STRUCTURES USED IN DRAINING AGRICULTURAL LAND 27 
As a general rule it is economy to make the drain deep enough to 
obviate necessity for inverted siphons. When this is impossible the 
inverted siphon should be used on the canal carrying least water, 
and possibility of flood discharges must be considered. A screen 
should be provided at the inlet structure to keep out weeds and 
trash. This screen should be inspected and cleaned frequently, 
otherwise it may become so badly clogged with trash that it will 
obstruct the flow and endanger the canal bank. 
MISCELLANEOUS STRUCTURES 
PUMP HOUSES 
Pumping from wells is being resorted to in some localities to 
drain lands damaged by irrigation seepage. Figure 18 shows a 
type of pump house used in Salt Kiver Valley, Ariz., which is a 
suitable shelter for electrically-driven, direct-connected plants. The 
lower part of the derrick, which is essential in pulling the pump for 
repairs, forms a part of the framework of the building. At the 
top is a removable hatch, and a section of the roof and wall over the 
door is also removable. A weir is desirable, but for small plants 
a cheaper arrangement brings the discharge pipe above the floor 
and carries it out to a less elaborate stilling pool and weir in the 
ditch. A concrete floor is provided, drop siding is used on the 
walls, and the top is covered with asbestos roofing. Belt-driven 
pumps will need longer housing, and where engines are used gal- 
vanized corrugated iron is recommended for covering walls and 
roof. 
On levee districts where gravity outlets are not available the loca- 
tion of the pumping plant is often determined by topographic con- 
ditions; but it should be such that pumped water will be conveyed 
as short a distance as possible. Stable foundation material should 
be present, and transportation of heavy machinery and fuel or power 
should be handled easily. 
The most common form of pumping plant consists of a structure 
supported on piling, with discharge pipes passing through or over 
the levee and suction pipes leading to a sump in the rear of the 
building. This requires long pipes with attendant friction losses, 
to overcome which sumps may be placed under the pump house and 
the structure located in the levee where the foundation alone or both 
the foundation and wall must serve as a dam. This requires careful 
design but permits economical operation and sometimes also in- 
volves cheaper construction than other arrangements, except per- 
haps for small plants with low lifts. 
Borings and a very careful examination of the formations at the 
proposed site must precede the design. Settlement under the floor is 
an important and difficult problem to handle. In some soils, where 
the pump is located some distance back of the levee, subsidence due 
to drainage may occur, and where located in the levee, settlement 
due to weight of adjacent fill must be anticipated, making it essential 
to construct carefully designed cut-off walls. 
Often where the lift is low the pump -house floor may be placed 
at an elevation such that flooding the motors or engines is not likely 
in case of accidents or forced suspension of pumping. The suction 
