Conservation Planning Existing Center Pivots

Illinois NRCS TrainingDecember 6, 2011

Springfield, Illinois

Runoff AssessmentCPNozzle

A Few Concepts First

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 on the circle:

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

On a Typical Pivot System?(System Capacity = 6 gpm / acre)

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

Radius Total Span Flow (ft) Area Area Required  (acres) (acres) (gpm)

130 1.2 1.2 7.2260 4.9 3.7 22.2390 11.0 6.1 36.6520 19.5 8.5 51.0650 30.5 11.0 66.0780 43.9 13.4 80.4910 59.7 15.8 94.8

1040 78.0 18.3 109.81170 98.7 20.7 124.21300 121.8 23.1 138.6

High Pressure Impact

High Pressure

Medium Pressure on Drop

Medium Pressure

Low Pressure on Drop

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 Program

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

and Runoff

CPNozzle Program

• Green-Ampt Option Should Not Be Used At This Time (12_01_11)

CPNOZZLE Important Input Variables

• System Wetted Length (ft)• System Capacity (GPM wo-gun)• Application Depth (in)• Soil Intake Family• Slope (constant or variable)• Residue Amount (const. or variable)• Sprinkler Diameter of Throw

Wetted Length (ft) = length from pivot to about 75% of wetted

radius of last sprinkler (exclude end gun)

Sprinkler Package Wetted Diameter‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑----------------------------High Pressure Impact (Constant Spacing) HHigh Pressure Impact (Variable Spacing) (80 - 110 ft)Medium Pressure Impact (70 - 90 ft)Low Pressure Impact (60 - 70 ft)Low Pressure w/Rotators (50 - 60 ft)Low Pressure Spray on Pipeline (30 - 40 ft)Low Pressure Spray on Drop Tubes (20 - 30 ft)Low Pressure Spray (180 degrees) (16 - 20 ft)Ultra Low Pressure (LEPA Spray Mode) (12 - 18 ft)Ultra Low Spray (LEPA Bubble Mode) ( 1 - 2 ft)--------------------------------------------------------------------------------------------

Listing of wetted diameter ranges for typical center pivot sprinkler packages.

NRCS INTAKE FAMILY DESCRIPTION---------------------------------------------------------------------------------------------------

--0.1 ‑‑‑‑‑‑‑‑ Clay, silty clay, silty clay loam

‑‑‑‑‑‑‑‑ Slowly permeable subsoils0.3 ‑‑‑‑‑‑‑‑ Silt loam, loam, very fine sandy loam, clay loam,

‑‑‑‑‑‑‑‑ silty clay loam, sandy clay loam‑‑‑‑‑‑‑‑ Slow to moderately slow permeable subsoils

0.5 ‑‑‑‑‑‑‑‑ Silt loam, loam, very fine sandy loam‑‑‑‑‑‑‑‑ Moderately slow permeable subsoils

1.0 ‑‑‑‑‑‑‑‑ Fine sandy loam, loamy fine sand, silt loam,‑‑‑‑‑‑‑‑ loam, very fine sandy loam, very fine sandy‑‑‑‑‑‑‑‑ Moderate, moderately slow, moderately permeable,‑‑‑‑‑‑‑‑ medium textured, moderately rapidly permeable‑‑‑‑‑‑‑‑ subsoils underlain by bedrock or mixed sand & gravel

1.5 ‑‑‑‑‑‑‑‑ Fine sandy loam, loam, sandy loam‑‑‑‑‑‑‑‑ Moderately rapid, rapidly, moderate subsoils underlain‑‑‑‑‑‑‑‑ by bedrock or mixed sand & gravel

2.0 ‑‑‑‑‑‑‑‑ Loamy fine sand or loamy sand‑‑‑‑‑‑‑‑ Moderately rapid to rapidly permeable subsoil

3.0 ‑‑‑‑‑‑‑‑ Loamy sand, loamy fine sand, fine sandy loam, fine sand‑‑‑‑‑‑‑‑ Rapidly permeable subsoils

Modeling Procedure• Enter background information (Producer,

Location, County, State, Designed By, Date). 

• System Wetted Length (ft). – Identify, and enter the center pivot system length.

• System Capacity without End Gun (gpm) – Enter the flow rate of the system with the end gun shut off, in gallons per minute.

• Application Amount (in) – Enter the application amount in inches.

Modeling Procedure• Wetted Diameter (ft) – Enter the

sprinkler/nozzle wetted diameter at the end of the pivot.

• Intake Family - Enter the NRCS Intake Family of the soil type from the Soil Survey, or as found in Chapter 2 of the National Irrigation Guide, Part 652.

• The program uses these values to select a soil water infiltration curve.

Weaselage: The field being modeled will rarely have

uniform soil types and slopes, so the user must make decisions on which position in the field to evaluate the

system. In some cases, the user should evaluate the system for different

positions in the field, creating different input scenarios. The scenario that could

potentially generate the greatest amount of runoff should be chosen.

Guidelines (draft 12/1/11)• Exclude separate soil type areas that are

less than 10% of the total field area.• Choose a position where the system will

cross the soil type with the lowest intake family value with the greatest slopes. In situations where the system would cross soil types with different intake families, model the soil with the lowest intake family value.

• Use an average slope when utilizing the constant slope option.

Guidelines (cont)• When the steepest position in the field occurs at

a higher intake family than other portions of the field, model separate scenarios (smallest intake family position, steepest slope position) and compare.

• The further distance away from the center point the worst case field conditions are, the greater their impact on runoff will be. In some instances, if the worst-case field conditions are close to the center point, the remainder of the field may determine the minimum sprinkler wetted diameter.

RUN CPNOZZLE

THE END

I can go nuts sometimes

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

THE END