Em4885 irrigation management practices to protect ground water

4 CHAPTER
Finally, different emission devices have different relationships defining how flow through
the device varies with a change in pressure. Flow through emission devices is generally
described by the equation:
Q = k x H x
where:
Q = flow through the device
k = some constant number depending on the device
H = pressure at the device
x = an “exponent,” depending on the device
The key fact is that the larger the exponent (“x” in the equation above), the larger the
variance in the flow with a variance in pressure. So-called “pressure compensating”
emitters commonly have exponents equal to .4 or less. A “laminar-flow” emitter has an
exponent that is close to 1.00. The laminar flow emitter is much more sensitive to pressure
differences in the system than a pressure compensating emitter. (The advantage of laminar
flow emitters are that they usually have larger openings and thus, are less susceptible to
clogging. Also, they are usually, but not always, less expensive than a pressure
compensating design.)
Always have a competent and experienced engineer/specialist design micro-irrigation
systems.
IP 2.04.03 - Have the Irrigation Water Analyzed to Enable Design
of an Adequate System of Water Treatment and Filtration
Objective
Ensure continued good performance from the system by preventing clogging of
emission devices.
Description
Once a micro-irrigation system has been designed and installed, ensuring a clean water
supply into the system becomes critical to efficient operation. Clogging of emission
devices is the single, biggest concern of managers. Clogging reduces distribution
uniformity and requires that the system be run longer to compensate. This may increase
surface runoff or deep percolation due to the non-uniformity of clogging.
Even with a clean water supply into a system, clogging may occur due to algal or bacterial
growths, or chemical precipitates. Thus, keeping a micro-irrigation system “clean” can
involve water treatment as well as water filtration.
60