center pivot irrigation system design - nrcs irrigation...

Applying Irrigation Water in Circles (vs. squares)

1) Economical

2) Low O & M

3) High Reliability

4) Central Delivery Point

Why (briefly)

Applying Irrigation Water in Circles (vs. squares)Why it’s a little trickier?

In a rectangular system eachsprinkler applies water to an Identically sized Area (A)

In a circular system the areaincreases as the radius increasesHence, each sprinkler applies water to a differently sized Area (A)

1 2 43

1 432

A1 = A2 = A3 = A4 A1 < A2 < A3 < A4

Circle Area ComputationsArea = π R2

Radius(ft.)

Total Area

(acres)

Spoke Area

(acres)

Flow Required

(gpm)

130 1.2 1.2 7.2

260 4.9 3.7 22.2

390 11.0 6.1 36.6

520 19.5 8.5 51.0

650 30.5 11.0 66.0

780 43.9 13.4 80.4

910 59.7 15.8 94.8

1040 78.0 18.3 109.8

1170 98.7 20.7 124.2

1300 121.8 23.1 138.6

How Does this Weigh up on a Typical System?(System Capacity = 6 gpm / acre)

Sprinklers are sized appropriatelyalong length of pivot to maintainuniform applications along linear length of the center pivot machine

How Does this Weigh up on a Typical System?

High Pressure


Medium Pressure


Low Pressure

0.2 0.3 0.4 0.50.1

Time (hrs)

0.0

1.0

2.0

3.0

4.0

0.0

Inta

ke R

ate

(in /

hr)

Soil / Water Intake Curves

1.0 Family

0.5 Family

0.3 Family

Sprinkler Pressure vs. Intake CharacteristicsTimed Rain Gauge Analysis Thunderstorm Intensity

Sprinkler Pressure vs. Intake CharacteristicsTimed Rain Gauge Analysis Thunderstorm Intensity

Low

High

Medium

Low Medium High

CPNozzle ProgramNew Version

• Windows Version• Similar Inputs• Better Visualization• Residue Component• Estimates Surface Storage and Runoff

CPNOZZLE Important Variables

• Application Rate• Soil Family• Field Position of Soil Family • Residue Amount• Slope• Sprinkler Radius of Throw

RUN CPNOZZLE

.

GIS – Toolkit Applications

Family 0.3 Family 0.5 Family 1Acres Potential Weighted Acres Potential Weighted Acres Potential Weighted

Spoke # Runoff % Runoff Runoff % Runoff Runoff % Runoff123456789

10

Total Weighted Runoff ____________Total Acres ____________Potential Runoff ____________

CPNOZZLE Example Composite Worksheet

Irrigation System Design (Some Basic Concepts)Don’t Over - Complicate

FIELDWe Want To Get This Up Here

WATER

Irrigation System Design (Some Basic Concepts)Don’t Over - Complicate

FIELD

We Want To Get This Up Here

WATER

Irrigation System Design (Some Basic Concepts)2 Important Parameters

1)Flow (most commonly given in gpm)

2)Pressure or Head (given in psi or ft. of water)

Bucket–Fulls Per Unit Time

SquirtingDistance

FLOW DETERMINATION

1) Crop / Soil Requirementsa) effective root zoneb) soil texture

2) Field Size

3) Water Source Limitationsa) physicalb) by permitc) other

Table 1. System Capacity in gallons per minute per acre (gpm/acre) for different soil textures needed to supply sufficient water for each crop in 9 out of 10 years. An application efficiency of 80% and a 50% depletion of available soil water were used for the calculations. ------------------------------------------------------------ Root Coarse Loam Zone Sand Fine and Depth and Loamy Sandy Sandy Silt Crop (ft) Gravel Sand Sand Loam Loam Loam ------------------------------------------------------------ POTATOES* 2.0 8.2 7.5 7.0 6.4 6.1 5.7 DRY BEANS 2.0 7.9 7.1 6.4 6.1 5.7 5.4 SOYBEANS 2.0 7.9 7.1 6.4 6.1 5.7 5.4 CORN 3.0 7.3 6.6 5.9 5.5 5.3 4.9 SUGARBEETS 3.0 7.3 6.6 5.9 5.5 5.3 4.9 SMALL GRAINS 3.0 7.3 6.6 5.9 5.5 5.3 4.9 ALFALFA 4.0 6.8 5.9 5.6 5.1 5.0 4.5 ------------------------------------------------------------ *Adjusted for 40% depletion of available water

Crop Requirements (gpm / acre)From NDSU: “Selecting a Sprinkler Irrigation System”

