Prepared in cooperation with the Bureau of Reclamation and Colorado River Basin Salinity 

Control Forum

Analysis of Historic Agricultural Irrigation Data from the 

Natural Resources Conservation Service Monitoring and 

Evaluation for Grand Valley, Lower Gunnison Basin, and 

McElmo Creek Basin, Western Colorado, 1985 to 2003

Open-File Report 2014–1261

U.S. Department of the Interior

U.S. Geological Survey
Front cover: Top left, typical weather station measuring wind run, solar radiation, maximum-minimum temperatures, relative humidity, and precipitation; top right, 

pressure transducer to measure air pressure. Middle left, Datapod and housing box; middle right, Datapod, interface, and signal conditioner for a magnetic induction 

pipeline flow sensor. Bottom right, typical inflow installation with a stilling well and float potentiometer.
Analysis of Historic Agricultural Irrigation 

Data from the Natural Resources 

Conservation Service Monitoring and 

Evaluation for Grand Valley, Lower 

Gunnison Basin, and McElmo Creek Basin, 

Western Colorado, 1985 to 2003

By John W. Mayo

Prepared in cooperation with the Bureau of Reclamation and Colorado River 

Basin Salinity Control Forum

Open-File Report 2014–1261

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2015

For more information on the USGS—the Federal source for science about the Earth, its natural and living 

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U.S. Government.

Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Mayo, J.W., 2015, Analysis of historic agricultural irrigation data from the Natural Resources Conservation 

Service monitoring and evaluation for Grand Valley, Lower Gunnison Basin, and McElmo Creek Basin, western 

Colorado, 1985 to 2003: U.S. Geological Survey Open-File Report 2014–1261, 176 p., http://dx.doi.org/

10.3133/ofr20141261.

ISSN 2331-1258 (online)
iii

Acknowledgments

While the USGS study found discrepancies in some of the results of the NRCS evaluation, 

the author of the USGS study respectfully recognizes the work performed by the NRCS staff to 

complete such a complex and long-running effort of field data collection and data analysis. The 

number of site-years evaluated over three salinity control units, with each site often requiring 

daily visits, would be very difficult to replicate today. Given the time frame that the evaluation 

was begun (early 1980s), electronic data collection instruments and office computer technologies were then in their infancy. The analysis software for the NRCS evaluation was hand coded 

in the Basic programming language and run on an early Tandy home computer. If errors in 

definitions in the analysis software occurred at the beginning of the evaluation, it would have 

been difficult to recognize those errors, and even more difficult to have the software modified 

later. The pioneering efforts by the staff of the NRCS evaluation to overcome many technical 

obstacles along the way led to the successful completion of a complex and worthwhile project. 

Overall, the results of the NRCS evaluation have been accurate and consistent and have provided real value to the salinity control activities in the Colorado River Basin.

Thanks are extended to Frank Riggle, NRCS, former Assistant State Conservationist 

for Water Resources (retired), NRCS, Denver, Colo. The original project was envisioned by 

Frank, and without his frequent consultation, this report would not have been possible. Thanks 

also to Travis James, Colorado River Basin Salinity Coordinator, NRCS, Salt Lake City, Utah; 

Jason Peel, Irrigation Water Management Specialist, NRCS, Denver, Colo.; Bob Rayer, Soil 

Survey Project Leader, NRCS, Grand Junction, Colo.; Denis Reich, former Water Resource 

Specialist, CSU Extension Service, Grand Junction, Colo.; Dr. Calvin Pearson, Agronomist, 

CSU Western Colorado Research Station, Grand Junction, Colo.; Dr. Horst Caspari, Viticulturist, CSU Western Colorado Research Station, Grand Junction, Colo.; Tom Trout, Research 

Leader, USDA–Agricultural Research Service, Fort Collins, Colo.; Dick Bartholomay, CSU 

Extension Service (retired), Grand Junction, Colo.; Dr. Lorenz Sutherland, former Conservation Agronomist (retired), NRCS, La Junta, Colo., and John Sottilare, Bureau of Reclamation, 

Grand Junction, Colo.
iv

Contents

Acknowledgments........................................................................................................................................iii

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................2

Purpose and Scope of the USGS Study ...........................................................................................3

Description of NRCS Evaluation Salinity Control Units ..................................................................3

USGS Study Methods....................................................................................................................................5

Interviews with NRCS Evaluation Staff.............................................................................................5

NRCS Printed Documentation ............................................................................................................5

Characterization of NRCS Evaluation Field Methods .....................................................................5

Analysis of the NRCS Evaluation Dataset.........................................................................................5

NRCS Evaluation Methods ...........................................................................................................................5

NRCS Data Collection Procedures ....................................................................................................6

NRCS Soil Moisture and Crop Evapotranspiration Determination ...............................................6

NRCS Equipment...................................................................................................................................7

NRCS Field Procedures .....................................................................................................................12

NRCS Dataset......................................................................................................................................12

USGS Study Findings on NRCS Evaluation..............................................................................................15

NRCS Annual Reports ........................................................................................................................15

NRCS Methods....................................................................................................................................16

Statistical Analysis of the NRCS Dataset .......................................................................................16

Temporal Analysis of NRCS Sites............................................................................................16

Types of Irrigation Systems and Crops Evaluated by Year..................................................20

Creation of NRCS Evaluation Site Maps ................................................................................22

Irrigation System Improvement Order....................................................................................25

Soil Physical and Chemical Properties ..................................................................................25

Site-Year Record Quality Determination................................................................................27

Summary Statistics and Charts of NRCS Evaluation ...........................................................28

Frequency Charts..............................................................................................................34

Deep Percolation versus Seasonal Irrigation Efficiency ...........................................37

Seasonal Irrigation Efficiency and Irrigation System Type........................................45

Deep Percolation and Crop Type....................................................................................50

Seasonal Irrigation Efficiency and Crop Type..............................................................54

Multiple Comparison Statistics ...............................................................................................58

Soil Moisture Balance Models.........................................................................................................60

Soil Moisture Balance Calculations .......................................................................................60

Soil Moisture Balance Inputs ..................................................................................................61

Evapotranspiration for Soil Moisture Balance Models..............................................61

Reference Evapotranspiration...............................................................................61

Crop Evapotranspiration Coefficient ....................................................................61

Stress Correction of Crop Evapotranspiration....................................................63

Site Physical Parameters for Soil Moisture Balance Models...................................64

Precipitation for Soil Moisture Balance Models.........................................................65

Irrigation Events for Soil Moisture Balance Models ..................................................68
v

Worksheets in the Soil Moisture Balance Model Spreadsheets ......................................69

Soil Moisture Balance Charts..................................................................................................70

Soil Moisture Balance Curve Best-Fit Procedures..............................................................76

Results for Baseline-Fit of Soil Moisture Balance Curves..................................................79

Baseline-Fit of Crop Evapotranspiration.......................................................................80

Baseline-Fit of Soil Moisture Balance Deep Percolation ..........................................81

Baseline-Fit of Seasonal Irrigation Efficiency .............................................................82

Potential Discrepancies in Results between SMB Models and NRCS Evaluation.........83

Quantifiable Discrepancies.............................................................................................84

Precipitation Discrepancies ..................................................................................84

Types of Evapotranspiration Discrepancies........................................................84

Reference Evapotranspiration Discrepancies....................................................84

Crop Consumptive Use Discrepancies.................................................................86

Crop Evapotranspiration Discrepancies..............................................................88

Crop Evapotranspiration Stress Correction Discrepancies .............................89

Irrigation Water Application Timing Discrepancies...........................................90

Non-Quantifiable Discrepancies....................................................................................90

Discrepancies due to Lack of NRCS Field Tests for Soil Water

Deficit Values ..............................................................................................90

Discrepancies due to Precipitation Data Collection Changes.........................90

Discrepancies due to Deep percolation Calculation changes ........................91

Seasonal Irrigation Efficiency Calculation Changes .........................................91

Undocumented NRCS Data Corrections..............................................................91

Discrepancies Due to Software Problems ..........................................................91

Discrepancies Due to Human Error......................................................................91

Sensitivity Analysis of SMB Models.......................................................................................92

Sensitivity Test Inputs ......................................................................................................92

Sensitivity Test Outputs....................................................................................................92

Crop Evapotranspiration Sensitivity Test Results........................................................92

DP Sensitivity Test Results ..............................................................................................93

Flood Irrigation DP Sensitivity Test Results.........................................................93

Sprinkler Irrigation DP Sensitivity Test Results ..................................................95

Seasonal Irrigation Efficiency Sensitivity Test Results ..............................................97

Flood Irrigation SIE Sensitivity Test Results ........................................................98

Sprinkler and Microspray Irrigation SIE Sensitivity Test Results....................99

Summary Tables of Sensitivity Test Results ...............................................................100

Flood Irrigation Sites .............................................................................................100

Sprinkler and Microspray Irrigation Sites .........................................................100

Suggested Revisions to NRCS Evaluation Results...........................................101

Summary......................................................................................................................................................102

References Cited........................................................................................................................................104

NRCS Evaluation Glossary........................................................................................................................106

Appendix 1. Contact Information for Research Access to NRCS Evaluation Data and

Instructions for Requests to Access the Data ........................................................................107

Appendix 2. Natural Resources Conservation Service (NRCS) Evaluation Software and 

Data Instructions for NRCS staff ...............................................................................................108
vi

Appendix 3. Additional NRCS Evaluation Summary Statistics ...........................................................136

Appendix 4. Additional Box Plot Charts .................................................................................................139

Appendix 5. Additional Multiple Comparison Tables ...........................................................................150

Appendix 6. Columns in the soil moisture balance deep percolation worksheet...........................156

Appendix 7. All Soil Moisture Balance Charts......................................................................................157

Appendix 8. Derivation of NRCS Evaluation Crop Coefficient Curves...............................................169

Appendix 9. 1988 Colorado Irrigation Guide Consumptive Use Tables for Grand Junction 

and Fruita.......................................................................................................................................173

Figures

1. Natural Resources Conservation Service evaluation salinity control units in

western Colorado .........................................................................................................................3

2. Photograph of a linear strip gage installed in an existing concrete weir...........................8

3. Photograph of a typical installed broad-crested weir with a linear strip gage .................9

4. Photograph of a typical inflow installation with a stilling well and float potentiometer ..9

5. Photograph of a typical weather station measuring wind run, solar radiation,

maximum-minimum temperatures, relative humidity, and precipitation.............................9

6. Photograph of a typical outflow installation with pressure transducer............................10

7. Photograph of a Datapod and housing box............................................................................10

8. Photograph of a Datapod, interface, and signal conditioner for a magnetic

induction pipeline flow sensor .................................................................................................10

9. Photograph of a magnetic induction flow sensor with signal conditioner and

Datapod recorder .......................................................................................................................11

10. Photograph of a pressure transducer to measure air pressure.........................................11

11. Photograph of a closed cell to generate air pressure for the pressure transducer

designed by Tom Trout, USDA-Agricultural Research Service, Kimberly, Idaho.............11

12. Irrigation systems monitored by evaluation year and irrigation system type from

1985 to 2003 for all usable site records in the Grand Valley, Lower Gunnison, and

McElmo Creek Units...................................................................................................................20

13. Deep percolation at Grand Valley Unit site 15 from 1985 through 1992 with constant

irrigation type and varying crop types ....................................................................................21

14. Seasonal irrigation efficiency at Grand Valley Unit site 21 from 1985 through 1995

with varying crop types and irrigation methods....................................................................22

15. Map of all Natural Resources Conservation Service evaluation site locations in the

Grand Valley Unit, western Colorado ......................................................................................23

16. Map of reported Natural Resources Conservation Service evaluation site locations

in the Lower Gunnison Unit, western Colorado.....................................................................24

17. Frequency chart of irrigation system types by system improvement order1 for all

usable sites in Grand Valley, Lower Gunnison, and McElmo Creek Units ........................34

18. Frequency chart of seasonal irrigation efficiency for all usable sites in Grand Valley, 

Lower Gunnison, and McElmo Creek Units............................................................................35

19. Frequency chart of deep percolation for all usable sites in Grand Valley, Lower

Gunnison, and McElmo Creek Units ........................................................................................36

20. Frequency chart of irrigation event duration in days for all usable sites in Grand

Valley, Lower Gunnison, and McElmo Creek Units ...............................................................37
vii

21. Scatter plot chart with LOESS trend line of deep percolation versus seasonal

irrigation efficiency for all usable Grand Valley, Lower Gunnison, and McElmo

Creek Unit sites from 1985 to 2003 ...........................................................................................38

22. Scatter plot chart with LOESS trend line of deep percolation versus seasonal

irrigation efficiency for Grand Valley Unit gold standard sites...........................................40

23. Box plot chart of deep percolation versus irrigation system types in order of

improvement (1–9) for all usable Grand Valley, Lower Gunnison, and McElmo Creek

Unit sites. .....................................................................................................................................42

24. Box plot chart of deep percolation versus irrigation system types in order of

improvement (1–9) for Grand Valley Unit gold standard sites.............................................43

25. Box plot chart of deep percolation versus irrigation system improvement order for

Lower Gunnison Unit gold standard sites...............................................................................44

26. Box plot chart of deep percolation versus irrigation system improvement order for

McElmo Creek Unit gold standard sites..................................................................................45

27. Box plot chart of seasonal irrigation efficiency versus irrigation system

improvement order for all usable sites in the Grand Valley, Lower Gunnison, and

McElmo Creek Units...................................................................................................................46

28. Box plot chart of seasonal irrigation efficiency versus irrigation system

improvement order for Grand Valley Unit gold standard sites............................................47

29. Box plot chart of seasonal irrigation efficiency versus irrigation system

improvement order for Lower Gunnison Unit gold standard sites .....................................48

30. Box plot chart of seasonal irrigation efficiency versus irrigation system

improvement order for McElmo Creek Unit gold standard sites ........................................49

31. Box plot chart of deep percolation versus crop type for all gold standard sites ............50

32. Box plot chart of deep percolation versus crop type for all gold standard flood

irrigation sites..............................................................................................................................51

33. Box plot chart of deep percolation versus crop type for all gold standard sprinkler

irrigation sites..............................................................................................................................52

34. Box plot chart of deep percolation versus crop type for all gold standard

microspray sites..........................................................................................................................53

35. Box plot chart of seasonal irrigation efficiency versus crop type for all gold

standard sites..............................................................................................................................54

36. Box plot chart of seasonal irrigation efficiency versus crop type for all gold

standard flood irrigation sites...................................................................................................55

37. Box plot chart of seasonal irrigation efficiency versus crop type for all gold

standard sprinkler irrigation sites............................................................................................56

38. Box plot chart of seasonal irrigation efficiency versus crop type for all gold

standard microspray sites.........................................................................................................57

39. Generalized crop coefficient curve Kc from United Nations Food and Agriculture

Organization Irrigation and Drainage Paper No. 56..............................................................62

40. Natural Resources Conservation Service evaluation crop coefficient curve for a

typical irrigation season ............................................................................................................63

41. Crop stress coefficient curve ...................................................................................................64

42. Comparison between mean season total effective precipitation for four Grand

Valley weather stations and mean season total Natural Resources Conservation

Service evaluation reported precipitation, corrected for effective precipitation, for

Grand Valley Unit gold standard sites from 1985 and 1995..................................................66

43. Precipitation comparisons for four Grand Valley weather stations with Natural

Resources Conservation Service evaluation reported precipitation.................................67
viii

44. Distribution of irrigation event durations in days for 12 soil moisture balance 

models ..........................................................................................................................................68

45. Soil moisture balance chart for Grand Valley Unit 1993 site 53, an alfalfa site with a

pipeline to gated surge irrigation system...............................................................................70

46. Soil moisture balance chart for Grand Valley Unit 1989 site 33, an alfalfa site with a

side-roll sprinkler irrigation system.........................................................................................72

47. Soil moisture balance chart for Grand Valley Unit 1989 site 27, a field corn site with

a pipeline to gated pipe flood irrigation system ....................................................................73

48. Soil moisture balance chart for Grand Valley Unit 1989 site 17, a wine grapes site

with a microspray sprinkler irrigation system .......................................................................74

49. Soil moisture balance chart for Grand Valley Unit 1991 site 49, a fall grain site with

a concrete ditch to gated pipe flood sprinkler irrigation system........................................75

50. Example of an SMB chart with a low value for the crop coefficient amplitude ..............77

51. Example of an SMB chart with a high value for the crop coefficient amplitude.............78

52. Example of an SMB chart with a value selected for the best-fit of the soil moisture

balance trace ..............................................................................................................................79

53. Chart of SMB model calculated season total crop evapotranspiration versus

Natural Resources Conservation Service evaluation reported season total crop

evapotranspiration showing site number, irrigation method (table 8), total days of

irrigation (d), and crop type for 12 Grand Valley SMB model sites ....................................81

54. Chart of season-total SMB model deep percolation versus Natural Resources

Conservation Service reported deep percolation for 12 Grand Valley SMB model

sites...............................................................................................................................................82

55. Chart of SMB model seasonal irrigation efficiency versus NRCS reported seasonal

irrigation efficiency for 12 Grand Valley SMB model sites..................................................83

56. Comparison between CoAgMet ETp with NRCS evaluation ETp for Fruita in 1992.........85

57. Comparison between Colorado State University CoAgMet ETp with Natural

Resources Conservation Service NRCS evaluation ETp for Grand Junction in 1993......86

58. Histogram of percent difference between Natural Resources Conservation Service

reported crop evapotranspiration and 1988 Colorado Irrigation Guide consumptive

use for all Grand Valley Unit gold standard sites ..................................................................87

59. Comparison between 1988 Colorado Irrigation Guide consumptive use and NRCS

reported ETc for the 12 soil moisture balance sites..............................................................88

60. Example of ZETA.wks spreadsheet crop coefficient curve with software coding

error in ZETA.wks program .......................................................................................................89

61. Sensitivity test results in soil moisture balance model deep percolation in inches

of water for flood irrigation system types...............................................................................94

62. Sensitivity test results in soil moisture balance model deep percolation in

relative percent difference for flood irrigation system types..............................................95

63. Sensitivity test results for soil moisture balance model deep percolation in inches

of water for sprinkler and microspray irrigation system types...........................................96

64. Sensitivity test results for soil moisture balance model deep percolation in relative

percent difference for sprinkler and microspray irrigation system types ........................97

65. Sensitivity test results for soil moisture balance model seasonal irrigation

efficiency in relative percent difference for flood irrigation system types.......................98

66. Sensitivity test results for soil moisture balance model seasonal irrigation

efficiency in relative percent difference for sprinkler irrigation system types................99

4-1. Box plot of deep percolation by soil type1 for all usable evaluation site-years ............140
ix

4-2. Box plot of seasonal irrigation efficiency by soil type1 for all usable evaluation

site-years ...................................................................................................................................141

4-3. Box plot of crop evapotranspiration by soil type1 for all usable evaluation

site-years ...................................................................................................................................142

4-4. Box plot of irrigation water infiltrated depth by soil type1 for all usable evaluation

site-years ...................................................................................................................................143

4-5. Box plot of deep percolation by crop rooting depth for all usable evaluation

site-years ...................................................................................................................................144

4-6. Box plot of seasonal irrigation efficiency by crop rooting depth for all usable

evaluation site-years................................................................................................................145

4-7. Box plot of irrigation water infiltrated depth by soil type for all usable evaluation

site-years ...................................................................................................................................146

4-8. Box plot of crop evapotranspiration by crop rooting depth for all usable evaluation

site-years ...................................................................................................................................147

4-9. Box plot of crop evapotranspiration by irrigation system type in improvement order

for all usable evaluation site-years .......................................................................................148

4-10. Box plot of irrigation water infiltrated depth by irrigation system type in

improvement order for all usable evaluation site-years ....................................................149

7-1. Soil moisture balance chart for Grand Valley Unit 1989 site 12, an alfalfa site with a

concrete ditch to siphon tube irrigation system..................................................................157

7-2. Soil moisture balance chart for Grand Valley Unit 1989 site 21, a newly-fall-seeded

alfalfa site with a pipeline to gated pipe irrigation system................................................158

7-3. Soil moisture balance chart for Grand Valley Unit 1989 site 33, a newly-fall-seeded

alfalfa site with a side-roll sprinkler irrigation system.......................................................159

7-4. Soil moisture balance chart for Grand Valley Unit 1993 site 33, an alfalfa site with a

side-roll sprinkler irrigation system.......................................................................................160

7-5. Soil moisture balance chart for Grand Valley Unit 1989 site 36, an alfalfa site with a

side-roll sprinkler irrigation system.......................................................................................161

7-6. Soil moisture balance chart for Grand Valley Unit 1993 site 36, an alfalfa site with a

side-roll sprinkler irrigation system.......................................................................................162

7-7. Soil moisture balance chart for Grand Valley Unit 1993 site 53, an alfalfa site with a

pipeline to gated surge irrigation system.............................................................................163

7-8. Soil moisture balance chart for Grand Valley Unit 1993 site 58, an alfalfa site with

an earth ditch to siphon tube irrigation system...................................................................164

7-9. Soil moisture balance chart for Grand Valley Unit 1989 site 17, a wine grapes site

with a microspray irrigation system......................................................................................165

7-10. Soil moisture balance chart for Grand Valley Unit 1989 site 26, a grain corn site with

a pipeline to gated pipe irrigation system ............................................................................166

7-11. Soil moisture balance chart for Grand Valley Unit 1989 site 27, a grain corn site with

a pipeline to gated pipe irrigation system. The corn crop was cut for silage................167

7-12. Soil moisture balance chart for Grand Valley Unit 1991 site 49, a fall grain site with

a concrete ditch to gated pipe irrigation system ................................................................168

9-1. Map of Colorado climate zones for crop consumptive use of water...............................174

9-2. Table of estimated seasonal crop consumptive use for Grand Junction, Colo..............175

9-3. Table of estimated seasonal crop consumptive use for Fruita, Colo...............................176
x

Tables

1. Characteristics of Grand Valley, Lower Gunnison, and McElmo Creek salinity

control units...................................................................................................................................4

2. Typical equipment purchased for Natural Resources Conservation Service 

evaluation.......................................................................................................................................8

3. Natural Resources Conservation Service evaluation annual report summary for the

Grand Valley Unit, 1985 to 2003.................................................................................................12

4. Natural Resources Conservation Service evaluation annual report summary for the

Lower Gunnison Unit, 1990 to 2003. .........................................................................................13

5. Natural Resources Conservation Service evaluation annual report summary for the

McElmo Creek Unit, 1993...........................................................................................................14

6. Years of site evaluations by site number for the Grand Valley Unit, western 

Colorado .......................................................................................................................................17

7. Years of site evaluations by site number for the Lower Gunnison Unit, western

Colorado .......................................................................................................................................19

8. Irrigation system types in order of improvement ..................................................................25

9. Original Natural Resources Conservation Service evaluation soil types, the

equivalent current soil type name, and a soil type code created for the USGS study

for all NRCS evaluation soil types............................................................................................26

10. Soil physical and chemical properties retrieved for Natural Resources

Conservation Service evaluation soil types ...........................................................................27

11. Number of usable and not usable site-year records by evaluation unit...........................28

12. Discrete variable summary statistics for all gold standard site records collected

between 1985 and 1996 in the Natural Resources Conservation Service evaluation.....28

13. Discrete variable summary statistics for only Grand Valley Unit gold standard site

records collected between 1985 and 1995 in the Natural Resources Conservation

Service evaluation......................................................................................................................29

14. Discrete variable summary statistics for only Lower Gunnison Unit gold standard

site records collected between 1991 and 1996 in the Natural Resources

Conservation Service evaluation .............................................................................................30

15. Discrete variable summary statistics for only McElmo Creek Unit gold standard 

site records collected in 1993 in the Natural Resources Conservation Service 

evaluation.....................................................................................................................................30

16. Continuous variable summary statistics for all gold standard site records collected

between 1985 and 1996 in Natural Resources Conservation Service evaluation............30

17. Continuous variable summary statistics for Grand Valley Unit gold standard site

records collected between 1985 and 1995 in Natural Resources Conservation

Service evaluation......................................................................................................................31

18. Continuous variable summary statistics for Lower Gunnison Unit gold standard site

records collected between 1991 and 1996 in Natural Resources Conservation

Service evaluation......................................................................................................................31

19. Continuous variable summary statistics for McElmo Creek Unit gold standard site

records collected during 1993 in Natural Resources Conservation Service 

evaluation.....................................................................................................................................32

20. Annual mean results by Unit and year for all reported Natural Resources

Conservation Service evaluation site records.......................................................................32

21. Annual Mean results by unit and year for gold standard Natural Resources

Conservation Service evaluation site records.......................................................................33
xi

22. Summary table of LOESS predicted values of deep percolation and seasonal

irrigation efficiency from figure 21...........................................................................................39

23. Summary table of LOESS predicted values of deep percolation and seasonal

irrigation efficiency from figure 22...........................................................................................41

24. Multiple comparisons performed on Natural Resources Conservation Service

evaluation dataset with yes-no indication of significant correlations for all usable

site-year records ........................................................................................................................58

25. Differences in median irrigation efficiency by system improvement order for all

usable site-year records ...........................................................................................................59

26. Multiple comparisons of deep percolation by improvement order irrigation system

type codes for all usable site-year records ...........................................................................59

27. Summary of sites selected from Natural Resources Conservation Service

evaluation dataset for soil moisture balance modeling.......................................................60

28. Site physical parameters required as inputs for soil moisture balance models .............65

29. Natural Resources Conservation Service evaluation reported irrigation event

details for the 12 Grand Valley Unit sites with soil moisture balance models..................68

30. Explanation of soil moisture balance chart elements ..........................................................71

31. Comparison between Natural Resources Conservation Service evaluation reported

deep percolation, precipitation, crop evapotranspiration, and seasonal irrigation

efficiency with soil moisture balance model results ............................................................80

32. Comparison between Natural Resources Conservation Service reported values

and eight sensitivity test results for mean season total ETc. at 12 SMB model sites .....93

33. Mean sensitivity test results for the seven SMB model flood irrigation sites for

deep percolation and seasonal irrigation efficiency..........................................................100

34. Mean sensitivity test results for the four sprinkler irrigation and one microspray

SMB model sites for deep percolation and seasonal irrigation efficiency ....................101

35. Suggested revisions to NRCS evaluation results................................................................101

3-1. Discrete variable summary statistics for all usable records collected between

1985 and 2003 in Natural Resources Conservation Service evaluation ..........................136

3-2. Continuous variable summary statistics for all usable records in all evaluation

units collected between 1985 and 2003 in Natural Resources Conservation

Service evaluation....................................................................................................................137

3-3. Discrete variable summary statistics for all nongold standard records, whether

usable or not, collected between 1985 and 2003 in Natural Resources

Conservation Service evaluation ...........................................................................................137

3-4. Continuous variable summary statistics for all nongold standard records, 

whether usable or not, collected between 1985 and 2003 in Natural Resources 

Conservation Service evaluation ...........................................................................................138

5-1. Table of irrigation system improvement order, type codes, and descriptions ...............150

5-2. Multiple comparison table of seasonal irrigation efficiency by crop type .....................150

5-3. Multiple comparison table of deep percolation by crop type...........................................151

5-4. Multiple comparison table of crop evapotranspiration by crop type ..............................151

5-5. Multiple comparison table of seasonal irrigation efficiency by soil type .......................152

5-6. Multiple comparison table of deep percolation by soil type.............................................152

5-7. Multiple comparison table of irrigation water infiltrated depth by soil type ..................153

5-8. Multiple comparison table of seasonal irrigation efficiency by evaluation unit............153

5-9. Multiple comparison table of deep percolation by evaluation unit .................................153

5-10. Multiple comparison table of crop evapotranspiration by evaluation unit.....................154
xii

Conversion Factors and Datum

Inch/Pound to SI

Multiply By To obtain

Length

inch 2.54 centimeter (cm)

foot (ft) 0.3048 Meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 0.4047 square kilometer (km2

)

Flow rate

gallons per minute (gal/min) 0.0022 cubic feet per second

Altitude as used in this report refers to distance above mean sea level.

5-11. Multiple comparison table of irrigation water infiltrated depth by evaluation unit.......154

5-12. Multiple comparison table of crop evapotranspiration by Natural Resources

Conservation Service evaluation gold standard years ......................................................154

5-13. Multiple comparison table of seasonal irrigation efficiency by crop rooting depth.....155

5-14. Multiple comparison table of deep percolation by crop rooting depth...........................155

5-15. Multiple comparison table of crop evapotranspiration by crop rooting depth..............155

6-1. Columns in the soil moisture balance deep percolation worksheet................................156

8-1. Sample crop data from Natural Resources Conservation Service evaluation crop

evapotranspiration spreadsheet “ZETA.wks” from 1999 ...................................................170

8-2. Sample before full cover constant values from Natural Resources Conservation

Service evaluation crop evapotranspiration spreadsheet “ZETA.wks” from 1999 .......171

8-3. Sample after full cover constant values from Natural Resources Conservation

Service evaluation crop evapotranspiration spreadsheet “ZETA.wks” from 1999 .......172
Analysis of Historic Agricultural Irrigation Data from the 

Natural Resources Conservation Service Monitoring and 

Evaluation for Grand Valley, Lower Gunnison Basin, and 

McElmo Creek Basin, Western Colorado, 1985 to 2003

By John W. Mayo

Abstract

The Natural Resources Conservation Service (NRCS) Monitoring and Evaluation (NRCS evaluation) for three salinity 

control units in western Colorado (Grand Valley, Lower Gunnison, and McElmo Creek) from 1985 to 2003 was a response to the 

Colorado River Basin Salinity Control Act (Public Law 93–320, July 24, 1974) and its amendments. The NRCS evaluated the 

effects on seasonal irrigation efficiency and deep percolation of irrigation water of various on-farm irrigation system improvements in the three salinity control units, and reported the results in a series of internal NRCS annual reports. Because of the large 

amount of effort and expense that went into the NRCS evaluation and the importance of the data to help quantify the changes 

to deep percolation, the NRCS has determined that having the evaluation results made public through a characterization and 

analysis of the results by the U.S. Geological Survey (USGS) could be of use to a wider audience of water managers and the 

general public. In 2011, the USGS, in cooperation with the Bureau of Reclamation and the Colorado River Basin Salinity Control Forum, began a study to evaluate the NRCS evaluation data to (1) document the methods of the evaluation, and (2) analyze 

and summarize the data collected during the evaluation. USGS scientists examined over 1,800 pages of NRCS evaluation annual 

reports, characterized the field methods of the evaluation, and rated the quality of the 292 site-years of data using criteria of 

completeness and internal consistency: in all, 268 records were usable, and 225 of the usable site-year records were of exceptional quality. USGS created a set of summary statistics and charts for the NRCS evaluation results. An order of technology 

improvement for the irrigation system types monitored in the NRCS evaluation was devised to rank the irrigation system types. 

It was found that as irrigation systems improve in technology, deep percolation (DP) of irrigation water decreases and 

seasonal irrigation efficiency (SIE) increases. The variance of DP decreases as irrigation system technology improves, while 

variance of SIE did not change with improvement order. When DP was plotted against SIE, a fitted curve showed that DP 

decreases at a steep rate as SIE increases from about 10 to 35 percent; for values of SIE above 35 percent, DP decreases more 

slowly. This has implications for the funding of irrigation improvement projects by NRCS. USGS created soil moisture balance (SMB) spreadsheet models for 12 Grand Valley Unit sites for a detailed examination of the NRCS results at those sites. In 

achieving a fit of SMB model results to NRCS results, several types of potential discrepancies were found. USGS explored possible sources of quantifiable and nonquantifiable discrepancies in the NRCS evaluation methodology and results. Mean seasontotal crop consumptive use of irrigation water for all Grand Valley Unit NRCS evaluation sites was found to be about 10 percent 

lower than 1988 Colorado Irrigation Guide published values for the Grand Valley. Mean annual Grand Valley weather station 

precipitation from 1985 to 1995 was 7.2 inches, while NRCS reported mean annual precipitation for the same period was only 

3.8 inches. To explore these discrepancies, sensitivity tests were performed on the SMB models by (1) changing weather station 

data sources, (2) using crop evapotranspiration stress correction or not, and (3) raising reference evapotranspiration to increase 

crop consumptive use to meet 1988 Colorado Irrigation Guide published values. There were no meaningful changes in SMB 

model results for either flood or sprinkler and microspray sites for variations of weather station precipitation data sources, for 

use of evapotranspiration stress correction or not, or for setting reference evapotranspiration at 100 percent of NRCS reported 

values. However, increasing reference evapotranspiration by 10 percent yielded possibly meaningful changes in SMB model DP 

and SIE for flood irrigation sites. For flood irrigation sites at 110 percent of reference evapotranspiration, mean DP decreased by 

12.5 relative percent (2.5 inches) and mean SIE increased by 2.4 relative percent. For sprinkler and microspray irrigation systems at 110 percent reference evapotranspiration, DP and SIE changes were judged not to be meaningful because of the very low 

mean reported DP of 1.1 inches for these sites. These changes suggest that the use of NRCS evaluation results as part of baseline 

calculations of salt loading may have underestimated salt load savings achieved from improvements in irrigation technology 
2 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

over the years. With these possible exceptions, results of the NRCS evaluation were found by USGS to be as accurate as could 

have been achieved at the time in such a complex, long-running data collection effort. Water managers will have to determine 

if suggested changes in NRCS evaluation DP and SIE results for flood irrigation sites warrant any recalibration of baseline salt 

loading calculations. 

Introduction

The increasing salinity levels in water delivered to Mexico and the Lower Colorado River Basin states in the early 1970s 

created concern about economic damages to downstream water users, resulting in the enactment of the Colorado River Basin 

Salinity Control Act (Salinity Control Act). The primary purpose of the Salinity Control Act was “to authorize the construction, 

operation, and maintenance of certain works in the Colorado River Basin to control the salinity of water delivered to users in 

the United States and Mexico” (Public Law 93-320, June 24, 1974). The Salinity Control Act was amended in October 1984 

through Public Law 98-569 to include language further directing agencies on their salinity control activities. Salinity control 

projects were initiated in Colorado starting with the Grand Valley Unit in 1979, the Lower Gunnison Basin Unit in 1988, and the 

McElmo Creek Unit in 1989. 

 In anticipation of the pending 1984 amendments to the Salinity Control Act, the U.S. Department of Agriculture (USDA) 

Natural Resources Conservation Service (NRCS) initiated a program in 1982 to make a variety of irrigation improvements to 

reduce on-farm deep percolation (DP) and irrigation ditch seepage as part of the effort to reduce the salt load potential to the 

Colorado River. The NRCS irrigation improvement work included piping or lining irrigation ditches, improving the on-farm 

irrigation systems, and providing irrigation management assistance to landowners. 

On-farm DP is excess irrigation water applied to the crop which infiltrates the soil below the crop root zone and enters the 

groundwater, whereas on-farm ditch seepage is water lost from irrigation water delivery ditches into the groundwater. Both DP 

and ditch seepage contribute to salt loading by dissolving the naturally-occurring salt in the soils which underlie the three salinity control units (Kenney and others, 2009) and ultimately transporting that dissolved salt to the Colorado River. 

