ARTESIAK WELLS. 



413 



HYDROGRAPHY. 

 THE RAINFALL. 



Fur the twenty years 1870 to 1889 the average annual rainfall at 

 Denver, as observed by the United States Signal Corps, was 14.113 inches, 

 having varied in this period from 8.85 to 20.12 inches. This may fairly 

 be considered the rainfall for the area of the Denver Basin, but it is doubt- 

 less considerably below that for the valley <>t' the Platte in general, for in 

 the mountains precipitation reaches a much higher figure. 

 Tabular statement of rainfall at Denver. 



DISCHARGE OF STREAMS (RUN-OFF). 



The monthly discharge of the streams, or run-off', has been calculated 

 for many catchment areas in the Rocky Mountain region by Mr. F. II. 

 Newell, of the hydrographic division of the < ideological Survey, from obsers a- 

 tions by that division and by engineers or others prior to the establishment 

 of irrigation work by the Survey. The run-off for the Platte Basin has 

 not been investigated, but for the ( 'ache la Poudre to the north and the 

 Arkansas to the south the following table has been prepared. 



The table gives the discharge from the drainage basin in two units. 

 In the first column is the total quantity of water flowing in a given period 

 reduced to equivalent depth in inches over the entire drainage basin; this 

 is immediately comparable with the rainfall upon the basin, usually given 

 in inches. The second column gives the average rate of flow per square 

 mile drained, in cubic feet per second, or second-feet. 1 



■One secou(l-foot = 62.5 pounds = 7.48 gallons. 



