Emitters: Wetted Diameter, Spacing,

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Emitters Wetted Diameter, Spacing, Number/Tree
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Why should I be concerned with wetted diameter
and spacing?

• From a practical perspective, one needs to get
  water to a significant portion of the potential
  root zone of the tree/shrub/plant so it doesnt
  die from an inability to intake water, or fall
  over during a windstorm from lack of an anchoring
  root system
• From a standards and specifications perspective
• PS 441 (Irrigation System, Trickle, 4/82)
  requires that Emitters shall be located to
  provide an overlap of the wetting pattern within
  the root zone.
• Draft PS 441 (Irrigation System, Microirrigation,
  2/00) requires that The number and spacing of
  emitters along the lateral line shall be adequate
  to provide water distribution to the plant root
  zone and percent plant wetted area (Pw).. Pw
  from NEH 623, Ch. 7

3
What exactly is Pw?

• Pw is the average horizontal area wetted in the
  top 6 to 12 inches of the root zone as a
  percentage of the total crop area. (NEH 623, Ch.
  7)

For a lone tree PwAw/Arz
emitter
Aw
Tree trunk
Surface area wetted
Arz
4
Percent Wetted Area Number of Emitters
Sw
e of emitters/tree
Se
Sp
Sr
5
Wetted diameter overlap
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Percent Wetted Area Number of Emitters
Eq. 7-1, NEH 623
33?Pw?50 NEH 623 40?Pw?50 NEH 652 Se?.8Sw
NEH 623
BUT, what is Sw (wetted diameter) ?.
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Wetted diameter is a function of

• emitter type, if not a point source
• emitter discharge
• duration of operation
• soil layering (horizontal)
• soil type
• any others?..

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Wetted diameter is a function of soil
Also see Table 6-16 of NEH 652 and BE CAREFUL
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Wetted diameter is a function of soil layering
Area in ft2 wetted from point source emitter
discharge of 1 gph
Taken from Table 7-2, NEH 623
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Wetted diameter is a function of discharge
duration - to a limit
1 gph for 2 hrs
1 gph for 2 hrs
1 gph for 8 hrs
4 gph for 2 hrs
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Wetted diameter is a function of emitter type
Micro sprinkler
Point source emitter
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Considerations for Emitter type and

• increases wetted area
• zigzag, pigtail etc..increases
• pulsing
• micro sprays
• cost (more emitters w/ less q)
• increase duration of flow
• FIELD TEST

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Emitter Spacing Number Recommendations for
Windbreaks
Taken from Table 7-2, NEH 623