In 1982, the NRCS also identified the need to establish an irrigation monitoring and evaluation program (NRCS evaluation) 

for the Grand Valley Unit to assess the effects of irrigation improvements on deep percolation and ditch seepage. As a result, the 

NRCS developed the “Monitoring and Evaluation Plan, Colorado River Basin Salinity Control Program for Grand Valley Unit, 

Colorado and Uinta Basin Unit, Utah, July 1982” (U.S. Department of Agriculture, 1982). The NRCS evaluation was a longterm monitoring plan which described uniform guidelines and procedures to (1) assess the effectiveness of the NRCS program to 

reduce salt loading to the Colorado River, (2) identify the economic costs and benefits of the on-farm improvements in irrigation system technology and management, and (3) provide a significant study of the wetlands affected by the irrigation improvement projects and the NRCS-installed wildlife habitat improvement projects to determine and track the wildlife habitat lost and 

replaced (U.S. Department of Agriculture, 1982). Salt loading in the rivers was not directly measured or estimated in the NRCS 

evaluation. This monitoring and evaluation plan was later extended to the Lower Gunnison Basin Unit in 1992 and the McElmo 

Creek Unit in 1993. 

The NRCS evaluation gathered a total of 292 site-years of irrigation application data between 1985 and 2003 at landowner 

sites in the three salinity control units. The evaluation sites were diverse in terms of crop types, acreage, soil types, and irrigation 

system types. The results of the evaluation were recorded by NRCS in internal annual reports beginning in 1985, which were 

shared with the Colorado River Basin Salinity Control Forum (Forum). The Forum was formed in 1973 by the Colorado River 

Basin States (Arizona, California, Colorado, Nevada, New Mexico, Utah, and Wyoming) to address the increasing salinity concentration in the Lower Colorado River and its impact on water users (Colorado River Basin Salinity Control Forum, 2013). 

In recent years, the NRCS realized a need, in working with the Forum, to perform a more formal analysis of the NRCS 

evaluation data for use by Colorado River Basin water managers in other agencies and groups. In 2011, the U.S. Geological 

Survey (USGS), in cooperation with the Bureau of Reclamation and the Colorado River Basin Salinity Control Forum, began a 

study to evaluate the NRCS evaluation data to (1) document the methods of the evaluation, and (2) analyze and summarize the 

data collected during the evaluation. The NRCS agreed to gather the existing physical documents from the evaluation, transfer 

the raw site data to Microsoft Excel spreadsheets, and assist the USGS in understanding the dataset. The term “NRCS evaluation” is used throughout this report to refer to the NRCS monitoring and evaluation study, and the term “USGS study” refers to 

the USGS analysis of the NRCS evaluation.
Introduction 3

Purpose and Scope of the USGS Study

The purpose of this report is to explain how and why the data were collected during the NRCS evaluation and to provide 

a published analysis for outside users to access and understand the results of the NRCS evaluation. NRCS has requested that 

records from the evaluation not be included in the final report. To protect the privacy of the landowners who participated in the 

NRCS evaluation, all references to personal information have been removed by NRCS from the evaluation data made available 

to the USGS study. The Forum’s primary interest in the NRCS evaluation data was to improve the management of salt loading 

in the Colorado River; therefore, neither the on-farm economic analysis nor the wildlife habitat study results are included in the 

USGS study. The methodology used by the NRCS evaluation is reviewed and the site data are summarized in tables and charts 

from a variety of statistical perspectives. In addition, daily soil moisture balance (SMB) calculations are presented for 12 representative sites as spreadsheet-based models (SMB models) to test the per-irrigation event data reported in the NRCS evaluation.

Description of NRCS Evaluation Salinity Control Units

Irrigation practices in the Grand Valley Unit, the Lower Gunnison Unit, and the McElmo Creek Unit (fig. 1) were evaluated 

by the NRCS in western Colorado. Table 1 contains a summary of characteristics for the three evaluation salinity control units.

!5

!5

!5

!5

Colorado River

Gunnison River

Mesa County

Delta County

Montrose County

Montezuma County

Delta

Cortez

Montrose

Green River

Grand Junction

Dolores River

Gunnison River

Colorado River

San Juan River

Uncompahgre River

San Rafael River

East Paradox Creek

Dolores River

San Juan River

State

107°0'0"W

107°0'0"W

108°0'0"W

108°0'0"W

109°0'0"W

109°0'0"W

110°0'0"W

110°0'0"W

39°0'0"N

39°0'0"N

38°0'0"N

38°0'0"N

NRCS Evaluation Salinity Control Units

Explanation

!5 NRCS Evaluation Cities

Major Rivers

Salinity Control Unit Boundaries

McElmo Creek

Lower Gunnison

Grand Valley

Major Highways (Regional)

State Boundary

County Boundary

 ́

0 15 30 60

Miles

Map Area

Colorado

Utah

Colorado

Utah

0 25 50 75 100 12.5

Kilometers

Figure 1. Natural Resources Conservation Service evaluation salinity control units in western Colorado.
4 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Table 1. Characteristics of Grand Valley, Lower Gunnison, and McElmo Creek salinity control units.

[Unit, salinity control unit; GIS, geographic information system; %, percent]

Characteristic Grand Valley Unit Lower Gunnison Unit McElmo Creek Unit Source of Data by Unit

Total acres in unit 121,125 624,210 185,469 GIS calculations, Frank Riggle, 

Natural Resources Conservation Service, written commun., May 2, 2013

Total irrigated acres in unit 61,000 175,000 34,000 All irrigated lands, Colorado 

Water Conservation Board, 

Division of Water Resources, 

Colorado’s Decision Support 

System, 2013

Main source(s) of irrigation 

water

Colorado River Gunnison River and 

Uncompahgre River

Dolores River U.S. Department of Agriculture, 

1986–2003

Estimated length of canals 

and laterals (miles)

200 canal & 500 lateral 128 canal & 438 lateral 117 canal & 225 Lateral John Sottilare, Bureau of Reclamation, Grand Junction field 

office; written commun., 

May 6, 2013

Annual precipitation- 2010 

(inches)

11.00 8.71 15.50 U.S. Department of Commerce, 

2013

Annual irrigation water diversion to unit (acre-feet 

per year)

1,550,000 519,000 105,200 John Sottilare, Bureau of Reclamation, Grand Junction field 

office; written commun., 

May 6, 2013

Total salt load contributed 

by unit (tons per year)

580,000 1,300,000 194,684 Frank Riggle, Natural Resources Conservation Service, 

written commun., May 3, 

2013

Agricultural salt load 

contributed by unit (tons 

per year)

537,000 840,000 154,009 Frank Riggle, Natural Resources Conservation Service, 

written commun., May 3, 

2013

Median farm size (acres) 16 440 (Delta County), 46 

(Montrose County)

57 National Agricultural Statistics 

Service, U.S. Department of 

Agriculture, 2009

Mean field size (acres) 8.3 32.7 23.9 Colorado Water Conservation 

Board, 2013 (Grand Valley 

Unit), National Agricultural Statistics Service, 

2009 (Lower Gunnison and 

McElmo Creek Units)

Predominant type of irrigation system89.1% improved flood, 

7.5% sprinkler, 3.4% 

microspray & drip

86.5% Improved flood, 

11.4% sprinkler, 2.1% 

microspray & drip 

67.6% sprinkler, 32.2% 

improved flood, 0.2% 

microspray & drip

U.S. Department of Agriculture, 

2012

Predominant crops Alfalfa, pasture grass, 

hay, corn, apples, 

peaches, grapes, pears

Alfalfa, pasture grass, 

hay, corn, dry beans, 

apples, peaches, 

grapes, pears

Alfalfa, pasture grass, 

hay, wheat, fruit

National Agricultural Statistics 

Service, 2009 (Grand Valley 

Unit), Delta County Development Inc., 2013 (Lower 

Gunnison Unit), Magnan and 

Seidl, 2004 (McElmo Creek 

Unit)

Mean altitude 

(feet above sea level)

4,700 5,000 6,400 U.S. Department of Agriculture, 

1986–2003

County Mesa Delta, Montrose Montezuma U.S. Department of Agriculture, 

1986–2003

Principal cities Grand Junction, Fruita, 

Palisade

Delta, Montrose Cortez U.S. Department of Agriculture, 

1986–2003
NRCS Evaluation Methods 5

USGS Study Methods

Interviews with NRCS Evaluation Staff

Interviews were conducted with current and retired NRCS staff who participated in the NRCS evaluation. These interviews 

provided insight into how the field data collection was accomplished and how the collected data were analyzed. The original raw 

data records of the NRCS evaluation were not retained after the completion of the project, so many details of how the evaluation 

was conducted are unavailable today. A partial reconstruction of the evaluation procedures and analytical methods was possible 

from personal recollection of the NRCS evaluation staff, primarily Frank Riggle, retired (formerly Assistant State Conservationist for Water Resources, USDA-NRCS, Colorado), who helped initiate the NRCS evaluation project in 1984. A series of presentations and discussions was given by USGS for various staff from NRCS to elicit feedback at several stages of the USGS study. 

This was helpful in refining the USGS study analysis methods, particularly for the soil moisture balance models.

NRCS Printed Documentation

More than 1,800 pages of printed NRCS evaluation annual reports and documentation were collected by NRCS staff and 

made available to the USGS. This documentation included all of the annual monitoring and evaluation reports for the three salinity control units, as well as documents that described the creation of the project. For analysis purposes, specific irrigation data 

from the NRCS Monitoring and Evaluation (M&E) reports were entered into two Microsoft Excel spreadsheets, one for season 

total results and one for individual irrigation event results. These documents were also scanned to an Adobe Acrobat PDF file 

(Adobe Systems, Inc., 2013) for archiving. To protect the privacy of the landowners who participated in the NRCS evaluation, 

all references to personal information have been removed by NRCS from the evaluation data made available to the USGS for 

this study. The USGS is not able to provide access to the redacted NRCS evaluation data. Independent researchers should apply 

directly to NRCS for access to these datasets: (1) the NRCS evaluation annual and irrigation event data by site in spreadsheet 

form, (2) the USGS study analysis and SMB spreadsheets, and (3) an Adobe Acrobat PDF file containing the redacted scanned 

NRCS evaluation annual reports plus supporting documents. See appendix 1 for information on requesting these datasets from 

NRCS. 

Characterization of NRCS Evaluation Field Methods

The NRCS evaluation field data collection methods were described and analyzed by the USGS study from information 

gathered in personal interviews, printed documentation, and written recollection of early field methods by one of the initial 

investigators of the NRCS evaluation (Frank Riggle, Natural Resources Conservation Service (NRCS) retired, written commun., 

June 27, 2011).

Analysis of the NRCS Evaluation Dataset

The NRCS and the USGS jointly developed the evaluation raw data spreadsheets for analysis. This dataset was reviewed 

by NRCS and USGS to rate the quality of the various site-year records, based on the criteria of completeness of the records and 

of internal consistency of the record data. Of the 292 total site-year records in the NRCS evaluation annual reports, this review 

led to the elimination of 24 site-year records, leaving 268 usable site-year records. A further qualification of the 268 usable 

site-year records yielded 225 gold standard records that were deemed to be most reliable in terms of completeness and internal 

consistency. Both the usable and gold standard site-year record sets were analyzed by the USGS using the statistical package 

S+ (Tibco Software, Inc., 1988–2008) and included summary statistics, scatter plots, histograms, box plots, ranked multiple 

comparison statistics using Tukey’s method, geographic information system (GIS) site maps created in ArcMap (Environmental Systems Research, Inc., 1999–2010), and SMB Microsoft Excel spreadsheet models (Microsoft Corporation, 2010) for a 

selected set of sites.

NRCS Evaluation Methods

Irrigated sites were selected to represent the variety of crops and irrigation system types common in the evaluation units. 

The NRCS monitoring was designed to capture changes to the net soil water balance from a variety of irrigation system 

improvements. The sample set needed to be (1) large enough to cover the range in irrigation system types, crops, soils, and 
6 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

geography typical in the salinity control units, and (2) collected over a long enough span of time to capture a range in annual 

conditions and to capture changes over time. It should be emphasized that the NRCS monitoring and evaluation was not 

designed to create a statistically significant dataset. Sites were selected to cover the range in conditions and depended on identifying landowners willing to cooperate in the study. The number of sites sampled each year and the number of sites sampled in 

total were predominantly driven by financial constraints and available staff. 

NRCS Data Collection Procedures

Each irrigation event was to be recorded throughout the irrigation season for each site. From the NRCS Monitoring and 

Evaluation Plan, 1984, “Data will be collected to determine the amount of irrigation water infiltrated into the soil.” “For each 

site on-farm water budgets will be prepared for each irrigation event, starting with pre-plant or start of growing season until crop 

harvest. The most significant output from the water budget is deep percolation.” The proposed water budget was defined as “...

deep percolation equals the amount of inflow plus rainfall prior to or during the irrigation event, less surface runoff and the net 

irrigation requirement [expressed as the amount of water needed to bring the soils profile to field capacity]” (U.S. Department of 

Agriculture, 1982). The NRCS in Colorado elected to use newly developed automated water measurement and digital recording 

equipment to capture more complete irrigation event data for each site for the full irrigation season.

Basic characteristics recorded at the start of the irrigation season for each site included the type of irrigation system, length 

of field run (feet), field slope (percent), field size (acres), soil type, crop type, planting and harvest dates, specific soil type, and 

soil water holding capacity. Periodic site data collected during the irrigation season included daily precipitation amount, irrigation event dates and durations, and water inflow to the field and outflow from the field during irrigation events. The initial soil 

water balance was estimated at the beginning of the season and was also calculated using the water balance method at the start 

and finish of each irrigation event. Reference or potential evapotranspiration (ETp) was calculated daily using data collected 

from two NRCS-operated weather stations. Crop evapotranspiration (ETc) was estimated using a time-dependent crop coefficient 

(Kc). The original NRCS Monitoring and Evaluation Reports used the abbreviation ETr for potential or reference evapotranspiration, and ETa for actual or crop time-dependent evapotranspiration. The abbreviations ETr

 and ETp, therefore,represent the same 

potential ET values, and ETa and ETc represent the same crop ET values. Throughout this report ETp and ETc will be used as they 

represent current usage.

The climate data collected from the NRCS weather stations to determine daily ETp included maximum and minimum temperature, relative humidity, wind run, solar radiation, and precipitation. The weather stations were typical Campbell Scientific 

instruments available in the 1980s. The Grand Valley Unit had two NRCS weather stations, the Lower Gunnison Unit had two 

weather stations, and the McElmo Creek Unit is assumed to have had one weather station (no record or site map is available). 

Daily ETp was calculated from the climate data using the Modified Penman equation for alfalfa (Grand Valley Annual Report, 

1985, in U.S. Department of Agriculture, 1986–2003). Initially the climate data were electronically transmitted from weather 

stations in each evaluation unit through the NRCS Snow Survey and Water Supply Forecasting Program (SNOTEL Network). 

The decision was made in 1985 to instead transmit the data through a radio-telemetry system due to a variety of technical problems associated with using the SNOTEL Network. 

Precipitation was measured at the two centrally located weather stations and also by rain gages at individual sites. Precipitation results for each site were published in annual reports for each salinity control unit. Daily ETp

 and weather data were not 

included in the printed annual reports. 

NRCS Soil Moisture and Crop Evapotranspiration Determination

Each soil type has a specific water holding capacity or field capacity (FC), which is the maximum amount of moisture that 

the soil can hold at a saturated equilibrium condition (Veihmeyer and Hendrickson, 1949). Field capacity for the initial soil types 

at the initial NRCS evaluation sites was determined empirically using a pressure plate technique in the U.S. Department of the 

Interior Bureau of Reclamation (Reclamation) laboratory facilities in Grand Junction, Colorado (Frank Riggle, NRCS, written 

commun., February 13, 2013). The water in the soil root zone has a lower practical limit called the wilting point (WP), below 

which irreversible damage to the plants occurs. Available water in the root zone is thus equal to FC minus WP. In irrigation management, it is typically assumed that 50 percent of the available water is readily available to the plant. When the water in the root 

zone falls below the readily available level, the crop is said to be stressed (U.S. Department of Agriculture, 1997).

Each crop type (corn, wheat, grapes, among others) has a specific evapotranspiration crop coefficient curve (Kc

), which is 

a time-dependent multiplier that varies with the growth stage of the crop (Allen and others, 1998). The ETp multiplied by the 

appropriate value of Kc determines the ETc for the crop stage based on the number of days from planting. Further adjustment 

of ETc was made by the NRCS for crop stress, although the method used was not documented in the annual reports. When the 

root zone water falls below the readily available level, crop stress suppresses the plant’s ability to transpire, which reduces the 
NRCS Evaluation Methods 7

effective ETc. Today, crop stress is usually modeled as a linear multiplier for ETc which decreases from 1 to 0 as soil moisture 

declines from the not readily available level to the wilting point (Allen and others, 1998). 

Soil water deficit (SWD) is the amount of water required to refill the crop root zone to bring the current soil moisture conditions up to FC for the given soil type. In 1985 and 1986, season-beginning (initial) soil moisture was determined by gravimetric 

analysis of soil samples (Frank Riggle, NRCS, written commun., February 13, 2013). For subsequent years, the gravimetric 

initial field SWD determination, if performed, was not reported. It was most likely determined at the beginning of the irrigation 

season by a hand estimate in the field. The 1990 Grand Valley Unit annual report states “All sites were probed before the start of 

the irrigation season to estimate soil moisture deficit before irrigation” (Grand Valley Annual Report, 1990, U.S. Department of 

Agriculture, 1986–2003). 

The SWD at the start of the first irrigation event of the season was calculated using the initial SWD, adding any daily precipitation, and subtracting the stress-corrected daily ETc

 from the season start date to the start date of the first irrigation. Subsequent values of start-of-irrigation SWD were determined by taking the SWD at the end of the previous irrigation, adding daily 

precipitation, and subtracting daily stress-corrected ETc from the end date of the previous irrigation event to the start date of the 

subsequent irrigation event. The SWD at the end of each event was calculated as the event beginning SWD minus the infiltrated 

depth of water. If the infiltrated depth exceeded the beginning SWD, then the excess was declared to be DP. There is no documentation of lab tests being used to determine the ending SWD.

The net amount of irrigation water applied to the crop in an irrigation event is calculated as 

Infiltrated Depth = Irrigation Inflow – Irrigation Outflow (1)

where

Infiltrated depth is the total net irrigation water, in inches, the field receives during the irrigation event,

Irrigation inflow is the total irrigation water, in inches, entering or applied to the field during the irrigation

event, and 

Irrigation outflow is the total irrigation water, in inches, that exits the field as runoff (“tail water”).

When the total infiltrated depth exceeds the SWD for a particular irrigation event, the excess water is assumed to enter the 

soil below the root zone as DP. This is a concern because it may eventually discharge to nearby rivers, carrying with it a load of 

salt and other minerals that have been leached from the soil. DP for the NRCS evaluation was calculated as

DP = Infiltrated Depth – Beginning SWD (2)

where

DP is deep percolation in inches of water,

Infiltrated Depth is the net irrigation water in inches applied during the irrigation event, and

Beginning SWD is the soil water deficit in inches existing at the start of the irrigation event.

This definition of DP by the NRCS evaluation is incomplete, as there is no inclusion of precipitation or crop evapotranspiration in the definition. Because the NRCS records clearly indicate that the effects of precipitation and crop evapotranspiration were 

taken into account when calculating DP for the evaluation sites, it must be assumed that this definition of DP (eq. 2) was simply in 

error when it was first written in the NRCS annual reports, and that the error was apparently propagated to later reports.

NRCS Equipment

The NRCS made the decision to purchase newly developed automated sensors and digital recorders to reduce the staffing 

needs and odd hours required to obtain a complete full-season irrigation dataset. Equipment names are for informational purposes only and do not constitute any type of product or other endorsement (table 2).

The decision was made in 1984 to start monitoring with sensors and recorders to equip 20 field sites in the Grand Valley 

Unit, and to establish two remote automated weather stations to obtain the climate data to calculate crop evapotranspiration and 

collect general precipitation information. In addition, manually read rain gages at each evaluation site were used to adjust the 

precipitation to represent more local conditions. The automated sensors and digital recorders arrived in early 1984 and were 

tested to understand their calibration, performance, and installation requirements. It was decided that the 20 sets of irrigation 

flow measurement equipment were sufficient to install 16 sites and to retain four complete sets of replacement equipment for use 

during the irrigation season, due to performance concerns with the newly developed installation configurations of using the flow 

sensors combined with digital reorders (Grand Valley Annual Report, 1985, in U.S. Department of Agriculture, 1986–2003).

The equipment purchased was relatively new technology and had not been extensively used for irrigation flow measurements. The 1984 irrigation season was used primarily as an installation period and provided a good learning experience in the 

use of automated flow recording equipment.

The sensors were run through a variety of tests to ensure performance and to design the best installation configurations. 

Much of the equipment had not been used for an irrigation monitoring field installation and the recorders needed moisture and 

climate protection. A variety of equipment boxes were adapted to provide needed security and climate protection (Grand Valley 

Annual Report, 1985, in U.S. Department of Agriculture, 1986–2003).
8 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Table 2. Typical equipment purchased for Natural Resources Conservation Service evaluation.

Manufacturer Product Model Number

Omnidata International Datapod DP211

Omnidata International Datapod DP112

Omnidata International Datapod DP219

Omnidata International Interface 301

Omnidata International Easy Logger EL824-GC

Omnidata International Polycorder 516GE-64-A

Drexelbrook Linear strip gauge 700-701-015

Drexelbrook Signal conditioner (unknown)

Robinson-Halpern Pressure transducer 152BP015DG35

Wescor, Inc. Pressure transducer (Unknown)

Signet Mighty-Mag flow sensor MK565

(manufacturer unknown) Soil moisture blocks (Gypsum) (unknown)

Wescor, Inc. Datapod DPX Series DPX-WL-01(3)

Scientific Engineering, Inc. Repeater (Unknown)

Tandy Corporation Computer Tandy 2000

Campbell Scientific Weather station (unknown)

Figure 2. Photograph of a linear strip gage installed in an existing 

concrete weir.

Figures 2 through 11 illustrate various field installations of monitoring equipment used in the NRCS evaluation.
NRCS Evaluation Methods 9

Figure 3. Photograph of a typical installed broad-crested weir with a 

linear strip gage.

Figure 4. Photograph of a typical inflow installation with a stilling well 

and float potentiometer.

Figure 5. Photograph of a typical weather station measuring wind run, 

solar radiation, maximum-minimum temperatures, relative humidity, and 

precipitation.
10 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Figure 6. Photograph of a typical outflow installation with pressure 

transducer.

Figure 7. Photograph of a Datapod and housing box.

Figure 8. Photograph of a Datapod, interface, and signal 

conditioner for a magnetic induction pipeline flow sensor.
NRCS Evaluation Methods 11

Figure 9. Photograph of a magnetic induction flow sensor with signal 

conditioner and Datapod recorder.

Figure 10. Photograph of a pressure transducer to measure air pressure.

Figure 11. Photograph of a closed cell to generate air pressure for the 

pressure transducer designed by Tom Trout, USDA-Agricultural Research 

Service, Kimberly, Idaho.
12 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

NRCS Field Procedures

To capture the net water on and off each site, the inflow was measured at the point where the water entered the head of the 

field and the outflow was measured at the point where all the runoff (tail) water left the end of the field. Thus, the calculated DP 

amounts include any head ditch and tail water ditch seepage in addition to water infiltrated in the field furrows.

The first four field sites in the Grand Valley Unit were installed in the spring of 1984 to test the field data collection equipment and installation. Although the automated data collection equipment provided the sampling frequency to collect a complete 

dataset, field staff were required to visit each site often enough to ensure the equipment and installation was functioning properly. Sediment in weirs, failed batteries, overheated recorders, wet electrical connections, debris, sensor drift, and other performance problems frequently compromised the data collection. During the first season, each site was visited at least once every 

day, particularly during the irrigation events, to ensure a complete and reliable dataset. In 1984, partial data were collected on 

the initial four sites but the dataset was not complete enough to be used in generating an annual summary report. Based on the 

lessons learned from installing the first 4 sites, 12 additional sites were installed during the 1984 irrigation season in preparation 

for the 1985 irrigation season.

During the 1984 irrigation field season, it was determined that repairing the data collection equipment in the field was not 

practical, and resulted in lost data when it occurred during an irrigation event. The NRCS evaluation team decided to install 16 

total sites and have 4 complete sets of replacement equipment. To have sufficient staff to cover the 16 sites distributed throughout the Grand Valley, 2 individuals were assigned for each to visit 8 sites per day during irrigation events. They carried two complete sets of sensors, recorders, and spare batteries. If a sensor or recorder was not working properly, a new one was installed 

immediately and the questionable equipment unit was returned from the field for repair or calibration. Although complete 

failures only occurred occasionally, having a ready replacement reduced the loss of irrigation event data. 

The 1985 Grand Valley Unit irrigation data were reviewed by NRCS State Office and NRCS West National Technology 

staff for collection method, completeness, and accuracy. The staff determined that the data represented a complete and accurate 

set of field data and were as good as could be collected. Their technical review also supported the need for each site to be visited 

periodically to ensure the weirs were functioning, the sensors were clear and calibrated correctly, and the recorders were operating properly. For the field data collected by the NRCS from 1985 through 1995, each site was visited and maintained every 2 to 

3 days during the field season, and equipment was calibrated and checked every day during the irrigation events (Grand Valley 

Annual Report, 1989, in U.S. Department of Agriculture, 1986–2003).

NRCS Dataset

The NRCS collected data from 1985 through 2002 in the Grand Valley Unit, 1991 through 2003 in the Lower Gunnison 

Unit, and for 1993 in the McElmo Creek Unit. These data represent full season and complete irrigation data for the sites sampled. The number of irrigation events and the total water balance reflect the typical performance for all irrigation events through 

a full season.

Tables 3 through 5 show data content summaries of the various annual reports for each of the three evaluation units. The 

site counts shown are the total number of sites, the number of site-year records usable in the USGS analysis, and the number 

of gold standard site-year records. It can be seen that the reports between 1985 and 1996 have the largest number of evaluation 

sites, and that most of the reports included a sufficient level of detail to be usable. Individual irrigation events were reported for 

most of those years, and ETc

 and precipitation records were shown.

Table 3. Natural Resources Conservation Service evaluation annual report summary for the Grand Valley Unit, 1985 to 2003.—Continued

[ETc, crop evapotranspiration; NA, not applicable; good map detail, roads and rivers shown; fair map detail, a few physical features shown; poor, no physical 

features shown]

Grand Valley Unit

Year Total Sites

Usable 

Site 

Records

Gold Standard Site 

Records

Annual 

Report

Site Map 

in Annual 

Report

Site 

Numbers 

on Map

Map Detail Level

Precipitation Data 

by Site

ETc

 Data 

by Site

Irrigation 

Event Data 

by Site

1985 16 14 14 Yes No NA NA Yes Yes Yes

1986 16 15 15 Yes Yes No Good Yes Yes Yes

1987 16 16 16 Yes No NA NA Yes Yes Yes

1988 18 18 18 Yes Yes No Good Yes Yes Yes
NRCS Evaluation Methods 13

Table 3. Natural Resources Conservation Service evaluation annual report summary for the Grand Valley Unit, 1985 to 2003.—Continued

[ETc, crop evapotranspiration; NA, not applicable; good map detail, roads and rivers shown; fair map detail, a few physical features shown; poor, no physical 

features shown]

Grand Valley Unit

Year Total Sites

Usable 

Site 

Records

Gold Standard Site 

Records

Annual 

Report

Site Map 

in Annual 

Report

Site 

Numbers 

on Map

Map Detail Level

Precipitation Data 

by Site

ETc

 Data 

by Site

Irrigation 

Event Data 

by Site

1989 19 19 19 Yes Yes Yes Good Yes Yes Yes

1990 25 25 25 Yes Yes Yes Poor Yes Yes Yes

1991 23 23 23 Yes Yes Yes Poor Yes Yes Yes

1992 24 24 24 Yes Yes Yes Fair Yes Yes Yes

1993 21 22 22 Yes Yes Yes Poor Yes Yes Yes

1994 12 12 12 Yes Yes Yes Poor Yes Yes No

1995 8 8 8 Yes Yes Yes Poor Yes Yes No

1996 0 0 0 NA NA NA NA NA NA NA

1997 0 0 0 NA NA NA NA NA NA NA

1998 0 0 0 Yes1 Yes Yes2 Poor NA NA NA

1999 11 4 0 Yes No NA NA No No Yes

2000 7 7 0 Yes No NA NA No No Yes

2001 3 2 0 Yes No NA NA No No Yes

2002 5 2 0 Yes No NA NA No No Yes

2003 0 0 0 NA NA NA NA NA NA NA

Total sites 224 211 196 NA NA NA NA NA NA NA

 1Grand Valley 1998 annual report contains site summary from 1985 to 1995. 

2

Grand Valley 1998 annual report site map shows 1995 sites.

Table 4. Natural Resources Conservation Service evaluation annual report summary for the Lower Gunnison Unit, 1990 to 2003.

—Continued

[ETp, crop evapotranspiration; NA, not applicable; good map detail, roads and rivers shown; fair map detail, a few physical features shown; poor, no physical 

features shown]

Lower Gunnison Unit

Year Site Count

Usable 

Site 

Records

Gold Standard Site 

Records

Annual 

Report

Site Map 

in Annual 

Report

Site 

Numbers 

on Map

Map Detail Level

Precipitation Data 

by Site

ETc

 Data 

by Site

Irrigation 

Event Data 

by Site

1990 0 0 0 Yes Yes Yes1 Good NA NA NA

1991 3 3 0 Yes No NA NA Yes No No

1992 5 3 3 Yes No NA NA Yes Yes Yes

1993 7 7 7 Yes Yes Yes Fair Yes Yes Yes

1994 6 6 6 Yes Yes Yes Fair Yes Yes No

1995 6 6 6 Yes Yes Yes Fair Yes Yes Yes

1996 4 2 1 Yes Yes Yes Fair Yes Yes Yes

1997 0 0 0 NA NA NA NA NA NA NA

1998 0 0 0 NA NA NA NA NA NA NA

1999 5 5 0 yes2 No NA NA No No Yes
14 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Table 4. Natural Resources Conservation Service evaluation annual report summary for the Lower Gunnison Unit, 1990 to 2003.

—Continued

[ETp, crop evapotranspiration; NA, not applicable; good map detail, roads and rivers shown; fair map detail, a few physical features shown; poor, no physical 

features shown]

Lower Gunnison Unit

Year Site Count

Usable 

Site 

Records

Gold Standard Site 

Records

Annual 

Report

Site Map 

in Annual 

Report

Site 

Numbers 

on Map

Map Detail Level

Precipitation Data 

by Site

ETc

 Data 

by Site

Irrigation 

Event Data 

by Site

2000 13 13 0 Yes No NA NA No No Yes

2001 7 3 0 Yes No NA NA No No Yes

2002 2 1 0 Yes No NA NA No No Yes

2003 4 2 0 Yes No NA NA No No Yes

Totals 62 51 23 NA NA NA NA NA NA NA

1

No site data were published in Lower Gunnison annual report for 1990, but site map shows two sites.

2

Lower Gunnison annual report for 1999 is shown in Grand Valley 1999 annual report.

Table 5. Natural Resources Conservation Service evaluation annual report summary for the McElmo Creek Unit, 1993.

[ETc, crop evapotranspiration; blank cells, not applicable]

McElmo Creek Unit

Year Site 

Count

Usable 

Site 

Records

Gold 

Standard Site 

Records

Annual 

Report

Site Map 

in Annual 

Report

Site 

Numbers 

on Map

Map 

Detail 

Level

Precipitation 

Data by Site

ETc

 Data 

by Site

Irrigation 

Event Data 

by Site

1993 6 6 6 Yes No Yes Yes Yes

No Grand Valley Unit sites were monitored during 1996 through 1998, and no Lower Gunnison Unit sites were monitored 

during 1997 and 1998. Starting in 1999 and continuing through 2003, data collection and analysis was managed by the Colorado 

State University Cooperative Extension (CSU Extension) program rather than the NRCS local field staff. There were a small 

number of Grand Valley Unit sites monitored during this period, with more focus placed on the Lower Gunnison Unit. The field 

methods for the 1999 through 2003 period are not as well documented, but the same field equipment was used as in the earlier 

evaluations, and data collection techniques were assumed to have been generally consistent with the earlier methods.

A review of the post-1996 evaluation data for the Grand Valley and Lower Gunnison Units indicates that many of the sites 

appear to have partial data and may or may not have captured every irrigation event through the full season. The CSU monitoring was done with limited staff and limited equipment covering both the Grand Valley and Lower Gunnison Units. The lack of 

available field staff and limited equipment resulted in partial datasets and is not necessarily a complete and reliable set of full 

season irrigation data. 

Because of the questionable reliability of post-1996 data, the subset of data from 1985 to 1996 for the Grand Valley and 

Lower Gunnison Units is considered the most complete and consistent set of data, and is referred to by the NRCS as the gold 

standard data (Frank Riggle, NRCS, oral commun., June 27, 2012). This terminology is therefore also used in this report. Determination of data quality is discussed in detail in the section “Site-Year Record Quality Determination.”

The site map columns in tables 3 through 5 indicate that many annual reports up to 1998 include site maps with the site 

numbers shown and have a level of detail in the base map that allows for general geospatial location of the sites using GIS methods. In particular, the inclusion of roads and highways enhances the ability to locate the sites. After 1998, none of the annual 

reports include site maps. Some of the maps do not include site numbers or have little or no detail in the base map, which makes 

it impossible to georeference the sites to actual features (roads) in GIS. The GIS site maps are shown in the section titled “Creation of NRCS Evaluation Site Maps.”
USGS Study Findings on NRCS Evaluation 15

USGS Study Findings on NRCS Evaluation

NRCS Annual Reports

The NRCS evaluation was originally intended for program support and to direct the NRCS as to where and how to best 

make irrigation improvements for salinity control. The evaluation was not done to support research other than directing the 

agency’s salinity control work. The original paper reports were filed in the NRCS field offices for each evaluation unit. Because 

the original data files for the NRCS evaluation were not retained after the end of the evaluation, the paper annual reports represent the remaining documentation of the irrigation monitoring. For the USGS study, the NRCS was able to recover the paper 

reports from multiple field offices. The collected irrigation monitoring data are shown in all of the annual reports as season-total 

values for each site. For some evaluation years, and for some of the evaluation units, the paper reports also include the original 

per-event irrigation data. If an annual report only shows season-total summary information but does not include the individual 

irrigation event records, the individual event data were not found and is considered to be no longer available.

The annual reports always included the irrigation season summary data for each site monitored, and for some years the 

annual reports also included individual irrigation event data for each site. Data for each site and for each irrigation season 

included the following items: 

• Site identification number

• Irrigation system type

• Crop type

• Field size (acres)

• Number of irrigations

• Irrigation water inflow (inches of water)

• Irrigation water outflow (inches of water)

• Infiltrated depth (inches of water)

• Precipitation (inches of water)

• ETc (inches of water)

• Deep percolation (inches of water) 

• Seasonal application efficiency (percent)

For the years when individual irrigation events were also reported, each site report also includes these data per site:

• Irrigation event number

• Irrigation start date

• Irrigation event duration (hours)

• Advance time – the length of time it takes for irrigation water to flow from the top to the bottom of a field when using 

flood irrigation (hours)

• Duration of each irrigation set (hours),

• Mean infiltration per event (inches of water)

• Number of furrows

• Mean furrow flow (gallons of water per minute)

• Inflow and outflow (inches of water)

• Soil water deficit (SWD) before the irrigation event (inches of water)

• Infiltrated depth at the end of the irrigation event (inches of water)
16 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

• Precipitation (inches of water)

• SWD after the irrigation event (inches of water)

• Total ETc (inches)

• Deep percolation (inches)

• Irrigation application efficiency (percent)

NRCS Methods

The USGS study was able to generally characterize the field methods of the NRCS evaluation. Due to the long time span of 

the NRCS evaluation (19 years) and personnel changes after the suspension of evaluations from 1997 through 1998 in all three 

evaluation units, there were changes in the field methods over time that were not fully documented. Because the primary records 

of the evaluation were not retained, many of these differences cannot be ascertained with certainty. Implications for the issues 

noted in this section are discussed in the later section “Potential Discrepancies in Results between SMB Models and NRCS 

Evaluation.”

