro-tidal Barrier Islands
Micro-tidal environments are those in which the tidal range is 0-2 m. Area in the Southwestern US which are within this range are those in the Gulf of Mexico. These Island tend to be long and thin with few inlet channels (see figure below and note that this figure will be used to describe all three tidal environments).
Representative cartoons of barrier islands formed in all three tidal settings (Prothero,1990)
In micro-tidal environments that tidal surge is not large enough to top the island in many places. Without continual overtopping by tidal surges there is not the opportunity for many tidal inlets to form. Barrier islands in micro-tidal environments are considered to be wave dominated barrier islands.
Meso-tidal Barrier Islands.
Meso-tidal barrier islands form in area in which the tidal range is from 2-4 m. The island systems which form in these environments tend to be shorter in length by slightly wider (see figure above). The reason for the shorter length is continual overtopping by the tidal surge. This allows the formation of many inlet channels and hence the formation of many distinct islands. Meso-tidal barrier islands are considered to be tidally dominated barrier islands.
Macro-tidal environments are in areas where the tidal range is > 4m. Macro-tidal areas are considered to be barrier island free (see figure above). Barrier islands exist in macro-tidal environments only very rarely when fluvial input is the dominant factor.