Ephemeral features Result of rise of sea level during the last 18,000 yrs Progressively being infilled with sediment. Vertically mixed - shallow, low volume, net flow from river toward ocean.
Salinity is uniform from surface to bottom increasing toward ocean.
Slightly stratified - somewhat deeper salinity increased from the head to the mouth. Two basic water layers can be identified separated by a zone of mixing. Net surface flow of low-salinity water toward ocean and net subsurface flow of marine water toward the head. Highly stratified - Deep water estuary, two distinct layers of fresh water overlying salt water. Little interaction between the two layers.