The use of instruments to measure the field inflow and outflow are judged to be sufficiently accurate. The NRCS evaluation 

relied on calculated soil moisture values at the start and end of each irrigation event rather than a laboratory measurement of soil 

moisture at those times. If consistent and documented laboratory testing had been done, a degree of “ground truthing” would 

have been available to check the accuracy of the SMB calculations.

Many individual irrigation event records are flagged in the results tables with the comment “Corrections have been applied 

to data,” but the specific nature of these corrections was not documented. For some of the individual irrigation event records, 

the internal soil moisture accounting does not add up mathematically, and no explanation is given for this inaccuracy. For the 

records starting in 1999, no ETc or precipitation was documented in the NRCS evaluation reports for any of the sites, and no 

internal consistency checks could be made for the soil moisture accounting. In addition, the start of season soil moisture values 

were not documented in the NRCS evaluation reports for any of the sites over the years. 

In addition, it was noted in 1990 that other factors could also influence the ETc soil water balance with actual soil water 

deficits: “In 1990, the water budget program was updated to more accurately estimate deep percolation for annual crops. In the 

past, deep percolation for the first irrigation and or pre-irrigation was considered to be any amount in excess of that required to 

fill the first foot of soil, and the full root profile was not taken into account. With this method, deep percolation estimates were 

higher than they should be. The updated program takes the full rooting profile into consideration. All the previous data from 

1986 to 1989 have been re-processed using the updated program to get a better estimate of deep percolation, soil moisture, and 

ETa” (Grand Valley Annual Report, 1990, in U.S. Department of Agriculture, 1986–2003). 

The reprocessed data for the previous years are not provided in the 1990 annual report, unfortunately, so there is no way 

to estimate the magnitude of the changes that the reprocessing may have caused. A data summary table published in the 1995 

Grand Valley Unit annual report for all Grand Valley sites from 1985 through 1995 shows site data values that are identical to those published in each original annual report (Grand Valley Annual Report, 1995, in U.S. Department of Agriculture, 

1986–2003). 

Another omission in data reporting was the failure to record the harvest (“cutting”) dates for alfalfa crops at any of the sites. 

These cutting dates had to be inferred from the SMB models created for the USGS study. 

An original NRCS evaluation document that was used as a data processing and software operation manual by the NRCS 

evaluation staff was located (Frank Riggle, NRCS retired, written communication, 2014) and is reproduced in appendix 2. This 

document provides rich detail on how the NRCS evaluation staff analyzed the site field data. 

Statistical Analysis of the NRCS Dataset

Temporal Analysis of NRCS Sites

Temporal analysis refers to repeated observations of a set of variables over time. In this case, the consecutive years of 

evaluation at the same evaluation site can be examined for changes in principal variables such as DP and SIE. Table 6 shows 

years of site evaluations by site number in the Grand Valley Unit. Note that after 1995, site numbers were re-used at new locations different from their 1985–1995 locations. The longest use of a site was for nine consecutive years. It is likely that different 

crops could have been grown at the same site over succeeding years, and that improvements in irrigation system technology 

were made at the same site over time. Some Grand Valley Unit sites were paired for comparison purposes. 
USGS Study Findings on NRCS Evaluation 17

At the time of the NRCS evaluation, a new irrigation technology using surge valves was of interest to the NRCS (Grand 

Valley Annual Reports, 1990 and 1991, in U.S. Department of Agriculture, 1986–2003) as a way to increase SIE and reduce DP. 

To measure the potential benefit from using surge valves, some evaluation sites (five in 1991, five in 1992, and two in 1993), 

were split into two parts, with standard PGP (pipeline gated pipe) technology used on one part, and PGS (pipeline gated surge) 

technology on the other part. 

Table 7 shows the years of site evaluations by site number for the Lower Gunnison Unit. Again, after 1996, the site numbers were re-used for different locations. There is no table for the McElmo Creek Unit, as the only year of evaluation for the six 

McElmo Creek sites (site numbers 21, 22, 23, 25, 26, and 27) was 1993.

Table 6. Years of site evaluations by site number for the Grand Valley Unit, western Colorado.

[*, site numbers were reused for different locations after 1995;.gap between 1995 and 1999 indicates that no sites were monitored during those years]

Gold Standard Evaluation Years Nongold Standard Evaluation Years

Site Number 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1999 * 2000 * 2001 * 2002 *

1 X

2 X

3

10 X X X

11 X X X X X X X

12 X X X X X X

13 X X X X X

14 X X X X X

15 X X X X X X X X

16 X X X X X X X X X

17 X X X X X X X

18 X X X X X X X

19 X X X

20 X X

21 X X X X X X X X X X

22 X

23 X X

24 X X X

25 X X X

26 X X X X X X X X X

27 X X X X X X X X

28 X X X X X

29 X X X X X

30 X X X X X X X X

31 X X X X X X X

32 X X X X X X X X X X

33 X X X X X X X

34 X

35 X X X

36 X X X X X X X

37 X X X X X X X X X

38
18 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Gold Standard Evaluation Years Nongold Standard Evaluation Years

Site number 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1999 * 2000 * 2001 * 2002 *

39 X X X X X

40

41 X X X

42 X

43 X X X

44 X X X

45 X X

46 X X X

47 X X X X X

48 X

49 X X

50 X

51 X X X

52

53 X X X

54 X X X

55 X X X

56 X X

57 X X X

58 X X

59 X

60 X X

61 X X

62 X

63 X

64 X

65 X

66 X 

858 X

WF1 X

WF2 X

Table 6. Years of site evaluations by site number for the Grand Valley Unit, western Colorado.—Continued

[*, site numbers were reused for different locations after 1995.]
USGS Study Findings on NRCS Evaluation 19

Table 7. Years of site evaluations by site number for the Lower Gunnison Unit, western Colorado.

[*, site numbers were reused for different locations after 1996.]

Gold Standard Evaluation Years Nongold Standard Evaluation Years

Site Number 1991 1992 1993 1994 1995 1996 1999 * 2000 * 2001 * 2002 * 2003 *

1 X X

2

2b X X

3 X

4 X

10 X X X

11

12

13

14

15

16

17 X X X X

18 X X X X X X

19 X X X

20 X X X X X X

21 X

22 X X

23 X X

24 X X X X

25 X

26 X X

26a X

27 X X

28 X X

29 X X

30 X

31 X

32 X

33 X

33a-1 X

33a-2 X

34 X X

34a

35 X X

36

36a X

36b X

36c X X

37

38 X X

127 X X
20 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Types of Irrigation Systems and Crops Evaluated by Year

Figure 12 shows a bar chart of irrigation system types which were monitored by evaluation year. The site counts are for all 

usable site records in all three evaluation units. Figure 12 shows that the preponderance of system types evaluated were concrete 

ditch to siphon tube (CDS), pipeline gated pipe (PGP), pipeline to gated surge (PGS), and side-roll sprinkler (SRS). 

EDF Earth Ditch to Feeder Ditch

EDS Earth Ditch to Siphon Tubes

CDS Concrete Ditch to Siphon Tubes

CDP Concrete Ditch Ported

PCS Ported Concrete Ditch to Surge

CGS Concrete Ditch to Gated Pipe Surge

CDG Concrete Ditch to Gated Pipe

GPP Gated Pipe

PGP Pipeline to Gated Pipe

PGS Pipeline to Gated Pipe Surge

SRS Side-roll Sprinkler

MIS Microspray

Explanation

0

2

4

6

8

10

12

EDF EDS CDS CDP PCS CGS CDG GPP PGP PGS SRS MIS

Number of Systems

Irrigation System Type

Irrigation System Types Evaluated by Year from 1985 through 2003 

for All Usable Evaluation Sites

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

Figure 12. Irrigation systems monitored by evaluation year and irrigation system type from 1985 to 2003 for all usable site records in the

Grand Valley, Lower Gunnison, and McElmo Creek Units. 
USGS Study Findings on NRCS Evaluation 21

Figure 13 shows the DP at Grand Valley Unit site 15 for 8 consecutive years, with a crop change but no change in irrigation 

technology. A concrete ditch to siphon tube system (CDS) was used. The crop changed from alfalfa to corn. Figure 13 shows 

that DP is generally higher for a corn crop than for alfalfa, primarily due to the need to irrigate the corn crop during the early 

plant stages when the actual net plant water extraction is still relatively low due to the small plant size and limited root zone 

(Frank Riggle, NRCS, written commun., May 3, 2013).

Figure 13. Deep percolation at Grand Valley Unit site 15 from 1985 through 1992 with constant irrigation type and varying crop types.

1985 1987 1989 1991

Year

5

10

15

20

25

Deep Percolation (inches)

1986 1988 1990 1992

Concrete Ditch to Siphon Tube

Irrigation System Throughout

Alfalfa

Alfalfa

Alfalfa

Alfalfa

Alfalfa

Corn

Corn

Corn

Deep Percolation at Grand Valley Unit Site 15 from 1985 through 1992

Figure 14 shows seasonal irrigation efficiency for Grand Valley Unit site 21 from 1985 through 1995. During this period, 

the crop changed from corn to grain to alfalfa, while the irrigation technology was upgraded from concrete ditch to siphon tube 

(CDS), to gated pipe (GPP), and finally to pipeline to gated surge (PGS). It can be seen that efficiency was roughly constant for 

CDS and GPP technology but increased after the establishment of the alfalfa crop and with the change to PGS technology in 

1991. Establishment of an alfalfa crop requires extra irrigation for plant development (Frank Riggle, NRCS, written commun., 

May 3, 2013). 
22 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Figure 14. Seasonal irrigation efficiency at Grand Valley Unit site 21 from 1985 through 1995 with varying crop types and irrigation 

methods.

Creation of NRCS Evaluation Site Maps

It was possible to create a GIS map of all of the evaluation sites in the Grand Valley Unit from 1985 to 1995 from site maps 

in the Grand Valley Unit annual reports, and also from manual mapping from memory of the site locations by several former 

NRCS evaluation staff (Frank Riggle, NRCS, written commun., June 27, 2011) (fig. 15). Not all sites in the Lower Gunnison 

River Unit could be mapped, because the site locations were not included in some of the annual reports for that area (fig. 16). No 

site location data were reported for the McElmo Unit; therefore, no site map could be created. A geospatial analysis of possible 

variations in irrigation technology type, DP, or irrigation efficiency by location was not attempted in the UGSG study due to the 

complexity of requiring a separate analysis map for each evaluation year.

1986 1988 1990 1992 1994

Year

20

30

40

50

60

70

80

Seasonal Irrigation Efficiency (percent)

1985 1987 1989 1991 1993 1995

Corn

Grain

Grain

Grain

Establish Alfalfa

Alfalfa

Alfalfa

Alfalfa

Alfalfa

Alfalfa

Alfalfa

CDS

CDS

GPP

GPP

GPP

GPP

PGS PGS

PGS

PGS

PGS

CDS is concrete ditch to siphon tube

GPP is gated pipe

PGS is pipeline to gated surge

Seasonal Irrigation Efficiency at Grand Valley Unit Site 21 from 1985 to 1995
Figure 15. Map of all Natural Resources Conservation Service evaluation site locations in the Grand Valley Unit, western Colorado.

!(

!( !(

!(!(

!(!(

!( !(

!(

!(

!(!(

!(!( !(!(

!( !( !( !(

!(

!(

!(

!( !( !(

!(

!(!(

!( !( !(!(

!(

!(

!(

!(!(!(!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

Grand Junction

£¤50

£¤6

£¤6

UV340

UV141

UV139

UV141

108°30'0"W

108°30'0"W

109°0'0"W

109°0'0"W

39°15'0"N

39°0'0"N

Grand Valley Unit Evaluation Sites

Explanation

!( Evaluation Sites

Weather Stations

!( Highline Lake!( Palisade

Salinity Control Unit Boundaries

Name

Grand Valley Salinity Control UnitMajor Highways (Regional)Rivers (Regional)

Urban Areas (Regional)

Urban Areas (Regional)

 ́

0 4 8 2

Map Area

Colorado

Fruita
Figure 16. Map of reported Natural Resources Conservation Service evaluation site locations in the Lower Gunnison Unit, western Colorado.

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!( !(

State

Grand Junction

£¤50

£¤550

£¤6

10

108°0'0"W

108°0'0"W

109°0'0"W

109°0'0"W

39°0'0"N38°0'0"N

Lower Gunnison Salinity Control Unit Evaluation Sites

Explanation

Lower Gunnison Unit Evaluation SitesType

!( Evaluation Sites!( Weather Station

Salinity Control Unit BoundariesName

Lower Gunnison Salinity Control UnitMajor Highways (Regional)Rivers (Regional)

Urban Areas (Regional)

Urban Areas (Regional)State Boundary

 ́

0 10 20 5

Miles

Map Area

Colorad

Utah

Delta

Montrose

0 9 18 27 36 4.5

Kilometers
USGS Study Findings on NRCS Evaluation 25

Irrigation System Improvement Order

The various irrigation system types fall into a natural order of increasing level of technical sophistication (table 8). The 

order shown in table 8 was determined by NRCS staff for the USGS study analysis. The NRCS combined some of the 13 original evaluation system types in creating this “improvement order” of 9 levels, based on close similarity in subtypes. One system 

type, cablegation, was excluded from the analysis at the request of NRCS. Cablegation was highly experimental at the time of 

the NRCS evaluation and was only present at site 13 in the Grand Valley Unit in 1985 and 1986. NRCS judged the results from 

those two records as unreliable.

As the irrigation system technology level increases, irrigation efficiency is expected to improve, and DP is expected to 

decrease. Measuring the changes in irrigation efficiency and DP as a result of improvement levels of irrigation system sophistication was one of the most important goals of the NRCS evaluation, and these results will be discussed in detail in the USGS 

study statistical analysis sections.

Table 8. Irrigation system types in order of improvement.

[NRCS, Natural Resources Conservation Service]

Improvement Level Combined System Type Codes Original NRCS Evaluation System 

Type Codes

System Type Code /

(Original System Type Codes)

1 EDF EDF Earth Ditch to Feeder ditch

2 EDS EDS Earth Ditch to Siphon tube

3 CDV CDS, CDP, CDG

Concrete ditch to various distribution 

methods: concrete ditch to siphon 

tube; concrete ditch ported; and 

concrete ditch to gated pipe

4 PCS PCS Ported concrete ditch to surge

5 CGS CGS Concrete ditch to gated pipe surge

6 GPP GPP, PGP Gated pipe, pipeline to gated pipe

7 PGS PGS Pipeline to gated surge

8 SRS SRS Side-roll sprinkler

9 MIS MIS Microspray

Soil Physical and Chemical Properties

The NRCS evaluation recorded a soil type for each site. These soil types have been modified over the years since the 

evaluation by the NRCS. Typically older soil type classifications are being combined into broader classifications. The current 

soil classifications are mapped by the NRCS at their Web Soil Survey site (U.S. Department of Agriculture, 2013); however, the 

NRCS does not publish a cross-reference of the changes being made from older classifications to current classifications. The 

Grand Junction NRCS office has a full-time soil scientist who manually cross-referenced the changes in the NRCS evaluation 

soil type names. All 23 of the soil types reported by the NRCS evaluation have changed their names since the evaluation. Table 

9 shows the original soil types, the current soil type, and a soil type code created for the USGS study to identify the soil type. 

The inclusion of soil slope ranges is part of the formal description of the soil type. Differences in slope may affect the hydrologic behavior of the soil type.
26 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Table 9. Original Natural Resources Conservation Service (NRCS) evaluation soil types, the equivalent current 

soil type name, and a soil type code created for the USGS study for all NRCS evaluation soil types (Bob Rayer, 

NRCS, Grand Junction, written commun., September 2011).

[Percent ranges in current soil type column are soil slope ranges; %, percent]

Original NRCS Evaluation Soil Type Current Soil Type USGS Study

Soil Type Code

Agua Fria Clay Loam Agua Fria clay Loam 1–6% AgFCL

Avalon Fine Silty Loam Avalon sandy loam, gravelly substratum, 

2–5% AvSL

Billings Silty Clay Loam Sagers silty clay Loam 0–2% SaSCL

Christianburg Silty Clay Loam Mesa clay loam 0–2% MeCL

Fruita Clay Loam Fruita clay loam 0–2% FrCL

Fruita Very Fine Sandy Loam Fruitland fine sandy loam 0–2% FrFSL

Fruitland Fine Sandy Loam Fruitland fine sandy loam 0–2% FrFSL

Genola Clay Loam Turley clay loam, 0–2% TuCL

Hanksville Silty Clay Loam Killpack silty clay, 2–5% KiSC

Mesa Clay Loam Mesa clay loam 0–2% MeCL

Mesa Gravelly Clay Loam Mesa gravelly clay loam 5–12% MeGCL

Mikim Clay Loam Mikim clay loam 1–3% MiCL

Notal Silty Clay Loam Mesa clay loam 0–2% MeCL

Panitchen Loam Barx—Panitchen complex, 3–12% BarPanComp

Persayo Silty Clay Loam Persayo silty clay loam 0–2% PeSCL

Ravola Clay Loam Turley clay loam, 0–2% TuCL

Ravola Fine Sandy Loam Sagerlite loam, 0–2% SaL-0-2

Ravola Loam Sagerlite loam, 0–2% SaL-0-2

Ravola Sandy Loam Sagerlite loam, 0–2% SaL-0-2

Ravola Very Fine Sandy Loam Sagerlite Loam 2-5% SaL-2-5

Shear Silty Clay Montrose-Delta Complex 0–2% MonDelComp

Stutzman Silty Clay Stutzman silty clay 0-2% StSC

Youngston Fine Sandy Loam Turley clay loam, 0-2% TuCL

The physical and chemical properties of these soil types were retrieved from the Soil Data Mart website (U.S. Department 

of Agriculture, 2012). Table 10 lists the soil physical and chemical properties retrieved for the USGS study. Each soil type is 

represented by a column of soil which is typically divided into one to four horizons. A soil horizon is a layer parallel to the soil 

surface whose physical characteristics differ from the layers above and below (U.S. Department of Agriculture, 2013). Because 

of the complexity of utilizing all soil horizons in an analysis, the USGS study limited the analysis to the first soil horizon, which 

has a depth ranging from 2 to 16 inches depending on the soil type. This is the layer that is exposed to the surface and potentially 

has the most influence on irrigation water uptake. These first horizon properties were then linked to each site record to enable 

analysis of site characteristics by soil physical and chemical properties. The results of a multiple comparison test analysis (Helsel and Hirsch, 2002) did not identify any specific physical or chemical property that correlated in a statistically significant way 

(p-value less than 0.05) with SIE, DP, and irrigation water infiltrated depth of the evaluation sites. While there were statistically 

significant differences found in SIE, DP, and irrigation water infiltrated depth by soil type in the multiple comparison tests, the 

individual physical and chemical properties of the different soil types did not explain these differences.
USGS Study Findings on NRCS Evaluation 27

Table 10. Soil physical and chemical properties retrieved for Natural Resources Conservation Service evaluation soil types.

[Mmhos per centimeter, milli-mhos per centimeter, a measure of electrical conductivity]

Layer Property Type Soil Properties Range of Values Units

1st Horizon Physical Horizon depth Inches

1st Horizon Physical Sand Percent

1st Horizon Physical Silt Percent

1st Horizon Physical Clay Percent

1st Horizon Physical Hydraulic conductivity Minimum, maximum, and mean Micrometers per second

1st 24 inches Physical Hydraulic conductivity Minimum 24 inches Micrometers per second

1st Horizon Physical Water capacity Minimum, maximum, and mean Inches per inch

1st Horizon Physical Linear extensibility Minimum, maximum, and mean Percent

1st Horizon Physical Organic matter Minimum, maximum, and mean Percent

1st Horizon Chemical pH Minimum, maximum, and mean

1st Horizon Chemical Salinity Minimum, maximum, and mean Mmhos per centimeter

Site-Year Record Quality Determination

A “site-year record” contains the data for one site for one irrigation season of evaluation. Because one site was often evaluated for multiple years, the site-year differentiates the different records for a site. For a site-year record to be judged complete, 

the record must have all the primary soil moisture balance input and output fields present: inflow, outflow, infiltrated depth, 

ETc, and DP. Further, a complete record has an internal SIE calculation for the cumulative season values of these five variables, 

which is mathematically consistent. The soil moisture balance for each irrigation event reported by the NRCS evaluation apparently was not required to balance exactly to zero. Checks of this balance in the USGS study showed imbalances of several tenths 

of an inch of water for some irrigation events, and more in a few cases. These imbalances were most likely due to the corrections 

applied to many of the records without explanation; hence, the imbalances cannot be strictly accounted for. 

To evaluate the site records over the course of the NRCS evaluation, the quality criteria used were (1) reasonable starting 

and ending irrigation dates, (2) reasonable frequency of irrigation events for the area, (3) reasonable number of irrigations for 

the area, (4) no obvious data omissions or arithmetic errors in the data, and (5) no reported notes of data collection problems or 

substantial amount of missed data. Based on these quality criteria, site-year records were classified for this analysis by the author 

and NRCS (Frank Riggle, NRCS, written commun., June 27, 2011) as (1) gold standard, (2) usable nongold standard, or (3) notusable. Using these criteria, and also any information available in the annual report narratives, the usable records from the evaluation years 1985 through 1996 were determined to best meet the criteria for accuracy and completeness. These were the evaluation years with the most consistent and best staffed field data collection procedures and analysis practices. The usable records for 

the years from 1985 to 1996 are therefore referred to in this report as the gold standard records. Gold standard records are those 

Grand Valley, Lower Gunnison, and McElmo Creek sites that were evaluated between 1985 and 1996 that have complete records 

with no missing values and for which the data values were internally consistent. Gold standard sites were not required to have 

individual irrigation event data, but 86 percent did have this information. Usable nongold standard sites were those which were 

evaluated after 1996 that had complete records which were internally consistent. Ninety-three percent of nongold standard sites 

had individual irrigation event data. The analyses in this report use the gold standard records, all usable records, or both sets.

Not-usable records were those with incomplete or inconsistent data values, used cablegation, had no soil type listed, or 

had trees as the crop type. Table 11 shows the number of gold standard, usable, and not-usable records by evaluation unit. Gold 

standard records represented 84.0 percent of all usable records and 78.4 percent of all evaluation records. Usable gold standard 

and nongold standard records represented 91.8 percent of all evaluation records. 
28 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Table 11. Number of usable and not usable site-year records by evaluation unit.

Site-Year Record Quality Grand Valley Lower Gunnison McElmo Creek Total Site-Year Records

Total records of all types 224 62 6 292

Gold standard usable 196 23 6 225

Nongold standard usable 15 28 0 43

Total usable records 211 51 6 268

Not-usable (cablegation) 2 0 0 2

Not-usable (incomplete or internally inconsistent data) 11 7 0 18

Not-usable (no soil type given) 0 1 0 1

Not-usable (crop type is trees) 0 3 0 3

Total not usable 13 11 0 24

Summary Statistics and Charts of NRCS Evaluation

Summary statistics were created by the USGS study for NRCS evaluation site variables such as crop type, field acreage, 

years of evaluation, irrigation system type, ETc, DP, and irrigation efficiency. Summary statistics were grouped by (1) all evaluation sites for all Units, (2) all sites in each evaluation basin, (3) crop type, (4) soil type, and (5) irrigation system type.

Depending on the analysis being performed, the USGS study utilized different sets of the evaluation data. For summary 

statistics, the complete span of usable site data from 1985 through 2003 is included (with non-usable site records removed). In 

addition, some summary statistics and charts use the gold standard subset of data. Finally, some statistics and charts also break 

out the statistics for each of the evaluation units. Appendix 3 contains tables of summary statistics for all usable records and for 

all nongold standard records.

Table 12 shows examples of discrete or grouped variable summary statistics for all gold standard site records; table 13 

shows the discrete variable summary statistics for all Grand Valley Unit gold standard evaluation site records, table 14 shows 

the discrete variable summary statistics for all Lower Gunnison Unit gold standard sites; and table 15 shows the discrete variable summary statistics for the McElmo Creek Unit gold standard site records collected in 1993. Table 16 shows examples of 

continuous variable summary statistics for all gold standard site records between 1985 and 1996; table 17 shows the continuous variable summary statistics for all Grand Valley Unit gold standard evaluation site records between 1985 and 1995; table 

18 shows the continuous variable summary statistics for all Lower Gunnison Unit gold standard site records between 1991 and 

1996; and table 19 shows the continuous variable summary statistics for all McElmo Creek Unit gold standard site records collected in 1993. Table 20 shows annual mean results by evaluation unit and year for all reported NRCS evaluation site records, 

and table 21 shows the same results for all gold standard site records.

Table 12. Discrete variable summary statistics for all gold standard site records collected between 1985 and 1996 in the Natural 

Resources Conservation Service evaluation.—Continued

[EDF, earth ditch to feeder tube; EDS, earth ditch to siphon tube; CDV, concrete ditch to various distribution methods; PCS, ported concrete ditch to surge; 

CGS, concrete ditch to gated pipe surge; GPP, gated pipe; PGS, pipeline to gated surge; SRS, side-roll sprinkler; MIS, microspray; GV, Grand Valley Unit; LG, 

Lower Gunnison Unit; ME, McElmo Creek Unit.]

Number of Usable 

Site-Year Records 

by Evaluation Unit

Number of SiteYear Records with 

Irrigation Event 

Data

Number of SiteYear Records by 

Irrigation System 

Type Codes

Number of SiteYear Records by 

Crop Type

Number of SiteYear Records by 

Irrigation System 

Type

Number of Site-Year 

Records by Irrigation Flow Type

Number of SiteYear Records by 

Irrigation

Distribution Type

GV: 196 No: 32 EDF: 2 Alfalfa: 73 Flood: 192 Feeder ditch: 2 Concrete ditch: 88

LG: 23 Yes: 193 EDS: 8 Beans: 12 Microspray: 10 Gated pipe: 60 Ditch: 1

ME: 6 CDV: 81 Corn: 55 Sprinkler: 23 Gated pipe surge: 41 Earth ditch: 10

PCS: 3 Fall grain: 25 Ported: 7 Pipeline: 126

CGS: 4 Grain: 2 Ported surge: 3

GPP: 57 Grapes: 10 Side-roll: 23

PGS: 37 Onions: 6 Siphon tube: 79
USGS Study Findings on NRCS Evaluation 29

Table 12. Discrete variable summary statistics for all gold standard site records collected between 1985 and 1996 in the Natural 

Resources Conservation Service evaluation.—Continued

[EDF, earth ditch to feeder tube; EDS, earth ditch to siphon tube; CDV, concrete ditch to various distribution methods; PCS, ported concrete ditch to surge; 

CGS, concrete ditch to gated pipe surge; GPP, gated pipe; PGS, pipeline to gated surge; SRS, side-roll sprinkler; MIS, microspray; GV, Grand Valley Unit; LG, 

Lower Gunnison Unit; ME, McElmo Creek Unit.]

Number of Usable 

Site-Year Records 

by Evaluation Unit

Number of SiteYear Records with 

Irrigation Event 

Data

Number of SiteYear Records by 

Irrigation System 

Type Codes

Number of SiteYear Records by 

Crop Type

Number of SiteYear Records by 

Irrigation System 

Type

Number of Site-Year 

Records by Irrigation Flow Type

Number of SiteYear Records by 

Irrigation

Distribution Type

SRS: 23 Orchard: 36 Spray: 10

MIS: 10 Pasture: 2

Spring grain: 1

Vegetable: 3

Table 13. Discrete variable summary statistics for only Grand Valley Unit gold standard site records collected between 1985 and 1995 

in the Natural Resources Conservation Service evaluation.

[CDG, concrete ditch to gated pipe; CDP, concrete ditch ported; CDS, concrete ditch to siphon tube; CGS, concrete ditch to gated pipe surge; EDF, earth ditch 

to feeder tube; EDS, earth ditch to siphon tube; GPP, gated pipe; MIS, microspray; PCS, ported concrete ditch to surge; PGP, pipeline to gated pipe; PGS, 

pipeline to gated surge; SRS, side-roll sprinkler; GV, Grand Valley Unit.]

Number of Usable 

Site-Year Records 

by Evaluation Unit

Number of SiteYear Records 

with Irrigation 

Event Data

Number of SiteYear Records by 

Irrigation System 

Type Codes

Number of SiteYear Records by 

Crop Type

Number of SiteYear Records by 

Irrigation System 

Type

Number of Site-Year 

Records by Irrigation Flow Type

Number of SiteYear Records by 

Irrigation 

Distribution Type

GV: 196 No: 23 CDG: 3 Alfalfa:67 Flood:169 Feeder ditch: 1 Concrete ditch: 86

Yes: 173 CDP: 7 Beans: 9 Micro: 10 Gated pipe:50 Ditch: 1

CDS:69 Corn:46 Sprinkler: 17 Gated pipe surge:34 Earth ditch: 6

CGS: 4 Fall grain:25 Ported: 7 Pipeline:103

EDF: 1 Grain: 1 Ported surge: 3

EDS: 5 Grapes:10 Side-roll:17

GPP: 1 Onions: 3 Siphon tube:74

MIS:10 Orchard:31 Spray:10

PCS: 3 Pasture: 2

PGP:46 Spring grain: 1

PGS:30 Vegetable: 1

SRS:17
30 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Table 14. Discrete variable summary statistics for only Lower Gunnison Unit gold standard site records collected between 1991 and 

1996 in the Natural Resources Conservation Service evaluation.

[CDS, concrete ditch to siphon tube; EDF, earth ditch to feeder tube; EDS, earth ditch to siphon tube; PGP, pipeline to gated pipe; PGS, pipeline to gated surge; 

LG, Lower Gunnison Unit]

Number of Usable 

Site-Year Records 

by Evaluation Unit

Number of SiteYear Records 

with Irrigation 

Event Data

Number of SiteYear Records by 

Irrigation System 

Type Codes

Number of SiteYear Records 

by Crop Type

Number of SiteYear Records by 

Irrigation System 

Type

Number of SiteYear Records by 

Irrigation Flow 

Type

Number of SiteYear Records by 

Irrigation 

Distribution Type

LG: 23 No: 9 CDS: 2 Beans:3 Flood: 23 Feeder ditch: 1 Concrete ditch: 2

Yes: 14 EDF: 1 Corn:9 Gated pipe: 10 Earth ditch: 4

EDS: 3 Grain:1 Gated pipe 

surge: 7 Pipeline: 17

PGP:10 Onions:3 Siphon tube: 5

PGS: 7 Orchard:5

Vegetable:2

Table 15. Discrete variable summary statistics for only McElmo Creek Unit gold standard site records collected in 1993 in the Natural 

Resources Conservation Service evaluation.

[SRS, side-roll sprinkler; ME, McElmo Creek Unit.]

Number of Usable 

Site-Year Records 

by Evaluation Unit

Number of SiteYear Records

with Irrigation 

Event Data

Number of SiteYear Records by 

Irrigation System 

Type Codes

Number of SiteYear Records

by Crop Type

Number of SiteYear Records by 

Irrigation System 

Type

Number of SiteYear Records by 

Irrigation Flow 

Type

Number of SiteYear Records by 

Irrigation 

Distribution Type

ME: 6 Yes: 6 SRS: 6 Alfalfa: 6 Sprinkler: 6 Side-roll: 6 Pipeline: 6

Table 16. Continuous variable summary statistics for all gold standard site records collected between 1985 and 1996 in Natural 

Resources Conservation Service evaluation.

[All water quantities are in inches; N, number of records; NA, not applicable; Std Dev, standard deviation]

Statistic Field

Size

Number of 

Irrigation 

Events

Irrigation 

Water 

Inflow

Irrigation 

Water 

Outflow

Infiltrated 

Irrigation 

Water 

Depth

Precipitation Evapotranspiration

Deep 

Percolation

Irrigation 

Efficiency

Minimum 1.4 2.0 11.4 0 3.7 0.4 2.2 0 14.0

1st Quartile 7.0 6.0 39.6 8.5 27.2 2.2 20.3 4.3 33.0

Mean 20.7 7.8 55.8 16.9 38.9 3.5 26.0 15.1 47.4

Median 15.0 7.0 52.5 15.0 37.5 2.9 25.2 12.9 44.0

3d Quartile 26.0 9.0 70.2 22.8 48.8 4.3 33.3 21.3 60.8

Maximum 327.3 22.0 123 80.1 87.9 11.8 41.3 70.7 97.8

Total N 226 226 226 226 226 226 226 226 226

NA 0 0 0 0 0 0 0 0 0

Std Dev 27.5 3.4 22.0 12.1 15.3 2.3 8.1 13.4 18.5
USGS Study Findings on NRCS Evaluation 31

Table 17. Continuous variable summary statistics for Grand Valley Unit gold standard site records collected between 1985 and 1995 in 

Natural Resources Conservation Service evaluation.

[All water quantities are in inches; N, number of records; NA, not applicable; Std Dev, standard deviation]

Statistic Field

Size

Number of 

Irrigation 

Events

Irrigation 

Water 

Inflow

Irrigation 

Water 

Outflow

Infiltrated 

Irrigation 

Water 

Depth

Precipitation Evapotranspiration

Deep

Percolation

Irrigation 

Efficiency

Minimum 1.4 2.0 11.4 0.0 3.7 0.4 2.2 0.0 18.0

1st Quartile 8.1 6.0 40.2 8.6 27.8 2.20 20.8 4.5 34.0

Mean 18.7 7.6 55.4 15.8 39.6 3.6 26.8 14.9 48.5

Median 15.0 7.0 52.3 15.1 37.7 2.9 27.0 12.8 45.5

3d Quartile 26.0 8.0 69.4 21.1 49.4 4.4 34.0 21.1 61.0

Maximum 54.0 22.0 102.7 42.6 77.6 11.8 41.3 60.4 97.8

Total N 196 196 196 196 196 196 196 196 196

NA 0 0 0 0 0 0. 0 0 0

Std Dev 13.7 3.2 19.9 9.2 14.6 2.3 8.2 12.7 17.8

Table 18. Continuous variable summary statistics for Lower Gunnison Unit gold standard site records collected between 1991 and 

1996 in Natural Resources Conservation Service evaluation.

