Improving Efficiency in Your Flood or Pivot Irrigation

Irrigation

Caleb CarterUW Extension Hay Workshop, Pinedale, WY February 20, 2015

Improving flood irrigation efficiency

What is the goal of flood

irrigation?

The water balance

Web Soil Survey

Obtain info on:• Soil type• H2O capacity• infiltration

http://websoilsurvey.sc.egov.usda.gov/App/HomePage.htm

Available soil moisture

• Field Capacity• 50% Available

Water• Permanent

Wilting Point• MAD

Strategies• Experience/observation

• Field leveling

• Lining ditches

• Gated pipe

• Improving irrigation

management

Boulder watershed study• Producer findings:

o Allows lengthened sets

o Can irrigate larger area

o More even distribution

o Increased yields

o Less labor intensive

o Feel that it is more efficient and has increased yields

Other considerations…

• Reduced return flows?

o Study in Laramie Basin

• Identified 74 wetlands

• Found that 65% of inflows were from irrigation

• Majority of that from subsurface flows

o Powell, WY example

Stream size

𝑠𝑡𝑟𝑒𝑎𝑚 𝑠𝑖𝑧𝑒 =𝑝𝑢𝑚𝑝 𝑑𝑖𝑠𝑐ℎ𝑎𝑟𝑔𝑒 (𝑔𝑝𝑚)

𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑓𝑢𝑟𝑟𝑜𝑤𝑠 𝑓𝑙𝑜𝑤𝑖𝑛𝑔

• Considerations

oLeaks minimal in delivery system?

oKeep stream size smaller than max

non-erosive stream size: 12.5 𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑠𝑙𝑜𝑝𝑒 𝑜𝑓 𝑓𝑖𝑒𝑙𝑑

Gross depth

𝐺𝑟𝑜𝑠𝑠 𝑑𝑒𝑝𝑡ℎ:

=1,155 𝑥 𝑠𝑡𝑟𝑒𝑎𝑚 𝑠𝑖𝑧𝑒 𝑔𝑝𝑚 𝑥 𝑡𝑖𝑚𝑒 𝑤𝑎𝑡𝑒𝑟 𝑎𝑝𝑝𝑙𝑖𝑒𝑑 (ℎ𝑟𝑠)

𝑓𝑢𝑟𝑟𝑜𝑤 𝑙𝑒𝑛𝑔𝑡ℎ 𝑓𝑡 𝑥 𝑤𝑒𝑡𝑡𝑒𝑑 𝑓𝑢𝑟𝑟𝑜𝑤 𝑠𝑝𝑎𝑐𝑖𝑛𝑔 (𝑖𝑛)

Soil Texture Ideal GrossApplication

Sandy 1.5 – 2 inches

Medium to Fine 2.5 – 3 inches

Cutoff ratio

𝑐𝑢𝑡𝑜𝑓𝑓 𝑟𝑎𝑡𝑖𝑜 =𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑎𝑑𝑣𝑎𝑛𝑐𝑒 𝑡𝑖𝑚𝑒

𝑠𝑒𝑡 𝑡𝑖𝑚𝑒

Target cutoff ratio per soil/system considerations.Sandy Soils Loamy Soils Clayey Soils

Without Reuse 0.5 0.70 0.9With Reuse 0.20 0.40 0.5Blocked Ends 0.7 0.85 0.95

Example• Soil = sandy

• Pump discharge =

760 gpm

• Furrow length =

2,600 ft.

• Set time = 24 hours

• System = no reuse

• Set size = 80 gates flowing

• Watered furrow spacing = 30 inches

• Observed advance time = 15 hours

Example (cont.)

• 𝒄𝒖𝒕𝒐𝒇𝒇 𝒓𝒂𝒕𝒊𝒐 =15 ℎ𝑟𝑠

24 ℎ𝑟𝑠= 0.63

• 𝒔𝒕𝒓𝒆𝒂𝒎 𝒔𝒊𝒛𝒆 =760 𝑔𝑝𝑚

80 𝑓𝑢𝑟𝑟𝑜𝑤𝑠= 9.5 𝑔𝑝𝑚 𝑝𝑒𝑟 𝑓𝑢𝑟𝑟𝑜𝑤

• 𝑮𝒓𝒐𝒔𝒔 𝒂𝒑𝒑𝒍𝒊𝒄𝒂𝒕𝒊𝒐𝒏 =1,155 𝑥 9.5 𝑔𝑝𝑚 𝑥 24 ℎ𝑟𝑠

2,600 𝑓𝑡 𝑥 30 𝑖𝑛= 3.4 𝑖𝑛

• Cutoff time: 0.63 > 0.5

• Gross application: 3.4 inches

Example (cont.)

Parameter Calculation Method Example

Desired cutoff ratio

Table 1 0.5

New Advance Time

Desired Cutoff Ratio x New set time

0.50 x 12 hrs = 6.0 hrs

Advance Time Ratio

New Advance Time ÷Original advance time

6 hrs ÷ 15 hrs = 0.40

Furrow Ratio Figure 2 0.6

New Number of Gates

Original Number of Gates x Furrow Ratio

80 x 0.60 = 48 gates

New Stream Size Equation 1 760 ÷ 48 = 15.6 gpm

New Gross Application

Equation 2(1155 x 15.6 x 12)

÷ (2600 x 30) = 2.8 in

Surge Irrigation Trials

• 26 trials

• No trial was less efficient

• Only half significantly decreased advance time

• Better for high infiltration soils

• First irrigation shows the most benefit

Surge irrigation – Cycles

Fraction of FieldCycle No.

