State Agricultural Society. 



425 



can be calculated according to formulas that have been deduced from 

 careful observation and measurements. The area drained is called the 

 "cachment area" of the watercourse. Allowance is to be made for 

 absorption of the rainfall into the soil, loss by evaporation, etc.; the 

 remainder will be the theoretical discharge of the stream. These fig- 

 ures of cachment area and theoretical discharge, for a number of the 

 principal rivers of California, are as follows. The areas are given in 

 square miles, and the discharge in cubic feet per second: 



Name of river. 



Cach. area. 



Discharge. 



Feather 



Kern 



American 



King's 



San Joaquin. 



Tuolumne 



Yuba 



Merced 



Cache Creek 



444,666 



340,882 

 285,532 

 282,426 

 256,649 

 241,320 

 220,111 

 187,077 

 181,152 



In order to get some idea of what these figures mean, suppose a river 

 to have=an average width of five hundred feet between the banks, dis- 

 charging a stream of water ten feet deep; the sectional area of the vol- 

 ume of water will be five thousand square feet. A velocity of three 

 miles per hour will be equal to about fo,ur and a half feet per second; 

 and if the above volume be supposed to flow with this velocity, the 

 amount discharged per second (disregarding friction) will be twenty- 

 two thousand five hundred cubic feet. A stream averaging three hun- 

 dred feet wide by three and a third' feet deep will have a sectional area 

 of one thousand square feet; and, flowing with a velocity of two miles 

 per hour (equal to say three feet per second), will discharge a volume 

 of three thousand cubic feet per second. With a sectional area of two 

 thousand square feet the discharge would be six thousand cubic feet per 

 second. These special cases will be recognized as approximating the 

 actual discharge of several of the large streams above named, at their 

 lower stages. We may pause to collate the relative discharge of canals 

 of different sectional areas. The highest velocity safely allowable to 

 the water within canal banks without endangering the stability of the 

 banks, is about two feet per second, or say one and a half miles per hour. 

 A canal stream one hundred and twenty feet wide on top, eighty-four 

 feet on the bottomland six feet deep, will have a sectional area of six 

 hundred and twelve square feet. At a maximum velocity of one and a 

 half miles per hour, the discharge per second would be one thousand 

 two hundred and twenty-four cubic feet. A width of stream sixty- 

 eight feet at top, thirty-two feet at bottom, and six feet deep, would have 

 a sectional area of three hundred square feet. At the above velocity 

 the discharge would be six hundred cubic feet per second. A width of 

 forty feet at top, twenty feet at bottom, five feet depth, would give sec- 



54_(agrl) 



