NINTH ANNUAL YEAR BOOK— PART XII 731 
legislature has enacted a law whereby a man may force a drain across 
his neighbor's land, and this law should be used whenever necessary. 
So far in this discussion we have only considered general conditions 
and what things it is proper to do. That part is important as it gives 
a starting point from which to discuss the more important question, How 
best to do the proper thing? That is a more difficult task, and in under- 
taking it I will only profess to give the result of my observation, ex- 
perience and study. It may well be asked: 
First — What is a safe depth below the surface? I would say from 
three to four feet. Sometimes it is necessary to go much deeper in order 
to procure a uniform grade, or for some other reason. As a rule that 
makes it better rather than worse. The only objection is the additional 
cost. There is a constant temptation to save money or labor by shallow 
tiling and ditching, but it will be a great mistake if you yield to the 
temptation. It is very easy to waste a hundred, or even a thousand, dol- 
lars, by laying a string of tile too near the surface. This is particularly 
true with large tile. A 12-inch tile should be laid four feet deep, if 
possible. Sometimes it is impossible on account of poor outlet or slight 
fall to get a drain three feet deep. In that case do the best you can. I 
have seen excellent results with a depth of a foot and a half at the out- 
let, or at the upper end. Such a drain will not drain a large area, but 
will do good work for a small area. If it is a main drain it will need 
lateral drains where otherwise they might not have been needed, and if 
a lateral drain, other laterals near; in some cass two or three times as 
many would be needed if the drain were deeper, so it will prove in the 
end very much more expensive to drain land with shallow drains than 
with deeper ones. 
Second — What is sufficient slope? In measuring slope engineers usually 
use one hundred feet of drain as a unit. That is to say, if an engineer 
should tell you that a drain has a slope of fifteen-hundredths, he would 
mean fifteen-hundredths of a foot to every hundred feet. The fall is 
usually expressed in hundredths of a foot rather than in tenths or inches, 
because it is convenient to use the decimal system, and we need a small 
subdivision, as we often have a very small amount of fall to apportion 
to a very long drain. Good drainage can be secured on a very small fall. 
Good authorities say as low as one hundredth, or even on a level, but the 
less the fall the more expensive the drainage. In this country I consider 
a slope of from ten to twenty-five hundredths a good practical condition 
for such drainage as will not be unusually expensive. This question of 
slope must always be considered in connection with the size of drain and 
volume of water, and I will give some tables in connection with those 
subjects that will involve all three questions. 
Third — How can we compute the proper size of a drain? It is abso- 
lutely necessary first to know the volume of water and the slope of the 
drain. In measuring the volume of water to be moved you must know 
the area to be drained, and the amount of rainfall. 
The area can be carefully measured if you like, but usually a rough 
estimate will answer every necessity. Then with the average rainfall 
known the problem should be easy; but some of this water sinks to sub- 
