A Word on Water

A Vital Measurement in Irrigation Audits

  

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A key measurement derived from an irrigation audit is distribution uniformity or DU.  An irrigation system has a good DU when an almost equal amount of water is applied on each square foot of irrigated landscape.  This is especially important for a grass area, since every bit of the area is covered by a very dense root system.  In constrast, shrubs and trees can get water from a more dispersed and deeper root system.  For these plant types, DU as determined from an irrigation audit can be less on a square foot basis.

DU is largely affected during the design process when sprinkler types are chosen.  This selection process includes a number of options:
*sprinkler spacing
*sprinkler location relative to landscape features
*fixed spray, rotating or drip
*water pressure at the sprinkler

In addition to these design choices, a number of other factors can affect DU as well.  These include wind conditions, plant interference with spray patterns and equipment damage.

Still it is the design and installation that has the greatest effect on the DU figures that are derived from an irrigation audit.  A single sprinkler is not manufactured with an ability to distribute water evenly over a certain area.  As the distance from the sprinkler head increases, water is applied over an increasingly bigger area of landscape.  Given this fact, sprinkler systems have to be designed so that individual spray patterns overlap in order to provide a good DU.  Poor spacing of sprinkler heads will adversely affect the DU.

In the end, an irrigation audit looks to find out if the DU for each irrigation valve meets a certain level.  This is based on the type of sprinkler head.  Fixed spray heads get a passing grade if the DU is 65 percent or more.  Rotating heads with a DU of 70 percent or more get a passing grade.