Lateral Design

Lateral DesignLateral Material/TypesDrip tape

Thin wall drip line

Heavy wall drip line

Polypipe with punch emitters

Polypipe with sprays

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Typical Layouts

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More layouts

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SDI9

Lateral installation10SDI burial depthCropBurial DepthLine spacingTrees and grapes>16 inches (0.4m)As per row spacingBerries, Vines> 8 inches (0.2m)As per row spacingRow crops corn, cotton 12 inches (0.3m) 24 80in (0.6 -2.03m)Raised beds single rowTomatoes, melons2-4 inches (0.05 0.1m)One line 4- 6 inches (0.1 -0.15m) from center of bedRaised beds double rowOnions, peppers, strawberries2-4 inches (0.05 0.1m)One line down center of bedRaised beds double row> 30 inch (0.75m) bed width3-6 inches (0.075 -0.15m)Two lines spaced the bed width apart11Tape orientationOne tape or more per bedHoles upwardTape thicknessTrend toward thickerTape materialsStretch vs. breakage12Lateral Line DesignImportant lateral characteristicsFlow rateLocation and spacing of manifoldsInlet pressurePressure difference

13Standard requiresPipe sizes for mains, submains, and laterals shall maintain subunit (zone) emission uniformity (EU) within recommended limits

Systems shall be designed to provide discharge to any applicator in an irrigation subunit or zone operated simultaneously such that they will not exceed a total variation of 20 percent of the design discharge rate.Start with average lateral

15Design objectiveLimit the pressure differential to maintain the desired EU and flow variationWhat effects the pressure differentialLateral length and diameterEconomics longer and smallerManifold locationslopeAllowable pressure loss (subunit)This applies to both the lateral and subunit. Most of the friction loss occurs in the first 40% of the lateral or manifold

Ranges from 2 to 3 but generally considered to be 2.5

DPs =allowable pressure loss for subunitPa = average emitter pressurePn = minimum emitter pressure17Emission Uniformity

18EU is related to Friction loss

19ExampleGiven: CV=0.03, 3 emitters per plant, qa = .43gph Pa=15 psi, EU=92, x=0.57

Find: qn, Pn, and P 20Solution

21Practice problem

22Flow rateWhere:l = Length of lateral, ft. (m).Se = spacing of emitters on the lateral, ft. (m).ne = number of emitters along the lateral.qa = average emitter flow rate, gph (L/h)

23Slope and topography

24Biggest mistake generally made by dealers. Why? Same reason NRCS does. It takes time to go out and survey.

Slope creates major problems with efficiency and uniformity ( e.g.. Drainage after shutoff)Four Cases

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Lateral Flow flat slope26

Lateral Flow 2% downhill slope27

Lateral flow 2% uphill slope28

Lateral flow varied slope29Manifold spacingSpacing is a compromise between field geometry and lateral hydraulics Lateral length is based on allowable pressure - head difference.Have the same spacing throughout the field in all crops 30Manifold LocationMore efficient to place in middle

two laterals extend in opposite directions from a common inlet point on a manifold, they are referred to as a pair of laterals. Manifold placed to equalize flow rates on the uphill and downhill laterals31

32Manifold placementzz0.00.51.00.850.10.561.20.890.20.601.40.920.30.651.60.940.40.691.80.960.50.722.00.980.60.752.20.990.70.782.41.000.80.812.61.000.90.832.751.00

33Determine optimum lateral lengthEU SlopeBased on friction loss limited to the allowable pressure difference (Ps)

34HydraulicsLimited lateral losses to 0.5DPsEquation for estimatingDarcy-Weisbach(best)Hazen-WilliamsWatters-Keller (easiest, used in NRCS manuals)35

C factorPipe diameter (in)130 1140< 3150 3130Lay flatHazen-Williams equationhf =friction loss (ft)F = multiple outlet factorQ = flow rate (gpm)C = friction coefficientD = inside diameter of the pipe (in)L = pipe length (ft)36Watters-Keller equation

hf = friction loss (ft)K = constant (.00133 for pipe < 5 .00100 for > 5)F = multiple outlet factorL = pipe length (ft)Q = flow rate (gpm)D = inside pipe diameter (in)37Multiple outlet factorsNumber of outletsFNumber of outletsF1.8511.7521.8511.752123456781.000.640.540.490.460.440.430.421.000.650.550.500.470.450.440.43910-1112-1516-2021-3031-70>700.410.400.390.380.370.360.360.420.410.400.390.380.370.3638Adjust length for barb and other minor losses

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OrOr use equation

Where Fe= equivalent length of lateral, ft)K = 0.711 for English units)B = Barb diameter, inD = Lateral diameter, in40Adjusted length

L = adjusted lateral length (ft)L = lateral length (ft)Se = emitter spacing (ft)fe = barb loss (ft)41Barb lossMore companies are giving a Kd factor now days

42ExampleGiven: lateral 1 diameter 0.50, qave=1.5gpm,Barb diameter 0.10 lateral 2 diameter 0.50, qave=1.5gpm, k=.25 Both laterals are 300 long and emitter spacing is 4 ft

Find: equivalent length for lateral 1 and hetotal for lateral 2 43Solution

Lateral 1Lateral 244Practice problem

45ProcedureStep 1 - Select a length calculate the friction loss

Step 2 adjust length to achieve desired pressure difference ( 0.5DHs)

46Step 3 - adjust length to fit geometric conditions

Step 4 - Calculate final friction loss

Step 5 Find inlet pressure

Step 6 Find minimum pressure

47Next step is to determine hPaired Lateral

Single Lateral Slope conditionsS > 0

S = 0

Slope ConditionsS < 0 and S > friction slope

48Last condition

S < 0 and S < Friction slope

Which ever is greater49Find minimum lateral pressureWhere S > 0 or S=0

Where S < 0 and S < Friction slope

Where S < 0 and S > friction slope

50Inlet pressureEstimate with the following equationSingle Lateral

Paired Lateral

Better to use computer program

51Handout Pressure summaryDesign ConsiderationsSelect emitter/flow rateDetermine required operating pressureCalculate friction lossQuick estimate use multiple outlet factorManufactures softwareBuilt spreadsheetDecide whether to use single or paired lateralsMake adjustments Determine h and hose EU

53 Practice problem

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Class design problem

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