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    Microirrigation design

    Oregon NRCS Engineering MeetingJanuary 11-14, 2005

    NaturalResourcesConservationServiceNRCS

    United States Department of Agriculture

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    Over viewWater requirement System Flow ratePressure 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 threemajor 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 bacterialpopulations.

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    System Flow rate

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    Depth of application .Net depth of application shall be sufficient to

    replace the water used by the plant during theplant peak use period.

    Applications shall include adequate water forleaching to maintain a steady state saltbalance.

    NRCS Standards

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    .Fn = 1.604 QNTE

    AFWhere:

    Fn = net application depth, in/day/design areaQ = discharge rate, gal/hr/emitterN = number of orifices or emittersT= hours of operation per day, 22 hours maximumE = field application efficiency, expressed as a decimal, not

    greater than 0.90 for design purposes.A = ft 2 of field area served by N (number of emitters)F = the design area as a percentage of the field area, expressed as

    a decimal1.604 = units conversion constant

    Depth of application

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    shall be adequate to meet the intended waterdemands during the peak use period

    shall include an allowance for reasonablewater losses (evaporation, runoff, and deeppercolation) during application periods.

    shall have the capacity to apply a specifiedamount of water to the design area within thenet operation period.

    System capacity .

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    should have a minimum design capacitysufficient to deliver the peak daily irrigationwater requirements in 90% of the timeavailable, but not to exceed 22 hours ofoperation per day.

    Field application efficiency (E) for designpurposes shall not exceed 90 percent.

    System capacity Continued

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    shall be adequate to provide water distributionto the plant root zone and percent plant

    wetted area (P w).

    Number and spacing of emitters .

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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 thehorizontal cross-sectional area of the rootsystem.smaller Pw is favored for economic reasons.rows spaced less than 6 ft. (1.83 m) apart, thePw may approach 100 %.

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    Wetted area single row

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    f

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    Components of a Drip system

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    Subunit Design

    Plant and emitter spacing Average emitter flow rate and allowablepressure head variationsDesired number of operating stationsOverall length of plant rows in field orsubsetNumber of plant rows in field or subsetField 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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    Emitters

    Flow is characterized bythe following equation

    q=kPx

    K and x obtained frommanufacture

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    Lateral Design

    Types of lateralsHeavy wall drip line

    Thin wall drip lineDrip tapePolypipe with punchemitters

    Polypipe with sprays

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    Slope and topography

    1 0 7

    9 8

    8 2 0 0

    8 2 0 0

    8 1 0 0

    8 1 0 0

    8 0 0 0

    8 0 0 0

    7 9 0 0

    7 9 0 0

    7 8 0 0

    7 8 0 0

    7 7 0 0

    7 7 0 0

    7 6 0 0

    7 6 0 0

    7 5 0 0

    7 5 0 0

    7 4 0 0

    7 4 0 0

    7 3 0 0

    7 3 0 0

    7 2 0 0

    7 2 0 0

    7 1 0 0

    7 1 0 0

    7 0 0 0

    7 0 0 0

    6 9 0 0

    6 9 0 0

    6 8 0 0

    6 8 0 0

    6 7 0 0

    6 7 0 0

    62 00

    6 20 0

    6 100

    6 10 0

    6000

    6 000

    59 00

    590 0

    5 80 0

    58 00

    57 00

    5 70 0

    5 600

    560 0

    550 0

    5 500

    54 00

    5400

    5 30 0

    530 0

    52 00

    52 00

    1 0 6

    1 0 5

    1 0 4 1

    0 3

    1 0 2

    1 0 1

    1 0 0

    9 9

    9 9

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    Hydraulics

    60

    133.'

    100

    '

    75.4

    75.1

    a

    e

    e

    ee

    f

    qS L

    Q

    S f S

    DQ J

    FL J h

    F= multiple outlet factor

    L= length of lateral (ft)

    Q= lateral flow rate (gpm)

    Se= emitter spacing (ft)

    Fe= equivalent length ofemitter connection loss

    qa= average emitter flow

    rate

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    Emission Uniformity

    Emission Uniformity Rating90 - 100% Excellent

    80 - 90% Good70 - 80% FairLess than 70% Poor

    ave

    v

    qq

    nC EU m in27.11

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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 aboveground at the ends of all mains, submains,

    and laterals to facilitate flushing. A minimumflow velocity of 1 ft/sec is consideredadequate for flushing.

