IV-25 



There are 80 other river basins in the United States having drainage 

 areas of over 1000 square miles; these, with the three river systems 

 already mentioned, account for land runoff from P5 percent of the 

 entire land area draining to the estuarine zone. Over half of these 

 are in the Gulf, Alaskan, and South Atlantic biophysical regions. 

 There are none in the Caribbean and Pacific Islands rem'ons. 



The ratio of drainage basin size to miles of ocean coastline in each 

 Region, as shown in Table IV.1.1, is an index of the relative impor- 

 tance of upland runoff conditions to the estuarine zone. In the 

 North Atlantic biophysical region, for example, -unoff comes on the 

 average only from a distance of 30 miles inland. In the South 

 Atlantic region, however, runoff comes from an averane distance of 

 182 miles, thus indicating that large river basins are far more 

 important to the estuarine zone in the South Atlantic renion than in 

 the North Atlantic. 



The ratio of runoff to total miles of tidal shoreline is an index of 

 the importance of land runoff in estuarine stratification and water 

 movement patterns. A low ratio means there is little runoff in pro- 

 portion to the size of the estuarine zone, as in the Caribbean 

 region, and water stratification generally is not significant in 

 this region, while hiqh ratios, as in the two Pacific renions, indi- 

 cate high proportionate land runoff and stratification-dominated 

 estuaries. 



