Microirrigation design

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Microirrigation design

• Oregon NRCS Engineering MeetingJanuary 11-14,
  2005

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• Over view
• Water requirement System Flow rate
• Pressure requirement
• Component design

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Wind breaks/trees
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Orchards
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Vine crops
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Nursery crops
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High Dollar crops
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Low Dollar crops
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Water Quality

• Water quality factors can be divided into three
  major categories
• physical clogging caused mostly by suspended
  solids,
• chemical clogging resulting from pH of the water,
  dissolved solids, sodium, calcium, magnesium and
  total iron and
• biological clogging resulting from algae and
  bacterial populations.

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System Flow rate
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NRCS Standards

• Depth of application.
• Net depth of application shall be sufficient to
  replace the water used by the plant during the
  plant peak use period.
• Applications shall include adequate water for
  leaching to maintain a steady state salt balance.
  

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Depth of application

• .
• Fn 1.604 QNTE AF
• Where
• Fn net application depth, in/day/design area
• Q discharge rate, gal/hr/emitter
• N number of orifices or emitters
• T hours of operation per day, 22 hours maximum
• E field application efficiency, expressed as a
  decimal, not greater than 0.90 for design
  purposes.
• A ft2 of field area served by N (number of
  emitters)
• F the design area as a percentage of the field
  area, expressed as a decimal
• 1.604 units conversion constant

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System capacity.

• shall be adequate to meet the intended water
  demands during the peak use period
• shall include an allowance for reasonable water
  losses (evaporation, runoff, and deep
  percolation) during application periods.
• shall have the capacity to apply a specified
  amount of water to the design area within the net
  operation period.

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System capacity Continued

• should have a minimum design capacity sufficient
  to deliver the peak daily irrigation water
  requirements in 90 of the time available, but
  not to exceed 22 hours of operation per day.
• Field application efficiency (E) for design
  purposes shall not exceed 90 percent.

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Number and spacing of emitters.

• shall be adequate to provide water distribution
  to the plant root zone and percent plant wetted
  area (Pw).

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Wetted Area
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Percent Wetted Area

• For widely spaced crops such as vines, bushes,
  and trees, a reasonable design objective is to
  wet at least one-third and up to one-half of the
  horizontal cross-sectional area of the root
  system.
• smaller Pw is favored for economic reasons.
• rows spaced less than 6 ft. (1.83 m) apart, the
  Pw may approach 100 .

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Wetted area single row
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Wetted area single plant
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Components of a Drip system
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Subunit Design

• Plant and emitter spacing
• Average emitter flow rate and allowable pressure
  head variations
• Desired number of operating stations
• Overall length of plant rows in field or subset
• Number of plant rows in field or subset
• Field topography

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Emitter types

• Long path emitters,
• Short orifice emitters,
• Vortex emitters,
• Pressure compensating emitters,
• Porous pipe or tube emitters.

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Emitter manufacturing variability

• The manufacturers coefficient of variation (CV)
  shall be less than 0.07 for point source emitters
  and less than 0.20 for line source emitters.

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Emitters

• Flow is characterized by the following equation
  qkPx
• K and x obtained from manufacture

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Lateral Design

• Types of laterals
• Heavy wall drip line
• Thin wall drip line
• Drip tape
• Polypipe with punch emitters
• Polypipe with sprays

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Design Considerations

• Select emitter/flow rate
• Determine required operating pressure
• Calculate friction loss
• Quick estimate use multiple outlet factor
• Manufactures software
• Built spreadsheet
• Decide whether to use single or paired laterals
• Make adjustments
• Check with flushing conditions

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Slope and topography
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Hydraulics
F multiple outlet factor L length of lateral
(ft) Q lateral flow rate (gpm) Se emitter
spacing (ft) Fe equivalent length of emitter
connection loss qa average emitter flow rate
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Emission Uniformity

• Emission Uniformity Rating
• 90 - 100 Excellent 80 - 90 Good 70 - 80
  Fair Less than 70 Poor

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Lateral Flow flat slope
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Lateral Flow 2 downhill slope
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Lateral flow 2 uphill slope
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Lateral flow varied slope
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Eurodrip program print out
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Lateral flow Plot
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System flushing.

• Appropriate fittings shall be installed above
  ground at the ends of all mains, submains, and
  laterals to facilitate flushing. A minimum flow
  velocity of 1 ft/sec is considered adequate for
  flushing.

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Manifold Design

• Needed information
• Flow rate
• Inlet location
• Pipe sizes
• Inlet pressure
• Flow variation
• Emissions uniformity

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Below ground
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Above ground
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Allowable pressure variations.

• Manifold and lateral lines.
• shall be designed to provide discharge to any
  applicator in an irrigation subunit operated
  simultaneously such that they will not exceed a
  total variation of 20 percent of the design
  discharge rate.

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Allowable Pressure Variations

• Greatest Emitter Discharge - Smallest Emitter
  Discharge x 100
• Average Emitter Discharge
• This is reported in Percent and must be less than
  or equal to 20

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Flushing

• Method
• Manual
• Manifold
• Size
• friction loss through manifold and valves
• Frequency

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Flush Manifold
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Main line design

• Size
• system flow rate
• pressure loss

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Filters

• shall be provided at the system inlet. Under
  clean conditions, filters shall be designed for a
  head loss of 5 psi or less.
• shall be sized to prevent the passage of solids
  in sizes or quantities that might obstruct the
  emitter openings.
• shall be designed to remove solids equal to or
  larger than one-fourth the emitter opening
  diameter, or the emitter manufacturer's
  recommendations, whichever is more stringent

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• shall provide sufficient filtering capacity so
  that backwash time does not exceed 10 of the
  system operation time. Within this 10 time
  period, the pressure loss across the filter shall
  remain within the manufacturer's specification
  and not cause unacceptable EU.
• Filter/strainer systems designed for continuous
  flushing shall not have backwash rates exceeding
  1.0 of the system flow rate or exceeding the
  manufacturer's specified operational head loss
  across the filter.

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Filter Design

• Select Type
• May need two
• Pre-filter and primary filter
• Size
• Flow rate
• Must account for pressure through filter
• Must account for pressure required to back flush

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Disc Filters
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Sand Media filter
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Screen filters
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Filter summary
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Chemigation.

• System EU shall not be less than 85 percent.
• Injectors and other automatic operating equipment
  shall be located adjacent to the pump and power
  unit, and include integrated back flow prevention
  protection.
• Shall be accomplished in the minimum length of
  time needed to deliver the chemicals and flush
  the pipelines.

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Select an Injection System

• Fertilizer
• Acid ( change ph, help against root intrusion and
  clogging)
• Chlorine ( prevent biological clogging)
• Other water amendments
• Pesticides
• Need safety devices ( State regulations)

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Injectors
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Storage tanks
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Pump Design

• Calculate TDH
• Size Pump

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Miscellaneous

• Automatic controls
• Pressure regulators
• Air vents/valves

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Summary

• Determine Plant information
• Spacing row/plant
• Water requirement
• Irrigation frequency
• Test water quality
• Select emitter/sprayer
• Type
• Spacing
• Discharge
• Emitter factors Cv, K, x
• Design Lateral normal/flushing
• size
• Flow rate
• Pressure requirement

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• Design Manifold Header-Flushing/Subunits
• size
• Flow rate
• Pressure requirement
• Emissions uniformity
• Air valves
• Design Mainline
• size
• Flow rate
• Pressure requirement
• Select Filter system
• Number/size
• Flushing - disposal
• Pressure requirement

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• Select injection system
• Type
• Size
• Safety considerations/features
• Controls
• Pump station
• Flow rate
• pressure