24 TILE DRAINAGE 



For laterals a three-inch tile will usually be found most 

 satisfactory, as it is large enough to carry off in a reason- 

 able time all the surplus water of our heaviest rains. The 

 danger in using smaller tile lies in the fact that it does not 

 take a great deal of sediment to fill them, and unless they 

 are laid on a perfectly true grade with a good fall their 

 efficiency will soon be diminished. A variation of an inch 

 below a true grade will result in filling a two-inch tile just 

 half full of sediment, while an inch of sediment in a three- 

 inch tile will only reduce its carrying capacity about one 

 fourth. Last fall we dug up some two-inch tile laid ten 

 years ago in a fine clay soil with only a slight fall, which 

 had become almost full of sediment and were practically 

 useless. It is pretty difficult to determine the proper size 

 of tile unless the detailed conditions under which they are 

 to be laid are known. Errors resulting from too small 

 tile are most serious in their effects and the only safe plan 

 is to be sure they are large enough even though the first 

 cost is somewhat greater. 



In regard to the fall of drains, it may be said that the 

 best rule is to have all the fall possible. A foot to the 

 hundred feet is desirable if it can be had. Cases will 

 sometimes occur where three inches or even less must be 

 accepted and in these instances the bottom of the ditch 

 must be carefully leveled and graded so that no sags will 

 occur. It is important, also, to have a uniform fall, that 

 is, not to change from one grade to another in the same 

 line of tile. In changing from a steep to a less steep grade 

 the velocity of the water is checked and there is danger of 

 sediment being deposited where the change is made. Of 

 course there is no objection to changing from a small grade 

 to a greater one for in this case the velocity will be in- 

 creased and the sediment will be the better carried onward. 



DEPTH AND DISTANCE APART OF DRAINS. 



The depth at which drains should be placed will depend 

 largely upon two conditions: First, the nature of the soil 



