STREAM FLOW EX I'K KI M KXTS 403 



With these formulc-e, we calculate the "most probable" discharge of 

 streanTB for any period in the year, and for conditions existing with 

 forest cover, and compare this (juantity directly with the actual dis- 

 charge after denudation. 



For the general conditions of the experiment, the reader is referred 

 to my article in the Proceedings of the Society of American For- 

 esters, Vol. VI, No. 1, 1911. Some discussion of this project has also 

 been given by Zon,^ in comparing it with the Swiss Experiment, whose 

 results are recently available. 



CALCULATIONS BY PRRIODS ^ 



1. Relations for the whole year, October 1, 1919, to September 30, 

 1920 : 



The precipitation and run-off of both streams is rather larger than 

 in the average year, especially in the spring flood period. 



Under the conditions existing, the most probable discharge of 

 stream B, with forest cover, would have been 7.G0S inches over 

 watershed.^ 



^ Corresponding, say, to 22 inches of precipitation over the watershed. This 

 expression permits us to disregard the area of the watershed. Hereafter the 

 abbreviation "ins. O. W." will be used. 



The actual discharge was 8.r)66 inches. 



Gain from removal of forest .958 inches or 12. G per cent. 



2. Relations in the spring flood, 1920 : 

 (a) First day of flood on A: 



The streams rose steadily from their winter rate without any marked 

 cessation of snow-melting. 



Stream A first passed into the flood stage on April 8. 



The most probable discharge of B, on this date, for the conditions 

 existing would be .0114 ins. O. W. 



The actual discharge was .01G.5 ins. O. W. 



' Zon, R. The Effects of Forests Upon Streamflow. Review in Journal of 

 Forestry, XVIII, 6, October, 1920, p. 625. 



-The Weather Bureau concurs in the statement of the preliminary calculations 

 of streamflow. 



It wishes to state, however, that in a number of respects the winter snowfall 

 cover, its melting, and the general flood conditions for 1910-20, place this year 

 in a class by itself, to some extent, as giving conditions more or less unlike 

 corresponding conditions prevailing in the f^rst stage of the experiment and 

 before Watershed B was denuded. 



