390 brown. EFFECTS OF SOIL CONSERVATION [Ch. 22 



extensive agricultural research, it seems apparent, as contended by 

 Osborne (1948) and Vogt (1948), that the nation faces a choice of 

 (1) control of its population increase, (2) a declining standard of living 

 within a generation or two, or (3) immediate action toward conserva- 

 tion of its productive soil resources. Despite the large expenditures 

 currently being made for reclamation of arid land and, to a lesser ex- 

 tent, drainage of wet lands, the most serious task confronting the na- 

 tion is the maintenance of its existing crop land, particularly preven- 

 tion of the estimated loss of 500,000 acres annually due to gullying and 

 other forms of erosion that make further productive use of the land 

 virtually impossible. 



SEDIMENT PROBLEMS 



Sediment problems can be conveniently grouped into four categories 

 (see Fig. 9) : (1) suspended-sediment concentration in water; (2) sedi- 

 mentation (including erosion and degradation) in natural stream chan- 

 nels, improved river channels and harbors, floodways, ditches, and 

 canals; (3) sedimentation (including scour) on land, improvements, 

 and habitats; (4) sedimentation in reservoirs. 



In each category specific problems can be related either (1) to the 

 need for control of one or more of the seven sources of sediment pro- 

 duction previously described or (2) to the need for control of sediment 

 at the site of the problem (for example, proper design of irrigation- 

 diversion works to exclude bed load at the head of main canals). A 

 detailed treatment of every type of problem in terms of its causes and 

 remedies would obviously be beyond the scope of this chapter (U. S. 

 Bureau of Reclamation, 1948b). Other chapters deal specifically with 

 several of these problems. The treatment here will be confined to the 

 relation of sediment control on the watershed to the alleviation of the 

 several types of problems. The urgent need for remedial action is 

 emphasized by the magnitude of sediment damages, which have been 

 estimated by the writer to be approximately $175,000,000 annually. 



Suspended-Sediment Concentration in Water 



Sediment suspended in flowing or impounded water may have a 

 harmful effect on (1) water supply, (2) recreation, (3) commercial 

 fishing, (4) flood control, and (5) power generation. 



Suspended sediment must be removed from surface water before it is 

 potable or suitable for most industrial uses. Garin and Forster (1940) 



