Microirrigation design
Oregon NRCS Engineering Meeting
January 11-14, 2005
United States Department of Agriculture
NRCS
Natural
Resources
Conservation
Service




Over view
Water requirement –System Flow rate
Pressure requirement
Component design
Wind breaks/trees
Orchards
Vine crops
Nursery crops
High Dollar crops
Low Dollar crops
Water Quality

Water quality factors can be divided into three
major categories:



physical clogging caused mostly by suspended solids,
chemical clogging resulting from pH of the water,
dissolved solids, sodium, calcium, magnesium and
total iron and
biological clogging resulting from algae and bacterial
populations.
System Flow rate
NRCS Standards
Depth of application.
 Net depth of application shall be sufficient to
replace the water used by the plant during the
plant peak use period.
 Applications shall include adequate water for
leaching to maintain a steady state salt
balance.
.
Depth of application
Fn = 1.604 QNTE
AF
Where:
Fn = net application depth, in/day/design area
Q = discharge rate, gal/hr/emitter
N = number of orifices or emitters
T= hours of operation per day, 22 hours maximum
E = field application efficiency, expressed as a decimal, not
greater than 0.90 for design purposes.
A = ft2 of field area served by N (number of emitters)
F = the design area as a percentage of the field area, expressed as
a decimal
1.604 = units conversion constant
System capacity.

shall be adequate to meet the intended water
demands during the peak use period

shall include an allowance for reasonable
water losses (evaporation, runoff, and deep
percolation) during application periods.

shall have the capacity to apply a specified
amount of water to the design area within the
net operation period.
System capacity Continued

should have a minimum design capacity
sufficient to deliver the peak daily irrigation
water requirements in 90% of the time
available, but not to exceed 22 hours of
operation per day.

Field application efficiency (E) for design
purposes shall not exceed 90 percent.
Number and spacing of emitters.

shall be adequate to provide water distribution
to the plant root zone and percent plant
wetted area (Pw).
Wetted Area
Percent Wetted Area



For widely spaced crops such as vines, bushes,
and trees, a reasonable design objective is to
wet at least one-third and up to one-half of the
horizontal cross-sectional area of the root
system.
smaller Pw is favored for economic reasons.
rows spaced less than 6 ft. (1.83 m) apart, the
Pw may approach 100 %.
Wetted area single row
Wetted area single plant
Components of a Drip system
Subunit Design

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Plant and emitter spacing
Average emitter flow rate and allowable
pressure head variations
Desired number of operating stations
Overall length of plant rows in field or
subset
Number of plant rows in field or subset
Field topography
Emitter types


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Long path emitters,
Short orifice emitters,
Vortex emitters,
Pressure compensating emitters,
Porous pipe or tube emitters.
Emitter manufacturing variability
The manufacturer’s coefficient of variation
(CV) shall be less than 0.07 for point
source emitters and less than 0.20 for line
source emitters.
Emitters


Flow is characterized by
the following equation
q=kPx
K and x obtained from
manufacture
Lateral Design

Types of laterals


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Heavy wall drip line
Thin wall drip line
Drip tape
Polypipe with punch
emitters
Polypipe with sprays
Design Considerations



Select emitter/flow rate
Determine required operating pressure
Calculate friction loss


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Quick estimate use multiple outlet factor
Manufacture’s software
Built spreadsheet
Decide whether to use single or paired laterals
Make adjustments
Check with flushing conditions
8200
8100
8000
7900
7800
7700
7600
7500
7400
7300
7200
7100
7000
6900
98
107
106
6000
105
3
1
0
5200
6800
6800
6700
8200
8100
8000
7900
7800
7700
7600
7500
7400
7300
7200
7100
7000
6900
6200
104
10
102
10
10
99
6700
Slope and topography
6200
6100
6100
6000
5900
5900
5800
5800
5700
5700
5600
5600
5500
5500
5400
5400
99
5300
5300
5200
Hydraulics
J ' FL
hf 
100
F= multiple outlet factor
L= length of lateral (ft)
Q1.75  S e  f e 
 Q= lateral flow rate (gpm)
J '  .133 4.75 
D  Se 
Se= emitter spacing (ft)
L qa
Q
Fe= equivalent length of
S e 60
emitter connection loss
qa= average emitter flow
rate
Emission Uniformity

Emission Uniformity Rating
90 - 100% Excellent
80 - 90% Good
70 - 80% Fair
Less than 70% Poor
Cv  qmin

EU  1  1.27  
n  qave

Lateral Flow flat slope
Lateral Flow 2% downhill slope
Lateral flow 2% uphill slope
Lateral flow varied slope
Eurodrip program print out
Lateral flow Plot
System flushing.