General Rule = 6 gpm / acre

(Crop Requirement) x (Field Size) =Flow Requirement

EXAMPLE(6 gpm / acre) x (125 acres) =

750 gpm

(Not Written in Stone but good guidelines to follow)

May also be physical or permit demanded constraints on pumping rate which dictate

PRESSURE or HEAD4 Main Considerations

1) To offset Elevation difference between source and delivery point

2) To compensate for Friction losses in the mainline delivery system

3) System Operational Requirements

4) Other Minor losses

Elevation Difference between water source and point of distribution

Vertical distance between pumping water surfaceand the field delivery point

(for center pivots use the highest point in the irrigatedfield for conservative calculations)

Surface WaterGround Water

Example 50 feet

Friction LossesMost friction losses in irrigation systems are developed in

the system mainline (transmission pipeline)(Significant friction loss also occurs in the pivot itself but

Is usually calculated and included as part of the operational pressure requirements)

Transmission PipelineMost often PVC but may also

be aluminum, steel or PE

Friction LossesImportant factors in the calculation pipe friction loss are:

• Pipe Inside Diameter (id)• Pipe Material • Pipe Length• Fluid Velocity or Flow Rate

Friction loss is typically calculated using one of several common equations:

(Hazen Williams equation or Darcy equation)

Hazen Williams Equation

H = 10.44LQ1.85

C1.85d4.87

Friction Losses

Where:

• H = head loss from friction (ft.)• L = length of pipe (ft.) • Q = flow (gpm)• C = friction factor (140 – 150 for PVC pipe higher number means smoother pipe)• d = inside diameter of pipe (in.)

Hazen Williams Equation

H = 10.44LQ1.85

C1.85d4.87

Friction Losses

ExampleIf 750 gpm is flowing through 1500 feet of new 8 inch ID PVC pipe

the friction loss will be{10.44 x (1500) x (750)1.85 } / {(150)1.85 x (8)4.87}

=12.3 feet

Operational Pressure Requirements

At the Center Pivot Consist of:

1) Pressure necessary to operate sprinklers and regulators satisfactorily (5 psi or greater above rated pressure of regulator) 2) Friction losses incurred in span pipe

Calculation is usually combined together with sprinkler packagespreadsheet

Requirements are commonly given at pivot point location

Elevation differences along pivot may also be included

Example pivot point requirement: 45 psi @ 750 gpm

Minor LossesThe majority of minor losses which will increase the overall head requirement can be caused by: 1) Small friction losses which occur due to fittings and deviations in pipeline alignment2) Extra losses through pump and suction pipe3) Friction loss incurred in well tubing4) Other

In large pipeline networks minor losses can be a substantialportion of the total head requirement

Typically in irrigation systems minor losses are not a large part of the total head requirement – Often times it is good enough tosimply add 5 to 10 feet to the final head calculation as an adjustmentfor any minor losses which may occur in the system

Example Pressure Totals

1) Elevation Head = 50 ft.

2) Friction losses in the mainline delivery system = 12.3 ft.

3) System Operational Requirements = 45 psi or 104 ft. (2.3 ft. of water = 1 psi)

4)Minor losses estimate = 10 ft.

Total Dynamic Head = 176 ft.

PUMP SELECTION

Flow (gpm)

Tota

l Dyn

amic

Hea

d (f

t.)

Full Impellor

30% Trim20% Trim

10% Trim85%

82%

79%

176

7500 1250

225

PUMP SELECTION

Flow (gpm)

Tota

l Dyn

amic

Hea

d (f

t.)

20% Trim 85%

82%

79%

0 1250

225

PUMP STUFF1) Pumps DO NOT make pressure (only flow)

The system to which the pump is attached creates resistance to flow (pressure)

2) Pump speed is proportional to output (flow) but the head that a pump can resist is proportional to the square of speed. (which means changing speed changes pump flow reasonably but changes head characteristics a whole bunch) (pump affinity laws)

3) Typically slower running pumps are used for low head - high volume applications.

4) Common speeds for irrigation pumps: 1200 RPM (flood pumps), 1800 RPM (sprinklers with moderate head requirements), 3600 RPM (sprinklers with high head requirements).

