30 BULLETIN 1408. IT. S. DEPARTMENT OF AGKICULTUKE 
Connections between canals and intersecting underdrains resemble 
in some respects that shown in Figure 16, but the discharge pipe will 
be much smaller and its lower end will discharge into a manhole. 
Usually it will be unnecessary to pave the canal. As a rule special 
gates and elaborate connections are not needed on underdrains since 
most properly built mains and laterals have flushing structures at 
the upper end. Water may be conducted to the tile line from small 
laterals as shown in Figure 19, the connection being made either with 
a T-junction or an elbow, depending on whether the line is to be ex- 
tended. The riser may be tile of the same size as the drain, but 
usually it does not need to be larger than 6 or 8 inches. In case 
surface run-off is to be admitted a regular surface-water inlet should 
be used. Ordinary drain tile may be used for tile ends on farm 
laterals, but on more important lines bell-end tile to prevent dis- 
placement will be preferable. Gravel should be placed around the 
tile at the connection and the earth should be well tamped or puddled 
in around the riser. Wherever possible tile ends should be located 
out of the way of farm machinery, but where such location is im- 
possible the top should be about 16 inches below the ground and cov- 
ered with gravel. Vitrified clay or concrete stoppers may be used 
for the cover. 
RELIEF-WELL CONNECTIONS 
Relief wells of various types are used to conduct ground water 
under pressure to closed drains or open ditches. Often a large 
number of small wells are sunk with augur or drill to drain land 
underlain with water-bearing shale formation. If the tile line 
reaches into the shale, casing is usually unnecessary; otherwise the 
well should be cased from the top of the shale to the tile line. This 
upper part may be cased with tile from 4 to 8 inches in diameter if 
the adjacent material can be excluded from the joints; otherwise an 
iron-pipe or wooden-box casing must be used. 
Many relief wells flow only at certain seasons, hence they must 
be located at one side of the drain to keep them free from silt. In 
shale the small wells should be drilled close to the drain line, to 
which they should be connected by a hole in the side several inches 
above the bottom of the tile. The well and the hole should be 
covered with a large piece of tile, surrounded by small pieces of tile 
and gravel. 
Some drainage systems include deep relief wells of large diameter, 
cased with iron pipe, as in artesian well practice. Here it is neces- 
sary to perforate the lengths extending into the formation under 
artesian head, the size, shape, and number of these openings depend- 
ing upon the nature of the formation. Casings should extend above 
ground and the covers should be secured against removal. T-junc- 
tions should be used at connections and the bottom of the outlet 
opening in the well casing should be several inches above the grade 
of the tile line into which it discharges. If manholes are near, wells 
should be connected with them. Gravel pockets which will discharge 
large quantities of water when tapped are occasionally found below 
the grade of the tile line. These may be connected to the drain by a 
structure similar to a small manhole, located at one side of the line. 