Appropriate fittings shall be installed above
ground at the ends of all mains, submains,
and laterals to facilitate flushing. A minimum
flow velocity of 1 ft/sec is considered
adequate for flushing.
Manifold Design
Needed information

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Flow rate
Inlet location
Pipe sizes
Inlet pressure
Flow variation
Emissions uniformity
Below ground
Above ground
Allowable pressure variations.
Manifold and lateral lines.

shall be designed to provide discharge to any
applicator in an irrigation subunit operated
simultaneously such that they will not exceed
a total variation of 20 percent of the design
discharge rate.
Allowable Pressure Variations
Greatest Emitter Discharge - Smallest Emitter Discharge x 100
Average Emitter Discharge

This is reported in Percent and must be less than or
equal to 20%
99.5
100
F
44 Tapes
10 Acres
132 gpm
294'
.29-.23 x 100 = 25%
.24
Emitter Discharge Variation
H
F
John Progress
100
99.5
1485'
ACRES: 10.0
GPM:
80
ZONES: 1
Emitter Discharge Variation
The greatest emitter discharge minus the smallest emitter
discharge divided by the average emitter discharge,
multiplied by 100, within the block.
SYSTEM CAPABILITIES
EURODRIP 0.875 - 15 MIL
LATERAL SPACING: 80"
DESIGN ET: 0.29" / ACRE / 10 HOURS
FIELD SCHEDULING: 10 HOURS / ZONE
SECTION VALVE
Must be less than 20 %
VACUUM/RELIEF
FLUSH VALVE
742.5'
AIR RELIEF
742.5'
WATER SOURCE
FILTER STATION
MAIN LINE
99.5
N
F
BOOSTER PUMP
F
ZONE DIVISION LINE
H
HEADER LINE 3" PVC
F
FLUSH LINE 2" PVC
294'
F
99.5
44 Tapes
5.0 Acres
Emitter Discharge Variation 66 gpm
44 Tapes
.29-.27 x 100 = 7.1%
5.0 Acres
.28
66 gpm Emitter Discharge Variation
Scale
1" = 200'
100
.29-.27 x 100 = 7.1%
.28
H
F
100
Flushing

Method


Manual
Manifold
Size
 friction loss through manifold and valves


Frequency
Flush Manifold
Main line design

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Size
system flow rate
pressure loss
Filters

shall be provided at the system inlet. Under clean
conditions, filters shall be designed for a head loss of
5 psi or less.

shall be sized to prevent the passage of solids in
sizes or quantities that might obstruct the emitter
openings.

shall be designed to remove solids equal to or larger
than one-fourth the emitter opening diameter, or the
emitter manufacturer's recommendations, whichever
is more stringent

shall provide sufficient filtering capacity so that
backwash time does not exceed 10% of the system
operation time. Within this 10% time period, the
pressure loss across the filter shall remain within the
manufacturer's specification and not cause
unacceptable EU.

Filter/strainer systems designed for continuous
flushing shall not have backwash rates exceeding
1.0% of the system flow rate or exceeding the
manufacturer's specified operational head loss across
the filter.
Filter Design

Select Type

May need two


Pre-filter and primary filter
Size



Flow rate
Must account for pressure through filter
Must account for pressure required to back
flush
Disc Filters
Sand Media filter
Screen filters
Filter
summary
Chemigation.

System EU shall not be less than 85 percent.

Injectors and other automatic operating
equipment shall be located adjacent to the
pump and power unit, and include integrated
back flow prevention protection.

Shall be accomplished in the minimum length
of time needed to deliver the chemicals and
flush the pipelines.
Select an Injection System
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Fertilizer
Acid ( change ph, help against root
intrusion and clogging)
Chlorine ( prevent biological clogging)
Other water amendments
Pesticides
Need safety devices ( State regulations)
Injectors
Storage tanks
Pump Design


Calculate TDH
Size Pump
Miscellaneous
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Automatic controls
Pressure regulators
Air vents/valves
Summary

Determine Plant information

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Test water quality
Select emitter/sprayer

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Spacing row/plant
Water requirement
Irrigation frequency
Type
Spacing
Discharge
Emitter factors Cv, K, x
Design Lateral – normal/flushing



size
Flow rate
Pressure requirement

Design Manifold Header-Flushing/Subunits

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Design Mainline

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
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size
Flow rate
Pressure requirement
Emissions uniformity
Air valves
size
Flow rate
Pressure requirement
Select Filter system

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
Number/size
Flushing - disposal
Pressure requirement

Select injection system


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Type
Size
Safety considerations/features
Controls
Pump station


Flow rate
pressure