REPORT ON FORESTS. 



163 



springs become sooner exhausted and it runs lower toward the 

 end of' the drought. The barren ground, having absorbed 

 much less water, has less flow from springs throughout. How 

 important this is upon the dry-season flow of these streams 

 becomes apparent from the following table : 



Computed Run-off^ in Gallons^ Daily per Square Mile, During 

 the Last Eight Months of 1881. 



April, . . 

 May, . 

 June, . . . 

 July, . 

 August, 

 September, 

 October, 

 Kovember, 



The economic importance of this effect lies in the greater 

 value of forested streams for water-power, and the smaller storage 

 reservoirs needed thereon to furnish a given daily supply of water 

 to cities. Illustrative of this, the Passaic will furnish for 9 months 

 of the year, from 100 square miles of water-shed, 45 horse-power 

 on 10 feet fall, whereas the Raritan will furnish but 41 and the 

 barren water-shed 28 horse-power. During the other 3 months 

 the Passaic will furnish an average of 36, the Raritan 32, and 

 the barren water-shed 20 horse-power. , 



To collect 570,000 gallons of water daily on one square mile 

 of water-shed we shall need storage reservoirs of the following 

 capacity : Passaic, 84,000,000 ; Raritan, 1 10,000,000, and barren 

 water-sheds, 126,000,000 gallons. 



The difference in cost of collecting a supply at the above rate 

 per square mile, therefore, upon the type of streams selected to 

 represent the forested and upon those representing the barren 

 conditions, would be about $8,400 per square mile. Both the 

 Passaic and Raritan exceed 800 square miles in catchment. For 

 such an area the saving would be $6,720,000. 



Taking the same size of catchment we find the excess of 

 water-power on the forested stream would be, for 100 feet fall. 