4 advance stages

5 advance stages

6 advance stages

On-time factor

1 1/4 1/5 1/6 1.02 1/2 2/5 1/3 1.93 3/4 3/5 1/2 2.64 1.0 4/5 2/3 3.15 ― 1.0 5/6 3.46 ― ― 1.0 3.8

Advance cycles

C𝒖𝒕𝒐𝒇𝒇 𝒄𝒚𝒄𝒍𝒆 =0.65 𝑥 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑙𝑎𝑠𝑡 𝑎𝑑𝑣𝑎𝑛𝑐𝑒 𝑐𝑦𝑐𝑙𝑒

Example

Cycle Type and Number

On-Time Factor x First Cycle On-Time

On-Time for Each Cycle

Advance Cycle 1 1.0 x 20 =20 minutes per

side

Advance Cycle 2 1.9 x 20 =38 minutes per

side

Advance Cycle 3 2.6 x 20 =52 minutes per

side

Advance Cycle 4 3.1 x 20 =62 minutes per

sideEach Cutback Cycle 0.65 x 62 =

40 minutes per side

• 1,000 ft field• 4 advance stages: 250 ft per stage

Surge Irrigation Limitations

• Surge valve cost: $1500 to

$2500

• Varied results

• Depends on soil type,

topography, management

• Lower infiltration rates may

lead to less water in root

zone

• Field leveling very important

Flood irrigation

• Efficient flood

irrigationoAlmost filling root

zone

o Utilizing or minimizing

runoff

Improving pivot efficiency

Pivot characteristics

Span

Span end(ft)

Area withinthe span (acres)

Discharge from span

(gpm)

1 180 2 14

2 360 7 42

3 540 12 71

4 720 16 99

5 900 21 127

6 1080 26 156

7 1260 30 184

OH 1310 9 56

Total 124 750

7 x 180 ft. spans

Span1 2 3 4 5 6 7

Potential problems in the field

• Sprinkler installation or maintenance problems

• Inadequate pressure at pivot point to provide

desired flow rate and uniformity

• System capacity is not appropriate

• Sprinkler placement that decreases uniformity an

does not provide evaporation savings that many

expect

• Runoff due to inappropriate sprinkler selection or

system operation

• Inappropriate monitoring of systems to ensure

proper operation

How much water are you applying?

System capacity (gpm/ac)

System flow rate for land acres of:

Depth applied (in/day)

Depth applied (in/wk)

Time to apply one

inch (days)120 130 160 2403.0 360 390 480 720 0.16 1.1 6.33.5 420 455 560 840 0.19 1.3 5.44.0 480 520 640 960 0.21 1.5 4.74.5 540 585 720 1080 0.24 1.7 4.25.0 600 650 800 1200 0.27 1.9 3.85.5 660 715 880 1320 0.29 2.0 3.46.0 720 780 960 1440 0.32 2.2 3.16.5 780 845 1040 1560 0.34 2.4 2.97.0 840 910 1120 1680 0.37 2.6 2.77.5 900 975 1200 1800 0.40 2.8 2.58.0 960 1040 1280 1920 0.42 3.0 2.48.5 1020 1105 1360 2040 0.45 3.2 2.2

Sprinkler spacing• Follow manufacturer

recommendations

• Keep sprinklers out of canopy if possible

• If in canopy, reduce spacing

• Narrow spacing for expensive sprinklers may not be advisable

• Get in field to see how good the coverage is when the crops are tall

• Check runoff when lateral aligns with row direction

Sprinkler height

Pivot efficiency

Monitor pressure/flow rate

Runoff potential

0.0

0.5

1.0

1.5

2.0

2.5

0.00 0.15 0.25 0.35 0.45 0.55 0.65 0.75 0.85 1.05 1.15 1.25 1.35

Rat

e (i

nch

es/h

ou

r)

Time (hours)

Infiltration rate-How fast soil takes in water

Application rate-How fast water is applied

Runoff potential

0.0

0.5

1.0

1.5

2.0

2.5

0.00 0.15 0.25 0.35 0.45 0.55 0.65 0.75 0.85 1.05 1.15 1.25 1.35

Rat

e (i

nch

es/h

ou

r)

Time (hours)

Infiltration rate-How fast soil takes in water

Application rate-How fast water is applied

Surface storage amount ponded

Surfacesaturates

Runoff potential

0.0

0.5

1.0

1.5

2.0

2.5

0.00 0.15 0.25 0.35 0.45 0.55 0.65 0.75 0.85 1.05 1.15 1.25 1.35

Rat

e (i

nch

es/h

ou

r)

Time (hours)

Infiltration rate-How fast soil takes in water

Application rate-How fast water is applied

Surface storage amount ponded

Surfacesaturates

Runoff PotentialWater that can move in or leave the field

Runoff begins

Reducing runoff• Short term:

o Speed up the pivot

• Long termo Increase wetted diameter

o Reduce gpm into pivot – be careful to meet crop needs

o Increase surface storage

• Special tillage – dammer dike

• Increase residue on soil surface

o Increase soil infiltration rate

• Tillage

• No-till

Hard to manage what you don’t measure

• Schedule irrigations

• Measure soil water

• Monitor pivot

• Control

Summary• Get sprinkler chart & ensure package is properly installed

• Determine if system capacity is adequate for your

location

• Ensure that pump and pivot are properly matched

• Buy good pressure gauge and operate system at design

pressure

• Operate system when crops are small and look for broken,

plugged sprinklers or pressure regulators, other leaks

• Observe water application in the outermost span on the

steepest portion of the field to see if you have runoff, if

problems exist:o Reduce the application depth

o Use reduced tillage to enhance surface storage and infiltration

o Eventually evaluate if different sprinkler package would help

o Select devices with large droplet size when renozzling

• Routinely maintain mechanical/electrical components

Questions?

Caleb CarterExtension Educator, Goshen County(307) 532-2436ccarte13@uwyo.edu

Web: www.uwextension.org/highplainscropsite