IV-29 



collects a proportionately less suspended load of sediment as it 

 comes down through the less-erodable volcanic mountains and pla- 

 teaus of the Pacific Northwest. 



The southern part of the Florida peninsula is far from the sources 

 of coastal plain sediment which has filled estuaries immediately to 

 the north. Locally derived sediments, combined with the results of 

 plant and animal activity, are the great estuarine modifiers in this 

 region. Mangrove swamps on the Southwest coast and coral reefs on 

 the Southeast (Figure IV. 1.17) are typical coastal formations. 



Table IV. 1.2 gives estimated total quantities of suspended sediments 

 entering the estuarine zone and shows the kinds of sediments typical 

 of each region. The data leading to this table include the effects 

 of human activity as well as natural sedimentation. The most signi- 

 ficant thing about this table 1s the paucity of data leading to 

 these estimates. The sediments carried by only 26 of the rivers 

 entering the estuarine zone have been measured sufficiently well to 

 permit even these estimates (IV-1-2). 



The great volume of sediments carried by the Mississippi, as 

 contrasted to the quantity carried by the Columbia, illustrates one 

 of the major differences between a river forming a delta and one 

 not forming a delta. The contrast between the sediment loads being 

 carried by the rivers of the Middle Atlantic and Chesapeake regions 

 and those of the South Atlantic and Gulf also illustrate why the 



