IRRIGATION EFFICIENCY
MODIFICATIONS
MERLIN N. NELSON
NRCS
1
Introduction
Basic system efficiencies
 Effects on Sprinklers by Pressure,
Terrain, and Wind
 Planning considerations
 Documentation tools and resources

2
System Types
3
LEPA - Bubbler mode 8”-18”
above soil, or drag socks
4
Efficiency Overview
NATIONAL IRRIGATION GUIDE

(Table 6-4)

–
–
–
–
–
Periodic move lateral
Traveling sprinkler (big guns)
Center pivot - standard
Linear (lateral) move
LEPA Center pivot or linear
60-75%
55-65%
75-85%
80-87%
90-95
5
Elevation changes in the field
6
Topic One --- Pressure
At Sprinkler Heads

Elevation changes within a field
– 2.3 feet of elev. change = 1 psi

System operation pressures
– STD. 442 allows a max. 20% pressure change
for sprinklers in a lateral. (i.e. 23 feet or 10 psi
friction loss max. for a 50 psi system)
7
Pressure effects pattern breakup
8
Typical Application Rates
9
Sprinkler pressure measurement
10
Topic Two --- Wind

Evaluations
11
NEH Section 15, Chapter 11
Table 11 - 9,10,11,12

40ft. x 60 ft. spacing --- 50 psi pressure


Wind
 0-4
 4-10
 10-15
 15-20

0.25 iph
11/64 nozzle
0.30 iph
3/16 nozzle
0.35 iph
13/64 nozzle
uniformity coefficient (CU)
85
85
84
81
83
84
74
78
81
70
73
74
12
3 Dimensional Patterns
13
Pattern graphic
14
Summary
Table 11-7 shows CU effects on 1.0 inch
gross application.
 Example: A CU of 74 % requires 1.0 inch
divided by 0.66 or 1.52 inch gross to irrigate
85% of the area adequately.
 A 75% efficient sprinkler that applies a
gross of 4 in. to get a net of 3 in., would
need to apply a gross of 6.04 in. for a 3 in.
net w/ 20 mph winds. Efficiency = 49.7%

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Where to get more information
Other training sessions - IWM II, III
 National and Montana Irrigation Guides
 National Engineering Handbook, Section
15, Chapter 11
 ASAE, other sources
 Request feedback of training session

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