however, as will be explained later, that in those same areas 

 wide-spread removal of vegetation and unwise tillage 

 practices have had an even greater influence by restricting 

 infiltration and promoting run-off. 



Another aspect of nonselective drainage over a large area is 

 the effect on stream volumes during the months of lesser rain- 

 fall. In some areas, with the disappearance of the swamps, 

 marshes, and other wet lands, and diminution of ground- 

 water stores, which once gradually fed their waters to the 

 streams by seepage and springs throughout the dry season, the 

 waters of these streams have tended to become low during 

 that season, and in some instances entirely disappear. This 

 has created serious problems of pure water supply for agri- 

 cultural and municipal uses, and of excessive pollution of 

 streams no longer sufficient in flow to carry the burden which 

 public works placed upon them at a time when their capacities 

 appeared adequate. 3 



Collateral to the damage done by drainage through its 

 cutting off part of the natural source of groundwater supply, 

 is the damage done in respect to other services of surface 

 waters. Fish in accessible fresh-water streams have for this 

 among other reasons all but disappeared; and the availability 

 of these streams for recreation has diminished. The wild 

 fowl, once so abundant, are having increasing difficulty in 

 finding breeding, feeding, and resting places, and as a result 

 of the consequent segregation are diminishing in quantity. 

 If for no other reason, a part of the drained submarginal and 

 marginal lands should be restored to some degree of wetness 

 in order to replenish and sustain the diminishing wildlife. 



[b] REMOVAL OF FOREST COVER. 



Of the original forest area of 816,158,000 acres in the United 

 States only 494,898,000 acres remain. Of the cleared area 

 a very large part is in pasture, but also a large part is more or 

 less intensively tilled and cropped. The way has thus been 

 opened for a considerable influence on the circulation of 

 waters by removal of natural vegetative cover. 



8 On the other hand, measurements in Iowa show no relation between drainage and stream 

 flow. See Sherman M. Woodward and Floyd A. Nagler, The Effect of Agricultural Drainage 

 Upon Flood Run-Off, Transactions of American Society of Mechanical Engineers, 1929, Vol. 

 93, pp. 821-839. 



2 4 



