IV-58 



ciently vigorous. Bottom sediments are rock and clay covered in 

 some places with fine mud. 



The characteristic sediment of the Alaskan estuarine region is 

 glacial flour, that extremely fine material ground from the land 

 and carried along by glaciers. Many of the estuaries and much of 

 the continental shelf off the western Alaskan coast are covered 

 with this material. 



Coral reefs, sand, and rocks are typical of estuarine bottoms in 

 the Pacific and Atlantic Islands. Except in extremely sheltered 

 areas, sediments are rare because pf the continuous wind and wave 

 action. 



A MORPHOLOGICAL CLASSIFICATION OF THE ESTUARINE ZONE 



The estuarine zone can be classified according to its local 

 morphology into major categories, several of which exist in each 

 of the estuarine biophysical regions. Within each of these cat- 

 egories, 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 svstem in one 

 region to similar estuarine systems in other regions. 



Figure IV. 1.23 illustrates each category. Table IV. 1.7 shows the 

 numbers of different kinds of estuarine systems in each estuarine 

 biophysical region. Unrestricted river entrances and embayments 

 dominate and are rather evenly distributed throughout all the regions. 



