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 accomplished. 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 follows 
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 Hue, and vegetation that may 
develop dangerous water roots, must be removed. Holes and de- 
pressions in the backfilling must be filled 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 line 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 Like a small hoe. For the 
removal of roots an apparatus involving a spiral cutter is used, or 
better still, a sort of wire brush. The latter is also useful in removing 
other obstructions and may easily be made by wrapping a piece of 
