Transcript Center Pivot Irrigation System Design

Applying Irrigation Water in Circles (vs. squares)
Why
(briefly)
1) Economical
2) Low O & M
3) High Reliability
4) Central
Delivery Point
Applying Irrigation Water in Circles (vs. squares)
Why it’s a little trickier?
In a rectangular system each
sprinkler applies water to an
Identically sized Area (A)
In a circular system the area
increases as the radius increases
Hence, each sprinkler applies
water to a differently sized Area (A)
1 2
1
2
3
A1 = A2 = A3 = A4
3 4
4
A1 < A2 < A3 < A4
How Does this Weigh up on a Typical System?
(System Capacity = 6 gpm / acre)
Circle Area Computations
Area = 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
Sprinklers are sized appropriately
along length of pivot to maintain
uniform applications along linear
length of the center pivot machine
How Does this Weigh up on a Typical System?
High Pressure
How Does this Weigh up on a Typical System?
Medium Pressure
How Does this Weigh up on a Typical System?
Low Pressure
Soil / Water Intake Curves
4.0
Intake Rate (in / hr)
3.0
1.0 Family
2.0
0.5 Family
0.3 Family
1.0
0.0
0.0
0.1
0.2
0.3
Time (hrs)
0.4
0.5
Sprinkler Pressure vs. Intake Characteristics
Timed Rain Gauge Analysis
Thunderstorm Intensity
Sprinkler Pressure vs. Intake Characteristics
Timed Rain Gauge Analysis
Thunderstorm Intensity
Low
Medium
High
Low
Medium
High
CPNozzle Program
New 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
.
CPNOZZLE
Example Composite Worksheet
Acres
Spoke #
1
2
3
4
5
6
7
8
9
10
Family
Potential
Runoff %
0.3
Weighted
Runoff
Acres
Family
Potential
Runoff %
0.5
Weighted
Runoff
Total Weighted Runoff
Total Acres
Potential Runoff
Acres
Family
Potential
Runoff %
1
Weighted
Runoff
____________
____________
____________
Irrigation System Design (Some Basic Concepts)
Don’t
Over - Complicate
We Want To Get This
FIELD
WATER
Up Here
Irrigation System Design (Some Basic Concepts)
Don’t
Over - Complicate
We Want To Get This
FIELD
WATER
Up Here
Irrigation System Design (Some Basic Concepts)
2 Important Parameters
1)Flow (most commonly given in gpm)
Bucket–Fulls
Per Unit Time
2)Pressure or Head (given in psi or ft. of water)
Squirting
Distance
FLOW
DETERMINATION
1) Crop / Soil Requirements
a) effective root zone
b) soil texture
2) Field Size
3) Water Source Limitations
a) physical
b) by permit
c) other
Crop Requirements (gpm / acre)
From NDSU: “Selecting a Sprinkler Irrigation System”
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
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 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
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
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
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)
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.)
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
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 @ 750 gpm
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
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
Total Dynamic Head (ft.)
225
Full Impellor
10% Trim
85%
20% Trim
176
82%
30% Trim
79%
0
750
Flow (gpm)
1250
PUMP SELECTION
Total Dynamic Head (ft.)
225
85%
20% Trim
82%
79%
0
1250
Flow (gpm)
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).
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 program
2) 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 checkbook
2) 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
Evapotranspiration
(Withdrawal)
Irrigation
(Deposit)
Soil Profile
(Account Balance)
Rain
(Deposit)
Deep Percolation (Withdrawal)
IRRIGATION SCHEDULING by
the CHECKBOOK METHOD
NDSU software
1) Baled Lotus spreadsheet which tracks soil
depletion throughout growing season
2) 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 setup
4) 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
EQIP
Irrigation 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 ____ 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
70%
0.21
3) Soils Information
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
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
Soil Name
Cumulative Available
Water to depth (in.)
4) Crop Data
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
Year
Robinson, ND Corn Crop Water Use
2000-2004 averages vs. 5.8 GPM / Acre
Rain or Soil Water
Dependant
0.3
System can meet Crop
Requirements @ 80% eff.
0.25
0.2
0.15
0.1
0.05
Date
9/18
9/4
8/21
8/7
7/24
7/10
6/26
6/12
5/29
0
5/15
Corn ET (in. / day)
0.35
5) Water Management Plan
2006
2007
2008
Corn
Potato
Wheat
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
4.25,50
2.70,60
3.25,50
Year
Crop
Managed Soil
Minimum Soil Available Water
(in., %)
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 Soils
Link
CH 1
link
CH 2
link
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
Electrical Center Pivot Operation
Electrical Center Pivot Operation
Last Tower Controlled
By Percent Timer
Electrical Center Pivot Operation
Next Tower Follows
When Micro-switch
Triggers
Electrical Center Pivot Operation
All Other Towers
Follow Similarly
Center Pivot 10 Conductor Span
Cable
Timer
End Gun
Forward
Reverse
Neutral
Safety
Ground
Power
Power
Power
THE END