NRCS Farm Irrigation Rating Index History and Use By Clare Prestwich Irrigation Engineer NRCS National Water and Climate Center

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

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

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

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

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

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

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

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.

Default Potential Efficiencies

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

Water Delivery Factor Maintenance Factor Soil Condition Factor

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

Sprinkler System Factors Climate Factor Sprinkler Design Factor Wind Factor

Surface System Factors Land Leveling Factor Tail water reuse factor

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

Rating Index Surface Systems Sprinkler System Micro System

Very easy to put into a program

Or spreadsheet

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

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

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

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 0.663 x 0.701 = 23.3

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

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

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 0.737 x 1.069 = 59.1

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

Guide lines for deep percolation and runoff

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

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.

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.

Comparison of the two methods

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