Page 227 - Biosystems Engineering

Design of Sustainable W ater Management Systems 205

1 mile

FIGURE 6.4 An aerial view of a fi eld irrigated by center-pivot systems in
Southern Manitoba, Canada.

the main line and laterals, friction losses will lead to a reduction in
water pressure generated by the irrigation pump at the source.
Although larger-diameter pipes have lower friction losses, the higher
capital cost of larger pipes has to be taken into consideration in rela-
tion to the higher operating cost of pressurizing the water. Generally,
the allowed pressure loss in the lateral is taken as 20 percent of the
operating pressure of the sprinkler head. The main line and laterals
also have fittings to divert and control the flow of water, which lead
to friction losses. Biosystems engineers consider the fluid mechanics
of flow through pipes and fittings to optimally design the piping
system and select the required size of the pump.

Drip Irrigation Systems
The drip irrigation system was the next major advance in irrigation
water conservation achieving water application efficiencies as high
as 90 percent (ASAE 1990). In this method, the water is applied at a
rate that will permit water to spread within the root zone by capillary
action. If the water is applied at a rate higher than the basic infiltra-
tion rate of the soil, the water will spread on the soil surface and infil-
trate the soil over a larger diameter. Alternatively, if water is applied
at a lower rate than the basic infiltration rate, the water will tend to