CANAL CONSTRUCTION. 65 



slightly increased cost, for they can then be used as 

 wagon loaders, and the earth hauled to any devSired 

 point. A large ditch 18 feet wide at bottom, 30 feet 

 at top, 4 feet in depth, with a four-foot additional em- 

 bankment, with a capacity of 6 feet in depth, 36 feet 

 at surface, and 18 feet at bottom, having a cross-sec- 

 tion of 162 square feet, with a current of two miles an 

 •hour, would, in twenty-four hours deliver sufficient 

 water to cover 940 acres i foot deep. A mile of such 

 a ditch could be built by three men with six teams in 

 eighteen days at a cost of about $400. By ordinary 

 methods such a ditch would cost several times this 

 amount. A ditch 8 feet at bottom, 20 feet at top, and 

 3 feet deep would cost approximately $200 a mile. A 

 lateral 4 feet at bottom, 12 feet at top, and 2^ feet 

 deep, carrying 3)^ feet in depth of water, can be built 

 at from ^75 to $100 a mile, and a small ditch 2 feet on 

 bottom, 8 feet at top, and 2 feet deep, can be con- 

 strudled with these graders for about $50 a mile. 

 These figures have been calculated somewhat lower by 

 the manufacturers of ditching machines, but we be- 

 lieve the estimates made herein are more conservatively 

 corre(5l than those of the makers. 



Form and Capacity. — To get the greatest possi- 

 ble velocity the ditch should be in the form of half a 

 pipe or a pipe split in half lengthwise. This would re- 

 quire the width of the ditch at the top to be exadlly 

 twice its depth in the center. In other words, it would 

 be as wide at the top as the length of the diameter of 

 the pipe, and one-half diameter deep from the center 

 to any point of the sides or bottom. A ditch of this 

 form offers less fri<5lion surface in proportion to its 



