They can form when a barrier island or sand bar builds up and provides partial shelter from the open sea, or when inundation of a former glacial valley produces a fjord.
The Knudsen relations and mixing diagrams are often used in determining nutrient budgets for these structures. Their magnification factors describe the effects of entrainment between their layers, and they exhibit non- geostrophic dynamics dominated by thermohaline forcing.  One type of them have a layer known as the halocline, while another type sees variance laterally thanks to the Coriolis effect.  They are categorized by circulation characteristics into classes including vertically homogeneous and salt wedge varieties.  They can form when a barrier island or sand bar builds up and provides partial shelter from the open sea, or when inundation of a former glacial valley produces a fjord. Mangrove colonies and salt marshes are typically associated with, FTP, these semi-enclosed structures that form where freshwater from a river mixes with seawater.
The Knudsen relations and mixing diagrams are often used in determining nutrient budgets for these structures.
{estuary}