STRUCTURES USED IN DRAINING AGRICULTURAL LAND 
31 
Kelief wells discharging into open ditches must be located and 
lined in the manner described above. The elevation of the T-junc- 
tion discharging into the ditch should be that of ordinary high 
water in the line of the drain (pi. 2, G) . 
CONNECTIONS FOR DIVERTING WATER 
Drainage water is valuable for irrigation if the percentage of 
alkali is not too high. When water is diverted by gravity from an 
open drain the required structures will be similar to those used in 
irrigation practice, consisting of a turnout gate located just above 
a check as shown in Plate 2, K. The elevation of the water is con- 
trolled by flashboards. The gate should be large and low enough 
to permit diversion with a checked 
head of only a few inches; otherwise 
the purpose of the drain will be 
defeated. 
When good fall exists on an under- 
drain, water may be diverted from it 
through a pipe having a flatter grade. 
This pipe must have tight joints and 
the connection should be made at a 
manhole and at an elevation slightly 
less than that of the outlet drain. 
A slide gate should be fitted on the 
diversion pipe and a similar gate may 
be installed on the outlet drain pipe; 
but the latter should be so constructed 
that it can not be completely closed 
unless the diversion pipe has a capac- 
ity equal to that of the drain. 
As a general rule, any considerable 
checking of the normal flow of drains 
is to be avoided. This is particularly 
true for underdrains and for any type 
when alkali is present, except perhaps 
in peat soils where it is necessary to 
practice subirrigation. In such sys- 
tems the level of the water in the small 
open drains is controlled by wooden 
check gates. If underdrains are used checking may be accomplished 
by means of slide gates at frequent intervals; these have a stem 
reaching to the ground surface through a pipe similar to an observa- 
tion well. 
Pumps on closed drains should be located at manholes with deep 
sumps, and for small plants on open drains a suitable sump should 
be provided at one side of the main channel in such a manner as to 
offer no obstruction to the flow. 
WATERING PLACES FOR LIVESTOCK 
In some localities special watering places for livestock must be pro- 
vided on underdrains and on open systems where stock are not per- 
mitted to graze on the banks. On open drains the channel bottom 
should be widened at one side, a flatter side slope excavated for 
Fig. 19. — Tile end to permit flushing 
