Journal of Agriculture, Victoria. [lo Feb., 1911. 



Engineers and water-masters engaged in distributing water rapidly 

 acquire a knowledge at sight of the volume of water flowing in moderate- 

 sized channels. After seeing several streams accurately gauged, and 

 reckoning in cusecs, and applying an old rule (a cusec will water 10 acres 

 of orchard in twenty -four hours), they can tell very nearly what volume 

 an irrigator is using, and whether he is doing so to the best advantage. 

 And it is not long before the irrigator himself becomes quite familiar with 

 cusecs and is able to judge if he is being fairly treated. A cusec, accord- 

 ing to the rule stated, is equal approximately to a depth of i-5th of a foot 

 or 2 1 inches. 



As a guide to those about to lay out a chamiel or series of ditches for 

 irrigating the' following tables are appended, and are computed for side 

 slopes in the ratio of it to i : — 



Discharge in Cubic Feet per Minute of Channel -flowing 1 foot deep. 



Discharge in Cubic Feet per Minute of Channel fiotving 2 feet deep. 



Discharge in Cubic Feet per Minute of Channel flowing j feet deep. 



These discharges are computed for earthen channels of regular section and free of weeds, &c. Dividing 

 these results bv 60 will give cubic feet per second, or " cusecs." 



To select the size of channel within the limits of the Tables for any particular area— An acre comprises 

 43,560 square feet, and, if watered 12 inches deep, would take the same number of cubic feet of water. 

 A 6-inch watering will tlierefore take half, or 21,780 cubic feet. Divided by 24 will give the number of 

 cubic feet required per Iiour : and divided again by 60 will give the cubic feet required per minute, which 

 in this case amounts to 15-125. Multiply tliis by the number of acres to be served and find the resulting 

 discharge in the Tables, whence tlie size of channel may be derived ; remembering that it is best in head 

 ditches not to have much fall, and in channels not to have tliem too shallow. If it is desired to water in 

 a less or greater time than 24 hours, use the time selected in making the computation, or if a greater or 

 less depth than 6 inches is required adopt a similar course. 



