Sprinkler Irrigation System Planning and Evaluation

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Center Pivot Lateral Move Solid set Planning and
Management Considerations Dale Heermann ARS
Retired Engineer
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Planning Considerations

• Field Size
• Available water supply
• Management ability
• Labor availability
• Crops to be grown
• Soils characteristics
• Intake Rate
• Water holding capacity

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Center Pivot Planning Considerations

• Field Size General needs large areas
• Available water supply meets crop needs
• Management ability Can manage multiple systems
• Labor availability Low labor requirements
• Crops to be grown must clear canopy
• Soils characteristics
• Intake Rate - runoff potential at outer end
• Water holding capacity can apply small depths

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Linear Move Planning Considerations

• Field Size General needs large rectangular
  areas
• Available water supply meets crop needs
• Management ability Can manage multiple systems
• Labor availability Labor required to move hose
• Crops to be grown must clear canopy
• Soils characteristics
• Intake Rate - Application rate constant along
  lateral
• Water holding capacity can apply small depths

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Solid set Planning Considerations

• Field Size Can be designed for irregular shapes
• Available water supply meets crop needs
• Management ability Can manage multiple systems
• Labor availability Minimum Labor unless hand
  move
• Crops to be grown Generally not a limitation
• Soils characteristics
• Intake Rate - Application rate function of
  spacing
• Water holding capacity can apply small depths

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Area is 4 times larger in outer band
Discharge must be 4 times as large
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Application rate is also higher
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Sprinkler selection for center pivot and linear
move systems

• High Pressure Impact- lower application rate
• Low Pressure (sprays, rotators, wobblers)
• Spacing and pattern radii affect application
  rate
• In canopy
• Truss height
• LEPA
• Must control runoff limit to lt 1
• Plant in circle for center pivot LEPA
• Minimizes soil evaporation
• Low capacity function of water holding capacity

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Sprinkler System Capacity

• Net Irrigation Capacity Function of Crop ET and
  precipitation which is function of local
  conditions

• Example of reducing capacity by 25 of net
  irrigation capacity based on soil water holding
  capacity and Eastern Colorado climatic
  conditions.
• One inch maximum depletion would be exceeded one
  out of two years.
• Five inch maximum depletion would not be
  exceeded.

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EVALUATION OBJECTIVES

• Changes Over Time
• Installed As Designed
• Properly Designed
• Nozzle Wear
• Pumping Plant Efficiency
• Declining Water Table

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CURRENT EVALUATION PROCEDURES
ASAE STANDARD 436.1 NRCS PROCEDURE
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EVALUATION PROCEDURE
PROVIDES AN ESTIMATE OF UNIFORMITY
BUT
A POOR ESTIMATE OF EFFICIENCY
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EFFICIENCY ESTIMATES

• MUST CONSIDER
• IRRIGATION TIMING
• RUNOFF
• ERRORS IN CATCH CANS
• 6.2 m/s - 25 (Loss)
• 2.5 m/s - 5 (Loss)

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FIELD PROBLEMS
CENTER PIVOT WITH SPRAYS
REQUIRES MANY CANS
WIND CAN CAUSE ERRORS
LABOR INTENSIVE
GROOVED OR SMOOTH PADS
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TEST EXAMPLE
GROOVED PAD TEST FOLLOWED BY SMOOTH PAD TEST
Both tests with low wind CU was 10 higher for
smooth pad test
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SUGGESTED PROTOCOL

• INVENTORY IRRIGATION SYSTEM
• Sprinkler Model
• Nozzle Size
• Spacing
• Pressure
• Elevation of Each Tower
• Pipe Sizes

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SUGGESTED PROTOCOLFIELD MEASUREMENT
VERIFY INVENTORY MEASURE - PRESSURE - DISCHARGE
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OUTPUTS
APPLICATION DEPTH NOZZLE PRESSURE COEFFICIENT
OF UNIFORMITY CHRISTIANSEN - CU LOW QUARTER -
DU
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SIMULATIONS
COMPARE SIMULATIONS WITH FIELD MEASUREMENTS OF PRE
SSURE AND DISCHARGE
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SIMULATIONS
OTHER BENEFITS
Evaluate new designs. Evaluate effect of
topography.
Use pump curve for change in elevation and
drawdown in water table.
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CATCH CAN ADVANTAGES
VISUAL REAL FIELD DATA SIMPLE TO INSTALL ACCEPTED
BY USERS DOES NOT NEED A COMPUTER
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DISADVANTAGES (CC)
Wind effects Night testing is best Evaporation Gro
oved pads Large number of cans Labor
intensive Extreme care for setup
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ADVANTAGES OF SIMULATION

• Less labor
• Wind not a problem
• Complete hydraulic analysis
• Eliminates catch can error
• Can be rerun easily for different operating
  conditions

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MULTIPLE RUNS

• Evaluate multiple designs
• Analyze effect of changes in drawdown
• Effects of elevation changes
• Effect of big gun operation
• Identify potential problems with nozzle wear,
  changes in pipe roughness, pumping plant, and
  water table depth.
• Effect of pressure regulators

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SIMULATION DISADVANTAGES
Need pattern shape and radius. Additional data to
trouble shoot. Understand models. Difficult
to obtain pump data. Difficult to obtain
elevation data. Need drawdown water level. Labor
to collect field data.
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Final Decision Factors and Evaluation

• Measurement is absolute necessity
• Scheduling is needed for efficiency
• Maximum depth to minimize evaporation
• Water holding capacity limits depth
• Applying more than needed reduces efficiency
• Consider differences in soils within field
• Crop requirements varies with season
• Crops have differing root zone requirements