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Yet, the dominating environmental factors listed above form a set 

 of natural guiding principles which govern the general character- 

 istics of the estuarine zone of the United States, and the occurrence 

 of various combinations of these environmental factors permits the 

 grouping of the national estuarine system into 10 geographical zones, 

 each governed by a different combination of environmental conditions. 



Characteristics of the Biophysical Regions 



North Atlantic Estuarine Region : Canadian border to Cape Cod. 



Cool, fertile waters with a large tidal range strike a steep, 

 indented coast with deep water close inshore, but protected from 

 the full force of the ocean waves by a wide continental shelf. 

 Moderate precipitation with heavy snowfall leads to heavy spring 

 river runoff which dominates local circulation. Natural erosion 

 and sedimentation are not severe problems, and the evolution of 

 drowned river valley estuaries is in an early stage in this region. 



Middle Atlantic Estuarine Region : Cape Cod to Cape Hatteras, 

 exclusive of Chesapeake Bay. 



A wide, gently sloping continental shelf with a smooth shoreline 

 is cut by the entrances of several major river systems carrying 

 moderate amounts of sediments. The same cool, fertile waters as 

 in the North Atlantic estuarine region wash this coastline but 

 with a smaller tidal range. The evolution of drowned river valleys 



