amount collected in the lowest quarter. You can then calculate the Distribution uniformity using the equation refered to later in this article. The resulting value will
give an indication of the uniformity of the applied water to the surface. 80% distribution uniformity is classed as ‘achievable’, but it should come as no great surprise to find that your system will fall below that level. There are several reasons why the uniformity could be low, but the likelihood is that it will be one, some or at the very worst, all of the following:
• The pressure at the sprinkler*
• Variation of the pressure in the operating set*
• Incorrect spacing of the sprinkler heads
• Incorrect or worn nozzles
• The water distribution pattern of the sprinkler
• Wind speed and direction
*Pressure variations may not be attributable to something as major as pump problems it could simply be a blocked or damaged filter.
'At least one study (Ainscough and Kiker 2002) has shown that well maintained irrigation systems, operated correctly, generally have a high and
acceptable DU. The uniformity of application of the irrigation water can be effectively
checked via a fairly
quick and simple method, it may pinpoint where
problems lie and, if corrected, should save both money and, of course, a valuable environmental resource that some day we may all be wishing for more of... water
Low Quarter Distribution Uniformity
Although there are other methods, low quarter distribution uniformity (DUlq) is now the method most commonly used for turf grass and golf (Burt et al; 1997, Millar et al; 2003). Instead of incorporating an absolute minimum it uses an average of the lowest quarter of the amount applied.
DUlq = 100 x avg' LQ V avg'
where,
DUlq = Low Quarter Distribution Uniformity
avg' LQ = Average of the lower 25% of sample
V avg' = Average catch-c
can volume
Although the figure produced is expressed as a percentage, DU is not an efficiency term (Burt et al; 1997) and should be considered as a ratio. Zoldoski et al; ( 1994) also argue that this method has flaws stating that the location of the Low Quarter may be in a single area within that being irrigated or may be made up from several smaller deficit areas. If however the figures are recorded in the location from which they are taken then this
80% -E
information can be almost seen at a glance. Therefore providing accurate recording is carried out, this problem may be overcome and closer examination of the system becomes possible. Ascertaining the uniformity of application of the system is therefore critical to ensuring the good health of the turf grass and the playability of the surface and doing so in a cost effective way in terms of both financial and environmental considerations. Good irrigation systems
should have a distribution uniformity of 90%. It has been accepted that a DU of 100% is impossible to achieve, (Solomon 1990, Burt et al; 1997, and others), all arguing that even rainfall does not achieve a uniformity of 100%. In their study on golf course irrigation uniformity, Miller et al; (2003) stated that DU values of 80% had been
set as achievable for golf
courses by the American Irrigation Association.
Achievable for golf courses 70% -R 55% -P
Excellent - Reasonable
Poor -S System should
be analysed to find the cause
The full article, with references, can be read on
www.pitchcare.com
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