Chapter 11: Sprinkle Irrigation - NRCS Irrigation ToolBox Home Page

Linear-Move Lateral
Self-propelled linear-move laterals combine the
structure and guidance system of a center-pivot
lateral with a traveling water feed system similar to
thal: of a traveling sprinkler.
Linear-move laterals require rectangular fields
free from obstructions for efficient operation. Measured
water distribution from these systems has
shown the highest uniformity coefficients of any
system for single irrigations under windy conditions.
Systems that pump water from open ditches
must be installed on nearly level fields. Even if the
system is supplied by a flexible hose, the field must
be fairly level in order for the guidance system to
work effectively.
A major disadvantage of linear-rnove systems as
compared to center-pivot systems is the problem of
bringing the lateral back to the starting position
and across both sides of the water supply line.
Since the center-pivot lateral operates in a circle, it
automatically ends each irrigation cycle at the Feginning
of the next, but because the linear-move
lateral moves from one end of the field to the other
it must be driven or towed back to the starting
position. However, the linear-move system can irrigate
all of a rectangular field, whereas the centerpivot
system can irrigate only a circular portion of
it.
Other Sprinkle Systems
Because of the recent concerns about availability
and cost of energy, interest has revived in the use
of perforated pipe, hose-fed sprinklers run on a grid
pattern, and orchard systems. They afford a means
of very low pressure (5 to 20 psi) sprinkle irrigation.
Often, gravity pressure is sufficient to operate the
system without pumps. Furthermore, inexpensive
low-pressure pipe such as unreinforced concrete and
thin-wall plastic or asbestos cement can be used to
distribute the water. These systems do have the
disadvantage of a high labor requirement when
being moved periodically.
Perforated Pipe
This type of sprinkle irrigation has almost become
obsolete for agricultural irrigation but continues
to be widely used for home lawn systems.
Perforated pipe systems spray water from 1116-in-
diameter or smaller holes drilled at uniform distances
along the top and sides of a lateral pipe. The
holes are sized and spaced so as to apply water uniformly
between adjacent lines of perforated pipeline
(fig. 11-10). Such systems can operate effectively at
pressures between 5 and 30 psi, but can be used
only on coarse-textured soils such as loamy sands
with a high capacity for infiltration.
Figure ll-10.-Perforoled
Hose-Fed Sprinkler Grid
pipe lateral in opcration.
These systems use hoses to supply individual
small sprinklers that operate at pressures as low as
5 to 10 psi. They can also produce relatively uniform
wetting if the sprinklers are moved in a systematic
grid pattern with sufficient overlap. However,
these systems are not in common use except
in home gardens and turf irrigation, although they
do hold promise for rather broad use on small farms
in developing countries where capital and power resources
are limited and labor is relatively abundant.
Orchard Sprinkler
A small spinner or impact sprinkler designed to
cover the space between adjacent trees with little or
no overlap between the areas wetted by neighboring
sprinklers. Orchard sprinklers operate at pressures
between 10 and 30 psi, and typically the diameter
of coverage Is between 15 and 30 ft. They are located
under the tree canopies to provide approximately
uniform volumes of water for each tree. Water
should be applied fairly evenly to areas wetted,
although some soil around each tree may receive little
or no irrigation (fig. 11-11). The individual sprinklers
can be supplied by hoses and periodically
moved to cover several positions or n sprinkler can
be provided for each position.