PLAN OF AN IRRIGATED FIELD. 193 



at intervals of 120 feet apart, parallel to the primary 

 ditch, and down the slope of 8 feet to the mile. These 

 are shown by the single dark lines. Other furrows are 

 made parallel to the secondary ditch, and 156 feet apart. 

 These shown hy the dotted lines are called check furrows. 

 The secondary ditches are made large enough to supply 

 11 of these first furrows, each of which communicates 

 with the secondary ditch, by means of a box, such as is 

 shown at fig. 61, (page 128), placed in the bank as seen 

 in the engraving, and opened and shut by a slide at the 

 head of each. When the gate at C is closed, the water 

 is turned into 11 of these boxes, and from them into the 

 connected furrows. The first check furrow stops the 

 flow, and dams the water back over the space of 165 feet 

 above it. As the slope of the ground is 8 feet to the 

 mile, the slope of the interval now covered with water is 

 nearly 3 inches, and the water must consequently be 3 

 inches deep at the check furrow before the upper portion 

 of the interval is watered. (Here a fault in the lay-out 

 is seen at first sight, because from the rapid absorption 

 of the water by the soil, either the lower portion must be 

 watered to excess, or the upper portion be left without a 

 sufficient supply. It is evident that this fault would be 

 obviated by making the check furrows nearer together, 

 say 50 or 60 feet, when the ground would be more quick- 

 ly covered, and more evenly watered. It is true that 

 some of the water would soak through the check furrow 

 on to the upper portion of the interval below it ; but this 

 would be an irregular and entirely a too hazardous pro- 

 ceeding to be adopted by a careful irrigator, and one that 

 would be excessively wasteful, both of water and crop. ) 

 When the interval has been watered sufficiently, the 

 check furrow is opened with the hoe at each main fur- 

 row, and the second strip is watered. The process is re- 

 peated until this half of the plot has been watered. The 

 boxes are then closed ; the gate at is opened, and the 

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