210 



INDIANA UNIVERSITY STUDIES 



crease in flood frequency in the Ohio Valley during the last forty 

 years. For instance, Professor Alfred J. Henry (Bulletin 'Z' of 

 the United States Department of Agriculture Weather Bureau) has 

 shown that by taking the severe floods of the last forty years, on 

 the Ohio River, there were 19 severe floods during the first 20 years, 

 and 32 during the last 20 years, ending 1910. Now if the last .30 

 years are divided into two equal periods and the first 15 years 

 compared with the last 15 years the order of frequency is reversed. 

 The following table taken from 'Bulletin Z' of the Weather Bureau 

 Publications shows the above in tabular form: 



TABLE No. 6. 





First period 



Second period 



First period 



Second 



Stations. 



of 20 years, 



of 20 years, 



of 15 years, 



period 





1870-1890. 



1891-1910. 



1881-1895. 



1896-1910. 



Pittsburg 



2 



9 



3 



8 



Cinceinnati 



6 



7 



8 



5 



Louisville 



5 



5 



7 



3 



Evansville 



6 



11 



8 



9 



Totals 



19 



32 



26 



25 



It is a fact that great floods are dependent upon excessive 

 rainfall; also it is a fact that deforestation and the increase of arti- 

 ficial drainage have a tendency to rush these excessive waters to 

 the main streams, causing the height of the flood to become greater 

 in a shorter length of time. Just how much that this will increase 

 the height cannot be determined until more data are accumulated, 

 showing the discharge of the streams and the amount of precipi- 

 tation over large and various areas. Mr. Henry suggests that 

 it will take at least 50 years to get together sufficient data to de- 

 termine the effect. 



The Lowering of the Wator Table 



ft is beginning to be a well known fact that the water table 

 over the entire State is being lowered. This is the case in several 

 states scattered over the United States, as in Michigan, Alabama^ 

 Florida, California, Colorado, Nebraska, South Dakota and Wash- 



