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 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. Surface Systems Sprinkler System Micro System Rating Index

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 • 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

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 • 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

29. Future Present Ac-ft / ac Ac-ft / ac Compute the water conserved • Water conserved with seasonal net irrigation of 2 ac-feet/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 • 8.6-3.4= 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