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In the Middle Atlantic region the estuarine zone consists primarily 

 of a few large droAvned river valley embayments (e.g., New York 

 Harbor, Delaware Bay, Narragansett Bay) and some small marsh and 

 barrier beach systems receiving only coastal fresh-water runoff. 

 The estuarine zone of the Gulf region, on the other hand, consists 

 mainly of moderate-sized embayments with barrier beaches and ex- 

 tensive marshes, but receiving river flow from upland drainage areas 

 and representing an intermediate state in the evolution of drowned 

 river valleys into coastal marshes. 



The South Atlantic region has two dominant types of estuarine 

 structure. From Cape Hatteras to about Jacksonville, Fla., there is a 

 general input of upland river drainage to the estuarine zone and the 

 estuarine systems are typical drowned river valleys in the later stages 

 of evolution represented by barrier beaches or coastal marshes backed 

 by extensive swamps. South of Jacksonville fresh- water runoff comes 

 primarily from local coastal drainage, and there are uniform and ex- 

 tensive barrier island beaches with long narrow embayments behind 

 them having continuous but generally narrow strips of marsh along 

 the embayments. This structure fades into the extensive swamplands 

 of the Everglades farther down the Florida Peninsula. 



Both the Pacific Northwest and Pacific Southwest regions have few 

 estuaries. The estuarine systems of the Northwest Pacific region tend 

 to be the mouths of rivers which have cut their way through 

 coastal mountain ranges, either of their own accord or aided by 

 glaciers as in the case of Puget Sound. Shallow coastal embayment^ 

 with little and sporadic river flow are characteristic of the few estu- 

 arine systems of the Southwest, except for San Francisco Bay, which 

 receives fresh water runoff from much of central California, 



Estuarine systems of the islands, both Atlantic and Pacific, are few 

 and consist mostly of embayments without major river inflows. 



The estuarine zone can be classified according to its local morphol- 

 ogy into 10 major categories, several of whi<*h exist in each of the 

 estuarine biophysical regions. Within each of these categories, the 

 similarities in structure reflect similarities in water movement, water 

 quality, and ecology which make it possible to apply lessons learned 

 in managing an estuarine system in one region to similar estuarine 

 systems in other regions. The morphological categories are : 



1.1. Smooth shoreline without mlets. 



1.2. Smooth shoreline with inlets. 



1.3. Smooth shoreline with small embayments. 



2.1. Indented shoreline without islands. 



2.2. Indented shoreline with islands. 

 3(. Marshy shoreline. 



4. Unrestricted river entrance. 



5.1. Embayment with only coastal drainage. 



5.2. Embayment with continuous upland river inflow. 

 6. Fjord. 



Unrestricted river entrances and embayments dominate the es- 

 tuarine zone and are rather evenly distributed throughout all the 

 regions, with the common type of estuarine system being a coastal 

 embayment with drainage from only the local coastal area. Many of 