[All water quantities are in inches; N, number of records; NA, not applicable; Std Dev, standard deviation]

Statistic Field

Size

Number of 

Irrigation 

Events

Irrigation 

Water 

Inflow

Irrigation 

Water 

Outflow

Infiltrated 

Irrigation 

Water 

Depth

Precipitation Evapotranspiration

Deep 

Percolation

Irrigation 

Efficiency

Minimum 3.0 4.0 16.7 5.3 7.3 1.0 13.4 0.0 14.0

1st Quartile 3.0 5.0 44.0 10.2 23.6 2.2 18.4 6.0 26.5

Mean 9.3 8.0 66.8 28.3 38.5 3.3 21.1 20.2 31.3

Median 7.0 8.0 66.2 19.1 38.3 3.0 21.5 16.4 29.0

3d Quartile 15.5 11.0 91.2 41.3 47.9 3.8 24.0 25.3 39.0

Maximum 23.0 17.0 123.0 80.1 87.9 6.8 29.1 70.7 55.0

Total N 23 23 23 23 23 23 23 23 23

NA 0 0 0 0 0 0 0 0 0

Std Dev 7.5 3.4 31.4 23.1 19.1 1.6 4.4 17.4 10.0
32 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Table 19. Continuous variable summary statistics for McElmo Creek Unit gold standard site records collected during 1993 in Natural 

Resources Conservation Service evaluation.

[All water quantities are in inches; Abbreviations: N, number of records; NA, not applicable; Std Dev, standard deviation]

Statistic Field

Size

Number of 

Irrigation 

Events

Irrigation 

Water 

Inflow

Irrigation 

Water 

Outflow

Infiltrated 

Irrigation 

Water 

Depth

Precipitation Evapotranspiration

Deep 

Percolation

Irrigation 

Efficiency

Minimum 48.4 12.0 14.1 3.0 11.1 2.0 19.8 0.0 74.9

1st Quartile 60.0 13.5 15.6 3.2 12.5 2.0 20.1 0.0 78.8

Mean 130.5 14.8 23.0 4.6 18.4 2.2 21.7 0.3 78.8

Median 94.0 15.0 23.2 4.7 18.6 2.1 21.0 0.0 79.3

3d Quartile 151.5 15.7 29.5 5.9 23.6 2.3 23.0 0.2 80.0

Maximum 327.3 18.0 32.7 6.5 26.2 2.4 24.8 1.7 80.2

Total N 6 6 6 6 6 6 6 6 6

NA 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Std Dev 105.9 2.1 8.2 1.6 6.6 0.2 2.1 0.7 2.0

Table 20. Annual mean results by Unit and year for all reported Natural Resources Conservation Service evaluation site records.

—Continued

[GV, Grand Valley Unit; LG, Lower Gunnison Unit; ME, McElmo Creek Unit; ETc, crop evapotranspiration; %, percent]

Evaluation 

Unit Year

Site Count 

(Total/

Year)

Mean 

Field 

Size 

(Acres)

Mean 

Number of 

Irrigations

Mean 

Inflow 

(Inches)

Mean 

0utflow 

(Inches)

Mean

Infiltrated 

Depth 

(Inches)

Mean

Precipitation

(Inches)

Mean 

ETc

(Inches)

Mean Deep

Percolation 

(Inches)

Mean

Seasonal

Irrigation

Efficiency 

(Percent)

GV 1985 16 20.4 7.6 63.1 16.8 46.3 7.8 24.3 27.7 29.4%

GV 1986 16 20.5 7.4 55.3 18.6 36.8 8.1 29.9 13.4 42.2%

GV 1987 16 19.4 6.6 53.5 16.1 37.4 4.3 30.1 12.6 46.3%

GV 1988 18 20.8 9.4 54.3 13.6 40.7 3.9 28.4 14.7 47.8%

GV 1989 19 20.7 8.9 52.9 14.4 38.5 2.7 27.5 12.4 49.2%

GV 1990 25 14.9 8.4 61.3 18.6 42.7 1.7 25.4 17.0 42.0%

GV 1991 23 15.2 7.2 56.4 14.9 41.5 2.2 26.6 15.9 45.3%

GV 1992 23 16.2 6.8 57.0 13.8 43.2 2.7 27.9 17.4 45.3%

GV 1993 22 17.1 7.4 51.9 15.1 36.8 3.4 27.0 11.8 48.3%

GV 1994 12 21.0 8.4 67.1 17.8 49.3 2.4 29.5 19.0 45.1%

GV 1995 8 29.8 4.4 42.2 16.6 25.6 2.2 12.9 11.9 32.5%

GV 1999 10 22.6 4.8 33.9 13.4 25.8 n/a n/a 8.4 35.7%

GV 2000 7 19.1 8.0 56.3 13.7 42.6 n/a n/a 14.0 50.7%

GV 2001 3 37.0 7.0 81.2 17.0 62.5 n/a n/a 26.0 47.1%

GV 2002 2 18.2 7.5 48.0 15.6 32.4 n/a n/a 5.5 56.0%

LG 1991 3 24.7 6.3 22.7 11.6 11.1 n/a n/a 13.9 12.2%

LG 1992 3 13.0 7.7 69.5 39.5 30.0 n/a n/a 12.6 25.1%

LG 1993 7 11.9 5.4 62.7 26.5 36.3 n/a n/a 20.6 25.0%

LG 1994 6 7.8 9.5 69.6 27.3 42.3 n/a n/a 20.4 31.5%

LG 1995 6 7.0 9.8 61.8 21.7 40.1 n/a n/a 23.2 27.3%

LG 1996 4 5.9 5.3 78.7 29.2 49.4 n/a n/a 29.8 25.0%
USGS Study Findings on NRCS Evaluation 33

Table 20. Annual mean results by Unit and year for all reported Natural Resources Conservation Service evaluation site records.

—Continued

[GV, Grand Valley Unit; LG, Lower Gunnison Unit; ME, McElmo Creek Unit; ETc, crop evapotranspiration; %, percent]

Evaluation 

Unit Year

Site Count 

(Total/

Year)

Mean 

Field 

Size 

(Acres)

Mean 

Number of 

Irrigations

Mean 

Inflow 

(Inches)

Mean 

0utflow 

(Inches)

Mean

Infiltrated 

Depth 

(Inches)

Mean

Precipitation

(Inches)

Mean 

ETc

(Inches)

Mean Deep

Percolation 

(Inches)

Mean

Seasonal

Irrigation

Efficiency 

(Percent)

LG 1999 5 20.4 6.5 52.1 16.2 36.1 n/a n/a 11.1 47.6%

LG 2000 14 13.9 6.5 57.7 19.1 38.6 n/a n/a 12.9 44.5%

LG 2001 7 18.7 5.8 45.2 10.4 33.4 n/a n/a 13.7 46.8%

LG 2002 2 17.0 5.5 62.3 28.1 34.2 n/a n/a 9.7 39.4%

LG 2003 3 14.3 6.0 60.5 25.5 34.9 n/a n/a 6.4 47.3%

ME 1993 6 130.5 14.8 23.0 4.6 18.4 n/a n/a 0.3 78.5%

GV means 14.7 20.8 7.3 55.6 15.7 40.1 3.8 26.3 15.2 44.4%

LG means 5.5 14.1 6.8 58.4 23.2 35.1 n/a n/a 15.8 33.2%

All means 10.6 22.1 7.4 55.6 18.3 37.3 3.8 26.3 14.9 40.3%

Table 21. Annual Mean results by unit and year for gold standard Natural Resources Conservation Service evaluation site records.

[GV, Grand Valley Unit; LG, Lower Gunnison Unit; ME, McElmo Creek Unit; ETc, crop evapotranspiration, %, percent]

Evaluation

Unit Year

Site Count 

(Total/

Year)

Mean 

Field 

Size 

(Acres)

Mean 

Number of

Irrigations

Mean 

Inflow 

(Inches)

Mean 

0utflow 

(Inches)

Mean

Infiltrated 

Depth 

(Inches)

Mean

Precipitation

(Inches)

Mean 

ETc

 

(Inches)

Mean Deep

Percolation 

(Inches)

Mean 

Seasonal 

Irrigation 

Efficiency 

(Percent)

GV 1985 14 21.5 7.4 54.1 16.3 37.8 7.6 23.8 19.8 33.3%

GV 1986 15 21.2 7.3 52.9 18.0 35.0 8.3 30.2 11.5 44.3%

GV 1987 16 19.4 6.6 53.5 16.1 37.4 4.3 30.1 12.6 46.3%

GV 1988 18 20.8 9.4 54.3 13.6 40.7 3.9 28.4 14.7 47.8%

GV 1989 19 20.7 8.9 52.9 14.4 38.5 2.7 27.5 12.4 49.2%

GV 1990 25 14.9 8.4 61.3 18.6 42.7 1.7 25.4 17.0 42.0%

GV 1991 23 15.2 7.2 56.4 14.9 41.5 2.2 26.6 15.9 45.3%

GV 1992 24 15.9 6.8 56.4 14.2 42.2 2.7 27.5 16.7 45.1%

GV 1993 22 17.1 7.4 51.9 15.1 36.8 3.4 27.0 11.8 48.3%

GV 1994 12 21.0 8.4 67.1 17.8 49.3 2.4 29.5 19.0 45.1%

GV 1995 8 29.8 4.4 42.2 16.6 25.6 2.2 12.9 11.9 32.5%

LG 1992 3 13.0 7.7 69.5 39.5 30.0 4.2 20.7 12.6 25.1%

LG 1993 7 11.9 5.4 62.7 26.5 36.3 1.9 18.8 20.6 25.0%

LG 1994 6 7.8 9.5 69.6 27.3 42.3 2.6 23.5 20.4 31.5%

LG 1995 6 7.0 9.8 61.8 21.7 40.1 5.1 20.3 23.2 27.3%

ME 1993 6 130.5 14.8 23.0 4.6 18.4 2.2 21.7 0.3 78.5%

GV means 17.8 19.8 7.5 54.8 16.0 38.9 3.8 26.3 14.9 43.8%

LG means 5.5 9.9 8.1 65.9 28.7 37.2 n/a n/a 19.2 27.3%

All means 14.0 24.2 8.1 55.6 18.4 37.2 3.6 24.6 15.0 39.8%
34 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

The NRCS evaluation dataset was graphically characterized using frequency charts (figs. 17-20), scatter plots (figs. 21-22), 

and box plots (figs. 23-26) of the primary continuous variables (ETc, irrigation efficiency, DP, water infiltrated depth, and irrigation event duration). These variables were grouped into discrete categories of evaluation area, irrigation system in improvement 

order, SIE, season total DP, and event days.

For some characterizations, two charts are shown: (1) for all usable site records, and (2) for all gold standard site records. In 

addition, the data for some charts are broken out into Grand Valley, Lower Gunnison, and McElmo Creek Units.

Frequency Charts

Figure 17 shows that the Grand Valley and Lower Gunnison Units are similar in the distribution of irrigation system types, 

with concrete ditch (CDV) and gated pipe (GPP) the predominant types. McElmo Creek’s six sites were all side-roll sprinkler 

(SRS) types.

0

20

40

60

80

100

120

CBG EDF EDS CDV PCS CGS GPP PGS SRS MIS

Precent of Sites

Irrigation System Type in Improvement Order

Frequency of Irrigation System Types in System 

Improvement Order by Evaluation Unit

GV Improvement Order LG Improvement Order ME Improvement Order

Figure 17. Frequency chart of irrigation system types by system improvement order1 for all usable sites in 

Grand Valley (GV), Lower Gunnison (LG), and McElmo Creek (ME) Units. [1

CBG, cablegation; EDF, earth ditch 

to feeder tube; EDS, earth ditch to siphon tube; CDV, concrete ditch to various distribution methods; PCS, 

ported concrete ditch to surge; CGS, concrete ditch to gated pipe surge; GPP, gated pipe; PGS, pipeline to 

gated surge; SRS, side-roll sprinkler; MIS, microspray.]
USGS Study Findings on NRCS Evaluation 35

Figure 18. Frequency chart of seasonal irrigation efficiency for all usable sites in Grand Valley (GV), Lower 

Gunnison (LG), and McElmo Creek (ME) Units. 

Figure 18 shows that SIE was mostly distributed from 30 to 80 percent for the Grand Valley Unit, from mostly 20 to 70 

percent for the Lower Gunnison Unit, and from 80 to 90 percent for the McElmo Creek Unit. The high McElmo Creek efficiencies are due to the use of side-roll sprinklers. 

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60 70 80 90 100

Percent of Sites

Seasonal Irrigation Efficiency (percent)

Frequency of Seasonal Irrigation Efficiency by

Evaluation Unit 

GV Irrigation Efficiency LG Irrigation Efficiency ME Irrigation Efficiency
36 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Figure 20 shows the frequency distribution of irrigation event durations for all usable sites. Most irrigation events ranged 

from 1 to 9 days in duration. Eight percent of the events exceeded 10 days, with three single outliers at 20, 24, and 27 days 

in duration (these single events are barely visible on chart). The peak at 2 days is for flood irrigated sites in the Grand Valley 

Unit, with no particular crop type predominating. The later peak at 9 days is due primarily to flood irrigation of alfalfa sites in 

the Grand Valley Unit. Most of the 10 day and longer events are for side-roll sprinkler sites in the Grand Valley Unit. The three 

outliers are (1) 20 days for concrete ditch to siphon tube irrigation of fall grain in the Grand Valley Unit; (2) 24 days for pipeline 

to gated pipe irrigation of fall grain in the Grand Valley Unit; and (3) 27 days for side-roll sprinkler irrigation of alfalfa in the 

McElmo Creek Unit.

0

10

20

30

40

50

60

70

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75

Percent of Sites

Season Total Deep Percolation (inches)

Frequency of Season Total Deep Percolation

by Evaluation Unit 

GV Deep Percolation LG Deep Percolation ME Deep Percolation

Figure 19. Frequency chart of deep percolation for all usable sites in Grand Valley (GV), Lower Gunnison 

(LG), and McElmo Creek (ME) Units. 

Figure 19 shows that generally DP was distributed from 0 to about 25 inches for the Grand Valley Unit, roughly the same 

for the Lower Gunnison Unit, and not above 5 inches for the McElmo Creek Unit.
USGS Study Findings on NRCS Evaluation 37

Deep Percolation versus Seasonal Irrigation Efficiency

One of the more important results from the NRCS evaluation is a determination of how DP varies with SIE changes. The 

NRCS investments in irrigation system improvements lead to increases in seasonal irrigation efficiency, as demonstrated by the 

irrigation system improvement order. The question then arises as to how much deep percolation is reduced for these investments 

in irrigation efficiency improvements. A scatter plot of DP versus SIE with a trend line of changes in DP for changes in SIE 

illustrates the dependency of DP on SIE (figs. 21 and 22).

The trend line method chosen for the USGS study is the LOESS smoothing curve (Helsel and Hirsch, 2002). LOESS stands 

for LOcal regrESSion. LOESS is a non-parametric statistical method, meaning that the data need not be normally (Gaussian) 

distributed. The LOESS method uses a nearest neighbor’s algorithm to select how much of the surrounding data are used to fit a 

local regression polynomial for each pair of DP and SIE values. The nearest data points are thus given the most weight in determining the LOESS local regression model for a given point. The result is a smoothing curve of running mean values (Helsel and 

Hirsch, 2002).

Two subsets of NRCS evaluation data were plotted for this analysis—all usable sites from 1985 to 2003 (268 pairs of data) 

and the Grand Valley Unit gold standard sites from 1985 to 1996 (168 data pairs). For the Lower Gunnison and McElmo Creek 

Units, there were not enough data points to calculate a reliable LOESS smoothing curve.

Figure 20. Frequency chart of irrigation event duration in days for all usable sites in Grand Valley, Lower Gunnison, and McElmo 

Creek Units.

0

2

4

6

8

10

12

14

16

18

20

Percent of Sites

Days

Frequency of Irrigation Event Duration for All Usable Sites 
38 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Figure 21. Scatter plot chart with LOESS trend line of deep percolation versus seasonal irrigation efficiency for all usable 

Grand Valley, Lower Gunnison, and McElmo Creek Unit sites from 1985 to 2003. 

Figure 21 plots DP against SIE for all 268 usable site-year records. In figure 21, the LOESS trend line (red trace) shows 

that as SIE increases from about 10 to 35 percent, a rapid decline occurs in DP. Above 35 percent SIE, DP continues to decline 

but at a slower rate. Because increases in SIE require more advanced irrigation technology, the implication is that improvements 

from the most primitive types of systems up to middle level irrigation technology yield the largest improvements in DP, while 

improvements from middle levels of system types to the most advanced types yield less improvement in DP by comparison. This 

could have policy implications for which on-farm improvement projects are selected for funding by water managers.

The LOESS trend line method does not provide a single prediction equation (as would a regression model), but it does produce predicted DP and SIE values along a line that approximates the distribution of the data. Table 22 shows a summary of the 

LOESS values of DP for approximately every 5 percent increase in value of SIE from 20 percent to 95 percent for the LOESS 

trend line in figure 21.

0 2 0 4 0 6 0 8 0 100

Seasonal Irrigation Efficiency (percent)

-10

10

30

50

70

Deep Percolation (inches)

Deep Percolation versus Irrigation Efficiency for All Usable Sites
USGS Study Findings on NRCS Evaluation 39

Table 22. Summary table of LOESS predicted values of 

deep percolation and seasonal irrigation efficiency from 

figure 21. 

[LOESS, Local regression trend line]

LOESS Seasonal

Irrigation Efficiency

(Percent)

LOESS Predicted

Deep Percolation

(Inches)

20.0 39.7

25.1 31.7

30.2 24.3

35.0 19.4

40.1 16.2

45.2 13.9

50.0 12.1

55.1 9.7

60.2 7.8

65.0 6.2

70.1 4.6

75.2 3.2

80.3 1.9

85.0 0.6

90.1 –0.6

95.2 –1.9

Because of the downward trend of the LOESS trend line as it approaches 100 percent SIE, the predicted values are actually 

negative starting at 90.1 percent SIE, which is a physical impossibility. This reinforces the fact that table 22 only represents an 

approximation and should not be expected to perfectly reflect the relation between DP and SIE for the scatter data in figure 21. 

This is particularly true for DP at the lowest and highest values of SIE where the underlying data are sparse.
40 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Figure 22. Scatter plot chart with LOESS trend line of deep percolation versus seasonal irrigation efficiency for Grand 

Valley Unit gold standard sites. 

0 2 0 4 0 6 0 8 0 100

Seasonal Irrigation Efficiency (percent)

-10

10

30

50

Deep Percolation (inches)

Deep Percolation versus Irrigation Efficiency for Grand Valley Gold Std Sites

Figure 22 shows the relation between SIE and DP for the 168 Grand Valley Unit gold standard sites. It is apparent by comparing figure 21 with figure 22 that the response of DP to changes in SIE for the Grand Valley Unit gold standard sites is very 

similar to that of the total population of usable sites in the NRCS evaluation. It should again be noted that the LOESS curve in 

figure 22 is an approximation and should not be expected to perfectly reflect the relation between DP and SIE for the scatter data 

in figure 22. The LOESS predicted values of DP for approximately every 5 percent from 20 percent SIE to 95 percent SIE for 

the Grand Valley Unit gold standard sites are shown in table 23.
USGS Study Findings on NRCS Evaluation 41

Table 23. Summary table of LOESS predicted values of 

deep percolation and seasonal irrigation efficiency from 

figure 22.

[LOESS, local regression trend line]

LOESS Seasonal

Irrigation Efficiency

(Percent)

LOESS Predicted

Deep Percolation

(Inches)

20.0 43.2

25.4 34.2

30.3 26.3

35.2 20.4

40.1 16.9

45.0 14.3

50.3 11.8

55.2 9.4

60.2 7.8

65.1 6.3

70.0 4.8

75.3 3.4

80.2 2.2

85.1 1.0

90.0 –0.2

95.3 –1.5

Deep percolation and irrigation system box plots are a convenient way to illustrate the differences between groups of data. 

The median value (50 percentile) for a category of data is shown as a red dot. The top of the box is the 75 percentile value for 

the data group, and the bottom of the box is the 25 percentile value. The span (height of box) from 25 to 75 percentile is called 

the interquartile range. The whiskers above and below the box show the largest and smallest data values within 1.5 times the 

interquartile range. Values outside this whisker range are shown as individual black dots. The values in parentheses at the top of 

each box are the number of samples represented by each box column.

Box plots were created for DP by irrigation system type (in system improvement order), and for SIE by irrigation system 

type in improvement order. Four datasets were used for these two plots: (1) all usable sites, (2) Grand Valley Unit gold standard 

sites, (3) Lower Gunnison Unit gold standard sites, and (4) McElmo Creek Unit gold standard sites.

Additionally, box plots were created for DP by crop type and SIE by crop type for all gold standard sites in the three evaluation units. Box plots of DP by crop type and SIE by crop type are shown separately for flood irrigation only, sprinkler irrigation only, and microspray irrigation only for all gold standard sites. Appendix 4 shows additional box plots of DP, SIE, crop 

evapotranspiration, and irrigation water infiltrated depth, grouped variously by soil type, crop rooting depth, irrigation system 

improvement order, and irrigation system type.

Figure 23 shows that as irrigation systems advance in order of improvement, the variability in DP (overall height of the 

blue boxes) is reduced. There is also a general decline in median DP for system types 7 through 9. This means that at higher levels of system technology, there is increased confidence that the amount of DP is more predictable, which is of benefit in terms of 

irrigation management. Because the more advanced irrigation technologies—by their design—contribute less DP as they apply 

water to the crop, they also make it less likely that the operator will contribute to DP through inattention or inexperience. 

It should be noted that a small amount of DP is necessary to manage salt in the root zone of the soil. How much DP is 

required to flush salt from the root zone is a function of crop salt tolerance, the incoming salt level of the irrigation water, and 

salt concentrations inherent in the type of soil (Frank Riggle, NRCS, written commun., April 20, 2013). This necessary DP is 

referred to as the “leaching requirement.” The leaching requirement for the Grand Valley Unit has been estimated to be from 5 to 

15 percent of annual ETc (Grand Valley Annual Report, 1989, in U.S. Department of Agriculture, 1986–2003).
42 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Figure 23. Box plot chart of deep percolation versus irrigation system types in order of improvement (1–9) for all usable 

Grand Valley, Lower Gunnison, and McElmo Creek Unit sites. 

12345678 9

Irrigation System Types in Order of Improvement

0

20

40

60

Deep Percolation (inches)

All Usable Sites Deep Percolation versus Improvement Order

EDF EDS CDV PCS CGS GPP PGS SRS MIS

 (4) (9) (92) (3) (4) (77) (46) (23) (10) 

EXPLANATION

Sample size

Data value greater than 1.5 times the

interquartile range outside the box

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

Interquartile range

(11)

EDF Earth Ditch to Feeder Ditch

EDS Earth Ditch to Siphon Tubes

CDV Concrete Ditch to Various Distribution

PCS Ported Concrete Ditch to Surge

CGS Concrete Ditch to Gated Pipe Surge

GPP Gated Pipe

PGS Pipeline to Gated Pipe Surge

SRS Side-roll Sprinkler

MIS Microspray

Irrigation System Types

Figure 24 shows the same general trend of declining DP and declining DP variability as the box plot shown in figure 23. 

This box plot includes only Grand Valley Unit gold standard records.
USGS Study Findings on NRCS Evaluation 43

Figure 24. Box plot chart of deep percolation versus irrigation system types in order of improvement (1–9) for Grand Valley 

Unit gold standard sites.

12345678 9

Irrigation System Types in Order of Improvement

0

20

40

60

Deep Percolation (inches)

Grand Valley Unit Gold Standard Sites Deep Percolation versus Improvement Order

EDF EDS CDV PCS CGS GPP PGS SRS MIS

 (1) (5) (79) (3) (4) (47) (30) (17) (10) 

EDF Earth Ditch to Feeder Ditch

EDS Earth Ditch to Siphon Tubes

CDV Concrete Ditch to Various Distribution

PCS Ported Concrete Ditch to Surge

CGS Concrete Ditch to Gated Pipe Surge

GPP Gated Pipe

PGS Pipeline to Gated Pipe Surge

SRS Side-roll Sprinkler

MIS Microspray

Irrigation System Types EXPLANATION

Sample size

Data value greater than 1.5 times the

interquartile range outside the box

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

Interquartile range

(11)

Figure 25 shows a box plot of DP by irrigation system improvement order for Lower Gunnison Unit gold standard sites. 

There is no clear trend of declining DP as the improvement order increases for Lower Gunnison Unit sites. This is most likely 

because of the limited number of samples for the Lower Gunnison Unit.
44 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Figure 26 shows that only side-roll irrigation systems are represented in the NRCS evaluation for the McElmo Creek Unit, 

and the DP is tightly grouped below 0.5 inch except for the one outlier at about 1.75 inches. This is quite low DP when compared with DP for other types of irrigation systems in the other units.

Figure 25. Box plot chart of deep percolation versus irrigation system improvement order for Lower Gunnison Unit gold standard sites. 

123456 7

Irrigation System Type in Order of Improvement

0

20

40

60

Deep Percolation (inches)

Lower Gunnison Unit Gold Standard Sites Deep Percolation versus Improvement Order

EDF EDS CDV PCS CGS GPP PGS

 (1) (3) (2) (0) (0) (10) (7) 

EDF Earth Ditch to Feeder Ditch

EDS Earth Ditch to Siphon Tubes

CDV Concrete Ditch to Various Distribution

PCS Ported Concrete Ditch to Surge

CGS Concrete Ditch to Gated Pipe Surge

GPP Gated Pipe

PGS Pipeline to Gated Pipe Surge

SRS Side-roll Sprinkler

MIS Microspray

Irrigation System Types EXPLANATION

Sample size

Data value greater than 1.5 times the

interquartile range outside the box

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

Interquartile range

(11)
USGS Study Findings on NRCS Evaluation 45

Figure 26. Box plot chart of deep percolation versus irrigation system improvement order for McElmo Creek Unit gold 

standard sites. 

Irrigation System Type in Order of Improvement

0.0

0.5

1.0

1.5

Deep Percolation (inches)

McElmo Unit Gold Standard Sites Deep Percolation versus Improvement Order

 8

SRS

(6)

EDF Earth Ditch to Feeder Ditch

EDS Earth Ditch to Siphon Tubes

CDV Concrete Ditch to Various Distribution

PCS Ported Concrete Ditch to Surge

CGS Concrete Ditch to Gated Pipe Surge

GPP Gated Pipe

PGS Pipeline to Gated Pipe Surge

SRS Side-roll Sprinkler

MIS Microspray

Irrigation System Types EXPLANATION

Sample size

Data value greater than 1.5 times the

interquartile range outside the box

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

Interquartile range

(11)

Seasonal Irrigation Efficiency and Irrigation System Type

Figure 27 shows a box plot for SIE by types of irrigation systems for all usable site-year records. Figure 27 demonstrates 

that as irrigation systems advance in order of improvement, the median values (red dot in the vertical box) of SIE increase, with 

the exception of MIS (microspray) irrigation in the far right box. It is possible that because the use of microspray systems was in 

its infancy in the Grand Valley Unit during the NRCS evaluation, the inherent high efficiency of microspray was not being fully 
46 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Figure 27. Box plot chart of seasonal irrigation efficiency versus irrigation system improvement order for all usable sites in 

the Grand Valley, Lower Gunnison, and McElmo Creek Units. 

1234 5678 9

Irrigation System Type in Order of Improvement

0

20

40

60

80

100

Seasonal Irrigation Efficiency (percent)

All Usable Sites Irrigation Efficiency versus Improvement Order

EDF EDS CDV PCS CGS GPP PGS SRS MIS

 (4) (9) (92) (3) (4) (77) (46) (23) (10) 

EDF Earth Ditch to Feeder Ditch

EDS Earth Ditch to Siphon Tubes

CDV Concrete Ditch to Various Distribution

PCS Ported Concrete Ditch to Surge

CGS Concrete Ditch to Gated Pipe Surge

GPP Gated Pipe

PGS Pipeline to Gated Pipe Surge

SRS Side-roll Sprinkler

MIS Microspray

Irrigation System Types EXPLANATION

Sample size

Data value greater than 1.5 times the

interquartile range outside the box

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

Interquartile range

(11)

optimized by the early adopters of this type of irrigation (Frank Riggle, NRCS, written commun., May 30, 2013). There is little 

difference in median SIE between SRS and MIS systems. However, this might simply imply that both systems are very similar 

in efficiency. No reduction in SIE variability is evident as the improvement level of the irrigation system increases. This may 

have been due to operators being in the learning phase with the more advanced types of irrigation technology during the NRCS 

evaluation.
USGS Study Findings on NRCS Evaluation 47

Figure 28 shows the change in SIE with increasing system improvement order for only the Grand Valley Unit gold standard 

sites. The pattern seen in figure 28 is quite similar to that of figure 27, which is to be expected because most of sites in figure 27 

are Grand Valley Unit sites. 

Figure 28. Box plot chart of seasonal irrigation efficiency versus irrigation system improvement order for Grand Valley Unit 

gold standard sites. 

12345678 9

Irrigation System Type in Order of Improvement

0

20

40

60

80

100

Seasonal Irrigation Efficiency (percent)

Grand Valley Unit Gold Standard Sites Irrigation Efficiency versus Improvement Order

EDF EDS CDV PCS CGS GPP PGS SRS MIS

EDF Earth Ditch to Feeder Ditch

EDS Earth Ditch to Siphon Tubes

CDV Concrete Ditch to Various Distribution

PCS Ported Concrete Ditch to Surge

CGS Concrete Ditch to Gated Pipe Surge

GPP Gated Pipe

PGS Pipeline to Gated Pipe Surge

SRS Side-roll Sprinkler

MIS Microspray

Irrigation System Types EXPLANATION

Sample size

Data value greater than 1.5 times the

interquartile range outside the box

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

Interquartile range

(11)

 (1) (5) (80) (3) (4) (53) (38) (17) (10) 
48 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Figure 29 shows the change in SIE with increases in system improvement order for the Lower Gunnison Unit. The results 

are highly variable and do not indicate a strong pattern of SIE increasing with irrigation system improvements.

Figure 29. Box plot chart of seasonal irrigation efficiency versus irrigation system improvement order for Lower Gunnison 

Unit gold standard sites. 

123456 7

System Improvement Order

10

20

30

40

50

Seasonal Irrigation Efficiency (percent)

Lower Gunnison Gold Standard Sites Irrigation Efficiency versus Improvement Order

EDF EDS CDV PCS CGS GPP PGS

 (3) (4) (12) (0) (0) (24) (8) 

EDF Earth Ditch to Feeder Ditch

EDS Earth Ditch to Siphon Tubes

CDV Concrete Ditch to Various Distribution

PCS Ported Concrete Ditch to Surge

CGS Concrete Ditch to Gated Pipe Surge

GPP Gated Pipe

PGS Pipeline to Gated Pipe Surge

SRS Side-roll Sprinkler

MIS Microspray

Irrigation System Types EXPLANATION

Sample size

Data value greater than 1.5 times the

interquartile range outside the box

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

Interquartile range

(11)
USGS Study Findings on NRCS Evaluation 49

Figure 30 indicates that SIE is clustered for the McElmo Creek Unit sites between 75 and 80 percent for five of the six 

sites, with the outlier still close at about 74.5 percent.

Figure 30. Box plot chart of seasonal irrigation efficiency versus irrigation system improvement order for McElmo Creek Unit 

gold standard sites. 

Irrigation System Type in Order of Improvement

74

76

78

80

Seasonal Irrigation Efficiency (percent)

McElmo Creek Unit Gold Standard Sites Irrigation Efficiency versus

Improvement Order

 8

SRS

(6)

EXPLANATION

Sample size

Data value greater than 1.5 times the

interquartile range outside the box

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

Interquartile range

(11) EDF Earth Ditch to Feeder Ditch

EDS Earth Ditch to Siphon Tubes

CDV Concrete Ditch to Various Distribution

PCS Ported Concrete Ditch to Surge

CGS Concrete Ditch to Gated Pipe Surge

GPP Gated Pipe

PGS Pipeline to Gated Pipe Surge

SRS Side-roll Sprinkler

MIS Microspray

Irrigation System Types
50 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Deep Percolation and Crop Type

Figure 31 shows the variation of DP by crop type for all gold standard sites. The large DP variability in grain is most likely 

caused by having only two samples of that crop type. There does not appear to be a strong correlation between DP and crop 

type, with the exception that onions and grain have higher median DP than the other crop types.

Figure 31. Box plot chart of deep percolation versus crop type for all gold standard sites. 

Alfalfa

Beans

Corn

Fall Grain

Grain

Grapes

Onions

Orchard

Pasture

Spring Grain

Vegetable

Crop

0

20

40

60

Deep Percolation (inches)

All Gold Standard Sites Deep Percolation versus Crop Type

EXPLANATION

Sample size

Data value greater than 1.5 times the

interquartile range outside the box

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

Interquartile range

(11)

 (73) (12) (55) (25) (2) (10) (6) (36) (2) (1) (3)
USGS Study Findings on NRCS Evaluation 51

Figure 32. Box plot chart of deep percolation versus crop type for all gold standard flood irrigation sites.

Alfalfa

Beans

Corn

Fall Grain

Grain

Grapes

Onion s

Orchard

Pasture

Spring Grain

Vegetable

Crop

0

20

40

60

Deep Percolation (inches)

All Gold Standard Flood Sites Deep Percolation versus Crop Type 

 (54) (12) (55) (22) (2) (0) (6) (36) (2) (0) (3)

EXPLANATION

Sample size

Data value greater than 1.5 times the

interquartile range outside the box

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

Interquartile range

(11)
52 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Figure 33. Box plot chart of deep percolation versus crop type for all gold standard sprinkler irrigation sites.

Alfalfa Beans Corn Fall Grain Grain Grapes Onions Orchard Pasture Spring Grai n

Crop

0

5

10

15

Gold Standard Sprinkler Irrigation Sites Deep Percolation versus Crop Type

Deep Percolation (inches)

 (19) (0) (0) (3) (0) (0) (0) (0) (0) (1)

EXPLANATION

Sample size

Data value greater than 1.5 times the

interquartile range outside the box

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

Interquartile range

(11)

Figures 32-34 show DP by crop type for flood irrigation, sprinkler irrigation, and microspray sites. The pattern seen for 

flood irrigation sites in figure 32 is quite similar to that of figure 31, which would be expected because 192 of the 225 site-year 

records in figure 31 represent flood irrigation. Figure 33 shows deep percolation for sprinkler irrigation sites. Almost all of the 

site-year records in figure 33 represent side-roll sprinkler irrigation of alfalfa, which typically has very low deep percolation. 

Figure 34 shows deep percolation for microspray sites, all of which are Grand Valley Unit grapes sites. The 10 sites in figure 34 

show a mean deep percolation of about 5 inches per season, which indicates the superior DP performance of microspray systems 

compared with flood irrigation systems.
USGS Study Findings on NRCS Evaluation 53

Figure 34. Box plot chart of deep percolation versus crop type for all gold standard microspray sites.

Crop

0

2

4

6

8

10

All Gold Standard Microspray Sites Deep Percolation versus Crop Type

Deep Percolation (inches)

EXPLANATION

Sample size

Data value greater than 1.5 times the

interquartile range outside the box

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

Interquartile range

(11)

(10)

Grapes
54 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Seasonal Irrigation Efficiency and Crop Type

Figure 35 shows SIE by crop type for all gold standard sites. SIE ranges from about 25 percent for grain up to about 75 

percent for grapes using microspray technology, as would be expected when comparing flood irrigation systems with microspray 

systems.

Figure 35. Box plot chart of seasonal irrigation efficiency versus crop type for all gold standard sites.

