IV-522 



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 

 extensive 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, Florida, 

 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 extensive 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 embayments 

 with little and sporadic river flow are characteristic of the few 



