Geomorphological Types of Estuaries

Bar-Built and Lagoonal

Bar-built or lagoonal estuaries form in the areas behind sandy barrier islands and usually drain relatively small watersheds. The exchange of water between the estuary and the sea occurs through tidal inlets. Astronomical tides and winds are the major forces controlling water circulation and water height. The areas behind barrier islands are generally subject to less wave action and this promotes the development of extensive wetlands. Bar-built estuaries are generally smaller than other estuarine types, suggesting that they have a higher surface area to volume ratio and, therefore, play a greater role in ecological processes than was previously thought. Well-studied examples of bar-built estuaries are found along the temperate and subtropical coasts of eastern North America, Europe, Asia, and the southern and eastern shores of Australia.

Riverine Estuaries

There are two fundamentally different riverine systems (Figure 2). First, are those that arise in the piedmont, have extensive watersheds, receive substantial freshwater discharge, but only a small portion of their watershed is

Figure 2 Generalized material flux patterns in a Riverine estuary.

covered by wetlands. Chesapeake Bay and San Francisco Bay in North America as well as the Eastern Scheldt in Northern Europe are well-studied examples of this type of riverine system. A second type of riverine system known as coastal plain estuaries are characterized by a much gentler slope with proportionally more wetlands than piedmont estuaries. Generally, these systems are less studied, smaller and have a lower, more sluggish flows.

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