Alfalfa

Beans

Corn

Fall Grain

Grain

Grapes

Onion s

Orchard

Pasture

Spring Grain

Vegetable

Crop

0

20

40

60

80

100

Seasonal Irrigation Efficiency (percent)

All Gold Standard Sites Seasonal Irrigation Efficiency versus Crop Type

EXPLANATION

Sample size

Data value greater than 1.5 times the

interquartile range outside the box

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

Interquartile range

(11)

 (73) (12) (55) (25) (2) (10) (6) (36) (2) (1) (3)
USGS Study Findings on NRCS Evaluation 55

Figure 36 illustrates the variability of SIE by crop type for all gold standard flood irrigation sites. Alfalfa sites comprise the 

largest group, with a median irrigation efficiency of about 50 percent, while the next largest group, orchard, has a median irrigation efficiency of about 65 percent. Alfalfa uses both flood and side-roll sprinkler irrigation, while orchards mainly use microspray irrigation.

Figure 36. Box plot chart of seasonal irrigation efficiency versus crop type for all gold standard flood irrigation sites.

Alfalfa

Beans

Corn

Fall Grain

Grain

Grapes

Onions

Orchard

Pasture

Spring Grain

Vegetable

Crop

0

20

40

60

80

Seasonal Irrigation Efficiency (percent)

All Gold Standard Flood Irrigation Sites Irrigation Efficiency versus Crop Type

 (54) (12) (55) (22) (2) (0) (6) (36) (2) (0) (3)

EXPLANATION

Sample size

Data value greater than 1.5 times the

interquartile range outside the box

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

Interquartile range

(11)
56 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Figure 37 shows the variability of SIE by crop type for all gold standard sprinkler irrigation sites. All but four of the sites 

that use sprinkler technology are alfalfa sites, found primarily in the Lower Gunnison Unit. Their median efficiency is almost 80 

percent. The low efficiency of the spring grain site corresponds with high DP reported for that site as seen in figure 33.

Figure 37. Box plot chart of seasonal irrigation efficiency versus crop type for all gold standard sprinkler irrigation sites.

Alfalfa

Beans

Corn

Fall Grain

Grain

Grapes

Onions

Orchard

Pasture

Spring Grain

Crop

40

50

60

70

80

90

100

Seasonal Irrigation Efficiency (percent)

All Gold Standard Sprinkler Irrigation Sites Irrigation Efficiency versus Crop Type

EXPLANATION

Sample size

Data value greater than 1.5 times the

interquartile range outside the box

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

Interquartile range

(11)

 (19) (0) (0) (3) (0) (0) (0) (0) (0) (1)
USGS Study Findings on NRCS Evaluation 57

Figure 38 shows a median SIE of about 75 percent for the 10 sites with grapes and microspray technology. These 10 sites 

are all located in the Grand Valley Unit.

Figure 38. Box plot chart of seasonal irrigation efficiency versus crop type for all gold standard microspray sites.

Crop

60

70

80

90

 (Seasonal Irrigation Efficiency (percent)

All Gold Standard Microspray Irrigation Sites Irrigation Efficiency versus Crop Type

Grapes

EXPLANATION

Sample size

Data value greater than 1.5 times the

interquartile range outside the box

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

Interquartile range

(11)

(10)
58 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Multiple Comparison Statistics

Continuous variables are made up of a series of measurements (for example, SIE), whereas discrete variables are categories 

(for example, crop type). Continuous variables are often grouped by discrete variables (for example, SIE by crop type). Tests 

were performed to determine whether the median value of a primary NRCS evaluation continuous variable (SIE, DP, ETc, or 

infiltrated depth of irrigation water) significantly differs when grouped by a discrete category variable (irrigation system type, 

crop type, soil type, evaluation unit, evaluation year, crop rooting depth, or number of irrigation events). For example, it is possible to test whether DP has different median values that are statistically significant when grouped by crop type.

A ranked multiple comparison test was performed using the USGS library functions in S-PLUS (Lorenz and others, 2011) 

to perform these tests (Helsel and Hirsch, 2002). The ranked test was used because the continuous variables were not necessarily normally distributed. The ranked multiple comparison test indicates whether a significant difference in median value exists 

between two categories, but does not give the actual magnitude of the differences between the categories. If a significant median 

difference between two categories was detected by the multiple comparison test, then a Hodges-Lehmann estimate of the value 

of the difference was performed in S-PLUS (Helsel and Hirsch, 2002). The Hodges-Lehmann estimate gives the percent difference in median value for the continuous variable between two categories of the group.

Some of the comparisons yielded statistically significant results at a 95 percent confidence level (table 24). A “yes” in a 

cell of table 24 indicates that a statistically significant difference was found for the column category of the continuous response 

row variable, while a “no” indicates that no statistically significant difference was found. For example, DP was not found to 

have significant differences in median values when grouped by evaluation year. Many of these relations would be expected, such 

as irrigation efficiency depending significantly on different types of irrigation system technology, or evapotranspiration being 

dependent on crop type. Other relations, such as infiltrated depth of irrigation water being dependent on evaluation year, are not 

intuitive. It is beyond the scope of the USGS study to provide a physical explanation of these test results; tables 24-26 characterize the NRCS evaluation results and are provided for use by water managers. See appendix 5 for the remainder of the multiple 

comparison test results.

Table 24. Multiple comparisons performed on Natural Resources Conservation Service evaluation dataset with yes-no indication 

of significant correlations for all usable site-year records.

[Yes indicates a statistically significant correlation was found at the 95 percent confidence level between the categories and the median continuous response 

variable; No indicates that no statistically significant correlation was found.

Continuous Response 

Variable Category Variables

Irrigation 

System Type in 

Improvement 

Order

Crop Type Soil Type Evaluation 

Unit

Evaluation 

Year

Crop Rooting 

Depth

Number of 

Irrigation 

Events

Irrigation efficiency Yes Yes Yes Yes Yes Yes No

Deep percolation Yes Yes Yes Yes No Yes No

Crop evapotranspiration No Yes No Yes Yes Yes No

Infiltrated depth No No Yes Yes Yes No No

Table 25 shows an example of a multiple comparison chart that compares SIE for various irrigation system types, while 

table 26 shows the comparison of DP for the same irrigation system types. To read the chart, use the following example. In table 

25 find the cell containing +36 in the row labeled “EDF” (earth ditch to feeder tube). The column irrigation system type for the 

+36 cell is PGS, or pipeline to gated surge. The conclusion from the value of +36 in this cell is that system type PGS (column) 

has a 36 percent greater median irrigation efficiency than system type EDF (row) as indicated by the + (positive) sign, and the 

36 percent value has a 95 percent confidence of being correct. If there had been a – (negative) sign on the 36, then the opposite 

conclusion would be drawn—that the median efficiency of the PGS column system type is 36 percent lower than the median 

efficiency of the EDF row system type. 

In terms of NRCS salinity reduction efforts, the positive values of SIE in table 25 for the more advanced types of irrigation 

systems are desirable because they demonstrate that SIE increases with the more advanced systems. Similarly, negative values 
USGS Study Findings on NRCS Evaluation 59

for DP in table 26 for the more advanced types of irrigation systems are also desirable, indicating that DP is reduced for more 

advanced system types. Positive values for SIE in table 25 indicate higher SIE for the advanced system types, while negative 

values of DP in table 26 indicate lower DP for the advanced system types. These results agree with the falling median DP and 

rising median SIE shown in the box plots for DP and SIE by irrigation system type (fig. 23 and fig. 27).

Table 25. Differences in median irrigation efficiency by system improvement order for all usable site-year records.

[Numbers at row and column intersections indicate the statistically significant difference between the median seasonal irrigation efficiency for the column 

system type as compared to the median seasonal irrigation efficiency for the row system type, significant at the 95 percent confidence level; EDF, earth ditch to 

feeder tube; EDS, earth ditch to siphon tube; CDV, concrete ditch to various distribution methods; PCS, ported concrete ditch to surge; CGS, concrete ditch to 

gated pipe surge; GPP, gated pipe; PGS, pipeline to gated surge; SRS, side-roll sprinkler; MIS, microspray]

Irrigation 

System 

Type

Difference in Median Seasonal Irrigation Efficiency of Column System

Type Over Row System Type (Percent)

EDF EDS CDV PCS CGS GPP PGS SRS MIS

EDF +36 +35 +36

EDS +20 +31 +52 +52

CDV +16 +35 +36

PCS

CGS +35

GPP +28 +30

PGS +20

SRS

MIS

Table 26. Multiple comparisons of deep percolation by improvement order irrigation system type codes for all usable site-year 

records.

[Numbers at row and column intersections indicate the statistically significant difference between the median seasonal irrigation efficiency for the column 

system type as compared to the median seasonal irrigation efficiency for the row system type, significant at the 95 percent confidence level; EDF, earth ditch to 

feeder tube; EDS, earth ditch to siphon tube; CDV, concrete ditch to various distribution methods; PCS, ported concrete ditch to surge; CGS, concrete ditch to 

gated pipe surge; GPP, gated pipe; PGS, pipeline to gated surge; SRS, side-roll sprinkler; MIS, microspray.]

Irrigation 

System 

Type

Difference in Median Deep Percolation of Column System Type

Over Row System Type (Inches)

EDF EDS CDV PCS CGS GPP PGS SRS MIS

EDF

EDS –8

CDV –9 –14 –12

PCS

CGS

GPP –10

PGS

SRS

MIS
60 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Soil Moisture Balance Models

To test the implicit data collection and data processing assumptions that resulted in the NRCS evaluation dataset, 12 sites in 

the Grand Valley Unit from 1989 to 1993 were selected for soil moisture balance (SMB) modeling. It was not possible to model 

sites in the other evaluation units due to a lack of daily ETc data for those units. The sites selected for modeling included four 

crops (alfalfa, corn, grapes, and fall grain), and five different irrigation system technologies (table 27). These choices represented 

a good cross-section of system types and crop types. 

Table 27. Summary of sites selected from Natural Resources Conservation Service evaluation dataset for 

soil moisture balance modeling.

[CDV, concrete ditch to various distribution methods; GPP, gated pipe; SRS, side-roll sprinkler; PGS, pipeline to gated surge; 

MIS, microspray.]

Crop Type Irrigation System Type Code Evaluation Years Number of Sites Modeled

Alfalfa CDV 1989 1

Alfalfa GPP 1989 1

Alfalfa SRS 1989, 1993 2, 2

Alfalfa PGS 1993 2

Corn GPP 1989 2

Grapes MIS 1989 1

Fall Grain CDV 1991 1

An SMB model is a mathematical spreadsheet model of the daily sum of water inputs and outputs for an evaluation site for 

one irrigation season. The USGS study SMB models enable the testing of assumptions contained in the reported NRCS evaluation data for the site being modeled. Per-irrigation-event data are required for the site, as well as daily ETp

 values. Site crop and 

soil characteristics are taken into account. Calculated daily SMBs are compared with reported balances. Customized ET crop 

coefficient curves are constructed for each site to enable calculation of ETc. 

The SMB models were created in Microsoft Excel 2010 (Microsoft Corporation, 2010). The original versions of these SMB 

model spreadsheets were built as part of another USGS study (Mayo, 2008). 

Soil Moisture Balance Calculations

The basic soil moisture formula is

Daily Ending Soil Moisture = Previous Daily Ending Soil Moisture + Daily Moisture Inputs – Daily Moisture Outputs (3)

where 

Daily Moisture Inputs are inches of precipitation and irrigation applied, and 

Daily Moisture Outputs are inches of ETc, runoff, and DP. 

Precipitation is the net precipitation, taking into account runoff from the rain event. The net irrigation applied to a floodirrigated field is the inflow to the field minus outflow, or tail water. For sprinkler irrigation, the net applied irrigation is the inflow 

to the sprinkler system minus a correction factor for wind effects and overspray.

To calculate DP with the SMB model, the field capacity, or soil moisture holding capacity at saturation, is used as the maximum amount of soil moisture that can be stored in the crop root zone for the day in question. The water balance is calculated for 

the day, which yields a trial ending soil moisture balance (eq. 3). The trial value is then compared with the field capacity for the 

soil type at the site. If the trial balance exceeds field capacity (FC), then the amount of water in excess of field capacity is considered to be DP that leaves the bottom of the root zone (eq. 4). In this case, the ending SMB is equal to FC (eq. 5). If the trial 

balance is less than the FC, then no DP has occurred, and the ending SMB is equal to the trial balance (eqs. 6 and 7).
USGS Study Findings on NRCS Evaluation 61

Trial Daily Ending Balance = Previous Daily Ending Balance + Precipitation + Irrigation – Runoff – ETc (4)

If Trial Daily Ending Balance > FC, then 

Deep Percolation = Trial Daily Ending Balance – FC, (5)

and Daily Ending Balance = FC (6)

Otherwise,

Deep Percolation = 0, (7)

and Daily Ending Balance = Trial Daily Ending Balance (8)

Soil Moisture Balance Inputs

Evapotranspiration for Soil Moisture Balance Models

The ET inputs required for the SMB models are reference evapotranspiration (ETp), crop evapotranspiration (ETc), and the 

crop coefficient (Kc), which when multiplied with ETp yields ETc. The presumed NRCS evaluation ETp data were used in the 

SMB models, as was a Kc curve equation developed by the USDA Agricultural Research Service (ARS). 

Reference Evapotranspiration

The ARS supported the NRCS evaluation by providing the Modified Penman equations for calculating alfalfa referenced 

ETp. The NRCS evaluation used data from the two NRCS weather stations shown in figure 15 (Grand Valley Annual Report, 

1985, in U.S. Department of Agriculture, 1986–2003). The only existing record of ETp data from the NRCS evaluation is 

contained in a spreadsheet dating from 1999 that was used by the CSU Extension to provide daily ETp values to the media in 

the Grand Valley (Colorado State University Cooperative Extension, 1999). That spreadsheet (ZETA.wks) contains daily ETp

data for Grand Junction and Fruita from 1989 through 1999. It was assumed for the USGS study that this is the same ETp data 

that would have come from the NRCS Evaluation weather stations. This assumption is difficult to fully test, as no other record 

of ETp data in the Grand Valley can be found from 1985 to 1991. Daily ETp is available starting in 1992 for Fruita and 1993 for 

Grand Junction from the CoAgMet network operated by Colorado State University (Colorado State University, 2013). Daily raw 

weather station data required for the Penman ETp equation (maximum and minimum temperature, vapor pressure, solar radiation, and wind run) are unavailable before 1992 for Fruita and 1993 for the Grand Valley. (It is possible to retrieve maximum 

and minimum temperature and precipitation.) This means that it is impossible to recreate the Penman equation ETp values prior 

to 1992 for comparison with the ZETA.wks spreadsheet ETp values. 

Comparisons of the ZETA.wks ETp values with CoAgMet ETp from 1992 to 1999 were made, and in general the ZETA.wks 

ETp is lower than comparable CoAgMet ETp by about 21 percent from 1992 through 1997 for some unknown reason. In 1998 

and 1999, the ZETA.wks ETp values are identical to the CoAgMet ETp values. This discrepancy will be discussed further in the 

section “Reference Evapotranspiration Discrepancies.”

Crop Evapotranspiration Coefficient

A Kc curve is used to adjust the daily ETp for the particular crop type and its actual evapotranspiration behavior. Each SMB 

model site requires a different Kc curve because the crop cycles vary by site, by planting date, and the length of time to harvest. 

Alfalfa crops usually have three or four cuttings or harvests each irrigation season, and the crop cycle for each cutting is different in amplitude and duration. To test the model assumptions, several types of Kc

 curves were created for each site and made 

selectable in the SMB models for comparisons. The original SMB models developed for the USGS Urban DP study (Mayo, 

2008) required extensive additions for this USGS study because of the need to incorporate Kc curves that varied by crop stage 

and multiple alfalfa cuttings per season. The Urban DP study only dealt with established grass lawns.

The Kc curve, which is generally accepted as a current standard, is the Kc curve presented in the United Nations Food and 

Agricultural Organization (FAO) Irrigation and Drainage Paper No. 56 (FAO-56; Allen and others, 1998), a generic representation of which is shown in figure 39. The FAO-56 paper was commissioned by the FAO to provide a global reference document 

for the calculation of evapotranspiration. The lead author was Dr. Richard Allen of the University of Idaho.
62 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Figure 39. Generalized crop coefficient curve Kc from United Nations Food and 

Agriculture Organization Irrigation and Drainage Paper No. 56 (from Allen and others, 

1998).

The FAO-56 Kc curve shows four stages of crop growth: initial, crop development, mid-season, and late season. Kc has a 

constant level in the initial stage of crop growth (Kc ini), increases during the crop development stage, holds at a constant level 

during mid-season (Kc mid), and gradually declines in late season to an end value (Kc end). Each site requires a custom Kc curve 

which depends on the planting data and harvest date. For alfalfa, which is harvested (“cut”) typically three or four times during 

an irrigation season, a series of Kc curves is required, with each cutting varying in length of days. Because the NRCS evaluation 

did not report the cutting dates for any of the alfalfa sites, these dates were inferred from the pattern of irrigation events for the 

site in discussions with a CSU extension agronomist (Calvin Pearson, Colorado State University Extension Service, oral commun., April 19, 2012). The amplitude of the Kc

 curve at each of the four stages of development was made adjustable in the SMB 

model spreadsheet for each site, as well as the overall amplitude of the entire season Kc curve(s). This adjustable amplitude is 

one of the keys to achieving the best fit of the model to the reported results for the site. 

To model the FAO-56 Kc curve, it was decided, based on published information (Allen and others, 1998) to standardize the 

proportion of the four periods of the Kc curve at 10 percent of the total period for the initial phase, 30 percent for crop development, 40 percent for mid-season, and 20 percent for late season. See appendix 6 for a listing of SMB model spreadsheet columns 

that pertain to Kc calculations.

The other Kc curve used in the SMB models is from the ZETA.wks spreadsheet and ultimately derived from the ARS 

publication “Scheduling Irrigations: A Guide for Improved Irrigation Water Management Through Proper Timing and Amount 

of Water Application” (Duke, 1987). The ARS-supplied crop coefficient equation results in the curve shown in figure 40 and is 

referred to as the NRCS Kc curve. 
USGS Study Findings on NRCS Evaluation 63

Figure 40. Natural Resources Conservation Service evaluation crop coefficient curve for a 

typical irrigation season (from Duke, 1987).

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

2/11/1989 4/2/1989 5/22/1989 7/11/1989 8/30/1989 10/19/1989

Crop Coefficient Multiplier

Date

NRCS Evaluation 

Crop Coefficient Curve Kc

The duration of the Kc curve in figure 40 is from March 15 to September 30, 1989. The FAO-56 Kc curve in figure 39 is 

quite different from the NRCS Kc curve in figure 40. In particular, no late season decline is provided for in the NRCS curve, and 

the ramp-up in Kc during the crop development stage is quite rapid. Also, no repetitive use of the Kc curve was apparent in the 

NRCS spreadsheet to accommodate multiple alfalfa crop cuttings, although this could have been applied by manipulating the 

ZETA.wks spreadsheet crop development dates manually. Once Kc reached the mid-season level, it stayed at that level for the 

remainder of the season. The duration of the ramp-up during crop development phase of the NRCS curve is set by the length of 

time from planting to full cover. The full-cover amplitude of the NRCS Kc curve is determined by the coefficient tables for each 

crop.

 No explanation can be given for the differing NRCS Kc equation, other than improvements that have been made in evapotranspiration science since the early 1980s when the NRCS evaluation curve was originally used. The relatively poor fit of the 

NRCS evaluation Kc

 equation to actual crop growth might explain some of the discrepancies in ETc and DP results that will be 

discussed in a subsequent section “Potential Discrepancies in Results between SMB models and NRCS Evaluation.” Both the 

FAO-56 Kc curve and the NRCS evaluation Kc curve were included as selectable choices for comparison purposes in the USGS 

study SMB models for comparison purposes, although in the final analysis, all models were set to use the NRCS evaluation Kc

curve. This will be discussed in more detail in the later section “Potential Discrepancies in Results between SMB Models and 

NRCS Evaluation.”

Stress Correction of Crop Evapotranspiration

The availability of soil moisture to the crop changes as the amount of moisture in the root zone varies between field capacity and wilting point. It is typically assumed in irrigation management that 50 to 60 percent of the moisture in the root zone is 

“readily available,” with the remainder being “not readily available” (Allen and others, 1998). The crop is said to be “stressed” 

when the soil moisture is in the not readily available range. Based on this assumption, it is possible to adjust the manner that the 

crop coefficient affects ETc. This is done by adding an additional multiplier Ks to the ETc equation:

ETc

 = ETp * Kc * Ks (9)
64 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

where

 ETc is crop evapotranspiration in inches,

 ETp is reference evapotranspiration in inches,

 Kc is the crop coefficient multiplier, and

 Ks is the stress coefficient multiplier.

 

In the Urban DP report (Mayo, 2008), a stress multiplier curve with the stress point set at 60 percent is shown (fig. 41), 

based on the FAO-56 report (Allen and others, 1998). Figure 41 shows that between the 60 percent total available water value 

and field capacity, the value of Ks is 1, so ETc performs as normal. Below the ETc stress point, Ks declines linearly from 1 to 0 at 

the permanent wilting point.

Figure 41. Crop stress coefficient curve (from Mayo, 2008).

Crop Stress Factor Ks

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 10 20 30 40 50 60 70 80 90 100

Percent Total Available Water (TAW)

Ks

Not Readily Available Water Readily Available Water (RAW)

 Permanent 

Wilting Point 

Field

Capacity 

(FC)

< Evapotranspiration Stress Point

The NRCS evaluation reports refer to “stress correction” of an unspecified type being applied to the evaluation results. In 

the SMB model spreadsheets used in the USGS study, the FAO-56 stress correction curve shown in figure 41 is applied to ETc

through the use of a Visual Basic macro program in Excel. As will be discussed in the later section “Crop Evapotranspiration 

Stress Correction Discrepancies,” it was necessary to switch off the stress correction in the SMB model spreadsheets to achieve 

the best match of model results with NRCS evaluation results.

Site Physical Parameters for Soil Moisture Balance Models

A number of physical parameters were required as inputs to calculations for the SMB models. Table 28 lists those 

parameters. 
USGS Study Findings on NRCS Evaluation 65

Table 28. Site physical parameters required as inputs for soil moisture balance models.

[commun., communication; NRCS, Natural Resources Conservation Service; CSU, Colorado State University; GIS, geographic information system; NOAA, 

National Oceanic and Atmospheric Administration; FAO, Food and Agricultural Organization of the United Nations; ETp, reference evapotranspiration; Kc, 

crop coefficient multiplier; Colorado Irrigation Guide, U.S. Department of Agriculture, 1988]

Parameter Note Source of Parameter

Crop rooting depth Determines total field capacity and wilting 

point

Jason Peel, NRCS, Ft. Collins, Colo., written 

commun., September 5, 2012

Reported site precipitation for season For comparison with weather station precipitationNRCS evaluation annual reports

Weather station to use for daily precipitation CSU Fruita Experiment Station, Walker Field 

Airport, CSU Orchard Mesa Experiment 

Station, NRCS Palisade weather station

Manually selected from GIS measurement of 

closest weather station to site

Weather station daily precipitation Historic records NOAA National Climate Data Center

Precipitation dataset to use NRCS reported or Weather station Manually selected for comparisons

ETp

 dataset to use CSU Fruita or CSU Orchard Mesa experiment station valuesManually selected from GIS measurement of 

closest weather station to site

Crop coefficient curve to use FAO Kc

 curves or NRCS Kc curves Manually selected for comparisons

Planting and harvest dates Sets start and end of season NRCS evaluation annual reports

Readily available water percent Typically set at 50 percent Manually selected

Site irrigated acres For conversion of irrigation water inflow 

quantities

NRCS evaluation annual reports

Site soil type Determines field capacity and wilting point NRCS evaluation annual reports, updated to 

current NRCS soil types

Field capacity for first 12 inches of soil Determined by soil type 1988 Colorado Irrigation Guide

Field capacity below first 12 inches of soil Determined by soil type 1988 Colorado Irrigation Guide

Wilting point for first 12 inches of soil Determined by soil type 1988 Colorado Irrigation Guide

Wilting point below first 12 inches of soil Determined by soil type 1988 Colorado Irrigation Guide

Assumed start of season soil moisture Not to exceed field capacity Manually selected for best-fit of SMB curve

Monthly mean Grand Valley irrigation water 

consumptive use by crop type

For comparison with SMB model monthly 

consumptive use

Colorado Irrigation Guide 1988

Precipitation for Soil Moisture Balance Models

Daily precipitation for the 12 Grand Valley Unit sites in the SMB models can be selected from among four different sets 

of historic weather data: (1) CSU Fruita Experiment Station, (2) NOAA weather station at Grand Junction Regional Airport 

(Walker Field), (3) CSU Orchard Mesa Experiment Station, and (4) NRCS Palisade weather station. These data were retrieved 

from the Colorado Climate Center (Colorado State University Colorado Climate Center, 2012). Historic weather data for the 

NRCS evaluation weather station at Highline Lake apparently were not preserved. The site map for the Grand Valley Unit 

was used to select the closest weather station to each of the 12 SMB model sites. A threshold value for effective precipitation 

is used in the models, which has the effect of disregarding the precipitation requirements below a small fraction of an inch of 

water, assuming that some of the precipitation that falls is lost to evaporation, runoff, and other processes and is not available to 

the crop. (U.S. Department of Agriculture, 1997). The effective precipitation threshold set for all the models was 0.05 inch of 

precipitation. 

When the mean irrigation season total precipitation for all four Grand Valley weather stations is compared with the mean 

reported NRCS evaluation precipitation for all gold standard Grand Valley Unit sites, some striking differences appear (fig. 42). 
66 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Figure 42. Comparison between mean season total effective precipitation for four Grand Valley weather 

stations and mean season total Natural Resources Conservation Service evaluation reported precipitation, 

corrected for effective precipitation, for Grand Valley Unit gold standard sites from 1985 and 1995.

0

2

4

6

8

10

12

1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995

Effec

tive Precipita

tion (inches)

Evaluation Year

Grand Valley Gold Standard Sites Irrigation Season Mean 

Reported Precipitation versus Mean Season Total Weather Station 

Precipitation

Mean Irrigation Season Weather Station Precipitation

Mean Reported Season Total Precipitation

For 1985 and 1986, the weather station precipitation (blue bars) and the NRCS evaluation reported precipitation (red bars) 

are in relatively good agreement. For the years after 1986, however, the mean precipitation for the four Grand Valley weather 

stations is substantially greater than the reported NRCS evaluation precipitation for all Grand Valley Unit gold standard sites. 

Mean annual Grand Valley weather station precipitation from 1985 to 1995 was 7.2 inches, whereas mean annual NRCS 

reported precipitation for Grand Valley Unit sites for those years was 3.8 inches. This is a relative percent difference (RPD) of 

61.8 percent. The RPD is calculated as the difference of the two values divided by the mean of the two values multiplied by 

100. RPD is used in this report when neither of the values being compared is considered to be more accurate than the other. 

For example, when an NRCS reported value of DP is being compared with an SMB model value of DP, neither value is considered to be inherently correct, so the RPD is calculated. In these cases, the term “relative percent difference” or RPD will be 

used. When standard percent difference (SPD) is being calculated, the term “standard percent difference” or SPD will be used. 

Standard percent difference is calculated as the difference between an old value and a new value, divided by the old value, then 

multiplied by 100. 

Figure 43 shows further detail for each weather station compared with the reported NRCS precipitation. The total season 

precipitation for each of the four weather stations generally agrees within a few inches for a particular year. Data from some 

weather stations are not shown in figure 43 for certain years when a month or more of data were missing for that year and 

weather station. 
Figure 43. Precipitation comparisons for four Grand Valley weather stations with Natural Resources Conservation Service evaluation reported precOceanic and Atmospheric Administration; NRCS, Natural Resources Conservation Service.]

02468

101214

Season total precipitation (inches)

Evaluation Year

Precipitation Comparisons for 4 Grand Valley Weather Stations with NRCS Evaluation Reporte

Precipitation

Fruita Experiment Station Walker Field NOAA Orchard Mesa Experiment Station Palisade Average for 4 Weather Stations Average N
68 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Irrigation Events for Soil Moisture Balance Models

Table 29 shows the reported duration of irrigation events for the 12 sites with SMB models. The mean duration of irrigation 

events for the 12 sites is 4.8 days, and the mean number of events is 9.3.

Table 29. Natural Resources Conservation Service evaluation reported irrigation event details for the 12 Grand Valley Unit sites with 

soil moisture balance models.

[CDS, concrete ditch to siphon tube; GPP, gated pipe; SRS, side-roll sprinkler; EDS, earth ditch to siphon tube; MIS, microspray; CDP, concrete ditch ported; 

GV, Grand Valley Unit]

Site Number Evaluation Year Crop Irrigation System 

Type

Number of

Irrigation Events

Mean Irrigation 

Event Duration 

(Hours)

Mean Irrigation 

Event Duration 

(Days)

GV-12 1989 Alfalfa CDS 7 98.0 4.1

GV-21 1989 Alfalfa GPP 8 191.5 8.0

GV-33 1989 Alfalfa SRS 15 196.0 8.2

GV-33 1993 Alfalfa SRS 11 198.1 8.3

GV-36 1989 Alfalfa SRS 12 133.4 5.6

GV-36 1993 Alfalfa SRS 10 129.5 5.4

GV-53 1993 Alfalfa GPS 8 37.6 1.6

GV-58 1993 Alfalfa EDS 5 97.0 4.0

GV-17 1989 Wine Grapes MIS 17 7.8 0.3

GV-26 1989 Field Corn GPP 8 109.8 4.6

GV-27 1989 Field Corn GPP 6 95.7 4.0

GV-49 1991 Fall Grain CDP 4 80.8 3.4

Totals 110

Mean values 9.3 114.6 4.8

Figure 44 shows the distribution of irrigation event durations in days for all 12 SMB model sites. Over 25 percent of the 

events (28 out of 110) lasted between 9 and 10 days. These 9- to 10-day events are predominately at side-roll sprinkler alfalfa 

sites. The length of irrigation events and how they are handled in the SMB models is discussed later in the section “Potential 

Discrepancies in Results between SMB Models and NRCS Evaluation.”

0

5

10

15

20

25

30

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Percent

Irrigation Event Duration (Days)

Frequency of Irrigation Event Duration in Days 

for 12 Soil Moisture Balance Models

Figure 44. Distribution of irrigation event durations in days for 12 soil moisture 

balance models.
USGS Study Findings on NRCS Evaluation 69

Individual irrigation event data for the 12 Grand Valley Unit Sites were reported in the NRCS evaluation reports and were 

used in the SMB models. The irrigation event data reported include the event start date, the duration of the event in hours, and 

the mean water inflow during the event in cubic feet per second (ft3/s), the soil water deficit before and after the event (inches), 

the depth of infiltration (inches), and precipitation (inches). For flood irrigation sites, the number of furrows, mean furrow flow 

in gallons per minute, and the total outflow (tail-water) in inches is also reported. 

Worksheets in the Soil Moisture Balance Model Spreadsheets

The SMB model spreadsheet contains multiple worksheets for each site. There are also general worksheets for data common to all sites: daily precipitation from each weather station, daily ETp

 calculated from data for each weather station, soil 

properties (field capacity and wilting point), and crop rooting depths.

Each site in the spreadsheet has the same set of worksheets which contain the following:

1. Crop coefficient worksheets that provides daily Kc curve values from planting to harvest, and in the case of alfalfa, a 

worksheet for each cutting. Two sets of crop coefficient worksheets are needed, one for the FAO-56 Kc model, and one 

for the NRCS evaluation Kc model. For an alfalfa site with four cuttings, eight crop coefficient worksheets would be 

needed.

2. A Kc summary worksheet that provides selectable columns of daily Kc values for the several Kc curve models. The 

entire season of Kc values for both types of Kc curves is brought together in this worksheet as a continuous series of Kc

values by date.

3. An NRCS evaluation data worksheet that contains per-event irrigation data from the NRCS evaluation annual reports, 

as well as calculations for per-day application amounts of irrigation water based on the reported number of hours of the 

event and the total infiltrated depth of water.

4. An NRCS evaluation irrigation schedule worksheet that contains the assumed irrigation event starting and ending 

dates, and the assumed cutting dates for alfalfa sites. In this worksheet, minor adjustments are made to the starting and 

ending times of some irrigation events where insufficient time for movement of irrigation equipment was accounted 

for in the original reported times. This particularly applies to side-roll sprinkler sites.

5. An irrigation season calendar worksheet that graphically shows the months and days of the irrigation season, the 

planting and harvest dates, duration of irrigation events, major precipitation events, and, in the case of alfalfa sites, the 

cutting dates.

6. A precipitation chart which shows reported precipitation between each irrigation event, and SMB calculated precipitation between and during irrigation events.

7. A deep percolation worksheet where the water inputs and outputs are used to calculate the daily SMB, and it is determined if any DP occurred on that day. See appendix 6 for a complete listing of columns which appear in the deep 

percolation worksheet.

8. An SMB chart worksheet where the daily model values are charted. Also, on the chart worksheet is a “control panel” 

where all of the model variables that are adjustable are combined in one place. This allows for the visual observation 

of changes in the SMB chart as the model constants and variables are adjusted. The control panel on the SMB chart 

worksheet contains:

• Selector for the type of Kc curve desired.

• Amplitude multipliers for each of the crop cycles of the Kc curves, either for the entire growing season, or for each 

cutting in the case of alfalfa, and an overall amplitude multiplier for each type of Kc curves.

• Two sets of Kc curve amplitude multipliers—one for weather station effective precipitation, and one for NRCS 

reported precipitation.

• A switch to turn off ETc stress correction.

• Field capacity and wilting points for the soil type at the site. Separate values are used for the first 12 inches of rooting depth and for the zone below 12 inches.

• Crop rooting depth.
70 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

• Percent of readily available water.

• Assumed value of soil moisture for the start of the season. (This was not reported in the NRCS evaluation.)

• Weather station and ETp data source selection.

• Per-event comparison tables of DP, precipitation, and ETc for NRCS evaluation reported values and the SMB model 

calculated values. The SMB calculated values are broken out for during and between irrigation events.

• A chart by month of typical crop consumptive use of irrigation water from the 1988 Colorado Irrigation Guide (U.S. 

Department of Agriculture, 1988) compared with the model calculated monthly consumptive use for the crop in 

question.

• A table of difference values between the NRCS reported soil moisture values and the SMB model calculated soil 

moisture values at the start and end of each irrigation event. By minimizing these difference values, the goodness of 

fit of the model SMB curve can be measured and optimized.

Soil Moisture Balance Charts

Figure 45 shows a typical SMB chart that was created by the USGS study for an alfalfa site. 

Figure 45. Soil moisture balance chart for Grand Valley Unit 1993 site 53, an alfalfa site with a pipeline to gated surge irrigation system. 

[NRCS, Natural Resources Conservation Service; GV, Grand Valley; ET, evapotranspiration; SWD, soil water deficit; SMB, soil moisture 

balance; DP, deep percolation; Kc

, crop coefficient; ETc, crop evapotranspiration; Crop Coefficient (Kc) curve (white trace) is not to 

scale.]

