Agriculture Reference
In-Depth Information
4.2.6.6 Drip/Micro-irrigation Evaluation
The most useful performance indicators for micro-irrigation field evaluations are the
statistical uniformity coefficient and the distribution uniformity.
Statistical Uniformity Coefficient
The statistical uniformity coefficient, U s (%), is defined as (Pereira, 1999 )
100 1
S q
q a
U s =
=
100(1
V q )
(4.32)
where
V q =
coefficient of variation (CV) of emitter flow
S q =
standard deviation (SD) of emitter flow (l/h)
q a =
average emitter flow rate (l/h).
Distribution Uniformity
The distribution uniformity, DU (%), is defined as:
100 Z lq
Z av
DU
=
(4.33)
where
Z lq =
average observed applied depths in the low quarter of the field (mm) and
Z av =
average observed applied depths in the entire field (mm).
Distribution uniformity is often named emission uniformity in trickle irrigation.
4.2.7 Improving Performance of Irrigation System
The most obvious way to improve the performance of an irrigation system is to
take remedial measures for correcting the fault/deficiency, which has been identified
during evaluation/diagnosis process. Besides, a number of techniques can be used in
the design of a system to increase its uniformity and efficiency. For surface irrigation
systems, the inflow rate can be matched with the soil intake rate, slope, and length
of run; and the cutoff time can also be matched thereby. For pressurized systems,
the technique includes using larger pipe sizes to minimize pressure differences due
to friction losses, using pressure regulators to minimize pressure differences due to
elevation differentials, using appropriate closer spacings or trickle emitters with low
manufacturing variations. Another technique is that water use is more efficient with
afternoon irrigations, as the evaporative loss is minimal.
Some common problems/faults and suggestive measures for improving the
performances are summarized below:
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