586 AGRICULTURAL REPORT. 
always a source of malarial disease. Nearly all can be drained at a comparatively 
small expense. After the surplus water has been removed, and the soil has been prop- 
erly subdued and civilized by cultivation, sach low ground often becomes the most 
productive and the most easily tilled of any portion of the farm. 
: Manner of laying out ditches.— 
Fig. 1. The accompanying diagram 
l | P Fig. 1, represents a large field 
that was actually draizfed in the 
manner shown. ‘The soil was a 
heavy clay loam, and the subsoil 
a. retentive caleareous clay. 
The ditches were made about 
forty feet apart over the entire 
field, During a portion of the 
time a small stream of water 
that would all pass through a 
four-inch tile flowed over the 
surface in the valley from B to 
L, where a main ditch was sunk 
to a minimum depth of three 
feet, in which a course of four- 
inch egg-sole tiles was laid. 
As there was a valley at B O, 
and at D D, submains of three- 
inch tiles were laid as repre- 
sented to connect with the main 
drain. The paralle} ditehes were 
then made up and down the 
slopes as nearly as practicable. 
From A the water would ran 
most readily to B B. AtG H 
short branches were made up the 
slope, in which one and a half- 
inch tiles were laid. At POthe 
; ditches all ran directly up the 
| islope. From F the water ran 
| either toward the main L or the 
| 
| 
} 
| 
| 
By 
\ \ ! 
am a 
sub-main D. From C the de- 
; Scent was more uniform toward 
D D. Hence parallel ditches 
were made as represented. The 
object in laying out the ditches 
in so many directions was to 
— 
have them extend, as nearly as 
practicable, directly op and, 
down the slopes, which is the 
true system of thorough under- 
draining. Intelligent tillers of the soil and engineers of extensive experience agree in 
this one point, that in a system of thorough underdraining it is better to have the 
ditches made up and down a slope rather than diagonally across it. Hence main and 
sub-imains must be formed in the valleys, and parallelsand branchesshould run up and 
down the slopes. Even when the strata crop out on the side of a slope, between 
which surplus water renders the soil too wet, it will always be found more satisfactory 
to cut the ditches up and down the slope, rather than in a diagonal direction across it. 
Determining the size of ditches.—The size of a ditch must depend, in a great measure, 
on the quantity of water to be conveyed through it. When an underdrain is made in 
a valley through which passes a stream sufficiontly large, during some of the months 
of spring and autumn, to 4] a six-inch tile, the capacity of the underdrain should be 
fully equal to the volume of the stream when at its greatest height. Ifa considerable 
portion of the stream flows over the surface of the ground during the period of pro- 
tracted storms, the ground will be liable to be gullied, and large quantities of the soil 
will be washed away... Previous to making a drain in such a place, it is an excellent 
practice to ascertain the capacity of the stream at high water, by making a temporary 
dam of sods, or with a board, aud fixing a square tube made of boards in the dam, 
throngh which the water may pass. A drain will often draw four times as much water 
in one part of a field as in another. Hence, no engineer can determine with certainty, 
Without practical calculation, what should be the size of the tiles or the capacity of 
the water-course to he formed. In case a stream of water is allowed to fiow for only 
a few days on the surface over a stone drain, the water will be likely to find a passage 
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