STRUCTURES USED IN DRAINING AGRICULTURAL LAND 29 
be submerged. For some types of pump installations, gates must 
be provided at the discharge structure. Discharge and suction pipes 
usually are steel, but sometimes they are reinforced concrete. The 
diameter should be sufficient to produce a velocity of not more than 
approximately 5 feet per second, and the intake and discharge ends 
must be enlarged to reduce losses. 
The house should be durable and fire proof. Galvanized cor- 
rugated metal is desirable for small plants, but excellent houses have 
been made of brick. Eeinforced concrete is well adapted to large 
structures and must be used on all plants where there is danger of 
flooding the machinery. The building should be well ventilated. 
Reinforcecl-concrete columns or pilasters must be carried up on the 
inside of the walls to support rails for a crane, which is an essential 
part of all except very small plants. 
Figure 12 shows the design of a pumping plant installed in Mult- 
nomah County drainage district No. 1, Oreg. This reinforced-con- 
crete structure has unusual features in that the wall of the plant is 
designed to withstand a high head of water, and the entire structure 
rests on a silty formation without rigid support. It was thought that 
the earth would settle and thus leave an opening beneath the floor if 
the structure were otherwise supported, which would be very hazard- 
ous particularly during the high-water period which sometimes lasts 
for several weeks. Five rows of sheet piling were placed beneath 
the floor. These are only 8 feet in length so that none of them would 
reach into what appeared to be a hard layer of sand beneath the silt 
and thus tend to prevent uneven settlement. The entire structure 
has settled about 3 inches since installation. 
The floor was designed against upward pressure, and an effort was 
made to reduce the pressure to some extent by filling with porous 
concrete five boxes each 1.5 feet square placed in the down-stream side 
of the sump. The structure is also provided with five sluiceways hav- 
ing openings 5 feet square for gravity discharge. Automatic gates 
are used. Emergency dams can be installed easily in case repairs 
must be made to gates or pipes. 
CONNECTIONS FOR FLUSHING DRAINS 
Often it is desirable to connect open drains and underdrains with 
irrigation or other canals for periodic flushing. This is the cheapest 
form of maintenance work that can be done. Figure 16 and Plate 
2, J, show connection to an open drain which passes through a cul- 
vert under an irrigation canal. The canal is lined with concrete, and 
riprap at the lower end of the outlet pipe and culvert prevents ero- 
sion of the embankment. The connection is made by an ordinary 
turnout gate. Use of this connection for sluicing has reduced main- 
tenance cost to a minimum, and has lowered the grade line of the 
main canal approximately 2 feet for several miles. 
Where a concrete box culvert is used, the connection should consist 
of a small concrete tower with a gate at one side of the upper canal, 
through which the flushing water may be discharged directly into the 
culvert instead of at its lower end as in the example shown. At 
flume crossings a gate may be provided, as shown in Plate 2, L. Un- 
stable soils below such a discharge will require a short paving of con- 
crete or riprap to prevent erosion. 