19.2

23.3

20.8

23.3

14.7

22.3

18.7

23.3

21.0

23.3

18.7

23.3

20.3

23.3

16.9

23.3

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

-4

-2

0

2

4

6

8

10

12

14

16

18

20

22

24

26

3/15/893/22/893/29/89

4/5/89

4/12/894/19/894/26/89

5/3/89

5/10/895/17/895/24/895/31/89

6/7/89

6/14/896/21/896/28/89

7/5/89

7/12/897/19/897/26/89

8/2/898/9/89

8/16/898/23/898/30/89

9/6/89

9/13/899/20/899/27/8910/4/89

10/11/8910/18/8910/25/89

11/1/8911/8/89

11/15/8911/22/8911/29/89

Precipitation & Etc (inches)

SWD, SMB, DP, Net Irrigation

(inches of water), Cutting Dates (unitless)

Date

NRCS Evaluation Site GV-53 1993 Soil Moisture Balance 

Net Irrigation Deep Percolation (DP) Net Precipitation

Field Capacity Soil Moisture Balance (SMB) Soil Water Deficit (SWD)

Wilting Point ETc Stess Point Cutting Dates

Crop Evapotranspiration (ETc) Crop Coefficient (Kc)

Permanent

Wilting

Point

Field 

Capacity

ET Stress 

Point
USGS Study Findings on NRCS Evaluation 71

The various curves and bars on the SMB chart represent different inputs, outputs, and calculated values for the SMB model. 

All values on the vertical axis are in inches of water. Outputs (water losses) from the model are negative on the vertical axis, and 

inputs (water gains) to the model are positive. The NRCS evaluation crop coefficient curve (white) is not to scale but is representative of the relative shape and amplitude of the crop coefficient over time, and shows the curve’s correspondence with stages 

of crop growth and harvests. Table 30 describes the chart elements.

Table 30. Explanation of soil moisture balance chart elements.

[NRCS, Natural Resources Conservation Service; ETp, reference evapotranspiration; ETc, crop evapotranspiration; Kc, crop coefficient; Ks, crop stress coefficient; %, percent]

Chart Element Description Display Units Data Source

Horizontal axis Irrigation season dates Days Date range for irrigation season

Vertical axis Inches of irrigation water Inches of water Negative to positive scale of inches of 

water

Yellow solid line Daily ETp Negative inches of water Calculated from product of ETp

, crop coefficient Kc

, and stress correction Ks

Red negative vertical bars Deep percolation events Negative inches of water Calculated from daily soil moisture balance 

greater than field capacity

Blue positive vertical bars Precipitation events Positive inches of water Daily precipitation data from National 

Weather Service Grand Junction weather 

station

Green positive vertical bars Net irrigation water applied Positive inches of water NRCS evaluation per-irrigation reports–

measured value of water inflow minus 

water outflow

White solid line Relative crop coefficient curve None–amplitude is adjusted 

for ease of viewing

Soil moisture balance model selection of 

crop coefficient curve

Brown solid line Permanent wilting point Inches of water NRCS soil properties data in Colorado 

Irrigation Handbook for 1988

Yellow dashed line ETc

 stress threshold Inches of water Soil moisture balance model constant 

setting—typically 50% of available soil 

water

Teal solid line Field capacity Inches of water NRCS soil properties data in Colorado 

Irrigation Handbook for 1988

Brown dots Reported NRCS soil water 

balances at beginning and 

ending of irrigation events

Inches of water NRCS evaluation per-irrigation reported 

soil water deficit values—converted to 

soil water balance values as field capacity minus reported soil water deficit

Grey solid line For crops with one harvest per 

season, negative pulse is the 

crop planting date; positive 

pulse is the crop harvest date. 

For alfalfa sites, there are no 

negative pulses, and positive 

pulses are cutting dates

For crops with one harvest 

season, amplitude is -1 

for planting and +1 for 

harvest. For alfalfa, amplitude is +1 for first cutting, 

+2 for second cutting, ETc

, 

and so forth.

NRCS evaluation per-irrigation reported 

values for crop planting and harvest 

dates. Alfalfa cutting dates are estimated.

Orange solid line Model calculated daily soil 

moisture balance

Inches of water Soil moisture balance model calculated 

value from net effect of daily water 

inputs and outputs 
72 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Figure 46. Soil moisture balance chart for Grand Valley Unit 1989 site 33, an alfalfa site with a side-roll sprinkler irrigation system. 

[NRCS, Natural Resources Conservation Service; GV, Grand Valley; ET, evapotranspiration; SWD, soil water deficit; SMB, soil moisture 

balance; DP, deep percolation; Kc

, crop coefficient; ETc, crop evapotranspiration; Crop Coefficient (Kc) curve (white trace) is not to 

scale.]

Figure 46 shows an SMB chart for alfalfa under a side-roll sprinkler irrigation system.

The use of side-roll irrigation technology with impulse sprinkler heads results in frequent irrigation events. Side-roll sites 

typically irrigate a 40-foot wide section of the field for 12 hours before the sprinkler set is moved. (U.S. Department of Agriculture, 1988). The fact that the soil moisture values in the middle of the season fall below the ET stress level is typical of side-roll 

sprinkler systems that practice “deficit” irrigation. This means that the soil moisture rarely if ever gets to field capacity, so the 

soil moisture is said to be in a deficit condition. 

19.7

21.1

20.2

21.3

19.8

21.1

19.2

20.3

17.4

18.8

17.6

18.6

17.5

18.5

17.3

18.3

17.1

17.7 17.4

18.5

17.6

18.7

17.8

18.9

17.2

19.4

18.3

20.4

18.7

20.9

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

-4

-2

0

2

4

6

8

10

12

14

16

18

20

22

24

26

3/15/893/22/893/29/89

4/5/89

4/12/894/19/894/26/89

5/3/89

5/10/895/17/895/24/895/31/89

6/7/89

6/14/896/21/896/28/89

7/5/89

7/12/897/19/897/26/89

8/2/898/9/89

8/16/898/23/898/30/89

9/6/89

9/13/899/20/899/27/8910/4/89

10/11/8910/18/8910/25/89

11/1/8911/8/89

11/15/8911/22/8911/29/89

Precipitation & Etc (inches)

SWD, SMB, DP, Net Irrigation

(Inches of Water), Cutting Dates (unitless)

Date

NRCS Evaluation Site GV-33 1989 Soil Moisture Balance

Deep Percolation (DP) Net Precipitation Net Irrigation

Field Capacity Soil Moisture Balance (SMB) Soil Water Deficit (SWD)

Wilting Point ETc Stess Point Cutting Dates

Crop Evapotranspiration (ETc) Crop Coefficient (Kc)

Permanent

Wilting

Point

Field 

Capacity

ET Stress 

Point
USGS Study Findings on NRCS Evaluation 73

Figure 47. Soil moisture balance chart for Grand Valley Unit 1989 site 27, a field corn site with a pipeline to gated pipe flood irrigation 

system. [NRCS, Natural Resources Conservation Service; GV, Grand Valley; ET, evapotranspiration; SWD, soil water deficit; SMB, soil 

moisture balance; DP, deep percolation; Kc

, crop coefficient; ETc, crop evapotranspiration; Crop Coefficient (Kc) curve (white trace) is not 

to scale.]

12.9

13.9

10.1

13.9

10.4

13.9

9.8

13.9

10.2

13.9

12.1

13.9

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

2

4

6

8

10

12

14

16

18

3/15/893/22/893/29/89

4/5/89

4/12/894/19/894/26/89

5/3/89

5/10/895/17/895/24/895/31/89

6/7/89

6/14/896/21/896/28/89

7/5/89

7/12/897/19/897/26/89

8/2/898/9/89

8/16/898/23/898/30/89

9/6/89

9/13/899/20/899/27/8910/4/89

10/11/8910/18/8910/25/89

11/1/8911/8/89

11/15/8911/22/8911/29/89

Precipitation & ETc (inches)

SWD, SMB, DP, Net Irrigation 

(inches of water), Cutting Dates (unitless)

Date

NRCS Evaluation Site GV-27 1989 Soil Moisture Balance

Net Irrigation Deep Percolation (DP) Net Precipitation

Field Capacity Soil Moisture Balance (SMB) Soil Water Deficit (SWD)

Wilting Point ETc Stess Point Plant Date / Harvest Date

Crop Evapotranspiration (ETc) Crop Coefficient (Kc)

PermanentWilting

Point

(-24.6)

(25.5)

Field 

Capacity

ETc Stress 

Point

Figure 47 shows an SMB chart for field corn using a gated pipe flood irrigation system.

Flood irrigation causes typically large amounts of DP for each event, particularly the initial event in the beginning of 

the season. Excess pre-irrigation or the first irrigation of the season is the biggest contributor to seasonal DP losses. The large 

amounts of DP are directly related to high infiltration rates during these irrigations due to freshly tilled soils, the need to germinate seeds, and the physics of flood irrigation that require application of more water at the top of the field than the root zone 

requires (Grand Valley Annual Report, 1988, in U.S. Department of Agriculture, 1986–2003).
74 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Figure 48. Soil moisture balance chart for Grand Valley Unit 1989 site 17, a wine grapes site with a microspray sprinkler irrigation 

system. [NRCS, Natural Resources Conservation Service; GV, Grand Valley; ET, evapotranspiration; SWD, soil water deficit; SMB, soil 

moisture balance; DP, deep percolation; Kc

, crop coefficient; ETc, crop evapotranspiration; Crop Coefficient (Kc) curve (white trace) is not 

to scale.]

10.0

11.9

11.2

13.9

12.8

13.9

13.3

13.9

12.6

13.9

13.4

13.9

12.5

13.4

11.6

12.6

11.3

13.2

9.2

10.2

8.3

9.3

6.8

8.2

7.6

8.9

7.5

8.6

8.0

9.5

5.7

7.97.9

10.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

-4

-2

0

2

4

6

8

10

12

14

16

3/15/893/22/893/29/89

4/5/89

4/12/894/19/894/26/89

5/3/89

5/10/895/17/895/24/895/31/89

6/7/89

6/14/896/21/896/28/89

7/5/89

7/12/897/19/897/26/89

8/2/898/9/89

8/16/898/23/898/30/89

9/6/89

9/13/899/20/899/27/8910/4/89

10/11/8910/18/8910/25/89

11/1/8911/8/89

11/15/8911/22/8911/29/89

Precipitation & ETc (inches)

SWD, SMB, DP, Net Irrigation

(inches of water), Cutting Dates (unitless)

Date

NRCS Evaluation Site GV-17 1989 Soil Moisture Balance

Net Irrigation Deep Percolation (DP) Net Precipitation

Field Capacity Soil Moisture Balance (SMB) Soil Water Deficit (SWD)

Wilting Point ETc Stess Point Plant Date / Harvest Date

Crop Evapotranspiration (ETc) Crop Coefficient (Kc)

Permanent

Wilting

Point

Field 

Capacity

ET Stress 

Point

Figure 48 shows an SMB chart for a wine grapes site that used a microspray sprinkler system. The use of microspray necessitated frequent irrigation events, which resulted in measurable DP in the early part of the irrigation season (April and May). The 

irrigation events stopped in August to stress the grapes in preparation for harvest, with a final burst of irrigation after harvest to 

prepare the vines for over-wintering (Horst Caspari, Viticulturist, Colorado State University Extension Service, written commun., April 7, 2012).
USGS Study Findings on NRCS Evaluation 75

Figure 49. Soil moisture balance chart for Grand Valley Unit 1991 site 49, a fall grain site with a concrete ditch to gated pipe flood 

sprinkler irrigation system. [NRCS, Natural Resources Conservation Service; GV, Grand Valley; ET, evapotranspiration; SWD, soil water 

deficit; SMB, soil moisture balance; DP, deep percolation; Kc

, crop coefficient; ETc, crop evapotranspiration; Crop Coefficient (Kc) curve 

(white trace) is not to scale.]

Figure 49 shows an SMB chart for fall grain site using a concrete ditch to gated pipe flood irrigation system. It can be seen 

that the early harvest date in July necessitated a short crop cycle with frequent intense irrigations. Each of these flood irrigations 

resulted in substantial DP. Appendix 7 includes all 12 of the SMB charts for completeness, including the five discussed in this 

section.

9.9

13.8

10.1

13.8

9.6

13.8

11.0

13.8

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

-10

-8

-6

-4

-2

0

2

4

6

8

10

12

14

16

18

3/15/913/22/913/29/91

4/5/91

4/12/914/19/914/26/91

5/3/91

5/10/915/17/915/24/915/31/91

6/7/91

6/14/916/21/916/28/91

7/5/91

7/12/917/19/917/26/91

8/2/918/9/91

8/16/918/23/918/30/91

9/6/91

9/13/919/20/919/27/9110/4/91

10/11/9110/18/9110/25/91

11/1/9111/8/91

11/15/9111/22/9111/29/91

Precipitation & ETc (inches)

SWD, SMB, DP, Net Irrigation

(inches of water), Cutting Dates (unitless)

Date

NRCS Evaluation Site GV-49 1991 Soil Moisture Balance

Net Irrigation Deep Percolation (DP) Net Precipitation

Field Capacity Soil Moisture Balance (SMB) Soil Water Deficit (SWD)

Wilting Point ETc Stress Point Plant Date / Harvest Date

Crop Evapotranspiration (ETc) Crop Coefficient (Kc)

Permanent 

Wilting

Point

Field 

Capacity 

ETc Stress 

Point

(20.5)

(-16.6)
76 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Soil Moisture Balance Curve Best-Fit Procedures

The SMB model spreadsheet parameters can be adjusted to match (“best-fit”), as closely as possible, NRCS soil water 

deficits that were reported at the beginning and ending dates of each irrigation event. A number of inputs to the SMB model can 

be varied by type and amplitude to achieve the best-fit of the SMB results. Once the constant values for the site (FC, WP, rooting 

depth, ETc stress threshold percent) are set in the SMB model, the parameters that can be adjusted to achieve the best-fit of the 

SMB trace are:

1. Type of Kc curve (NRCS or FAO-56).

2. Amplitude of the Kc curve, with separate amplitude values for each alfalfa cutting.

3. Duration of Kc curve, with separate durations for each alfalfa cutting.

4. Daily ETp, depending on whether the site is closer to the Fruita or Grand Junction NRCS weather station.

5. Daily precipitation for the closest of four Grand Valley weather stations (Fruita, Walker Field, Orchard Mesa, or 

Palisade), or NRCS reported season total precipitation for that site.

6. Soil moisture balance at the start of season (assumed, since this was not reported by NRCS).

7. ETc stress correction setting on or off.

These input parameters are manipulated to achieve the best-fit of the SMB curve, which then results in the best match of 

SMB model ETc to NRCS reported ETc, SMB model precipitation to NRCS reported precipitation, and SMB model DP to NRCS 

reported DP. In this report, this best-fit match to NRCS reported values is called the “baseline-fit.” To achieve the baseline-fit, 

the difference (error) in soil moisture value between the orange trace and the red dot at each irrigation event is calculated. The 

goal for adjusting the model is to minimize the sum of all the beginning and (separately) all of the ending event errors. If the two 

errors are non-zero, then the goal is to balance the beginning and ending error sums. This indicates that the SMB trace is closest 

to the starting and ending irrigation event SMB values, respectively. 

The NRCS Kc

 curve can be adjusted in overall amplitude, but lacks the ability to change the shape of the curve, as this 

is set by the crop season length for the NRCS Kc equation. (See appendix 8 for details of the NRCS Kc curve derivation.) For 

alfalfa sites, the NRCS Kc equation was restarted after each presumed cutting date. Each NRCS Kc equation can have its amplitude adjusted independently for each alfalfa crop cycle.

For the final analysis, it was decided that using the NRCS Kc curves would be most appropriate to model the NRCS evaluation data, if a best-fit could be achieved with the NRCS Kc

 curve. Because a best-fit of the SMB curve at each site could be 

achieved using the NRCS Kc curves, the use of the FAO-56 curves was not necessary. All examples of SMB charts in this report 

will be shown using NRCS Kc curves.

Figure 50 shows what happens when the amplitude for the Kc curve is set too low to achieve a best-fit. This creates a low 

value of daily ETc, making the orange SMB curve in the chart track above the reported soil water deficit values, because the ETc

output from the model is insufficient.
USGS Study Findings on NRCS Evaluation 77

Figure 50. Example of an SMB chart with a low value for the crop coefficient amplitude. [NRCS, Natural Resources Conservation 

Service; GV, Grand Valley; ET, evapotranspiration; SWD, soil water deficit; SMB, soil moisture balance; DP, deep percolation; Kc, crop 

coefficient; ETc

, crop evapotranspiration; Crop Coefficient (Kc) curve (white trace) is not to scale.]

16.9

22.2

19.2

21.7

16.4

18.8

17.1

20.0

17.8

20.4

17.3

19.8

18.4

20.3

18.9

20.8

17.0

19.2

17.9

20.1

18.1

20.4

17.6

19.8

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

-4

-2

0

2

4

6

8

10

12

14

16

18

20

22

24

26

3/15/893/22/893/29/89

4/5/89

4/12/894/19/894/26/89

5/3/89

5/10/895/17/895/24/895/31/89

6/7/89

6/14/896/21/896/28/89

7/5/89

7/12/897/19/897/26/89

8/2/898/9/89

8/16/898/23/898/30/89

9/6/89

9/13/899/20/899/27/8910/4/89

10/11/8910/18/8910/25/89

11/1/8911/8/89

11/15/8911/22/8911/29/89

SWD, SMB, DP, Net Irrigation

Precipitation & Etc (inches)

(inches of water), Cutting Dates (unitless)

Date

NRCS Evaluation Site GV-36 1989 Soil Moisture Balance

Net Irrigation Deep Percolation (DP) Net Precipitation

Field Capacity Soil Moisture Balance (SMB) Soil Water Deficit (SWD)

Wilting Point ETc Stess Point Cutting Dates

Crop Evapotranspiration (ETc) Crop Coefficient (Kc)

Permanent

Wilting

Point

Field 

Capacity

ET Stress 

Point

Figure 51 shows what happens when the amplitude for the Kc curve is set too high to achieve a best-fit. This creates a high 

value of daily ETc, making the orange SMB curve in the chart track below the reported soil water deficit values, because the ETc

output from the model is overstated. 
78 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Figure 51. Example of an SMB chart with a high value for the crop coefficient amplitude. [NRCS, Natural Resources Conservation 

Service; GV, Grand Valley; ET, evapotranspiration; SWD, soil water deficit; SMB, soil moisture balance; DP, deep percolation; Kc, crop 

coefficient; ETc

, crop evapotranspiration; Crop Coefficient (Kc) curve (white trace) is not to scale.]

16.9

22.2

19.2

21.7

16.4

18.8

17.1

20.0

17.8

20.4

17.3

19.8

18.4

20.3

18.9

20.8

17.0

19.2

17.9

20.1

18.1

20.4

17.6

19.8

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

-4

-2

0

2

4

6

8

10

12

14

16

18

20

22

24

26

3/15/893/22/893/29/89

4/5/89

4/12/894/19/894/26/89

5/3/89

5/10/895/17/895/24/895/31/89

6/7/89

6/14/896/21/896/28/89

7/5/89

7/12/897/19/897/26/89

8/2/898/9/89

8/16/898/23/898/30/89

9/6/89

9/13/899/20/899/27/8910/4/89

10/11/8910/18/8910/25/89

11/1/8911/8/89

11/15/8911/22/8911/29/89

Precipitation & Etc (inches)

SWD, SMB, DP, Net Irrigation

(inches of water), Cutting Dates (unitless)

Date

NRCS Evaluation Site GV-36 1989 Soil Moisture Balance

Net Irrigation Deep Percolation (DP) Net Precipitation

Field Capacity Soil Moisture Balance (SMB) Soil Water Deficit (SWD)

Wilting Point ETc Stess Point Cutting Dates

Crop Evapotranspiration (ETc) Crop Coefficient (Kc)

Permanent

Wilting

Point

Field 

Capacity

ET Stress 

Point

Figure 52 shows how the error between reported soil water deficit and calculated SMB is minimized (best-fit) when the 

orange trace is closest to the red dots across the season, or at least a balanced distance between each pair of beginning event and 

ending event dots.
USGS Study Findings on NRCS Evaluation 79

Figure 52. Example of an SMB chart with a value selected for the best-fit of the soil moisture balance trace. [NRCS, Natural Resources 

Conservation Service; GV, Grand Valley; ET, evapotranspiration; SWD, soil water deficit; SMB, soil moisture balance; DP, deep 

percolation; Kc

, crop coefficient; ETc, crop evapotranspiration; Crop Coefficient (Kc) curve (white trace) is not to scale.]

16.9

22.2

19.2

21.7

16.4

18.8

17.1

20.0

17.8

20.4

17.3

19.8

18.4

20.3

18.9

20.8

17.0

19.2

17.9

20.1

18.1

20.4

17.6

19.8

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

-4

-2

0

2

4

6

8

10

12

14

16

18

20

22

24

26

3/15/893/22/893/29/89

4/5/89

4/12/894/19/894/26/89

5/3/89

5/10/895/17/895/24/895/31/89

6/7/89

6/14/896/21/896/28/89

7/5/89

7/12/897/19/897/26/89

8/2/898/9/89

8/16/898/23/898/30/89

9/6/89

9/13/899/20/899/27/8910/4/89

10/11/8910/18/8910/25/89

11/1/8911/8/89

11/15/8911/22/8911/29/89

Precipitation & Etc (inches)

SWD, SMB, DP, Net Irrigation

(inches of water), Cutting Dates (unitless)

Date

NRCS Evaluation Site GV-36 1989 Soil Moisture Balance

Net Irrigation Deep Percolation (DP) Net Precipitation

Field Capacity Soil Moisture Balance (SMB) Soil Water Deficit (SWD)

Wilting Point ETc Stess Point Cutting Dates

Crop Evapotranspiration (ETc) Crop Coefficient (Kc)

Permanent

Wilting

Point

Field 

Capacity

ET Stress 

Point

Results for Baseline-Fit of Soil Moisture Balance Curves

The SMB models were initially baseline-fit to the NRCS evaluation reported results as closely as possible. Then various 

adjustments were temporarily made in the model inputs to perform a sensitivity analysis of some of the assumptions of the 

NRCS evaluation SMB accounting. Table 31 summarizes the precipitation, ETc, DP, and SIE results for the baseline-fit of the 12 

SMB model sites, with the NRCS reported values for each site. The input values used for the baseline-fit SMB model in table 31 

are NRCS reported precipitation, no ETc stress correction applied, and NRCS ETp. 
80 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Table 31. Comparison between Natural Resources Conservation Service evaluation reported deep percolation, precipitation, 

crop evapotranspiration, and seasonal irrigation efficiency with soil moisture balance model results.

[NRCS, Natural Resources Conservation Service, SMB, soil moisture balance, DP, deep percolation in inches of water; Precip, precipitation in inches of 

water; Calc, calculated; ETc, crop evapotranspiration; SIE, seasonal irrigation efficiency]

Site

Number

NRCS

Reported 

Precip

SMB Model 

Season

Total Precip

NRCS

Reported 

Crop ETc

Total SMB 

Model Season

Total ETc

NRCS

Reported

DP

Total SMB 

Model Season

Total DP

NRCS

Reported

SIE

SMB

Model SIE

GV-12 1989 2.8 2.8 39.3 39.7 19.0 19.7 51.1 50.0

GV-21 1989 2.8 2.8 31.6 34.4 23.5 22.4 35.7 37.0

GV-33 1989 2.8 2.8 20.7 22.0 0.0 0.0 80.1 80.1

GV-36 1989 2.8 2.8 31.4 31.7 0.0 0.0 80.5 80.5

GV-17 1989 3.0 3.0 23.3 28.0 2.9 1.8 75.7 79.3

GV-26 1989 2.4 2.4 17.7 22.4 10.7 8.2 32.0 38.4

GV-27 1989 2.3 2.3 21.0 22.1 49.8 48.8 21.0 22.2

GV-49 1991 0.8 0.8 13.8 14.3 30.9 31.2 27.8 27.1

GV-33 1993 3.9 3.9 30.6 30.9 2.4 4.3 73.2 68.2

GV-36 1993 3.9 3.9 24.2 26.6 0.0 2.1 79.9 72.7

GV-53 1993 4.0 4.0 34.8 31.6 12.9 12.3 54.9 55.8

GV-58 1993 4.7 4.7 36.7 39.2 4.3 3.6 52.4 53.5

Mean values 3.0 3.0 27.1 28.6 13.0 12.9 55.4 55.4

Median values 2.8 2.8 27.4 29.4 7.5 6.2 53.7 54.7

Baseline-Fit of Crop Evapotranspiration

Figure 53 shows a comparison of NRCS reported ETc (horizontal axis) with SMB model ETc (vertical axis) for the 12 

model sites. The red dotted trace is a one-to-one line. Each symbol is labeled for the site number, year of evaluation, irrigation method code (table 8), season total number of irrigation days, and the crop type. It can be seen that the various symbol 

groups are clustered along the one-to-one line. A linear regression trend line has also been created through the 12 model values. 

R-squared (R2) is a measure of how close the data are to a fitted regression line (y represents calculated SMB ETc, and x represents NRCS reported ETc

 in the equation). The R2 for this trend line is 0.9289, indicating that much of the variance in the 12 data 

points is explained by the regression equation. The four flood alfalfa sites are to the right, indicating reported ETc in the range of 

30 to 40 inches per season, while the four side-roll alfalfa sites are clustered between about 20 to 30 inches of ETc per season. 

The two flood corn sites show about 20 inches of reported ETc

 per season. No correlation between reported ETc and the season 

total days of irrigation is evident in figure 53. 
USGS Study Findings on NRCS Evaluation 81

Figure 53. Chart of SMB model calculated season total crop evapotranspiration versus Natural Resources Conservation 

Service evaluation reported season total crop evapotranspiration showing site number, irrigation method (table 8), total days of 

irrigation (d), and crop type for 12 Grand Valley SMB model sites. [SMB, soil moisture balance; ETc

, crop evapotranspiration; ID, 

identification; NRCS, Natural Resources Conservation Service; GV, Grand Valley Salinity Control Unit; EDS, earth ditch to siphon 

tube; CDG, concrete ditch to gated pipe; CDS, concrete ditch to siphon tube; PGP, pipeline gated pipe; PGS, pipeline to gated surge; 

SRS, side-roll sprinkler; MIS, microspray; R2, measure of goodness of fit of data to regression line.]

GV-12 89

CDS 29d

alfalfa

GV-21 89

PGP 64d

alfalfa

GV-53 93

PGS 13d

alfalfa

GV-58 93

EDS 20d

alfalfa

GV-33 89

SRS 123d

alfalfa

GV-33 93

SRS 91d

alfalfa

GV-36 89

SRS 67d

alfalfa

GV-36 93

SRS 54d

alfalfa

GV-17 89

MIS 5d

grapes

GV-26 89

PGP 37d

corn

GV-27 89

PGP 24d

corn

GV-49 91

CDG 14d

fall grain

0

10

20

30

40

50

60

0 5 10 15 20 25 30 35 40 45 50

SMB Model Calculated ETc (inches)

NRCS Evaluation Reported ETc (inches)

Season-Total SMB Model ETc versus NRCS Reported ETc

Coded for Crop Type and Irrigation Method and labeled with site ID, Irrigation System Type 

and Irrigation Days, using NRCS Reported Precipitation for SMB Models

Alfalfa Flood Alfalfa Side-Roll Grapes Microspray Corn Flood

Fall Grain Flood 1 to 1 line Computed Trend Line

Trend Line Equation

y = .9011x + 4.162

R2 = 0.9289

Baseline-Fit of Soil Moisture Balance Deep Percolation

Figure 54 shows site parameters for the 12 SMB model sites on a DP comparison plot similar to figure 53. The symbol 

codes and labels are the same as in figure 53. It can be seen that the alfalfa groups are clustered along the one-to-one line. A linear regression trend line has also been created through the 12 model values. The R2

 for this trend line is 0.9927, indicating that 

almost all of the variance in the 12 data points is explained by the regression equation. Three of the four flood alfalfa sites (green 

diamonds) have reported DP in the range of about 13 to 25 inches per season, while the four side-roll alfalfa sites (red diamonds) 

are grouped with less than 5 inches of DP per season. The two flood corn sites (yellow triangles) are widely separated. No correlation between reported DP and the season total days of irrigation is evident in figure 54. 
82 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Figure 54. Chart of season-total SMB model deep percolation versus Natural Resources Conservation Service 

reported deep percolation for 12 Grand Valley SMB model sites. [SMB, soil moisture balance; DP, deep percolation; 

ID, identification; NRCS, Natural Resources Conservation Service; GV, Grand Valley Salinity Control Unit; EDS, earth 

ditch to siphon tube; CDG, concrete ditch to gated pipe; CDS, concrete ditch to siphon tube; PGP, pipeline gated 

pipe; PGS, pipeline to gated surge; SRS, side-roll sprinkler; MIS, microspray; R2

, measure of goodness of fit of data to 

regression line.]

GV-12 89

CDS 29d

alfalfa

GV-21 89

PGP 64d

alfalfa

GV-53 93

PGS 13d

alfalfa

GV-58 93

EDS 20d

alfalfa

GV-36 89

SRS 67d

alfalfa

&

GV-33 89

SRS 123d

alfalfa

GV-33 93

SRS 91d

alfalfa

GV-36 93

SRS 54d

alfalfa

&

GV-17 89

MIS 5d

grapes

GV-26 89

PGP 37d

corn

GV-27 89

PGP 24d

corn

GV-49 91

CDG 14d

fall grain

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60

SMB Model season Total Deep Percolation (inches)

NRCS Evaluation Reported Season Total Deep Percolation (inches)

Season-Total SMB Model Deep Percolation versus NRCS Reported Deep Percolation

Alfalfa Flood Alfalfa Side-Roll

Grapes Microspray Corn Flood

Fall Grain Flood 1 to 1 line

y = 0.9742x + 0.1266

R2 = 0.9927

Baseline-Fit of Seasonal Irrigation Efficiency

Figure 55 shows site parameters for the 12 SMB model sites on an SIE comparison plot similar to figure 53. It can be seen 

that the alfalfa and corn groups are roughly clustered along the one-to-one line. A linear regression trend line has also been created through the 12 model values. The R2

 for this trend line is 0.9772, indicating that much of the variance in the 12 data points 

is explained by the regression equation. The four alfalfa flood sites (green diamonds) have reported SIE in the range of about 30 

to 50 percent, while the four side-roll alfalfa sites (red diamonds) are clustered with SIE around 70 to 80 percent. The two flood 

corn sites have SIE values (yellow triangles) around 20 to 40 percent. No correlation between reported SIE and the season total 

days of irrigation is evident in figure 55. 
USGS Study Findings on NRCS Evaluation 83

Figure 55. Chart of SMB model seasonal irrigation efficiency versus NRCS reported seasonal irrigation efficiency for 12 Grand 

Valley SMB model sites. [SMB, soil moisture balance; ID, identification; NRCS, Natural Resources Conservation Service; GV, Grand 

Valley Salinity Control Unit; EDS, earth ditch to siphon tube; CDG, concrete ditch to gated pipe; CDS, concrete ditch to siphon tube; 

PGP, pipeline gated pipe; PGS, pipeline to gated surge; SRS, side-roll sprinkler; MIS, microspray; R2

, measure of goodness of fit of 

data to regression line.]

GV-12 89

CDS 29d

GV-21 89

PGP 64d

alfalfa

GV-53 93

PGS 13d

alfalfa

GV-58 93

EDS 20d

alfalfa

GV-33 89

SRS 123d

alfalfa

GV-36 89

SRS 67d

alfalfa

GV-33 93

SRS 91d

alfalfa

GV-36 93

SRS 54d

alfalfa

GV-17 89

MIS 5d

grapes

GV-26 89

PGP 37d

corn

GV-27 89

PGP 24d

corn

GV-49 91

CDG 14d

fall grain 

0.0

20.0

40.0

60.0

80.0

100.0

120.0

0.0 20.0 40.0 60.0 80.0 100.0 120.0

SMB Model Seasonal Irrigation Efficiency (percent)

Reported Seasonal Irrigation Efficiency (percent)

SMB Model Seasonal Irrigation Efficiency versus NRCS Reported Seasonal Irrigation Efficiency 

Alfalfa Flood Alfalfa Side-Roll

Grapes Microspray Corn Flood

Fall Grain Flood 1 to 1 line

Trend Line Equation

y = 0.9287x + 3.9861

R2 = 0.9772

Potential Discrepancies in Results between SMB Models and NRCS Evaluation 

Any model of a physical process entails a number of assumptions as to how to create and manipulate the model. The 

primary reason for creating a model for this report was first, to understand the assumptions which were implicit (if sometimes 

unstated) in the NRCS evaluation reported results, and second, to examine whether those assumptions were an appropriate way 

to evaluate the raw data. By adjusting the SMB model inputs to achieve a baseline-fit, the primary assumptions of the NRCS 

data accounting were discovered, and the consequences of those setting choices by the NRCS evaluation became apparent. It is 

not the purpose of this report to suggest that the NRCS evaluation results are “right” or “wrong.” However, the NRCS evaluation results can be tested in the light of current day understanding, and can be compared with published outside standards, to get 

an indication of whether the evaluation results stand the scrutiny of objective examination.

After discussing several sources and types of uncertainty in the NRCS data which create discrepancies with the SMB models in the sections below, a sensitivity analysis will be shown that tests the effect of three sets of trial inputs on the SMB model 

results. These three sets of inputs are (1) the closest Grand Valley weather station precipitation or NRCS reported precipitation; 

(2) the use of crop evapotranspiration stress correction or not; and (3) the use of NRCS reported ETp

, or a 10 percent upward 

adjustment in ETp to match published standards of crop consumptive use. The sensitivity analysis will suggest some possible 

offsets to the NRCS results that result from these tests.

Several sources of uncertainty and discrepancies arise that can affect the NRCS evaluation results. These sources are (1) 

precipitation, (2) evapotranspiration, (3) soil moisture balance accounting, (4) NRCS methodology changes, (5) NRCS software 

problems, and (6) human error. Some of these discrepancies can be quantified, and some cannot be quantified.
84 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Quantifiable Discrepancies

Precipitation Discrepancies

The basic differences in precipitation between published Grand Valley weather station data and NRCS reported values were 

discussed earlier in the section “Precipitation for Soil Moisture Balance Models.” The question arises as to whether the differences in per-site precipitation as reported by the NRCS and the precipitation at the four Grand Valley weather stations have an 

effect on the performance of the SMB models. To test this, the SMB models are set up to use either NRCS reported per-site precipitation or the closest Grand Valley weather station effective precipitation values. It is possible in the SMB model spreadsheet 

to easily switch any or all of the model sites back and forth between these two precipitation choices. 

There is not a ready explanation for the discrepancy in weather station precipitation and NRCS reported precipitation. Precipitation values at each Grand Valley Unit NRCS evaluation site were reported to be collected from two sources: (1) the NRCSoperated weather stations at Highline Lake (western Grand Valley) and Palisade (eastern Grand Valley) (see map fig. 15), and 

(2) local rain gages that were manually operated by the field owner. It is not documented in the annual reports how discrepancies 

between these two sources were resolved by the NRCS evaluation. How often the local rain gages were read or maintained was 

not recorded, which could have resulted in inaccurate readings. The precipitation discrepancies shown in figure 42 and figure 

43 appear to be systematic over the years of the evaluation. The NRCS evaluation annual reports make vague remarks about 

“adjustments” being made to precipitation readings without specifying how the adjustments were made. The NRCS evaluation 

does not report the dates when precipitation events occurred, so it is not possible to compare the NRCS evaluation reported precipitation to weather station records on a daily basis. The reported precipitation was simply totaled from the start of one irrigation event to the start of the next event. 

