IV-62 



with the common type of estuarlne system being a coastal embay- 

 ment with drainaqe from only the local coastal area. Many of 

 these latter embayments have larqe marsh areas, but the Middle- 

 Atlantic, South Atlantic, and Gulf are the regions in which marshes 

 are the predominant feature in some parts of the estuarlne zone. 



WATER MOVEMENT IN THE ESTUARINE ZONE 



The unique nature of water movement and circulation patterns in 

 the estuarine zone 1s the result of the meeting and mixing of 

 fresh river water and salty ocean water of slightly greater den- 

 sity under the oscillating influence of the tide. There may be 

 additional complicating factors such as temperature and wind act- 

 Ion, but the resulting circulation nearly always reflects the 

 interaction of river flow and estuary shape with the tidal flow 

 of the ocean water. 



General water movement patterns are Dredictable for each cate- 

 gory of estuarine shape. Where there is little or no fresh water 

 inflow, water moves toward and away from the shore, being re- 

 flected Into currents paralleling the shore 1n some cases. On 

 ocean beaches, this parallel type of water movement builds sand- 

 spits and barrier islands to begin the transformation of drowned 

 river valleys Into embayments and coastal marshes, as Illustrated 

 by Figure IV. 1.24. 



Where fresh water runoff reaches the sea as a series of small 



