THE IRRIGATION AGE. 



83 



inch the entire width of the ditch, enabling one to 

 make a ditch absolutely true to the engineer's specifi- 

 cations. 



The same principle that applies io tLe construc- 

 tion of drainage ditches is also true of those made for 

 irrigation purposes except that it is nvt desirable to 

 have an irrigation ditch with so great a grade. By 

 shaving out an irrigation ditch from the solid strata 

 of earth, leaving banks and bottom perfectly smooth, 

 the banks remain firmer than when constructed in any 

 other manner, and as a consequence there is less seep- 

 age. In districts where water carries silt possessing 

 cementing qualities, if the ditch is perfectly shaped and 

 the wetted perimeter is perfectly smooth, a very small 

 quantity of this silt will cement the ditch, making it 

 practically impervious to seepage, an advantage that 

 can hardly be overestimated when it is taken into con- 

 sideration that there are many irrigated ditches in 

 in the West which 75 per cent of all water turned 

 ; into the ditches is lost through seepage in the mains 

 alone. 



Agricultural scientists are constantly devoting 

 greater attention to the subject of ditches. The suc- 

 cess attained in reclaiming the 150,000,000 acres of 

 arid lands and 1,000,000 acres of swamp lands in this 

 country, which it is estimated can be converted into 

 fertile areas, depends almost entirely on the construc- 

 tion of ditches. It is not, however, in the reclaiming 

 , of the present worthless lands that the country will 

 ! derive the greatest benefit from the construction of 

 i ditches. There is scarcely a county in the humid sec- 

 ; tion of America in which land already under cultiva- 

 ' tion cannot be increased in productiveness from 25 to 



the state for drainage. It is probable that the wet 

 lands of Iowa are proportionately not greater than in 

 most central states. How to make a perfect waterway, 



A recently constructed ditch built with dipper dredge, showing . the 

 vertical banks and waste banks constructed immediately adja- 

 cent to the ditch and demonstrates why ditches 'con-, 

 structed in this manner cave and are filled by 

 erosion in a short time. 



therefore, ought to be of the greatest interest to every 

 one interested in the improvement' of agricultural lands. 

 The initial expense of reclaiming these lands by 

 . scientifically correct ! ditches is not greater than ex- 

 cavating irregular channels with no thought of Nature's 



Perspective view of Austin Drainage Excavator excavating a ditch 8 feet deep and 6 feet on bottom, showing shape of ditch and width of 

 berm when banks are sloped 1 to 1; also shape of ditch with same width of bottom when banks are sloped 1^5 to 1. 



50 per cent through the construction of ditches com- 

 bined with under drainage. 



The drainage engineers of Iowa State College, at 

 Ames, Iowa, estimate that in that state 41.7 per cent 

 of all agricultural lands are without adequate drain- 

 age and that $406,235,500 could be profitably spent in 



laws and in the one case the first cost represents the 

 entire expense of producing a permanent waterway, 

 while in the other an irregular channel is dug which 

 becomes rapidly choked by caving banks and accu- 

 mulated silt and cost of maintenance will in a short 

 time exceed original expense of construction. 



