904 
Foresights are readings on stations 
whose elevation is to be found. fFore- 
sights are minus quantities and are to 
be subtracted from the height of the 
sight line. This gives the elevation of 
the station road. 
Laying Out a Drainage System—Records 
The first thing in laying out a drain- 
age system is to tramp over the land to 
be drained and find out the lay of the 
land and then set up some flagpoles. Just 
a straight stick with a cloth on top will 
do, if you do not have regular surveyor’s 
poles. These are placed so that the chain- 
man can chain the levels. 
A Preliminary Survey 
It may be exact or it may be taken 
roughly. It may be necessary to make 
a topographic map of the whole area to 
be drained. In this sort of a map put 
in streams, etc. After this you should de- 
cide on some definite plan. Decide on 
some bench mark. Then go ahead and 
take your level notes from which you 
could figure your total available fall. 
Should chain all the lengths in order to 
know accurately how much tile you will 
need. Then make a statement and put 
down how many 8&8-inch, 6-inch, 4-inch and 
3-inch and then total up and see how 
much it will cost. 
Contour Maps, Relief Maps 
A. contour line is simply a line connect- 
ing all points of equal elevation. To 
make a contour map take the elevation of 
every certain distance, say 100 feet. This 
distance is regulated by the topography 
of the land to be drained. Sometimes 
make a topographical map and then be- 
low make a relief map. Every farm sub- 
ject to drainage or irrigation needs to be 
provided with a contour map. Such a 
map will show the proper location of 
drains or irrigation ditches. 
Profile Maps 
These show a cross section of the strata 
through which the line of tile is to pass 
They will show you the depth to be dug 
at each station. In preparing profile maps 
use a scale of four feet to the inch ver- 
tically, and 100 feet to the inch horizon- 
tally. The tile line should be in red ink. 
ENCYCLOPEDIA OF PRACTICAL HORTICULTURE 
Permanent Map 
Plane table. The permanent map 
should be accurate so that in after-years 
it would be possible to go out in the field 
and locate the drainage system or any 
part of it immediately. 
Details of Drainage 
The bearing of the line is the angle 
which it makes with the magnetic 
needle. 
Length of Laterals 
This should not exceed 800 or 1,000 
feet for 3-inch tile and may be 2,500 feet 
for 6-inch tile. 
Amount of Fall 
Fall is the common term for slope of 
land or for total head when applied to 
drains. 
Available fall is the fall that can be 
given to a drain in a prescribed distance, 
and may be greater than the fall of the 
surface. 
Grade of a drain is the rate of fall 
expressed in decimals of one foot per 100 
feet. A uniform grade is simplest, but 
it is often necessary to change the grade. 
When this is done it is best to change 
from a less to a greater grade. A change 
from a greater to a less fall would check 
the velocity and cause silting of the 
drain. If it is necessary to change the 
grade, it is a good plan to use a silt 
basin. 
Silt Basins 
Silt basins are small cisterns in the 
drain extending to the surface and af- 
fording a means of cleaning out the silt. 
They help to collect flood water quickly. 
They prevent the drain from being 
clogged and becoming silty. They may 
afford watering places for stock. In a 
smiall drain a large 12-inch tile may be 
used by standing on end. Larger basins 
may be used made of brick, or boxed up 
with wood, and should be three feet in 
diameter, so that a man can enter and 
clean out the silt. 
Collars 
The use of collars is obsolete. Gravel 
or straw may be used in heavy soils where 
convenient, to allow water to enter tile 
more readily. The big problem in clay 
