ion: FIG. 86.
_A_ represents a poorly laid tile-drain. It is poorly graded, and has
partly filled with soil. It has lost more than half its water carrying
capacity. _B_ was properly graded, and has kept free from sediment.]

The main drains should be located in the lowest parts of the fields,
indicated by courses taken by water after a rain or by small streams
running through the farm.

The lateral drains, if surface or open ditch drains, should run across
the slopes; if under drains, they should run up and down the slopes.

_Grade or slope of the drain._

The grade of the drain should be sufficient to cause a flow of the
water. In the case of open ditches it should not be steep enough to
cause too rapid a current and a consequent serious washing of the
banks of the ditch. Large, deep ditches will carry water with a grade
of one inch to a hundred feet.

_Tile drains._

Covered or under drains are made of brush, poles, planks, stones,
tiles, etc. (Figs. 83-84). Where tiles can be obtained at reasonable
prices they are considered best. Tiles are made of clay and are burnt
like brick. They are more lasting than wood and are easier and cheaper
to lay than stone, unless the stone must be gotten rid of.

The most approved form of drain tile is the round or circular form.
These are made in sizes ranging from two and one-half to six and eight
inches in diameter, and in pieces one foot in length.

The size used depends on the length of the drain, the amount of water
to carry, the frequency of heavy rainfalls and the character of the
soil.

The distance apart varies from twenty-five feet in heavy soils to
over two hundred feet in light soils. The usual depth is about three
feet, though the farther apart the deeper they are put.

A lateral tile drain should enter a main at an acute angle to prevent
too great a check in the current.

In putting in a drainage system the first thing to be done is to make
a plan of the ground and determine the slope of the land and the grade
of the drain. The ditches are then staked out and the digging
proceeds. In digging the ditches plows are sometimes used to throw out
the top soil, then the work is finished with spades and shovels.

Professional ditchers use special tools and they take out only
sufficient earth to make room for the tiles (Fig. 85). The tiles are
then laid end to end, the joints covered with a piece of sod, some
grass, straw, paper or clay, to prevent loose soil sift