NRCS Farm Irrigation Rating Index

1
NRCS Farm Irrigation Rating Index

• History and Use
• By
• Clare Prestwich
• Irrigation Engineer
• NRCS National Water and Climate Center

2
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

3
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 1980s

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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
Irrigation Skill and Action Factor
Soil Moisture/Scheduling Factor
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Water Delivery Factor
Maintenance Factor
Soil Condition Factor
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System Factors for all Systems
Water Distribution Control Factor
Conveyance Efficiency Factor
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Sprinkler System Factors
Climate Factor
Sprinkler Design Factor
Wind Factor
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Surface System Factors
Land Leveling Factor
Tail water reuse factor
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Micro System Factors
Climate Factor
Trickle Design Factor
Emitter Clogging Factor
Wind Factor
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Rating Index
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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

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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