Under-reported precipitation in the NRCS evaluation would have resulted in under-reporting of DP, because missing precipitation would lead to lower soil moisture balances, and thus a reduced tendency to create DP during irrigation and heavy rain 

events. Over-reporting of precipitation would have the opposite effect of over-reported DP. Changes in the amount of DP that 

results from switching between NRCS reported precipitation and Grand Valley weather station precipitation will be shown in the 

“Sensitivity Analysis” section.

Types of Evapotranspiration Discrepancies

There are several ways that ET affects the SMB models. The first way is through the daily values of ETp, which are dependent on raw weather station data and on the calibration of the Penman ET equation to the local agricultural area. Higher ETp

results in higher values of ETc, which can result in a lower amount of DP for the season.

The second way that ET affects the SMB models is the season total ETc, which can also be called crop consumptive use. 

The 1988 Colorado Irrigation Guide (U.S. Department of Agriculture, 1988) includes a set of tables for typical monthly and season total crop consumptive use of water by crop, agricultural area, and climate zones within the agricultural areas. This enables a 

comparison between NRCS reported season-total ETc and season total consumptive use from the Irrigation Guide. 

The third way that ET affects the SMB model is in the shape, duration, and amplitude of the crop coefficient equation 

for Kc. A possible software error in the ZETA.wks spreadsheet is discussed below in the section “Crop Evapotranspiration 

Discrepancies.”

The final way in which ET affects the SMB model is through the use of a stress correction based on readily available soil 

moisture levels. The basics of this have been discussed in the section “Stress Correction of Crop Evapotranspiration.” 

Reference Evapotranspiration Discrepancies

The language in the NRCS evaluation annual reports contains evidence that the calculation methods for ETp changed over 

the course of the evaluation. These changes are not well documented. The 1988 Grand Valley annual report states: “Potential 

evapotranspiration was calculated using a Modified Penman equation developed by the ARS in Fort Collins, Colorado. The 

measured data parameters included wind run, solar radiation, maximum and minimum temperatures, relative humidity, and precipitation. The calculated ETp

 results were calibrated with the ETp results gathered by the ARS on the Colorado State University 

Experimental Farm in the Grand Valley” (Grand Valley Annual Report, 1988, in U.S. Department of Agriculture, 1986–2003). 

How this calibration was accomplished is not stated.

A comparison was made for this report between daily ETp

 reported by NRCS and daily ETp from the Grand Junction and 

Fruita weather stations operated by CoAgMet in the Grand Valley. Daily weather data have been published for Fruita since 1992, 

and for Grand Junction since 1993. Unfortunately, there are no CoAgMet or other weather data available that would allow for an 

ETp comparison prior to 1992.

Figure 56 shows a comparison between daily ETp for the Fruita CoAgMet station with NRCS reported ETp for 1992. The 

blue trace (ZETA.wks Fruita reference ETp

) indicates that NRCS ETp is systematically lower than CoAgMet ETp (red trace) by a 

mean value of 23.1 percent for the 1992 season. Similar differences occur until 1998 and 1999, when the NRCS ETp is identical 
USGS Study Findings on NRCS Evaluation 85

to CoAgMet, indicating that the CSU staff who were operating the NRCS evaluation at that time changed their ETp source. Not 

counting 1998 and 1999, NRCS ETp has a mean season total difference from CoAgMet for 1992 to 1997 of 21.2 percent.

Figure 56. Comparison between CoAgMet ETp with NRCS evaluation ETp for Fruita in 1992. [ETp, reference 

evapotranspiration; NRCS, Natural Resources Conservation Service; CSU, Colorado State University; CoAgMet, 

Colorado Agricultural Meteorological Network ZETA.wks; NRCS ETp

 software program.]

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

1992 Reference ET (ETp) Comparison between NRCS Fruita and CSU 

CoAgMet Fruita Weather Station

1992 ZETA Fruita Reference ETp 1992 CoAgMet Fruita Reference ETp

Figure 57 shows a different story for the Grand Junction ETp for 1993. The NRCS ETp is close to the CoAgMet daily values, with a season total difference of only 6.1 percent. The differences vary by subsequent years, with some years having NRCS 

ETp higher than CoAgMet, and some years being lower. The same convergence between NRCS ETp and CoAgMet ETp occurs 

starting in 1998. From 1993 to 1997, the NRCS ETp has a mean lower value of 6.7 percent. 
86 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Figure 57. Comparison between Colorado State University (CSU) CoAgMet ETp with Natural Resources Conservation Service 

NRCS evaluation ETp

 for Grand Junction in 1993. [ETp, reference evapotranspiration; NRCS, Natural Resources Conservation 

Service; CSU, Colorado State University; CoAgMet, Colorado Agricultural Meteorological Network; ZETA.wks, NRCS ETp

 software 

program; GJ, Grand Junction.]

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

1993 Reference ET (ETp) Comparison between NRCS Grand Junction and CSU 

CoAgMet Grand Junction Weather Station

1993 ZETA GJ Reference ETp 1993 GJ CoAgMet Reference ETp

Crop Consumptive Use Discrepancies

Crop consumptive use in this analysis means the same thing as crop evapotranspiration. The 1988 Colorado Irrigation 

Guide (U.S. Department of Agriculture, 1988) published expected consumptive use values for each major agricultural area of the 

state. Monthly and season total consumptive use values are available for both Fruita and Grand Junction. See appendix 9 for the 

crop consumptive use tables for Grand Junction (fig. 9-2 in appendix 9) and Fruita (fig. 9-3 in appendix 9), as well as a climate 

zone map of Colorado that shows peak monthly use for pasture grasses in the climatic zones (fig. 9-1 in appendix 9). The Grand 

Valley, for example, has two climate zones, one each for alfalfa and for orchards (fig. 9-2). These zones roughly divide the 

Grand Valley Unit north and south of I-70. Using the crop consumptive use tables, comparisons can be made between NRCS 

reported season total ETc

. The length of season implied in the consumptive use tables corresponds generally to the reported 

planting and harvest dates in the NRCS annual reports.

When these consumptive use values are compared with NRCS evaluation reported ETc, some differences are apparent. The 

1988 Colorado Irrigation Guide numbers are representative of typical years, so actual values would vary somewhat with wet or 

dry years. But the NRCS evaluation data covers both wet and dry years as well, so a comparison can be made on mean. Figure 

58 shows the frequency (histogram) chart of different values of standard percent difference (not RPD) between NRCS ETc and 

1988 Colorado Irrigation Guide consumptive use for all 196 Grand Valley Unit gold standard site-years. It can be seen that 73 

percent of the NRCS sites (red bars) have lower season-total ETc

 than the Irrigation Guide standards, while 27 percent (blue 

bars) have higher ETc than the Irrigation Guide standards. The median ETc difference is -8.7 percent. If NRCS ETc matched consumptive use guidelines, one would see most of this distribution to be close to zero percent difference, symmetrical about zero, 

and not be so widely spread.
USGS Study Findings on NRCS Evaluation 87

Figure 59 shows the 1988 Colorado Irrigation Guide consumptive use, season total NRCS reported ETc, and season total 

SMB model ETc plotted for the 12 SMB model sites. The NRCS reported ETc has a mean value that is 8.7 percent lower than 

consumptive use. The SMB model ETc for baseline-fit settings is 11.1 percent lower than consumptive use. Site GV-33 89 is a 

special case because in 1989, it was newly seeded to alfalfa the previous fall. This slows the growth of the crop in the spring, 

and would account for lower season-total ETc.

It was found that increasing ETp for the 12 SMB models by 10 percent would increase the mean consumptive use for the 

SMB model sites (season total ETc) to less than a 2 percent difference from mean 1988 Colorado Irrigation Guide consumptive 

use. Therefore, a trial increase of SMB model ETp by 10 percent is included in the sensitivity analysis.

Figure 58. Histogram of percent difference between Natural Resources Conservation Service reported crop evapotranspiration and 

1988 Colorado Irrigation Guide consumptive use for all Grand Valley Unit gold standard sites. [ETc, crop evapotranspiration; NRCS, 

Natural Resources Conservation Service; 1988 Colorado Irrigation Guide, U.S. Department of Agriculture, 1988.]

0

5

10

15

20

25

30

-201 to -300-101 to -200-91 to -100-81 to -90-71 to -80-61 to -70-51 to -60-41 to -50-31 to -40-21 to -30-11 to 20-6 to -100 to -51 to 56 to 1011 to 2021 to 3031 to 4041 to 5051 to 6061 to 7071 to 8081 to 9091 to 100101 to 200201 to 300

Percent of Total Sites

Reported Season Total Crop Evapotranspiration (inches)

Standard Percent Difference between NRCS Evaluation Reported Season-Total Crop -

Evapotranspiration (ETc) and Colorado Irrigation Guide Consumptive Use 

for all Grand Valley Gold Standard Sites

ETc Greater than Consumptive Use ETc Less than Consumptive Use

73 percent of sites 

are below 

consumptive 

use guidelines

27 percent of sites 

are above 

consumptive 

use guidelines

Mean reported ET is 8.7 percent lower

than consumptive use

196 total site years
88 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Figure 59. Comparison between 1988 Colorado Irrigation Guide consumptive use and NRCS reported ETc for the 12 soil 

moisture balance sites. [ETc

, crop evapotranspiration; NRCS, Natural Resources Conservation Service; SMB, soil moisture 

balance; GV, Grand Valley; 1988 Colorado Irrigation Guide, U.S. Department of Agriculture, 1988.]

0

10

20

30

40

50

GV-12

1989

GV-21

1989

GV-33

1989

GV-36

1989

GV-17

1989

GV-26

1989

GV-27

1989

GV-49

1991

GV-33

1993

GV-36

1993

GV-53

1993

GV-58

1993

Comparison of Season Total Crop Evapotranspiration (ETc) for NRCS 

Reported and Soil Moisture Balance (SMB) Models, and Colorado 

Irrigation Guide Consumptive Use for 12 Soil Moisture Balance Model Sites

NRCS Reported ETc by Site SMB Model ETc by Site Consumptive Use by Site

GV-33 89 is newly 

seeded alfalfa

Evaluation Sites

Crop Evapotranspiration (ETc) inches

Crop Evapotranspiration Discrepancies

The NRCS evaluation staff recognized that there was a problem with their ETc software in 1987. This language is from 

the 1987 Grand Valley annual report: “At the beginning of this portion of the project an ET program using a Modified Penman 

equation was developed with the assistance of the ARS Staff in Fort Collins, Colorado. This year ARS Staff at Grand Junction 

provided us (NRCS) with an ET program for disseminating daily ET information to local TV, radio, and newspapers. Though the 

two programs use the same basic equation, the variables in the equation must be different, because there is a significant variance 

between the predicted two ET totals for the season of about 1 inch per month. This discrepancy needs to be resolved” (Grand 

Valley Annual Report, 1987, in U.S. Department of Agriculture, 1986–2003). 

It has been confirmed (Dick Bartholomay, CSU Cooperative Extension, retired, oral commun., September 10, 2013) that 

the ET program created for media use by the Grand Junction ARS staff was the ZETA.wks spreadsheet (Colorado State University Cooperative Extension, 1999), which has been discussed previously in the section “Reference Evapotranspiration” under 

“Soil Moisture Balance Inputs” and is documented in appendix 6. 

The 1987 annual report does not report which software program had higher or lower ET. No further mention of a resolution 

to this problem occurs in subsequent annual reports. The most likely answer was discovered during the USGS study when the 

design of the ZETA.wks spreadsheet was carefully studied. A coding error was found in the calculation of the Kc

 crop coefficient 

which caused the crop coefficient values to be incorrect. Figure 60 shows the results of the coding error. The rising value of Kc

in the rapid growth phase of the crop cycle takes a sudden jump upward at Kc = 0.600. This results in an overstatement of ETc

when this crop coefficient equation is used. Compare this curve to the Kc curve in figure 40, which represents the correction 

made to the ZETA.wks software code by the USGS study. This could be the source of the 1 inch per month discrepancy noted in 

the 1987 annual report.
USGS Study Findings on NRCS Evaluation 89

Figure 60. Example of ZETA.wks spreadsheet crop coefficient curve with software coding error in ZETA.wks 

program. [Kc, crop coefficient; NRCS, Natural Resources Conservation Service; ZETA.wks, NRCS ETp software 

program.]

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

11/3/1988

12/23/1988

2/11/1989

4/2/1989

5/22/1989

7/11/1989

8/30/1989

10/19/1989

12/8/1989

1/27/1990

NRCS ZETA Crop Coefficient (Kc) 

with Software Error

Crop Coefficient (Kc)

Date

Because the ZETA.wks spreadsheet version that was obtained by USGS was dated December 1999, and the coding error 

was still present, it is assumed that this ZETA.wks spreadsheet coding error was present from the beginning. It is thus likely that 

the incorrect ETc mentioned in the annual report quote above was coming from the ZETA.wks spreadsheet, and that the correct ETc

 was being calculated by the ARS-provided software (coded in Basic) being used by the NRCS evaluation staff. If this 

assumption is correct, then the reported ETc

 values in the NRCS evaluation annual reports would not have contained this error.

Crop Evapotranspiration Stress Correction Discrepancies

Stress correction is a contemporary method to increase the accuracy of ETc calculations for a crop. The SMB model spreadsheets use the FAO-56 stress correction method, as was described in the section “Evapotranspiration for Soil Moisture Balance 

Models.” Some method of ETc stress correction was also performed in the NRCS evaluation. The NRCS annual reports for 

1985 through 1988 mention that “The crop coefficient and stress adjustments used were supplied by ARS in Grand Junction and 

Fort Collins.”, and “The soil water deficits were calculated ... using an adjustment factor based on the days since precipitation 

or irrigation to simulate plant stress” (Grand Valley Annual Report, 1987, in U.S. Department of Agriculture, 1985). The actual 

method of applying this stress adjustment is not given. It was found while manipulating the SMB models that a baseline-fit could 

not be achieved unless the SMB model stress correction algorithm was disabled. With SMB model stress correction turned on, 

7.1 percent more ETc was required to achieve the baseline-fit. This would indicate that the NRCS reported results do not reflect 

the use of a rigorous stress correction procedure. The sensitivity analysis will include a factor for turning the stress correction off 

and on in the SMB models to measure the effect of stress correction on DP and SIE.
90 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Irrigation Water Application Timing Discrepancies

Initially, the design of the SMB models was such that the total net irrigation water inflow (inflow minus outflow) was 

assumed to have a constant rate of application over the duration of the event. The net inflow was converted to inches (using 

the field size), a per-day application value was calculated in inches using the number of event days, and the daily applications 

were applied equally over the event days. In trying to achieve the baseline-fit for the 12 sites, it became evident that dividing the 

applied irrigation water over the duration of the event was not allowing a baseline-fit of the SMB models to the NRCS reported 

values. The solution was in realizing that the NRCS soil moisture accounting assumed that all the irrigation water was applied 

instantaneously at the beginning of each irrigation event. While this may seem counter-intuitive, there is some logic in its favor. 

Fields are typically divided into sections (sets) for irrigation application. Each set usually lasts either 12 or 24 hours, after 

which the irrigation water is applied to the next set. When a typical irrigation event is analyzed set by set, it is apparent that there 

are an equal number of days between irrigations for each set, and that the season-total number of irrigation days for each set is 

the same. Thus, there should be no season-total ETc differences from one set to the next. 

The accounting of soil water deficits in the NRCS evaluation depends on the assumption that the irrigation water is completely applied as soon as the irrigation event starts. This starts the ticking of the ETc

 clock, which runs until the start of the next 

irrigation event. The value of NRCS reported SWD at the beginning of that next event is dependent on the daily ETc and precipitation that occur from the very beginning of one event (the same day the irrigation event starts) to the start day of the subsequent 

event. Recall that SWD is the field capacity minus the current soil moisture amount, which is described as the deficit amount 

of water below field capacity in the soil. For example, a soil profile with a field capacity of 20 inches, which has a current soil 

water amount of 16 inches, would have a 4-inch soil water deficit. In a sense, the NRCS accounting only looks at the first set of 

each event, and assumes that the set had a duration of zero hours, achieving the ending SWD value immediately.

To achieve a baseline-fit, the SMB model was changed from taking into account the entire duration of the event to assuming that each event lasts for 24 hours. It is not possible in the SMB model to have two different simultaneous values of soil water 

balance (event beginning SWD and ending SWD) on the beginning day of an event, so allowing for 24 hours delay is the shortest amount of time in which the model can achieve the ending event SWD. An analysis of this 24-hour difference between SMB 

model accounting and NRCS accounting shows that the loss of one day of ETc

 for every irrigation event in the SMB models 

requires a mean value of 6.1 percent more ETc to be input to the models to reach the NRCS reported SWD value at the start of 

the next event. This is an offset in the SMB model ETc which can be allowed for when analyzing the difference in ETc inputs 

between the SMB models and the NRCS sites.

Non-Quantifiable Discrepancies

Discrepancies due to Lack of NRCS Field Tests for Soil Water Deficit Values

The most likely source of errors in SWD values at the beginning of each irrigation event is the reliance by the NRCS evaluation on calculated SWD values at the start and end of each irrigation event, without using field measurements of SWD values 

to cross-check the calculated SWD values. An initial SWD for the season was determined by NRCS using a gravimetric analysis 

in 1985 and 1986, but whether this practice was continued was not reported in subsequent years. There is some indication that 

a “hand-feel” method of soil moisture determination was used in later years (Frank Riggle, NRCS, written commun., August 8, 

2013). For whatever reason, the start of season soil moisture was never reported by NRCS. 

The evaluation staff must have realized the computed SWD values at the start and end of each event were subject to 

cumulative errors, because the 1989 Grand Valley annual report stated: “Actual field soil moisture needs to be compared with 

computer generated values using crop ET data to determine if adjustments have to be made. Current techniques and equipment 

available are time consuming and do not provide an accurate estimate of actual soil moisture conditions” (Grand Valley Annual 

Report, 1987, in U.S. Department of Agriculture, 1986–2003). The 1990 Grand Valley annual report noted: “Currently the monitoring water budget program does not have the capacity to adjust for high water table. Additionally, there is no equipment on 

hand that could give a quick reliable estimate of soil moisture in the field to make needed adjustments to the computer generated 

values” (Grand Valley Annual Report, 1990, in U.S. Department of Agriculture, 1986–2003).

It is not stated in subsequent annual reports whether this problem was ever solved. If a quick field method for measuring 

SWD had been available, the calculated SWD values from the soil moisture software could have been compared with measured 

SWD at each site and corrected if necessary. 

Discrepancies due to Precipitation Data Collection Changes

The NRCS evaluation precipitation field methods changed after 1987. From 1985 through 1987, site precipitation was measured using a rain gage at every evaluation site. After 1987, only “some” sites had precipitation measured using rain gages, and 

the number of sites with gages was not reported. The other source of precipitation data for each site was the two NRCS operated 

weather stations. The 1985 through 1987 Grand Valley annual reports state: “The precipitation was electronically recorded at the 
USGS Study Findings on NRCS Evaluation 91

two weather stations (NRCS). On-site precipitation was also recorded at each of the monitored locations” (Grand Valley Annual 

Reports, 1985–1987, in U.S. Department of Agriculture, 1986–2003). Then, the 1988 through 1995 Grand Valley annual reports 

state: “The precipitation was electronically recorded at the two weather stations (NRCS). On-site precipitation was also recorded 

at some of the monitored locations” (Grand Valley Annual Reports, 1988–1995, in U.S. Department of Agriculture, 1986–2003).

Refer to the sections titled “Precipitation for Soil Moisture Balance Models” for more details regarding precipitation discrepancies in the NRCS evaluation reports.

Discrepancies due to Deep percolation Calculation changes

There were changes in the calculation method used for season total DP. The 1990 Grand Valley annual report states, “In 

1990, the water budget program was updated to more accurately estimate deep percolation for annual crops. In the past, deep 

percolation for the first irrigation and or pre-irrigation was considered to be any amount that was in excess of that required to fill 

up the first foot of soil; the full root profile was not taken into account. With this method, deep percolation estimates were higher 

than what they should be. All previous data from 1986 to 1989 have been re-processed using the updated program to get a better 

estimate of deep percolation, soil moisture, and ETc” (Grand Valley Annual Report, 1990, in U.S. Department of Agriculture, 

1986–2003). The changed DP values due to this retroactive per-site change are not shown in the 1990 annual report, so presumably the data available to the USGS study from the annual reports from 1985 to 1989 contain the original DP values, not the 

corrected values. It is thus impossible to determine the effect of this change on reported DP values.

Seasonal Irrigation Efficiency Calculation Changes

There was a change in the formula used to calculate SIE in 1990. The Grand Valley annual report for 1990 states, 

“In the past, the overall seasonal irrigation application efficiency was computed erroneously: it was calculated as 

the mean of all individual site irrigation efficiencies. In 1989 and 1990, the overall mean efficiency was calculated 

using the seasonal irrigation efficiency formula shown at the bottom of table 2 and defined on page 16. This formula 

is also used for calculating individual irrigation efficiency as was done in the past. The overall irrigation efficiency 

for the past five years has been recalculated and provided in table 4. These values are slightly lower than previously 

reported” (Grand Valley Annual Report, 1990, in U.S. Department of Agriculture, 1986–2003). The formulas referred 

to in the quote are:

Table 2 formula: Seasonal Irr. Eff. = (vol. of inflow – vol. of outflow)/Vol. of inflow x 100

Table 4 formula: Seasonal Irr. Eff. = (vol. of inflow – vol. of outflow – D.P.)/Vol. of inflow x 100

Note the absence of DP in the table 2 formula. The changed SIE season total values were reported in table 4 of the 1990 

Grand Valley annual report as a six-year summary of values by year. 

Undocumented NRCS Data Corrections 

All of the NRCS annual reports have asterisks for many of the tables of individual site records stating that “corrections 

have been applied to the data.” The exact nature of these corrections is never documented. In addition, there are individual irrigation event data records scattered throughout the annual reports where the basic arithmetic of water balance calculations does 

not “add up” for the irrigation event. These records were excluded from the USGS study analysis when these tables obviously 

were in error mathematically. Refer to the section titled “Site-Year Record Quality Determination” for a discussion of how the 

usability of records was determined.

Discrepancies Due to Software Problems

The 1994 Grand Valley annual report mentions unspecified software problems that were being encountered: “Data downloading, processing, and evaluation is being done using several computer programs. These programs have been in place for several years but problems still exist. Existing programs need to be updated when problems are encountered. It would be beneficial 

to have one M&E team member with computer programming knowledge” (Grand Valley Annual Report, 1994, in U.S. Department of Agriculture, 1986–2003). No mention in subsequent annual reports was found about whether these software problems 

were ever solved or exactly what kinds of problems they were causing.

Discrepancies Due to Human Error

Finally, one must recognize the inherent problems in collecting field data and keeping accurate records over the period of 

19 years, with many changes in staff during those years. Even the most rigorous of projects will have some human error which is 

impossible to quantify.
92 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Sensitivity Analysis of SMB Models

A review was done by the USGS to ensure that the SMB models were free from calculation and assumption errors. Three 

crop scientists in the NRCS and the Colorado State University Extension Service provided reviews and input as to the accuracy of the SMB models and configuration variables, particularly the ETc

 assumptions (Lorenz Sutherland, Natural Resources 

Conservation Service, oral commun., September 13, 2012; Calvin Pearson, Colorado State University Extension Service, oral 

commun., April 7, 2012; and Frank Riggle, Natural Resources Conservation Service, oral commun., August 24, 2013). 

The baseline-fit discussed in previous SMB model sections shows that the 12 SMB models can be made to match NRCS 

evaluation results at those sites. But do the SMB model assumptions which must be made in order to achieve this baseline-fit 

withstand scrutiny in light of current practices in irrigation system analysis? In the end, can the NRCS evaluation methods and 

results be accepted as accurate?

A sensitivity analysis shows the effect on SMB model results when various changes are made to the model inputs. The 

analysis shows which changes in model inputs result in the largest changes in model outputs. In particular, it is of interest to 

measure variations in model DP and SIE. The estimation of DP and SIE are some of the most important results from the NRCS 

evaluation, and tests of the accuracy of DP and SIE go to the heart of the NRCS evaluation conclusions. When a sensitivity 

analysis was done using three sets of variables, discrepancies were seen between the NRCS reported ETc, DP, and SIE and the 

SMB model values. This sensitivity analysis shows some possible effects of manipulating the SMB model inputs to move the 

SMB models away from the baseline-fit. 

Sensitivity Test Inputs

There are three sets of model inputs, each having two values, which are manipulated in the sensitivity tests. These pairs of 

inputs are 

1. Closest Grand Valley NOAA or CSU weather station precipitation or NRCS reported precipitation; 

2. Crop evapotranspiration stress correction used or not; and

3. NRCS reported daily ETp, or a 10 percent upward adjustment in ETp to match published standards of crop consumptive 

use. 

This results in eight combinations of inputs. By setting the SMB model inputs to these eight combinations, it is possible to 

calculate the value changes in the SMB model outputs.

Sensitivity Test Outputs

SMB model outputs for DP and SIE were measured for changes from the various input combinations. Results are reported 

separately for flood irrigation systems and sprinkler irrigation systems. The resulting changes in ETc are also reported. While ETc

is not strictly an SMB model output, it is an intermediate result which affects DP and SIE, and it is changed by modifying the 

sensitivity test inputs.

Crop Evapotranspiration Sensitivity Test Results

Table 32 shows the changes in SMB model season total ETc when various sensitivity tests are performed. All percent difference values in table 32 are relative percent difference (RPD). The SMB model ETc

 is 5.4 percent higher even at the “baseline-fit” 

settings in test 1 because of the minimum 1 day irrigation event requirement for the SMB models, as discussed in the previous 

section “Irrigation Water Application Timing Discrepancies.” Test 3 only changes the precipitation data source from the test 

1 conditions, and shows by yielding the same results as test 1 that precipitation data source has no effect on ETc, as would be 

expected. Test 2 includes the use of stress correction, and test 4 includes stress correction and also changes the precipitation 

setting choice. Tests 2 and 4 both result in model ETc that is 12.8 percent higher than reported ETc. This shows that the while the 

precipitation selection does not affect the sensitivity results for ETc, the use of stress correction increases the mean ETc relative 

percent difference by 7.4 percent (12.8–5.4 = 7.4) over reported ETc. 

Tests 5 and 7 both yield a model ETc that is 14.7 percent higher than reported, indicating again that precipitation setting selection does not affect ETc

. Tests 6 and 8 result in a 22.3 percent higher model ETc than reported results. The difference 

between tests 1 and 5 show that an increase of 10 percent in ETp increases ETc by 9.3 percent (14.7 – 5.4 = 9.3) over reported 

ETc. It would be expected that increasing ETp by 10 percent should yield a similar increase in ETc, and this is confirmed by this 

result. The largest difference between reported and model results occurs with tests 6 and 8, resulting in a 16.9 percent difference 

over baseline results when weather station precipitation is selected, stress correction is turned on, and 110 percent reference is 

used. 
USGS Study Findings on NRCS Evaluation 93

Table 32. Comparison between Natural Resources Conservation Service reported values and eight sensitivity test results for mean 

season total ETc. at 12 SMB model sites.

[NRCS, Natural Resources Conservation Service; ETp, reference evapotranspiration; ETc, crop evapotranspiration, SMB, soil moisture balance.]

Sensitivity Test 

Number

Stress

Correction

Setting

Precipitation 

Setting

Reference ETp

Setting (Percent)

NRCS Reported 

ETc for 12 SMB 

Sites

(Mean Inches)

Model ETc

 for

12 SMB Sites

(Mean Inches)

Relative Percent 

Difference Between 

Reported and SMB 

Model ETc

 (Percent)

1 Off Reported 100 27.1 28.6 5.4

2 On Reported 100 27.1 30.8 12.8

3 Off Weather station 100 27.1 28.6 5.4

4 On Weather station 100 27.1 30.8 12.8

5 Off Reported 110 27.1 31.4 14.7

6 On Reported 110 27.1 33.9 22.3

7 Off Weather station 110 27.1 31.4 14.7

8 On Weather station 110 27.1 33.9 22.3

DP Sensitivity Test Results

Flood Irrigation DP Sensitivity Test Results

The blue bars in figure 61 and figure 62 show the sensitivity test results for differences in flood irrigation DP between the 

SMB models and NRCS reported results. Figure 61shows differences in inches of water, while figure 62 shows relative percent 

difference between SMB model results and NRCS reported results. The baseline-fit results in both figures are the first pair of 

bars on the left (test 1). The baseline-fit test settings are NRCS reported precipitation, crop stress correction setting off, and ETp

at NRCS reported levels. 
94 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Figure 61. Sensitivity test results in soil moisture balance model deep percolation in inches of water for flood irrigation system 

types. [%, relative percent; SMB, soil moisture balance; DP, deep percolation; NRCS, Natural Resources Conservation Service; Precip, 

precipitation; WS, weather station; ETp

, reference evapotranspiration.]

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

Test 1

Stress off 

NRCS Precip

100% ETp

Test 2

Stress on 

NRCS Precip

100% ETp

Test 3

Stress off

WS Precip 

100% ETp

Test 4

Stress on

WS Precip 

100% ETp

Test 5

Stress off

NRCS Precip

110% ETp

Test 6

Stress on 

NRCS Precip

110% ETp

Test 7

Stress off

WS Precip

110% ETp

Test 8

Stress on

WS Precip 

110% ETp

SMB Model DP minus NRCS Reported DP (mean inches)

Sensitivity Test Number

Sensitivity Tests of Deep Percolation (DP) for Flood Irrigation 

Soil Moisture Balance Model (SMB) Sites (inches of water) 
USGS Study Findings on NRCS Evaluation 95

Figure 62. Sensitivity test results in soil moisture balance model deep percolation in relative percent difference for flood 

irrigation system types. [%, relative percent; SMB, soil moisture balance; DP, deep percolation; NRCS, Natural Resources 

Conservation Service; Precip, precipitation; WS, weather station; ETp

, reference evapotranspiration.]

-30.0

-25.0

-20.0

-15.0

-10.0

-5.0

0.0

Test 1

Stress off

NRCS Precip 

100% ETp

Test 2

Stress on 

NRCS Precip

100% ETp

Test 3

Stress off 

WS Precip

100% ETp

Test 4

Stress on

WS Precip 

100% ETp

Test 5

Stress off

NRCS Precip 

110% ETp

Test 6

Stress on 

NRCS Precip 

110% ETp

Test 7

Stress off 

WS Precip

110% ETp

Test 8

Stress on

WS Precip 

110% ETp

Model DP minus NRCS Reported Deep Percolation (mean percent)

Sensitivity Test number

Sensitivity Tests of Deep Percolation (DP) for Flood 

Soil Moisture Balance Model Sites 

 (relative percent difference)

For flood irrigation sites, in the first 4 tests shown in figure 61 the model mean DP was lower than mean NRCS reported 

DP by less than an inch of water. Stress correction setting and precipitation setting made little difference in the results of the four 

tests. When weather station precipitation replaced NRCS reported precipitation (3d and 4th tests), the difference between SMB 

model and NRCS reported DP decreased to less than 0.5 inch. These differences are shown as percent differences from NRCS 

reported values in figure 62. The changes seen in the 5th through 8th tests in figure 61 indicate that when ETp

 is increased by 10 

percent to raise the season total ETp to match 1988 Colorado Irrigation Guide consumptive use values, mean DP for the seven 

flood model sites decreased by a range of 2.9 to 2.2 inches when compared with NRCS reported DP for the seven flood SMB 

sites. The effect is about the same regardless of the precipitation setting or whether the crop stress is on or off. In figure 62, the 

5th through 8th tests result in a mean DP of about 13 percent lower than NRCS reported DP. 

Sprinkler Irrigation DP Sensitivity Test Results

The red bars in figure 63 (in inches) and figure 64 (in relative percent difference) show the sensitivity test results for sprinkler and microspray sites. Sensitivity tests 1, 2, 7, and 8 show model DP being higher than NRCS reported DP by about 0.5 inch. 

Tests 5 and 6 show slightly lower model DP compared with NRCS reported DP of about a negative 0.5 inch. Tests 3 and 4 show 

greater model DP between 1 and 2 inches, which is the largest difference in sensitivity results for sprinkler and microspray DP. 

This occurred when weather station precipitation was substituted for NRCS reported precipitation. This result could be anticipated from the discrepancies in weather station versus reported precipitation discussed earlier.
96 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Because sprinkler and microspray sites tend to have very low season total DP (compared to flood sites), small changes in 

precipitation of a few inches in a season could result in greater changes in SMB model DP. The mean NRCS reported DP for 

the five model sprinkler and microspray sites is only 1.1 inches. Thus an increase of 1 to 2 inches in SMB model DP is a large 

percentage change but is not of interest in absolute terms.

Figure 63. Sensitivity test results for soil moisture balance model deep percolation in inches of water for sprinkler and microspray 

irrigation system types. [%, relative percent; SMB, soil moisture balance; DP, deep percolation; NRCS, Natural Resources 

Conservation Service; Precip, precipitation; WS, weather station; ETp

, reference evapotranspiration.]

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

Test 1

Stress off 

NRCS Precip 

100% ETp

Test 2

Stress on 

NRCS Precip

100% ETp

Test 3

Stress off 

WS Precip

100% ETp

Test 4

Stress on

WS Precip

100% ETp

Test 5

Stress off

NRCS Precip

110% ETp

Test 6

Stress on

NRCS Precip 

110% ETp

Test 7

Stress off 

WS Precip

110% ETp

Test 8

Stress on

WS Precip

110% ETp

Model DP minus NRCS Reported DP (mean inches)

Sensitivity Test Number

Sensitivity Tests of Deep Percolation (DP) for Sprinkler 

and Microspray Soil Moisture Balance Model (SMB) Sites

 (inches of water) 
USGS Study Findings on NRCS Evaluation 97

Seasonal Irrigation Efficiency Sensitivity Test Results

SIE is determined in part by the magnitude of DP. SIE is calculated as 

SIE = (Inflow – Outflow – DP) / Inflow (10)

where

SIE is seasonal irrigation efficiency,

Inflow is the amount of water entering a field,

Outflow is the amount of water leaving a field, and

DP is deep percolation of irrigation water downward from the field.

If there are no changes in inflow or outflow, as is the case in the sensitivity tests, a decrease in DP results in an increase to 

SIE, because DP is subtractive in equation 10. 

-30.0

-10.0

10.0

30.0

50.0

70.0

90.0

110.0

Test 1

Stress off

NRCS Precip

100% ETp

Test 2

Stress on

NRCS Precip

100% ETp

Test 3

Stress off

WS Precip

100% ETp

Test 4

Stress on

WS Precip

100% ETp

Test 5

Stress off

NRCS Precip

110% ETp

Test 6

Stress on

NRCS Precip

110% ETp

Test 7

Stress off

WS Precip

110% ETp

Test 8

Stress on

WS Precip

110% ETp

SMB Model DP minus NRCS Reported DP (mean percent)

Sensitivity Test Number

Sensitivity Tests of Deep Percolation (DP) 

for Sprinkler and Microspray Soil Moisture Balance 

Model Sites (relative percent difference)

Figure 64. Sensitivity test results for soil moisture balance model deep percolation in relative percent difference 

for sprinkler and microspray irrigation system types. [%, relative percent; SMB, soil moisture balance; DP, deep 

percolation; NRCS, Natural Resources Conservation Service; Precip, precipitation; WS, weather station; ETp

, reference 

evapotranspiration.]
98 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Flood Irrigation SIE Sensitivity Test Results

Figure 65 shows the flood irrigation sensitivity test results in relative percent difference for SIE. The baseline-fit results 

(test 1) on the left are for NRCS reported precipitation, crop stress correction setting off, and ETp at NRCS reported levels. In 

tests 1 through 4, one can see that there is a difference in SIE between mean NRCS reported flood and mean SMB flood model 

results of less than 1 percent for model sites. When crop stress correction is turned on (test 2), not much change is evident. 

