Center Pivot Irrigation System Design

1
Applying Irrigation Water in Circles (vs. squares)
Why (briefly)

• Economical
• Low O M
• High Reliability
• Central Delivery Point

2
Applying Irrigation Water in Circles (vs. squares)
Why its a little trickier?
In a circular system the area increases as the
radius increases Hence, each sprinkler applies
water to a differently sized Area (A)
In a rectangular system each sprinkler applies
water to an Identically sized Area (A)
1
4
3
2
2
4
3
1
A1 lt A2 lt A3 lt A4
A1 A2 A3 A4
3
How Does this Weigh up on a Typical
System? (System Capacity 6 gpm / acre)
Circle Area Computations
Sprinklers are sized appropriately along length
of pivot to maintain uniform applications along
linear length of the center pivot machine
Area p 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
4
How Does this Weigh up on a Typical System?
High Pressure
5
How Does this Weigh up on a Typical System?
Medium Pressure
6
How Does this Weigh up on a Typical System?
Low Pressure
7
(No Transcript)
8
Sprinkler Pressure vs. Intake Characteristics Time
d Rain Gauge Analysis Thunderstorm Intensity
9
Sprinkler Pressure vs. Intake Characteristics Time
d Rain Gauge Analysis Thunderstorm Intensity
Low
Medium
High
Low
Medium
High
10
CPNozzle Program New Version

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

11
CPNOZZLE Important Variables

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

RUN CPNOZZLE
12
GIS Toolkit Applications













.


13
CPNOZZLE Example Composite Worksheet
14
Irrigation System Design (Some Basic
Concepts) Dont Over - Complicate
Up Here
We Want To Get This
FIELD
WATER
15
Irrigation System Design (Some Basic
Concepts) Dont Over - Complicate
Up Here
We Want To Get This
FIELD
16
Irrigation System Design (Some Basic Concepts) 2
Important Parameters

1. Flow (most commonly given in gpm)

BucketFulls Per Unit Time

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

Squirting Distance
17
FLOW DETERMINATION

• Crop / Soil Requirements
• a) effective root zone
• b) soil texture
• 2) Field Size
• 3) Water Source Limitations
• a) physical
• b) by permit
• c) other

18
Crop Requirements (gpm / acre) From NDSU
Selecting a Sprinkler Irrigation System
General Rule 6 gpm / acre
19
(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
20
PRESSURE or HEAD 4 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
21
Elevation Difference between water source and
point of distribution
Vertical distance between pumping water
surface and the field delivery point (for center
pivots use the highest point in the
irrigated field for conservative calculations)
Example 50 feet
Surface Water
Ground Water
22
Friction Losses
Most 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 Pipeline Most often PVC but may
also be aluminum, steel or PE
23
Friction Losses

• Important 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)
24
Friction Losses
Hazen Williams Equation H
10.44LQ1.85 C1.85d4.87

• 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.)

25
Friction Losses
Hazen Williams Equation H
10.44LQ1.85 C1.85d4.87
Example If 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
26
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 package
• spreadsheet
• Requirements are commonly given at pivot point
  location
• Elevation differences along pivot may also be
  included
• Example pivot point requirement
• 45 psi _at_ 750 gpm

27
Minor Losses
The 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
alignment 2) Extra losses through pump and
suction pipe 3) Friction loss incurred in well
tubing 4) Other In large pipeline networks
minor losses can be a substantial portion 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 to simply add 5 to 10 feet to the final
head calculation as an adjustment for any minor
losses which may occur in the system
28
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)
• Minor losses estimate 10 ft.
• Total Dynamic Head 176 ft.

29
PUMP SELECTION
225
Full Impellor
10 Trim
85
20 Trim
82
30 Trim
176
Total Dynamic Head (ft.)
79
750
0
1250
Flow (gpm)
30
PUMP SELECTION
225
85
20 Trim
82
Total Dynamic Head (ft.)
79
0
1250
Flow (gpm)
31
PUMP STUFF
1) 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).
32
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
33
CPED PROGRAM

• Rewritten for use by NRCS in EQIP program
• Evaluates sprinkler package coefficient of
  uniformity (must be at least 85 according to
  NRCS sprinkler standard)
• Uses pump input parameters to give an entire
  system evaluation
• Sprinkler inputs set up similar to OUTLETS
  program

