205 



In the first period ( ISKO-ISUS) oi" nine years there were forty-seven 

 floods lasting 116 days. There were 506 days of low water. 



In the second period (1899-1907) of nine years there were fifty-eight 

 floods lasting 170 days. There were 292 days of low watei'. The rainfall 

 decreased .17 of an incli ]ier year. 



The Ohio River was nicasui-cd at A\ heeling. W. Va. It drains a basin 

 of 23,S20 square miles. 



In the first period (lss2-ls;)4) of thirteen years there were forty-six 

 Hoods lasting 143 .lajs. There were 1,.333 days of low water. 



In the second period (1S95-1907) of thirteen years tliere were fifty- 

 nine floods lasting ISS da:4s. There were l,t!09 days of low water. Tho 

 rainfall decreased .11 of an incli aiimiaLly. 



The data here cited for the above mentioned rivers is also true for 

 many other streams, but these will serve as good examples of what has 

 been and is taking place wherever deforestation has occurred. In such 

 rivers as the Ohio, Cumberland, and Wateree, changes are most conspicuous, 

 and it is in these that most of the foresi has been remo\'ed, while least 

 change appear in those streams where most of the forests remain.' 



This state of affairs is what we should expect, but the data given for 

 the rivers referred to prcjves this by direct observation and leaves the 

 matter no longer a question of guesses or opinion. 



From what has just been said it is certain that as deforestation prog- 

 resses floods will, with equal amounts of precipitation, become more fre- 

 quent and increase in severity. To l)e sure, there are other factors that 

 enter someAvhat into any consideration of the cause of floods. Among 

 these may be mentioned rainfall, season of the year and temperature, 

 character of the soil, presence of lakes w^hich might impound a good part 

 of the "run-olf" temporarily and afterwards gradually supply it to the 

 streams, and thus while at first preventing flood afterwards lessen the 

 length;\- perioils of low water. Also the question of whether the land is 

 nearly level or very hilly and steep is important. A lieavy precipitation 

 might do no damage whatsoever in th( former case, whereas in the latter 

 am )ng steep and deforested land the destruction might be appalling. 



But after w^e have considered all these points ;ind many others that 

 might l)e mentioned, the fact remains that the chief cause of the frequent 



' Hall, Wm. :ind .Maxwell, Hu. l''orest Service Circular 170, p. :i. 



