of the proposed trench, these strings will
be in line on a grade 5-1/2 feet above the grade the drain will have.
As the cut at the station is known, the height of the string above the
top of the stake is easily determined. These strings will reveal any
inaccuracy in the survey. The workman can test every part of the bottom
of the trench by use of a rod 5-1/2 feet high, the top end being
exactly in line with the strings when the lower end is placed on the
correct grade of the trench. This device is better than running water
where grades are slight.

A drain scoop should be used in bottom of the trench to make a resting
place for the tile that will prevent any displacement by the soil when
the trench is filled.

Depth of Trenches.--Underdrains may be placed too deep in close soils
for best results. In an early day it was advised that the drains be put
down 4 feet deep. We now know that a tight clay soil may give best
results from a drain only 28 inches deep, or even a little less. In a
looser soil 3 feet is a better depth, and in porous swamp lands the
drain may well go 4 feet deep, thus permitting increase in distance
between drains.

Connections.--The laterals should enter the branches and mains near the
top, so that the water will be drawn out rapidly. The tile should be
laid with close joints at the top, so that the water may enter more
freely from the sides than the top. No covering other than moist soil
is needed unless there is very fine sand, when paper over the joints
will serve a good purpose. After some moist soil from the sides of the
trench has been tramped upon the tile, the trench may be filled by use
of a breaking-plow or winged scraper.

Permanency Desired.--The expense of underdrainage demands care in every
detail of the work. The grade of the trenches should be carefully
tested. Every piece of tile should be examined. The outlet should be
guarded against displacement or entrance by animals. A good plan is to
lay the last few pieces of tile in a close-fitting wooden box, and to
protect the end with iron rods placed 2 inches apart.

If the drain is on a true grade, so that no silt will collect, there
need be no fear concerning its continued efficiency, provided water
does not run in it all the time. If it carries the water from springs
continuously, plant-roots may fill it, and tree roots are quite sure to
do so when opportunity offers. This is notably true in case of elms and
willows, but protecti