28 BULLETIN 190, U. S. DEPARTMENT OF AGRICULTURE. 



The more pervious material excavated should be placed adjacent 

 to the tile. The backfilling may be done by means of a plow with 

 three or more horses and a long pole evener, or by means of a scraper 

 or "go-devil." All the spoil should be returned to the trench and 

 should be banked over it so that future settling will not leave a 

 depression over the drain. 



Various types of trenching machinery, some of which are suitable 

 for use on irrigated land, are on the market. The choice of machine 

 may well be left with the contractor, however, and the question will 

 not be discussed here. 



MAINTENANCE. 



If a canal is to retain its efficiency it must be well maintained. At 

 least twice each year (more often if necessary) vegetation should be 

 removed from the channel and banks, and such material as has fallen 

 into the channel taken out. Any damaged places must be repaired to 

 prevent further trouble. Tumbleweeds are a source of much diffi- 

 culty, and it seems practically impossible to keep them out of drainage 

 canals. They soon form serious obstructions and it is necessary to 

 remove them at frequent intervals; this is generally done by men 

 equipped with forks and rakes. Fortunately, these weeds generally 

 disappear when drainage is accompHshed. Perhaps the most difficult 

 thing to deal with is "blow sand," which, during a high wind, may 

 completely obstruct a canal in a few hours. From the very nature 

 of the conditions maintenance is difficult and costly, and it foUows 

 that every endeavor should be made, during construction, to reduce 

 the amount of maintenance necessary. When it is realized that the 

 annual cost of maintaining open canals is often 10 per cent of the first 

 cost, the need for correct design and careful construction is apparent. 



A properly designed and well-constructed tile system requires little 

 maintenance. Obstructions in the hne, and vegetation that may 

 develop dangerous water roots, must be removed. Holes and de- 

 pressions in the backfilling must be ffiled and the burrowing of animals 

 prevented. 



A number of types of tile-cleaning devices have been developed. 

 These are useful during construction in keeping the suspended matter 

 in movement until the flow of water is large enough to create sufficient 

 velocity to carry the material along. After the system is put in opera- 

 tion they may be used to clean out water roots that may have pene- 

 trated the tile Hne through the joints, or to clear the line of obstruc- 

 tions caused by sand or silt. One of these devices is in the nature of 

 an auger, while another kind is built hke a small hoe. For the 

 removal of roots an apparatus involving a spiral cutter is used, or 

 better stiU, a sort of wire brush. The latter is also useful in removing 

 other obstructions and may easily be made by wrapping a piece of 