POWER REQUIREMENTS

Horsepower Required = TDH x Q 3954 x n

Where n = wire to water efficiency(pump efficiency minus a little -

good first guess is .75)

EXAMPLE{(176 ft.) x (750 gpm)} / {3954 x .75} =

44.3 hp

CPED PROGRAM

1) Rewritten for use by NRCS in EQIP program2) Evaluates sprinkler package coefficient of

uniformity (must be at least 85% according to NRCS sprinkler standard)

3) Uses pump input parameters to give an entire system evaluation

4) Sprinkler inputs set up similar to OUTLETS program

RUN CPED

IRRIGATION WATER MANAGEMENT

By the Checkbook Method

1) Treats soil profile as a checkbook2) Water is the $3) Inputs and outputs are measured or estimated and

the balance is tracked throughout the growing season

4) Can be tracked by hand, in a spreadsheet or with other software

Checkbook Account Transfers

Deep Percolation (Withdrawal)

Rain(Deposit)

Irrigation(Deposit)

Evapotranspiration(Withdrawal)

Soil

Prof

ile(A

ccou

nt B

alan

ce)

IRRIGATION SCHEDULING by the CHECKBOOK METHOD

NDSU software1) Baled Lotus spreadsheet which tracks soil

depletion throughout growing season2) Estimates crop water use based on daily high

temperature input and days past emergence of particular crop

3) Soil available water inputs are entered at setup4) Contains historical weather record for several

sites in ND and MN.5) Actual soil water measurements can be entered to

keep record closer to actual

RUN IRRIGATION

EQIPIrrigation Water Management Plan

Worksheet

Example

1) Plan Purpose / General Details

General statements outlining where the producer is currently at and how he plans to improve his water management through the use of an irrigation scheduling and or crop water monitoring plan.

Open with regards to the producers beginning and ending points.

Producer must implement the use of checkbook type irrigation scheduling by the end of the three year contract as a minimum.

2) System Capacity / Field Information

Flow(gpm) 750 Total Area(acres) 132 System Efficiency(%) 75

Daily Application Rates at ____ efficiencyDaily application rate at 100% efficiency (in / day) = (0.053) x Flow(gpm) / Area(acres)

100% 0.30 90% 0.27 80% 0.24 70% 0.21

3) Soils Information

Soil NameFarland Grail Stady Bryant

Field Acreage 46 44 38 2Field Percentage 35.4 33.9 29.2 1.5Irrigation Group 8c 10c 6i 8c

Cumulative Available Water to depth (in.)

Top 1 foot 2.5 2.5 2.5 2.5Top 2 feet 4.5 4.5 4.5 4.5Top 3 feet 6.5 6.5 5.5 6.5Top 4 feet 8.5 8.5 6.0 8.5Top 5 feet 10 10.5 6.5 10.0

4) Crop Data

Year2006 2007 2008

Crop Corn Potato WheatFull Rooting Depth (ft.) 4.0 2.0 3.5Suggested MAD (%)* 50 40 50

Avg. Annual Water Use 25.9 23.2 18.8Est. annual no. days crop water

use exceeds system capacity25 23 18

Robinson, ND Corn Crop Water Use 2000-2004 averages vs. 5.8 GPM / Acre

00.05

0.10.15

0.20.25

0.30.35

5/15

5/29

6/12

6/26

7/10

7/24 8/

7

8/21 9/

4

9/18

Date

Cor

n ET

(in.

/ da

y)

Rain or Soil WaterDependantSystem can meet CropRequirements @ 80% eff.

5) Water Management Plan

Year2006 2007 2008

Crop Corn Potato WheatManaged Soil Farland Stady Farland

Managed Crop Rooting Depth (ft.) 4.0 2.0 3.0Managed Available Water Total

(in.)8.5 4.5 6.5

MAD (in.) 4.25 1.8 3.25Deficit for Rainfall (in.) 0.50 0.1 0.50

Managed Soil Water (in.) 3.75 1.7 2.75Minimum Soil Available Water

(in., %)4.25,50 2.70,60 3.25,50

CSP Irrigation Water Management

Evaluation Sheet

1) Evaluates an irrigation system and management scheme for placement/eligibility in the CSP program

RUN CSP program

Irrigation Handbook Modifications

Located in Section II of EFOTG

Chapter 1: Definitions of useful terminiology

Chapter 2: Irrigation group classification designations and descriptions (These have changed with this version of the guide)

Individual County Soils Classification (in soils section)

Cnty SoilsLink

CH 1link

CH 2link

Electrical Center Pivot Operation

1) 3 Phase Electric Power so that motors can be easily reversed and consequently the machine will reverse directions

2) Motor power is 480 V 3Ph, Control power is 120 V 1Ph

3) Main power supply is delivered to main control panel at pivot point. Control and motor power is delivered to each tower via a 10 or 11 conductor cable mounted on top of span

4) Timer circuit controls last tower, it runs when timer is activated. The rest of the towers play catch up through the use of micro-switches


Last Tower Controlled By Percent Timer


Next Tower Follows When Micro-switch

Triggers


All Other Towers Follow Similarly

Center Pivot 10 Conductor Span Cable

Power

Power PowerGround

Forward

NeutralReverse

Safety

TimerEnd Gun

THE END

center pivot irrigation system design - nrcs irrigation...

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