194 



IRRIGATION. 



other part of the plot is irrigated in the same manner. 

 The size required for the secondary ditch, or rather that 

 of the gate at A, by which the ditch is supplied, must be 

 proportioned to the quantity of land irrigated by it. If 

 the plot is 160 acres, the gate should have an area of at 

 least 144 square inches, if the flow is continual, and a 

 proportionately larger area if the flow is intermittent. 

 The size of the boxes should be in proportion, or 14 1 ], 

 square inches for each inside measurement. A box 7 1 1 4 

 inches wide by 5 inches deep inside measure, and having 



Fig. 82. PLAN OP FURROWS FOR AN IRREGULAR SURFACE. 



a gate or slide to open 2 inches, would give 14 1 !, square 

 inches of water under a head of 3 inches, which is a usual 

 arrangement for supply. 



This plan is an excellent one, and pointed out as an 

 illustration of ordinary irrigation, could hardly be excelled. 

 With modifications, it offers a method of preparing the 

 surface of gently sloping ground that is applicable to a 

 wide diversity of instances. 



The plot given in the illustration is drawn to scale of 