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    Manifold Design

    Needed informationFlow rateInlet location

    Pipe sizesInlet pressureFlow variation

    Emissions uniformity

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    Above ground

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    Manifold and lateral lines.

    shall be designed to provide discharge to anyapplicator in an irrigation subunit operatedsimultaneously such that they will not exceeda total variation of 20 percent of the designdischarge rate.

    Allowable pressure variations.

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    Greatest Emitter Discharge - Smallest Emitter Discharge x 100 Average Emitter Discharge

    This is reported in Percent and must be less than orequal to 20%

    Allowable Pressure Variations

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    F

    F

    F

    F

    F

    SECTION VALVE

    VACUUM/RELIEF

    FLUSH VALVE

    AIR RELIEF

    WATER SOURCE

    FILTER STATION

    BOOSTER PUMP

    MAIN LINE

    ZONE DIVISION LINE

    HEADER LINE 3" PVC

    FLUSH LINE 2" PVC

    SYSTEM CAPABILITIESEURODRIP 0.875 - 15 MILLATERAL SPACING: 80"DESIGN ET: 0.29" / ACRE / 10 HOURSFIELD SCHEDULING: 10 HOURS / ZONE

    H

    H

    John ProgressACRES: 10.0GPM: 80ZONES: 1

    NScale

    1" = 200'

    44 Tapes10 Acres132 gpm

    99.5100

    99.5 100

    44 Tapes5.0 Acres66 gpm

    99.5

    99.5

    100

    100

    44 Tapes5.0 Acres66 gpm

    H

    .29-.23 x 100 = 25% .24

    .29-.27 x 100 = 7.1% .28

    .29-.27 x 100 = 7.1% .28

    1485'

    742.5' 742.5'

    294'

    294'

    Emitter Discharge Variation

    Emitter Discharge Variation Emitter Discharge Variation

    Emitter Discharge VariationThe greatest emitter discharge minus the smallest emitterdischarge divided by the average emitter discharge,multiplied by 100, within the block.

    Must be less than 20 %

    F

    F

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    Flushing

    MethodManual

    ManifoldSizefriction loss through manifold and valves

    Frequency

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    Main line design

    Sizesystem flow ratepressure loss

    Fil

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    Filters

    shall be provided at the system inlet. Under cleanconditions, filters shall be designed for a head loss of5 psi or less.

    shall be sized to prevent the passage of solids in

    sizes or quantities that might obstruct the emitteropenings.

    shall be designed to remove solids equal to or largerthan one-fourth the emitter opening diameter, or the

    emitter manufacturer's recommendations, whicheveris more stringent

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    shall provide sufficient filtering capacity so thatbackwash time does not exceed 10% of the systemoperation time. Within this 10% time period, thepressure loss across the filter shall remain within themanufacturer's specification and not causeunacceptable EU.

    Filter/strainer systems designed for continuous

    flushing shall not have backwash rates exceeding1.0% of the system flow rate or exceeding themanufacturer's specified operational head loss acrossthe filter.

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    Sand Media filter

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    Screen filters

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    Filter

    summary

    Chemigation

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    Chemigation.System EU shall not be less than 85 percent.

    Injectors and other automatic operatingequipment shall be located adjacent to thepump and power unit, and include integratedback flow prevention protection.

    Shall be accomplished in the minimum lengthof time needed to deliver the chemicals andflush the pipelines.

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    Select an Injection System

    Fertilizer Acid ( change ph, help against rootintrusion and clogging)Chlorine ( prevent biological clogging)Other water amendmentsPesticidesNeed safety devices ( State regulations)

    Injectors

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    Injectors

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    Storage tanks

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    Pump Design

    Calculate TDHSize Pump

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    Miscellaneous

    Automatic controlsPressure regulators

    Air vents/valves

    Summary

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    SummaryDetermine Plant information

    Spacing row/plantWater requirementIrrigation frequency

    Test water quality

    Select emitter/sprayerTypeSpacingDischarge

    Emitter factors C v, K, xDesign Lateral normal/flushingsizeFlow ratePressure requirement

    f

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    Design Manifold Header-Flushing/SubunitssizeFlow ratePressure requirementEmissions uniformity

    Air valvesDesign Mainline

    sizeFlow ratePressure requirement

    Select Filter systemNumber/sizeFlushing - disposalPressure requirement

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    Select injection systemType

    SizeSafety considerations/featuresControls

    Pump stationFlow ratepressure