Center Pivot Training Flow Requirements

The easy way QT = DA (not a true equation if Q is in cfs) Q (flow rate) is in cfs (or acre-in/hr) T (time) is in hours D (depth) is in inches A (area) is in acres Note: 449 gpm = 1 cfs

The easy way Complete Worksheet

Let’s Compare QT = DA From NEH Part 623 Chapter 11: (aka NEH Section 15 Chapter 11) (11-42c) What is the difference between these two equations?

The hard(er) way System Capacity for a center pivot is generally expressed in: gallons per minute or gallons per minute per acre But first: calculate the gross irrigation requirement

Gross Irrigation Requirement GIR is in inches per “f” days

Gross Irrigation Requirement Adjustments: ET c is the average daily crop ET during: 5 day period for shallow rooted crops 10 day period for medium rooted crops 20 day period for deep rooted crops (alfalfa)

Gross Irrigation Requirement P e is assumed to be zero if rainfall is not dependable during the peak water use period.

Gross Irrigation Requirement E a is the application efficiency Typical value is 85% for center pivots

Irrigation System TypeEfficiency Border - Graded Border80% Border - Level or Basin90% Border – Guide70% Border - Contour Level field crop70% Border - Contour - Level Rice80% Border - Contour - Level Rice - Side Inlets85% Border - Border Ditch60% Furrow - Level or Basin90% Furrow - Graded Furrow75% Furrow - Contour furrow75% Furrow – Corrugations75% Furrow – Surge80% Subirrigation – Subirrigated75% Flood – Controlled60% Flood – Uncontrolled50% Flood - Contour Ditch60% Sprinkler - Big Gun or Boom60% Sprinkler - Hand Line or Wheel Line70% Sprinkler - Solid Set (above canopy)75% Sprinkler - Solid Set (below canopy)80% Center Pivot80% Center Pivot (Low Pressure Improved)83% Center Pivot - Low Pressure Precision Application (LEPA)92% Center Pivot - Low Elevation Spray Application (LESA)89% Center Pivot - Low Pressure In Canopy (LPIC)87% Center Pivot - Mid Elevation Spray application(MESA)85% Center Pivot - Variable Rate Irrigation (VRI)87% Lateral Move82% Lateral Move (LEPA, LESA, LPIC, MESA)87% Lateral Move (VRI)87% Micro, Point Source90% Micro, Sprays85% Micro, Continuous Tape90% Micro, Subsurface Drip Irrigation (SDI)92%

Gross Irrigation Requirement K f is the adjustment factor for frequency of wetting Remember what ET is? 1.2 for daily irrigations with < 80% ground cover 1.1 for irrigations every 2 days 1.05 for daily irrigation with full crop cover When there is a lack of information, use 1.0

© Irrigation Association

Gross Irrigation Requirement All this, and what do we get? A value for D that we can use in QT=DA This is the depth, in inches, of our irrigation application, adjusted for a bunch of things

Gross Irrigation Requirement Complete Worksheet