Sand Deposited on Alluvial Bottoms by Freshets, 1901, Catawba County, North Carolina 



rapidity of run-off and it is the rapidity 

 of run-off that counts in flood produc- 

 tion. It is a matter of elementary 

 physics, merely, to show that the rapid- 

 ity or velocity of run-off from a rough 

 surface such as a forest covered one 

 would not be as great as from a smooth 

 one of the same slope, whether the sub- 

 surface were saturated or not. 



The writer feels very certain trom 

 his field studies that the absorptive 

 capacity of the average Southern Appa- 

 lachian forest area is very materially 

 greater than the absorptive capacity of 

 the average cleared field in the same re- 

 gion, and this balance in absorptive 

 capacity in favor of the forest is a po- 

 tent factor in preventing or mitigating 

 flood disasters. Up to a certain maxi- 

 mum limit of rainfall that would vary 

 in each individual case, the forest cover 

 would prevent any run-off at all ; if the 

 rainfall be doubled the forest cover 



would retain half of it; if quadrupled 

 a fourth ; and if in torrential down- 

 pours it retained only a tenth, say, of 

 the rain that fell, it is still just so far 

 beneficial in its influence and without 

 it the resulting flood would be just so 

 much the worse. It is illogical to con- 

 clude that the forest has no beneficial 

 influence merely because it fails to con- 

 trol floods entirely, and it is in the very 

 worst floods that any ameliorating in- 

 fluence is most needed. It may be 

 remarked that the writer knows no 

 kind of vegetation on cleared land in 

 the Appalachians that exerts anything 

 like as great a conserving influence on 

 the rainfall as the forest does, simply 

 because the covering of humus and lit- 

 ter in the forest is both thicker and a 

 more efficient absorptive agent than any 

 vegetable cover on the cleared land. 



In regard to the quotation from the 

 French engineer, Mr. St. Clair, on page 



221 



