Applying Irrigation Water in Circles (vs. squares)

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# Applying Irrigation Water in Circles (vs. squares) - PowerPoint PPT Presentation

Applying Irrigation Water in Circles (vs. squares). Why (briefly ). Economical Low O &amp; M High Reliability Central Delivery Point. Applying Irrigation Water in Circles (vs. squares). Why it’s a little trickier?. In a circular system the area increases as the radius increases

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Presentation Transcript

Applying Irrigation Water in Circles (vs. squares)

Why

(briefly)

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

Applying Irrigation Water in Circles (vs. squares)

Why it’s a little trickier?

In a circular system the area

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

2

3

4

2

3

4

1

A1 < A2 < A3 < A4

A1 = A2 = A3 = A4

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 = π R2

Soil / Water Intake Curves

4.0

3.0

1.0 Family

2.0

Intake Rate (in / hr)

0.5 Family

0.3 Family

1.0

0.0

0.0

0.1

0.2

0.4

0.3

0.5

Time (hrs)

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

RUN CPNOZZLE

CPNOZZLE

Example Composite Worksheet

Irrigation System Design (Some Basic Concepts)

Don’t Over - Complicate

Up Here

We Want To Get This

FIELD

WATER

WATER

Irrigation System Design (Some Basic Concepts)

Don’t Over - Complicate

Up Here

We Want To Get This

FIELD

Irrigation System Design (Some Basic Concepts)

2 Important Parameters

• 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

• 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”

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

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
• 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

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)
• Minor losses estimate = 10 ft.
• Total Dynamic Head = 176 ft.

PUMP SELECTION

225

Full Impellor

10% Trim

85%

20% Trim

82%

30% Trim

176

79%

750

0

1250

Flow (gpm)

PUMP SELECTION

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

• 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

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

Checkbook Account Transfers

Evapotranspiration

(Withdrawal)

Irrigation

(Deposit)

Rain

(Deposit)

Soil Profile

(Account Balance)

Deep Percolation (Withdrawal)

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

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.

CSP Irrigation Water Management

Evaluation Sheet

• 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)

CH 1

CH 2

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

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

Center Pivot 10 Conductor Span Cable

Timer

End Gun

Forward

Reverse

Neutral

Safety

Ground

Power

Power

Power