Category E - Tidal lagoons or barrier enclosed lagoons
Shallow, circular to slightly elongated basins with simple shorelines and extensive intertidal area.
These estuaries generally have a narrow entrance to the sea which is usually constricted by a sand spit or barrier. Sand bars and shoals, called ebb and flood tidal deltas, occur at the mouth of the estuary on shores where there is littoral drift (movement of particles such as sand along the shore, due to wind and waves). On shores where there is no such drift, funnel shaped entrances occur which have no sand bodies in their mouth.
The tidal prism - the difference between the mean high-water volume and the mean low-water volume of the estuary – makes up a large proportion of the total volume of water in the basin, and the proportion of water contributed during any tidal cycle by the river is very small. As a result, the ocean is responsible for the movement of water in the estuary.
Two-dimensional mixing, circulation and resuspension due to wind happen at high tide, and Category E estuaries are well flushed because much of their water leaves on the outgoing tide. The combination of the resuspension of bottom sediment by waves and the strong flushing mean that these estuaries often have homogenous, sandy bottom sediment.
These estuaries are also well mixed because the strong flushing, mixing by wind and shallow depths mean that water densities don't become stratified (i.e., form layers), and the salinity is close to that of the ocean's. At high tide, when any screening from the ebb tidal delta is minimised, ocean swell can resuspend sediment in the entrance of estuaries with wider mouths.
Category E estuaries are representative of features commonly called tidal lagoons or barrier enclosed lagoons.