314 



FORESTRY AND IRRIGATION 



July 



average weekly mean of each stream 

 for the entire period was then ob- 

 tained. The percentage deviation 

 from this mean, above or below, for 

 each week in the three years and the 

 average deviation for the entire period 

 were then calculated for each stream. 

 The average deviation from the mean 

 flow thus obtained should give us a 

 ready means of comparing directly 

 the variations of the two streams and 



moderate topography, natural reser- 

 voirs, and favorable geological con- 

 ditions of the Wallkill is somewhat 

 stronger in promoting evenness of 

 stream flow than the compact forest 

 cover of the Esopus basin. At the 

 same time the margin of difference 

 between the regularity of the two 

 streams is so small as to establish be- 

 yond doubt that the forest cover of 

 the Esopus does exert a strong con- 



The Esopus at Big Indian, N. Y. 



the relative evenness and uniformity 



j 



of their discharge. 



It was thus found that the aver- 

 age deviation from the mean weekly 

 flow is 78.24 per cent, in the case of 

 the Wallkill and 83.69 per cent, in the 

 case of the Esopus, the latter thus 

 showing a slightly more irregular dis- 

 charge than the former. The con- 

 clusion to which we are thus brought 

 \:, that the combined influence of the 



serving and regulating influence upon 

 the flow of that stream. This is es- 

 pecially true when we recall how un- 

 favorable the other factors of topog- 

 raphy and geology upon that catch- 

 ment area are to equablex stream flow. 

 The forest cover of the Esopus thus 

 appears to overcome to a large degree 

 the unfavorable effects of steep topog- 

 raphy, hard and dense surface rocks r 

 and marked deficiency in natural stor- 



