14 



The land 



The shape of the land along the land-sea interface goes far toward 

 determining what water movement and circulation patterns exist in 

 particular local areas and, consequently, how fast a particular estua- 

 rine system will rid itself of pollutants. Within the general compass 

 of the estuarine regions discussed in the preceding section there are 

 different structural types which define patterns of water movement 

 typical of particular structures, no matter what the external environ- 

 ment may be. 



Alaska presents the greatest variety of estuarine form and structure 

 of any of the estuarine regions. Nearly all kinds of systems typical of 

 other regions are found there. In addition, Alaska has the only glaci- 

 ated coast and most of the fjords found in the United States. 



Characteristic of the North Atlantic region is a very irregular, hilly 

 coastline with deep water close inshore and long, narrow embayments 

 with open access to the sea. Estuarine systems within the Chesapeake 

 Bay region consist of a group of branched rivers entering the Chesa- 

 peake Bay itself, which is in turn the former valley of the Sueque- 

 hanna River. 



In the Middle Atlantic region the estuarine zone consists primarily 

 of a few large drowned river valley embayments (for example. 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, con- 

 sists 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, 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 embayments with little 

 and sporadic river flow are characteristic of the few estuarine 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. 



