126 



IRRIGATION INVESTIGATIONS IN CALIFORNIA. 



at Lake Fordyce. This may be considered typical for all the reservoirs, 

 measurements were as follows: 



Evaporation at Lake Fordyce. 

 [Furnished by Mr. W. F. Englebright, chief engineer South Yuba Water Company. Elevation, 6,500 feet.] 



The 



Date. 



Aug. 10, 

 Aug. 11, 

 Aug. 12, 

 Aug. 13, 

 Aug. 14, 

 Aug. 15, 

 .\^Ug. 16, 

 Aug. 17, 

 Aug. 18, 

 Aug. 19, 

 Aug. 20, 

 Aug. 21, 



1900 . 

 1900. 

 1900. 

 1900. 

 1900 . 

 1900 . 

 1900 . 

 1900. 

 1900. 

 1900. 

 1900. 

 1900 . 



Date. 



Aug.22,1900 



Aug.23,1900 



Aug. 24, 1900 



Aug. 25,1900 



Aug.26,1900 



Aug. 27, 1900 



Aug. 28, 1900 



Aug.29,1900 



Aug. 30, 1900 



Aug.31,1900 



Total for 22 days . 



Average, one-sixth of an inch per day, and would probably average this .for 

 one hundred and twenty days each year, or 5J0 inches. 



In the storage of water for industrial purposes the uncertainty of the character 

 of the seasonal rainfall makes it prudent and desirable to permit the reservoirs to 

 fill during the earlier rains, and not leave the possibility of husbanding a supph' 

 to the uncertainty of succeeding rains. Hence it generally happens that when 

 the heavy storms of the late winter and spring months occur these storms find the 

 reservoirs full and the flood wav'e passes down without being diminished by the 

 capacities of the reservoirs. This is true to a limited extent of reservoirs above 

 the snow line, for in these cases the snow constitutes a reservoir of far greater 

 capacity than is ordinarily obtained behind dams. It also happens that in late warm 

 rains or rapid melting of snows that reservoirs are alreadj- full, and that the 

 reservoir capacitj^ does not diminish the flood volumes. 



It would appear, therefore, that however useful artificial reservoirs are for 

 domestic and industrial purposes they can not be relied upon, except under excep- 

 tional circumstances, to decrease the height of late winter and spring floods. 



FOKESI STORAGE. 



On the South Fork of the North Fork m'c have a watershed area of 139 square 

 miles which was gaged on September 19, 1900, after three successive seasons of 

 deficient rainfall, and gave a minimum run off of 113 cubic feet per .second, or 0.8 

 cubic foot per second per square mile. This area is well covered with timber and 

 brush, and in one hundred and twenty days gives a minimum run off of 1,441,152,000 

 cubic feet. The drainage basin of the North Fork is more heavily timbered than the 

 basin of the other forks, and con.sequently has a deeper .sOil, and although only one- 

 tenth the total drainage area it furnishes 75 per cent of the low-water flow of the 

 entire drainage basin above Parks Bar. 



