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IRRIGATION INVESTIGATIONS IN CALIFORNIA. 



rainfall of moment from May to September. The streams during these months, 

 therefore, depend upon natural or artificial storage. Natural storage is had by snow 

 and by the slow run off of water retained in afforested and brush-covered soils. 

 Artificial storage has reached a very efficient stage on the South Fork. 



The mean distribution of precipitation is shown on the map accompanying this 

 report and also on the section which shows the increase due to elevation (fig. 1). This 

 ranges from 20 inches at Marysville, in the valley, to 70 inches at the summit of the 

 Sierras.^ 



Snow storage of water is depended on during the latter part of April and into 

 July. The run off until June is superabundant for all purposes, but begins to fall 

 below the necessities of dependent industries from July until autumnal rains. Snow 

 storage has not been made a subject of extended observation, except by Mr. W. F. 

 Englebright, the chief engineer of the South Yuba Water Company, through whose 



Fig. 1.— Diagram showing variation in precipitation with altitude. 



courtesy the writer is enabled to present the following instructive diagram of the 

 rate of accumulation, depth, and rate of melting of snow at Lake Fordyce (fig. 2). 

 This lake has an elevation of 6,500 feet above tide level, and is in a region over 

 which annual precipitation in melted snow is 70 inches. 



The variation in depth of snow in different seasons and the effect of late cold 

 seasons ai'e distinctl}^ shown on the diagram. 



Snow begins to accumulate late in November and reaches its maximum depth of 

 packed snow in March. The lower readings on the gage rod, following higher 

 readings during the winter months, generally indicate a packing of the snow. Melt- 

 ing begins in March and continues quite regularly until the middle of June or early 

 in July; short storms during Api'il and Maj' cause offsets in the curve, which resumes 

 a parallel line. A series of cold and heavy storms in April, 1896, caused the snow 

 to last until July .5, while the clear wann spring of 1897 caused it to disappear on 

 the 7th of June. 



'These figures and the isohyetal lines on the general map are taken from a map prepared under 

 the writer's direction for the California Water and Forest Association, showing the drainage area, 

 mean annual rainfall, and forest distribution throughout the State. 



