90 



MORPHOLOGY OF THE ESTTJARINE ZONE 



Those characteristics shown in table IV. 1.6 describe differences in 

 structure and form of the estuarine zone among the estuarine re^ons. 

 The descriptive ratios presented in this table result from combining 

 areas and distances characteristic of the estuarine zone of each region. 

 Such ratios are numerical indices of the relative sizes of the estuarine 

 zone in each region and also give quantitative measures of its relative 

 composition among regions. Their greatest value, however, is in com- 

 paring individual estuarine systems so as to apply the lessons learned 

 in one estuary to the problems of another. 



Alaska has by far the longest general coastline and tidal shoreline 

 as well as the greatest estuarine water area of any estuarine region, 

 but the Chesapeake Bay region has a much greater proportion of esta- 

 rine shoreline and area for its size than any of the other regions. Estu- 

 rine systems within the Chesapeake Bay region consist of a group of 

 branched rivers entering the Chesapeake Bay itself, which is in turn 

 the former valley of the Susquehanna River. The estuarine systems on 

 the western side of the bay tend to be surrounded with somewhat 

 hillier land and less extensive marsh areas than those on the eastern 

 shore, though nearly all systems tributary to the bay are drowned river 

 valleys. 



The Middle Atlantic and Gulf estuarine regions have about equal 

 amounts of tidal shoreline and estuarine water areas per mile of ocean 

 coastline, but in the Middle Atlantic region the estaurine zone con- 

 sists primarily of a few large drowned river valley embayments (e.g. 

 New York Harbor, Delaware Bay, and Narragansett Bay) and some 

 small marsh and barrier beach sy^ms receiving only coastal fresh 

 water runoff. The estaurine 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 in the gulf region. 



The North Atlantic is unlike any of the other regions in overall 

 structure, but is similar to Puget Sound and southeast Alaska. Char- 

 acteristic of the North Atlantic region are very irregular, hilly coast- 

 lines with deep water close inshore and long, narrow embayments with 

 open access to the sea. 



The South Atlantic region has two dominant types of estuarine 

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

 eral 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 beaches or coastal marshes backed by extensive swamps. 

 South of Jacksonville freshwater runoff comes primarily from local 

 coastal drainage, and there are uniform and extensive barrier island 

 beaches with long narrow embayments behind them. Continuous but 

 generally narrow strips of marsh lie 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 



