Four Subdivisions of Estuaries

Reynaldo B. Legaspi

1. Drowned River Valleys

Drowned River Valleys -are most

extensively developed along coastlines with

relatively low and wide coastal plains.

Chesapeake Bay which is located on the mid-Atlantic coast of the United States.

2. Fjord-type Estuaries

Fjord-type Estuary

-are deep, U-shaped coastal

indentures gouged out by glaciers and

generally with a shallow sill at their mouths

formed by terminal glacial

deposits.

The famous fjords of Norway

3. Bar-built Estuaries •shallow basins, often partly exposed at low

tide•enclosed by a chain of offshore bars or barrier islands•broken at intervals by inlets (thus insuring “a free connection with the sea”•Sometimes the sand bars are deposited offshore, but in other instances the barriers may represent former coastal dunes that have become isolated by recent gradual rises in sea levels. •In the former case the estuary develops from a former marine area, while in the latter case it develops on a flooded area of former coastal plain. 

The “sounds” behind the “outer banks” of North Carolina (Cape Hatteras National Seashore Park)

4. Estuaries produced by Tectonic Processes

Estuaries produced by

tectonic processes -are coastal

indentures formed by geological

faulting or by local subsidence, often with a large inflow

of fresh water.San Francisco Bay