







SPRAY IRRIGATION. 
9 
A simple way to develop ground water is to dig a sump or pit in a 
swamp, in a sidehill-spring bog, or in seeped lands bordering a stream 
or canal. In many cases, where water-bearing sand or gravel can be 
reached near the surface, the sump furnishes a very cheap water sup- 
ply which can be enlarged to considerable storage by removal of ma- 
terials. Pumping from a sump or pit requires the simplest kind of 
machinery and is a possible source of water for spray irrigation in 
many of the trucking districts of the Kast and the sur- 
face irrigated districts of the West. 
Shallow open wells are a modification of sumps, but 
- generally are deeper and smaller in diameter. Their use 
as sources for irrigation water usually is limited to spe- 
cial cases where the materials passed through above the 
water stratum will stand without expensive curbing, and 
where the water-bearing materials are coarse, resembling 
gravel or porous rock, and need little screening. 
A common way of developing ground water is by the 
use of one or more well points. A well point (fig. 3) 
consists of a section of galvanized-iron pipe which is 
perforated, usually with elliptical holes, and has a sharp 
iron plug swaged into place in one end and is threaded 
on the opposite end. The point is screwed into galva- 
nized wrought-iron pipe and driven into the earth to the 
_water-bearing stratum. Extra heavy “guaranteed ” 
wrought-iron pipe should be used if the pipe is to be 
driven through hard, resistant materials. When used in 
coarse materials the perforations may be left uncovered, 
although it usually is necessary to cover the body of the 
point with a perforated brass jacket to prevent sand 
being drawn into the pump. Where very fine sand is 
encountered a fine mesh gauze is placed between the pipe 
and jacket. For irrigation wells it is advisable to use 
as large perforations as possible, and many wells which 
yield considerable sand in the beginning improve in this 
respect as they are pumped. Points of this type are 




Fic. 3.—Well 
point. 
made up to 4 inches in diameter. Two-inch points and smaller can 
be driven by hand through soil and sandy materials to a depth of 50 
to 75 feet, while those larger in diameter usually require a machine 
for sinking. 
_ Piston or plunger pumps may be connected directly to the casing 
of a driven well when the water comes within suction lift, which 
is practically 25 feet at sea level and becomes less as the altitude 
increases (see Table 5). Where the water draws down to a greater 
distance from the pump it is necessary to sink the pump in a pit, 
66687 °—Bull. 495172 

