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 1980’s

4. 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

5. What it is not Replacement for on site evaluations
A finite farm or field application efficiency, or specific deep percolation and runoff amounts

6. 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

7. 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

8. 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

9. 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.

10. Default Potential Efficiencies

11. Management Factors Water Measurement Factor
Irrigation Skill and Action Factor
Soil Moisture/Scheduling Factor

12. Water Delivery Factor
Maintenance Factor
Soil Condition Factor

13. System Factors for all Systems
Water Distribution Control Factor
Conveyance Efficiency Factor

15. Sprinkler System Factors
Climate Factor
Sprinkler Design Factor
Wind Factor

16. Surface System Factors
Land Leveling Factor
Tail water reuse factor

18. Micro System Factors Trickle Design Factor Climate Factor
Emitter Clogging Factor
Wind Factor

19. Rating Index
Surface Systems
Sprinkler System
Micro System

20. Very easy to put into a program

21. Or spreadsheet

22. FIRI use
Use extensively during the 1994 Irrigation induced erosion survey
Project ranking and comparison for NRCS programs (e.g. EQIP, CSP)

23. Example
Pasture irrigated by uncontrolled flood with 3000ft of earth ditch on sandy loam soil. Water delivered on a18 day rotation limited rate

24. 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

25. Present Condition System MGT= .9 x .94 x .96 x .98 x .85 x .98 = .663
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 x = 23.3

26. Future
Operator wants to change to a graded furrow system with land leveled fields and tail water reuse. Ditch replaced with gated pipe

27. 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

28. Future Condition System MGT = .96 x .94 x 1 x .98 x .85 x .98 = .737
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 x = 59.1

29. Compute the water conserved
Water conserved with seasonal net irrigation of 2 ac-feet/ac
Present
Ac-ft / ac
Future
Ac-ft / ac

30. Guide lines for deep percolation and runoff

31. 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
= 5.2 ac-ft/ac saved

32. 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.

33. 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.

34. Comparison of the two methods

35. 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