RUN CPED
34
IRRIGATION WATER MANAGEMENT By the Checkbook
Method

• Treats soil profile as a checkbook
• Water is the
• Inputs and outputs are measured or estimated and
  the balance is tracked throughout the growing
  season
• Can be tracked by hand, in a spreadsheet or with
  other software

35
Checkbook Account Transfers
Evapotranspiration (Withdrawal)
Irrigation (Deposit)
Rain (Deposit)
Soil Profile (Account Balance)
Deep Percolation (Withdrawal)
36
IRRIGATION SCHEDULING by the CHECKBOOK
METHOD NDSU software

• Baled Lotus spreadsheet which tracks soil
  depletion throughout growing season
• Estimates crop water use based on daily high
  temperature input and days past emergence of
  particular crop
• Soil available water inputs are entered at setup
• Contains historical weather record for several
  sites in ND and MN.
• Actual soil water measurements can be entered to
  keep record closer to actual

RUN IRRIGATION
37
EQIP Irrigation Water Management Plan
Worksheet Example
38
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.

39
2) System Capacity / Field Information
Flow(gpm) 750 Total Area(acres) 132 Total Area(acres) 132 System Efficiency() 75 System Efficiency() 75
Daily Application Rates at ____ efficiency Daily application rate at 100 efficiency (in / day) (0.053) x Flow(gpm) / Area(acres) Daily Application Rates at ____ efficiency Daily application rate at 100 efficiency (in / day) (0.053) x Flow(gpm) / Area(acres) Daily Application Rates at ____ efficiency Daily application rate at 100 efficiency (in / day) (0.053) x Flow(gpm) / Area(acres) Daily Application Rates at ____ efficiency Daily application rate at 100 efficiency (in / day) (0.053) x Flow(gpm) / Area(acres) Daily Application Rates at ____ efficiency Daily application rate at 100 efficiency (in / day) (0.053) x Flow(gpm) / Area(acres)
100 0.30 90 0.27 80 0.24 80 0.24 70 0.21
40
(No Transcript)
41
3) Soils Information
Soil Name Farland Grail Stady Bryant
Field Acreage 46 44 38 2
Field Percentage 35.4 33.9 29.2 1.5
Irrigation Group 8c 10c 6i 8c
Cumulative Available Water to depth (in.)
Top 1 foot 2.5 2.5 2.5 2.5
Top 2 feet 4.5 4.5 4.5 4.5
Top 3 feet 6.5 6.5 5.5 6.5
Top 4 feet 8.5 8.5 6.0 8.5
Top 5 feet 10 10.5 6.5 10.0
42
4) Crop Data
Year 2006 2007 2008
Crop Corn Potato Wheat
Full Rooting Depth (ft.) 4.0 2.0 3.5
Suggested MAD () 50 40 50
Avg. Annual Water Use 25.9 23.2 18.8
Est. annual no. days crop water use exceeds system capacity 25 23 18
43
(No Transcript)
44
5) Water Management Plan
Year 2006 2007 2008
Crop Corn Potato Wheat
Managed Soil Farland Stady Farland
Managed Crop Rooting Depth (ft.) 4.0 2.0 3.0
Managed Available Water Total (in.) 8.5 4.5 6.5
MAD (in.) 4.25 1.8 3.25
Deficit for Rainfall (in.) 0.50 0.1 0.50
Managed Soil Water (in.) 3.75 1.7 2.75
Minimum Soil Available Water (in., ) 4.25,50 2.70,60 3.25,50
45
CSP Irrigation Water Management Evaluation Sheet

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

RUN CSP program
46
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)
47
Cnty Soils Link
48
CH 1 link
CH 2 link
49
Electrical Center Pivot Operation

• 3 Phase Electric Power so that motors can be
  easily reversed and consequently the machine will
  reverse directions
• Motor power is 480 V 3Ph, Control power is 120 V
  1Ph
• 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
• 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

50
Electrical Center Pivot Operation
51
Electrical Center Pivot Operation
Last Tower Controlled By Percent Timer
52
Electrical Center Pivot Operation
Next Tower Follows When Micro-switch Triggers
53
Electrical Center Pivot Operation
All Other Towers Follow Similarly
54
Center Pivot 10 Conductor Span Cable
Timer
Forward
End Gun
Reverse
Neutral
Safety
Ground
Power
Power
Power
55
THE END