NRCS Farm Irrigation Rating
Index
History and Use
By
Clare Prestwich
Irrigation Engineer
NRCS National Water and Climate Center
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The Need
• A uniform and objective evaluation method
for planning irrigation water conservation
• Method of documenting present water use as
well as the effects of changes made by
improving both irrigation system and
management
• Reduce the need for difficult and time
consuming complete seasonal field
evaluations
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The Process
• Multidisciplinary team was
formed from several western
states and a national committee
• Basic data and procedures
originated as a result of a west
wide water conservation
emphasis program during the
1980’s
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The Results
• Farm Irrigation Rating Index (FIRI)
• Assist Offices
– Plan water management improvements
– Estimate water conserved by improved
management
– Estimate the runoff and deep percolation
– Provide a tool for follow up and
document accomplishment in water
management
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What it is not
• Replacement for on site evaluations
• A finite farm or field application
efficiency, or specific deep percolation
and runoff amounts
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What it is
• A procedure for comparing improvements
or changes
– Year to year
– Field, Farm and project level
• Relative rating
• A season long evaluation not a single
event
• Composed of three elements
– Management
– System
– Potential efficiency
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Management
• Water management is the human element.
Decisions scientifically based, knowledge
to operate the system, and maintenance
performed.
• The management element is defined by 6
factors
–
–
–
–
–
–
Water measurement
Soil moisture monitoring and scheduling
Irrigation skill
Maintenance
Water delivery constraint
Soil Condition
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System Element
• Factors selected according to irrigation
type
• System element is defined by nine factors
–
–
–
–
–
–
–
–
–
Water distribution control
Conveyance efficiency
Land leveling
Climatic
Sprinkler design
Wind
Tail water reuse
Emitter clogging
Trickle design
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Potential Efficiency Element
• A measure of the optimum application
efficiency for the method of irrigation
being used
• Values based on full canopy cover
and systems are well designed and
maintained.
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Default Potential Efficiencies
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Management Factors
Water Measurement Factor
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Irrigation Skill and Action Factor
Soil Moisture/Scheduling Factor
Water Delivery Factor
Maintenance Factor
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Soil Condition Factor
System Factors for all
Systems
Water Distribution Control Factor
Conveyance Efficiency Factor
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Sprinkler System Factors
Climate Factor
Sprinkler Design Factor
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Wind Factor
Surface System Factors
Land Leveling Factor
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Tail water reuse factor
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Micro System Factors
Trickle Design Factor
Emitter Clogging Factor
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Climate Factor
Wind Factor
Rating Index
FIRI  PE  SYS  MGT
SYS  Wc  Ce  L  R
 Wc  Ce  C W  Sd
Surface Systems
Sprinkler System
 Wc  Ce  C W  T  E
MGT  M d  S  I  M  D  Sc
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Micro System
Very easy to put into a
program
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Or spreadsheet
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FIRI use
• Use extensively during the 1994
Irrigation induced erosion survey
• Project ranking and comparison for
NRCS programs (e.g. EQIP, CSP)
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Example
Pasture irrigated by uncontrolled flood
with 3000ft of earth ditch on sandy
loam soil. Water delivered on a18 day
rotation limited rate
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Present condition
• Potential Efficiency - 50
• Management
– No water measurement .9
– Schedules based on Plant indicators .94
– Irrigation Skill – Lacks full attention
– Maintenance – good .98
– Water Delivery – fix rotation limited rate
.85
– Soil Condition – conservation tillage .98
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Present Condition
• System
–
–
–
–
Control at - Farm delivery .94
Conveyance – 3000ft earth ditch .91
Unleveled fields - .82
No tail water reuse -1.0
• MGT= .9 x .94 x .96 x .98 x .85 x .98 = .663
• SYS = .94 x .91 x .82 x 1 =.701
• FIRI = 50 x 0.663 x 0.701 = 23.3
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Future
• Operator wants to change to a graded
furrow system with land leveled fields
and tail water reuse. Ditch replaced
with gated pipe
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Future Condition
• Potential Efficiency – change to
graded furrow 50 to 75
• Management changes
– Add measuring device .90 to .96
– Scheduling - no change .94
– Irrigation skill - follows plan .96 to 1
– Maintenance - no change .98
– Delivery - no change .85
– Soil tillage - no change .98
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Future Condition
• System
–
–
–
–
Control – change to each set .94 to 1
Conveyance – change to gated pipe .91 to .99
Land – change to laser level .82 to 1
Add tail water reuse – change 1 to 1.08
• MGT = .96 x .94 x 1 x .98 x .85 x .98 = .737
• SYS = 1 x .99 x 1 x 1.08 = 1.069
• FIRI = 75 x 0.737 x 1.069 = 59.1
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Compute the water
conserved
• Water conserved with seasonal net
irrigation of 2 ac-feet/ac
Present
2
 8.6 Ac-ft / ac
.233
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Future
2
 3.4 Ac-ft / ac
.591
Guide lines for deep
percolation and runoff
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Problems
• Management Section has greatest weight
– More subjective to the person doing rating
• NRCS required to report water saved or
conserved
– FIRI rating taken as actually efficiency
– More water saved than available
• Most states restrict water rights to 4 to 5
ac-ft/ac
– From our example
• 8.6-3.4= 5.2 ac-ft/ac saved
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Possible changes
• Update Potential Efficiencies
• Add systems like LESA, MESA, SDI, etc.
• Update Management factors to reflex
current Technology
– Soil moisture/scheduling Flow measurement,
etc.
• Change computation method from straight
multiplication to a statistical method.
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• Original method
– PE x f1 x f2….x Fn
• Proposed method
– PE x (1-sqrt((1-f1)2+(1-f2)2….+(1-fn)2))
• The multiplication approach essentially assumes a
worst case scenario where each influence has full
weight regardless of the other factors
• The Statistical approach recognizes that if one
condition is poor, that the influence of another
variable is not as great as it would be if it were the
only problem.
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Comparison of the two
methods
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Value of FIRI
• Still an Effective tool
• Quick, uniform and provides reasonable
comparisons
• Users need to be realistic
– Better input gives better comparison
– Not meant for black box use
• Still a relative value
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