When weather station precipitation replaces NRCS reported precipitation (tests 3 and 4), the difference between SMB model and 

NRCS reported SIE decreases to about 0.5 percent. 

Figure 65. Sensitivity test results for soil moisture balance model seasonal irrigation efficiency in relative percent 

difference for flood irrigation system types. [%, relative percent; SMB, soil moisture balance; SIE, seasonal irrigation 

efficiency; NRCS, Natural Resources Conservation Service; Precip, precipitation; WS, weather station; ETp

, reference 

evapotranspiration.]

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Test 1

Stress off 

NRCS Precip

100% ETp

Test 2

Stress on 

NRCS Precip

100% ETp

Test 3

Stress off 

WS Precip 

100% ETp

Test 4

Stress on

WS Precip

100% ETp

Test 5

Stress off 

NRCS Precip

110% ETp

Test 6

Stress on

NRCS Precip

110% Etp

Test 7

Stress off 

WS Precip

110% ETp

Test 8

Stress on

WS Precip

110% ETp

SMB Model SIE minus NRCS Reported SIE (mean percent)

Sensitivity Test Number

Sensitivity Tests of Seasonal Irrigation Efficiency 

(SIE) for Flood Soil Moisture Balance Model (SMB) Sites 

(relative percent difference)
USGS Study Findings on NRCS Evaluation 99

The changes seen in tests 5 through 8 (fig. 65) indicate that when ETp is increased by 10 percent to raise the season total 

ETp (ETp=110 percent) to more closely match 1988 Colorado Irrigation Guide consumptive use values, mean SIE for the seven 

flood model sites increases in magnitude by about 2 to 2.7 percent. The increases in SIE for flood sites is greatest for NRCS 

precipitation and crop stress setting off and least for weather station precipitation and crop stress setting on. None of these 8 test 

results show dramatic differences between SMB model results and NRCS reported results.

Sprinkler and Microspray Irrigation SIE Sensitivity Test Results

Figure 66 shows the sprinkler and microspray sensitivity test results in relative percent difference for SIE. All eight tests 

show higher SIE for the SMB models when compared with NRCS reported SIE. The differences range from about 1.5 to 3.7 

percent. None of the 8 test results show dramatic differences between SMB model results and NRCS reported results. 

Figure 66. Sensitivity test results for soil moisture balance model seasonal irrigation efficiency in relative percent difference 

for sprinkler irrigation system types. [%, relative percent; SMB, soil moisture balance; SIE, seasonal irrigation efficiency; NRCS, 

Natural Resources Conservation Service; Precip, precipitation; WS, weather station; ETp

, reference evapotranspiration.]

-1.0

0.0

1.0

2.0

3.0

4.0

5.0

Test 1

Stress off -

NRCS Precip -

100% ETp

Test 2

Stress on -

NRCS Precip -

100% ETp

Test 3

Stress off -

WS Precip -

100% ETp

Test 4

Stress onWS Precip -

100% ETp

Test 5

Stress off -

NRCS Precip -

110% ETp

Test 6

Stress on -

NRCS Precip -

110% ETp

Test 7

Stress off -

WS Precip -

110% ETp

Test 8

Stress onWS Precip -

110% ETp

Model SIE minus NRCS Reported SIE (mean percent)

Sensitivity Test Number

Sensitivity Tests of Seasonal Irrigation Efficiency (SIE) for 

Sprinkler and Microspray Soil Moisture Balance Model (SMB) Sites

(relative percent difference)
100 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Summary Tables of Sensitivity Test Results

Flood Irrigation Sites

Table 33 shows a summary of results for the eight sensitivity tests for mean changes in DP and SIE from NRCS reported 

values for the seven SMB model flood irrigation sites. The percent difference values in table 33 are relative. In table 33, the 

results for tests 1 through 4 are combined as mean values, as are the results for tests 5 through 8. Isolating the values for tests 1 

through 4 in one group and tests 5 through 8 in a separate group has the effect of ignoring the effects of setting stress correction 

on or off or selecting different precipitation sources, showing only the effect of setting ETp to either 100 percent (tests 1 through 

4) or 110 percent (tests 5 through 8). 

It can be seen in table 33 that there is a small decrease of 2.6 percent (0.5 inches) in DP for flood sites for the sensitivity tests 1 through 4 that keep ETp

 at 100 percent of the NRCS reported values. When ETp is increased to 110 percent to bring 

the SMB ETc into closer agreement with 1988 Colorado Irrigation Guide consumptive use values, mean DP decreases by 12.5 

percent (2.5 inches). Although a decrease of 2.6 percent (0.5 inches) in DP for tests 1 through 4 is probably not important in an 

absolute sense, a decrease of 12.5 percent (2.5 inches) in DP for tests 5 through 8 could be meaningful, given the relatively high 

NRCS reported mean DP of 21.6 inches for the seven SMB model flood sites. 

Likewise, test results of SIE for flood sites are combined in table 33 into the same two groups with ETp at 100 and 110 

percent, respectively. Tests 1 through 4 result in a mean increase of SIE of 0.7 percent, whereas tests 5 through 8 result in a mean 

increase of SIE of 2.4 percent. The 2.4 percent increase in SIE for flood sites with 110 percent ETp may be of interest to water 

managers, while the 0.7 percent change resulting from tests 1 through 4 is probably not of interest. 

Table 33. Mean sensitivity test results for the seven SMB model flood irrigation sites for deep percolation and seasonal irrigation 

efficiency.

[%, relative percent; DP, deep percolation; SIE, seasonal irrigation efficiency; SMB, Soil Moisture Balance; precip, precipitation; ETp, reference evapotranspiration; 

stress, evapotranspiration stress correction; NRCS, Natural Resources Conservation Service]

Irrigation

System

Type

Site Variable

NRCS Reported Mean 

Values for 7 SMB Model

Flood Sites

Sensitivity Test Results

Grouped by Tests Having Either 100% ETp

 Or 110% ETp

With Results in Inches of DP and Percent SIE 

and

(Difference in Test Results from NRCS Reported Mean 

Values

for 7 SMB Model Flood Sites

In Inches and Relative Percent Difference)

Tests: 1-4

Stress: Any

Precip: Any

ETp

: 100%

Tests: 5-8

Stress: Any

Precip: Any

ETp

: 110%

Flood Deep percolation 21.6 inches

21.0 inches 

(-0.5 inch,

-2.6 %) 

19.0 inches

(-2.5 inches,

-12.5 %)

Flood Seasonal irrigation

efficiency 39.3 % 40.3 %(+0.7 %) 

43.2 %

(+2.4 %) 

Sprinkler and Microspray Irrigation Sites

Table 34 shows a summary of results for the eight sensitivity tests for changes in mean DP and SIE from NRCS reported 

values for the five SMB model sprinkler and microspray irrigation sites. The percent difference values in table 34 are relative. 

In table 34, the results for tests 1 through 4 were combined as mean values, as are results for tests 5 through 8. It can be seen in 

table 34 that the DP results are mixed, with tests 1 through 4 having an increase in DP of 59.7 percent (1.0 inch), while tests 5 

through 8 have a decrease in DP of 16.5 percent (0.1 inch). Because the NRCS reported mean DP is only 1.1 inches for these 

five sites, the DP percentage changes in table 34 for tests 1 through 4 and for tests 5 through 8 appear large; however, neither of 
USGS Study Findings on NRCS Evaluation 101

the test groups resulted in large changes in the actual amount of DP. In general, sprinkler and microspray systems have very low 

DP, so changes of an inch or less in DP are not particularly meaningful in the real world. 

Test results of SIE for sprinkler and microspray sites are combined in table 34 into the same two groups as for DP. In tests 

1 through 4, SIE increases by 2.3 percent, and in tests 5 through 8, SIE increases by 3.3 percent. However, because it has been 

determined that the decreases in DP shown in table 34 are not meaningful because of the very low mean DP value of 1.1 inches, 

the 2.3 percent and 3.3 percent changes in SIE should not be considered to be meaningful either.

Table 34. Mean sensitivity test results for the four sprinkler irrigation and one microspray SMB model sites for deep percolation and 

seasonal irrigation efficiency.

[%, relative percent; DP, deep percolation; SIE, seasonal irrigation efficiency; SMB, soil moisture balance; precip, precipitation; ETp, reference evapotranspirtion; 

stress, evapotranspiration stress correction; NRCS, Natural Resources Conservation Service]

Irrigation

System

Type

Site Variable

NRCS Reported Mean 

Values for 5 SMB Model

Sprinkler & Microspray 

Sites

Sensitivity Test Results

Grouped by Tests Having Either 100% ETp

 Or 110% ETp

With Results in Inches of DP and Percent SIE 

and 

(Difference in Test Results from NRCS Reported Mean 

Values

for 5 SMB Model Sprinkler and Microspray Sites

In Inches and Relative Percent Difference)

Tests: 1-4

Stress: Any

Precip: Any

ETp

: 100%

Tests: 5-8

Stress: Any

Precip: Any

ETp

: 110%

Sprinkler and microspray Deep percolation 1.1 inches

2.1 inches

(+1.0 inch,

59.7 %)

1.0 inches

(-0.1 inch,

-16.5 %)

Sprinkler and microspray Seasonal irrigation

efficiency 68.3 % 74.8 %(+2.3 %) 

78.0 %

(+3.3 %) 

Suggested Revisions to NRCS Evaluation Results

Suggested revisions to NRCS evaluation results based on the sensitivity tests for flood and sprinkler irrigation systems are 

summarized in table 35.

Table 35. Suggested revisions to NRCS evaluation results.

[NRCS, Natural Resources Conservation Service]

Irrigation System Type Deep Percolation Seasonal Irrigation Efficiency

Flood Reduce NRCS reported values

by 12.5 relative percent 

Increase NRCS reported values

by 2.4 relative percent

Sprinkler and Microspray No change No change
102 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

The suggested revisions in DP and SIE in table 35 for flood irrigation sites may be of interest to water managers who have 

relied on the NRCS evaluation results over the years for decision making, but only the users of this analysis can determine 

whether these differences are large enough to warrant a revision of their interpretation of the NRCS evaluation results. There are 

no suggested changes to sprinkler and microspray results from the NRCS evaluation. Overall, the NRCS evaluation results were 

found to most likely be as accurate as could have been achieved in such a complex, long-running data collection effort, especially with early versions of computers and automated field equipment. Any discrepancies found in the NRCS evaluation results 

are important to understand because water managers use results of the NRCS evaluation, along with many other sources, as a 

baseline to predict the effects of irrigation on salinity in the rivers and to develop salinity control policy. Accurately estimating 

salt loading from irrigation use is always a challenging task, so increasing the accuracy of baseline data could help in creating better salt loading models. Discussions with NRCS salinity control managers indicate that the cost per ton of salt reduction 

(which is used for salinity control project planning) would be reduced somewhat if changes in DP and SIE assumptions were 

implemented (Travis James and Ed Wicker, NRCS, oral commun., August 7, 2013). 

The overall implication of less DP and more SIE than reported from the NRCS evaluation would be that the salinity control 

projects that have been undertaken over the years by NRCS, Reclamation, and the Salinity Control Forum possibly have resulted 

in a greater amount of salt reduction than had been originally calculated. 

Summary

The increasing salinity levels in water delivered to Mexico and the Lower Colorado River Basin States in the early 1970s 

created concern about economic damages to downstream water users, resulting in the enactment of the Colorado River Basin 

Salinity Control Act (Salinity Control Act). As part of that effort, the U.S. Department of Agriculture Natural Resources Conservation Service (NRCS) established a program in 1982 to make on-farm irrigation system improvements to reduce deep percolation (DP) and irrigation ditch seepage. In 1982 the NRCS also initiated a monitoring and evaluation study (NRCS evaluation) 

of irrigation water application practices in the Grand Valley Salinity Control Unit located in western Colorado. One part of the 

NRCS evaluation was an effort to assess the effectiveness of the NRCS irrigation system improvement program in reducing 

salt loading in the Colorado River. Salt loading in the river was not directly measured or estimated in the NRCS evaluation. The 

NRCS evaluation was later extended to the Lower Gunnison Unit in 1992 and the McElmo Creek Unit in 1993. 

The NRCS evaluation gathered a total of 287 site-years of irrigation application data at landowner sites in the three Units 

between 1985 and 2003. The evaluation sites were diverse in terms of crop types, acreage, soil types, and irrigation system 

types. The results of the evaluation were recorded by NRCS in internal annual reports, and were also shared with the Colorado 

River Basin Salinity Control Forum (Forum). In 2011, the U.S. Geological Survey (USGS), in cooperation with the Bureau of 

Reclamation and the Colorado River Basin Salinity Control Forum, began a study to evaluate the NRCS evaluation data to (1) 

document the methods of the evaluation, and (2) analyze and summarize the data collected during the evaluation. The NRCS 

gathered the existing physical documents from the evaluation, transferred the raw site data to Microsoft Excel spreadsheets, and 

assisted the USGS in understanding the dataset. The term “NRCS evaluation” is used throughout this report to refer to the NRCS 

monitoring and evaluation study, and the term “USGS study” refers to the USGS analysis of the NRCS evaluation.

Irrigation practices in the Grand Valley Unit, the Lower Gunnison Unit, and the McElmo Creek Unit were evaluated by the 

NRCS in western Colorado. To characterize the methodology of the NRCS evaluation, interviews were conducted by the UGSG 

study with available current and retired NRCS staff who participated in the NRCS evaluation. To summarize the NRCS evaluation results, the raw data from over 1,800 pages of printed NRCS evaluation annual reports and documentation were entered 

into two Excel spreadsheets, one for season total results, and one for individual irrigation event results. The entire set of printed 

NRCS evaluation documents were scanned to an Adobe PDF file. Any information which might lead to personal identification 

of the evaluation participants was redacted by NRCS from the evaluation documents before scanning. The NRCS field data collection methods were summarized from the results of the interviews and printed documents. The raw irrigation event data were 

analyzed for quality and rated on the basis of completeness and internal consistency.

The NRCS evaluation sites were selected to represent the variety of crops and irrigation systems common in the evaluation units. Individual irrigation event data were collected, and a water budget was computed for each site. Basic characteristics 

recorded by the evaluation at the start of the irrigation season for each site included the type of irrigation system, length of field 

run (feet), field slope (percent), field size (acres), soil type, crop type, planting and harvest dates, specific soil type, and soil 

water holding capacity. Periodic site data collected during the irrigation season included daily precipitation amount, irrigation 

event dates and durations, and water inflow to the field and outflow from the field during events. The initial soil water balance 

was estimated at the beginning of the season, and was also calculated using the water balance method at the start and finish of 

each irrigation event. Reference evapotranspiration (ETp

) was calculated daily from weather station data. Crop evapotranspiration (ETc

) was estimated using a time-dependent crop coefficient (Kc). DP values were calculated using the infiltrated depth 
Summary 103

of water from each irrigation event and the initial soil water deficit for each event. Electronic instruments were used to collect 

inflow and outflow data in the field. Numerous problems were encountered and overcome with the instrumentation.

Potential causes of inaccuracy in field collection results are summarized by the USGS study. Tables are presented that summarize the span of years that each site in the three salinity control units was evaluated.

Geographic information system (GIS) maps of the approximate locations for evaluation sites in the Grand Valley Unit and 

the Lower Gunnison Unit were generated. No site location data was reported for the McElmo Creek Unit. Bar charts show the 

distribution of different irrigation system types evaluated over the duration of the evaluation, and scatter plots show examples of 

the evolution of irrigation technology and crop type changes at two sites. 

An improvement order was established to rank the irrigation system types by level of technological sophistication. The soil 

types originally reported in the evaluation have changed names since the evaluation, and a cross-reference table of original to 

current soil type names is shown. The quality of data for each site-year record was evaluated based on completeness and internal 

consistency, which resulted in the creation of several classes of data. Of the 292 total evaluation site-year records, 268 were 

determined to be usable for analysis, while 225 records from 1985 to 1996 (from all three Salinity Control Units) were determined to be the most complete and consistent of the evaluation records. These records were labeled as gold standard records in 

this report. Analyses in this report are performed with either all usable records, gold standard records, or both sets.

Summary statistics were generated for each evaluation unit for discrete and continuous site variables. Tables of summary 

statistics grouped by discrete and continuous variables are shown for each of the three evaluation units. A table of annual mean 

results for field data for all sites, and for gold standard sites by year and Unit is shown. Frequency charts are shown for irrigation system types, NRCS reported seasonal irrigation efficiency, and NRCS reported deep percolation by evaluation unit. A 

chart showing frequency of irrigation event duration is shown. Scatter plots with a LOESS curve for deep percolation versus 

seasonal irrigation efficiency was created for all usable site records and for all gold standard site records. In general, these scatter 

plots show that DP decreases with increasing seasonal irrigation efficiency (SIE), but the rate of decrease in DP declines above 

SIE values of about 35 percent. The implication is that as irrigation technology improvements raise SIE, the rate of payoff in 

decreased DP is smaller for the most advanced irrigation technologies.

Box plots of deep percolation by system improvement order were created for all usable sites and separately for Grand Valley, Lower Gunnison, and McElmo Creek Units. Where enough site-years of data exist (all usable sites and Grand Valley Unit 

gold standard sites), these box plots show a decline in the variance of deep percolation as system improvement order improves, 

and reduced median deep percolation for irrigation system types pipeline to gated surge, side-roll sprinkler, and microspray. 

Similar box plots of seasonal irrigation efficiency by system improvement order show that efficiency increases as system 

improvement order increases, but the variance in seasonal irrigation efficiency is not reduced. Box plots of deep percolation and 

seasonal irrigation efficiency by crop type are also presented.

Multiple comparison statistics are shown to explore correlations of irrigation efficiency, deep percolation, crop evapotranspiration, and irrigation water infiltrated depth by discrete categories such as system improvement order, crop type, soil type, 

evaluation unit, evaluation year, crop rooting depth, and number of irrigation events. 

Soil moisture balance (SMB) models were used to test the data collection and data processing assumptions of the reported 

NRCS evaluation dataset. SMB models were created for 12 gold standard sites selected from the Grand Valley Unit having various evaluation years, crop types, and irrigation system types. An SMB model is a spreadsheet model of the daily sum of water 

inputs and outputs for an evaluation site for one irrigation season. Per-irrigation-event data are required for the site, as well as 

daily reference evapotranspiration, ETp values. Crop and soil characteristics for each site are also considered. Calculated daily 

soil moisture balances are compared with NRCS reported balances in a soil moisture balance chart. 

The various required inputs to SMB models are discussed: reference evapotranspiration (ETp

), crop coefficient (Kc), ETc 

stress correction, precipitation, and irrigation event data. The worksheets needed to construct an SMB model are discussed. The 

elements of the SMB chart are explained, and examples of SMB charts for several different crop types and irrigation system 

types are discussed. The procedure to produce a “baseline-fit” of the SMB model to the NRCS evaluation results for each site is 

given, including example charts. A comparison table of baseline-fit results for SMB models and NRCS reported results is shown 

for precipitation, ETc, DP, and SIE , and comparison charts for the baseline fit results are shown and discussed.

Potential discrepancies in results between SMB models and NRCS evaluation are listed for quantifiable and non-quantifiable discrepancies. Quantifiable discrepancies which are discussed are precipitation, ETp

, crop consumptive use, ETc, ET stress 

correction, and irrigation water application timing. Mean season-total crop consumptive use of irrigation water for all Grand 

Valley Unit NRCS evaluation sites was found to be about 8.7 percent lower than 1988 Colorado Irrigation Guide published 

values. Mean annual Grand Valley weather station precipitation from 1985 to 1995 was 7.2 inches, while NRCS reported mean 

annual precipitation for the same period was only 3.8 inches. Non-quantifiable discrepancies that are discussed include lack of 

soil water field tests, precipitation data collection changes, DP calculation changes, seasonal irrigation efficiency calculation 

changes, undocumented data corrections, software problems, and human error. 

A sensitivity analysis is described which measures changes in SMB model results with changes in three SMB input variables: (1) source of precipitation data, (2) use of ETc

 stress correction or not, and (3) use of NRCS reported ETp, or increasing 
104 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

reported ETp by 10 percent to match published consumptive use values. The changes in ETc, DP, and SIE output variables were 

measured and reported. Changes in DP and SIE were grouped for flood irrigation systems and sprinkler irrigation systems. All 

results for sensitivity tests are in relative percent difference. ETc was found not to increase over baseline-fit levels when precipitation was changed from NRCS reported to Grand Valley weather station sources. ETc

 increased by 7.4 percent over baseline 

when stress correction was switched on, and ETc increased by 9.3 percent over baseline when ETp was increased 10 percent to 

bring ETc up to published consumptive use values. It would be expected that increasing ETp by 10 percent should yield a similar 

increase in ETc, and this is confirmed by this result.

Separate bar charts (for inches of change and percent change) of DP sensitivity test results for flood irrigation sites and 

sprinkler and (or) microspray sites show changes in SMB model DP results in comparison to NRCS reported values from the 

sensitivity tests. Separate bar charts of percent changes in SIE sensitivity results for flood irrigation sites and sprinkler/microspray sites show the changes in SMB model SIE for changes in from the sensitivity tests. 

Sensitivity test results for changes in precipitation sources or use of evapotranspiration stress correction were found not to 

be meaningful in absolute magnitude for both flood and sprinkler sites. Sensitivity test changes resulting from ETp values of 100 

percent of NRCS reported values were also found not to be of meaningful magnitude for both flood and sprinkler sites. Changing ETp

 to 110 percent was found to be meaningful for flood irrigation sites, but not for sprinkler and microspray sites. 

When ETp was increased to 110 percent for flood sites to match 1988 Colorado Irrigation Guide crop consumptive use 

values, the mean DP for flood irrigation SMB model sites decreased by 12.5 relative percent (2.5 inches), and SIE increased 

2.4 relative percent when compared with NRCS reported values for the 7 SMB model flood irrigation sites. These suggested 

changes to NRCS reported values for flood irrigation sites may be of interest to water managers. For sprinkler and microspray 

sites, the resulting changes in DP and SIE for ETp values of 110 percent were not judged to be of interest because the reported 

mean value of DP for sprinkler and microspray sites is quite low to begin with (1.1 inches). 

The NRCS evaluation results have been used in past years as part of the basis for estimating reductions in salt loading 

due to irrigation system improvements, so changes of the magnitude found in this analysis will have to be evaluated by water 

managers and their organizations to determine whether any change in salt loading baseline calculations are warranted. Lower DP 

and higher SIE in the calculations for salt loading would suggest that more salt load savings have been achieved than previously 

estimated using the original reported NRCS evaluation results.

References Cited

Adobe Systems, Inc., 2013, Adobe Reader XI software for Windows: San Jose, Calif., Adobe Systems, Inc. 

Allen, R.G., Pereira, L.S., Raes, Dirk, and Smith, Martin, 1998, Crop evapotranspiration—Guidelines for computing crop water 

requirements—Irrigation and drainage paper 56: Rome, Italy, Food and Agriculture Organization of the United Nations, 

290 p.

Colorado River Basin Salinity Control Forum [2013]: Colorado River Basin Salinity Control Forum web site, accessed June 19, 

2013, at http://www.coloradoriversalinity.org/organization.php.

Colorado State University Colorado Climate Center [2012], Daily data access: Colorado State University web page, accessed 

June 19, 2012, at http://ccc.atmos.colostate.edu/dly_form.html.

Colorado State University Cooperative Extension, 1999, ZETA.wks evapotranspiration spreadsheet.

Colorado State University, 2013, CoAgMet homepage monthly summaries: Colorado State University web page, accessed 

August 20, 2013, at http://ccc.atmos.colostate.edu/~coagmet/.

Colorado Water Conservation Board, 2013, Division of Water Resources, Colorado’s Decision Support System (CDSS) All Irrigated Lands: Colorado Water Conservation Board, accessed May 2, 2013, at http://cdss.state.co.us/Pages/CDSSHome.aspx.

Delta County Development, Inc., 2013, Delta County Agriculture web page, accessed 5-3-13 at URL http://www.

deltaareadevelopment.org/agriculture.html; [no longer available].

Duke, Harold, 1987, ed., U.S. Department of Agriculture, 1987, Scheduling irrigations—A guide for improved irrigation water 

management through proper timing and amount of water application, December 1987, 76 p. 

Environmental Systems Research, Inc., 1999–2010, ArcMap, version 10.0: Redlands, Calif., Environmental Systems Research, 

Inc. 
References Cited 105

Helsel, D.R., and Hirsch, R.M., 2002, Statistical methods in water resources: U.S. Geological Survey Techniques of WaterResources Investigations, book 4, chap. A3, 510 p.

Higgins, J.J., 2004, Introduction to modern nonparametric statistics: Pacific Grove, California, Duxbury Press, 384 p.

Kenney, T.A., Gerner, S.J., Buto, S.G., and Spangler, L.E., 2009, Spatially referenced statistical assessment of dissolved-solids 

load sources and transport in streams of the Upper Colorado River Basin: U.S. Geological Survey Scientific Investigations 

Report 2009–5007, 50 p. [Available at URL http://pubs.usgs.gov/sir/2009/5007.]

Lorenz, D.L., and others, 2011, USGS library for S-PLUS for Windows—Release 4.0: U.S. Geological Survey Open-File Report 

2011-1130, [Available at http://water.usgs.gov/software/S-PLUS/.]

Magnan, Nick, and Seidl, Andy, 2004, The economic base of Montezuma County, Colorado: Colorado State University, June 

2004 EDR 04–02, 35 p., accessed May 3, 2013, at http://dare.colostate.edu/pubs/EDR/EDR04-02.pdf.

Mayo, J.W., 2008, Estimating the effects of conversion of agricultural land to urban land on deep percolation of irrigation water 

in the Grand Valley, western Colorado: U.S. Geological Society Scientific Investigations Report 2008-5086, 58 p.

Microsoft Corporation, 2010, Office 2010 software for Windows: Redmond, Washington, Microsoft Corporation.

TIBCO Software Inc., 1988–2008, Spotfire S-PLUS 8.1 for Windows: Somerville, Mass., TIBCO Software Inc.

U.S. Department of Agriculture, 1982, Monitoring and evaluation plan, Colorado River Basin Salinity Control Program for 

Grand Valley Unit, Colorado and Uinta Basin Unit, Utah, July 1982: USDA-Soil Conservation Service, 93 p. 

U.S. Department of Agriculture, 1986–2003, Grand Valley salinity program monitoring and evaluation annual reports: Grand 

Junction, Colorado, Soil Conservation Service, Grand Junction Area Office, variously paged.

U.S. Department of Agriculture, 1988, 1988 Colorado Irrigation Guide: U.S. Department of Agriculture, Soil Conservation Service, Denver, Colorado, variously paged.

U.S. Department of Agriculture, 1997, National engineering manual, irrigation guide, Chapter 3 Crop growth characteristics: 

U.S. Department of Agriculture Natural Resources Conservation Service.

U.S. Department of Agriculture, 2009, Colorado agricultural statistics 2009, National Agricultural Statistics Service, Colorado 

Field Office, 2008 Preliminary, 2007 Revised: U.S. Department of Agriculture, accessed May 2, 2013, http://www.nass.usda.

gov/Statistics_by_State/Colorado/Publications/Annual_Statistical_Bulletin/bulletin2009.pdf. 

U.S. Department of Agriculture, 2012, Soil Data Mart website: U.S. Department of Agriculture, accessed August 13, 2012, 

http://soildatamart.nrcs.usda.gov/.

U.S. Department of Agriculture, 2013, National Cooperative Soil Survey (NCSS) web soil survey: U.S. Department of Agriculture, accessed June 3, 2013, at http://websoilsurvey.nrcs.usda.gov/app/.

U.S. Department of Commerce, 2013, National Oceanic and Atmospheric Administration, National Climate Data Center: U.S. 

Department of Commerce, accessed May 3, 2013, at www1.ncdc.noaa.gov.

Veihmeyer, F.J., and Hendrickson, A.H., 1949, The application of some basic concepts of soil moisture to orchard irrigation: 

Proceedings of Washington State Horticultural Association, v. 45, p. 25–41.

ISSN 2331-1258 (online)

http://dx.doi.org/10.3133/ofr20141261
106 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

NRCS Evaluation Glossary

These definitions are from the 1989 Grand Valley annual report (Grand Valley Annual Report, 1989, in U.S. Department of 

Agriculture, 1986–2003), and were repeated in most of the other annual reports.

Volume of Inflow— The total volume of inflow to the field was measured with electronic flow recorders at most sites or 

from flow meters located at some sites. The inflows have been converted to an mean depth in inches over the entire field.

Volume of Outflow (runoff)— The total volume of surface outflow from the field was measured with electronic flow 

recorders and converted to a mean depth in inches over the entire field. For sites with microspray or side-roll sprinkler systems, 

outflow values were considered to be evaporation losses; 10 and 20 percent respectively of inflow volume.

Infiltrated Depth— The infiltrated depth in inches equals the inflow minus the outflow. This gave the mean amount of water 

in entering the soil over the entire field.

Precipitation— The precipitation was electronically measured and recorded at the two weather stations. On-site precipitation was also recorded manually at some of the monitored locations.

Potential Evapotranspiration (ETp)—Potential evapotranspiration was calculated using a modified Penman equation 

developed by the Agricultural Research Service (ARS) in Fort Collins, Colorado. The measured data parameters included wind 

run, solar radiation, maximum and minimum temperatures, relative humidity, and precipitation. The calculated ETp results were 

calibrated with ETp

 results gathered by ARS on the Colorado State University Experimental Farm in the Grand Valley.

Actual Crop Evapotranspiration (ETa)—Actual evapotranspiration was calculated using the ETp times a crop coefficient 

based type of crop and stage of development and stress factor based on days since precipitation or irrigation. The crop coefficient and stress adjustments were supplied by the ARS in Grand Junction and Fort Collins.

Soil Water Deficit (S.W.D.)—The soil water deficit was computed as 1) the measured pre-season S.W.D. plus ETc minus 

effective rainfall prior to the first irrigation and 2) post-irrigation S.W.D. plus ETc minus effective rainfall after the first irrigation.

Deep Percolation (D.P.)—Deep percolation equals the infiltrated water depth minus the soil water deficit in inches at the 

time of irrigation. The deep percolation was calculated using a computerized water budget program.

Seasonal Irrigation Efficiency—The seasonal/individual irrigation efficiency, expressed as a percentage, equals the volume 

of inflow minus the volume of outflow minus the deep percolation times one hundred, divided by the volume of inflow.
Appendix 1. Contact Information for Research Access to NRCS Evaluation Data and Instructions for Requests to Access the Data 107

Appendix 1. Contact Information for Research Access to NRCS Evaluation Data 

and Instructions for Requests to Access the Data

To protect the privacy of the landowners who participated in the Natural Resources Conservation Service (NRCS) evaluation, all references to personal information have been removed by NRCS from the evaluation data made available to the USGS 

for this study. The USGS is not able to provide access to the redacted NRCS evaluation data. Independent researchers should 

apply directly to NRCS for access to these redacted datasets: (1) the NRCS evaluation annual and irrigation event data by site 

in spreadsheet form, (2) the USGS study analysis and soil moisture balance model spreadsheets, and (3) an Adobe PDF file containing all of the scanned NRCS evaluation annual reports plus supporting documents. 

NRCS Instructions for Requests to Access NRCS Evaluation Data 

The parties would agree that certain information may be withheld from parties relative to 1619 which stipulates that 

“Information requested is withheld based on Exemption 3 of the FOIA, 5 U.S.C. 552(b)(3). Exemption 3 permits the 

government to withhold information in NRCS’ records specifically exempted from disclosure by another Federal 

Statute. In this case, Section 1619 (b) of the Food, Conservation and Energy Act of 2008”. NRCS would always be 

receptive to an individual FOIA request to evaluate what is needed by the given party. FOIA requests should be sent 

to:

Colorado NRCS FOIA Officer

Denver Federal Center Building 56, Room 2604

P.O. Box 25426

Denver, CO 80225

The U.S. Department of Agriculture (USDA) prohibits discrimination against its customers. If you believe you experienced discrimination when obtaining services from USDA, participating in a USDA program, or participating in a program that receives financial assistance from USDA, you may file a complaint with USDA. Information about how to 

file a discrimination complaint is available from the Office of the Assistant Secretary for Civil Rights. USDA prohibits 

discrimination in all its programs and activities on the basis of race, color, national origin, age, disability, and where 

applicable, sex (including gender identity and expression), marital status, familial status, parental status, religion, 

sexual orientation, political beliefs, genetic information, reprisal, or because all or part of an individual’s income is 

derived from any public assistance program. (Not all prohibited bases apply to all programs.)

To file a complaint of discrimination, complete, sign, and mail a program discrimination complaint form, available at 

any USDA office location or online at www.ascr.usda.gov, or write to:

USDA

Office of the Assistant Secretary for Civil Rights

1400 Independence Avenue, SW

Washington, DC 20250-9410

Or call toll free at (866) 632-9992 (voice) to obtain additional information, the appropriate office, or to request documents. Individuals who are deaf, hard of hearing, or have speech disabilities may contact USDA through the Federal 

Relay service at (800) 877-8339 or (800) 845-6136 (in Spanish). USDA is an equal opportunity provider, employer, 

and lender.

Persons with disabilities who require alternative means for communication of program information (e.g., Braille, large 

print, audiotape, etc. .) should contact USDA’s TARGET Center at (202) 720-2600 (voice and TDD).
108 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Appendix 2. Natural Resources Conservation Service (NRCS) Evaluation 

Software and Data Instructions for NRCS staff

The following document—Colorado River Salinity Control Project Monitoring and Evaluation Programs—was scanned 

and converted to Microsoft Word for inclusion in this report. The format reflects that of the original document. Conversion errors 

were corrected to the extent possible; however, some formatting and typographical errors may remain. There is no date given for 

the document.

COLORADO RIVER SALINITY CONTROL PROJECT MONITORING AND EVALUATION 

PROGRAMS

INTRODUCTION

The Colorado River Salinity Control {CRSC) Project is an activity of 

the Soil Conservation Service, U.S. Department of Agriculture, to monitor and evaluate the effects of irrigation on the salinity levels of 

the Colorado River. The CRSC Project is being carried out in three different areas in Colorado and includes the Grand Valley Unit, the Lower 

Gunnison Unit and the McElmo Unit.

At all three areas, several sites have been equipped with automated 

data sensors and loggers that permit the monitoring of both irrigation 

inflow and outflow. In addition, there are several weather stations that 

periodically collect and transmit climatological data for crop evapotranspiration (ET) determination.

The Grand Valley Unit has two completely automated weather stations 

that periodically transmit readings to a recorder located in the Grand 

Junction Field Office. The Lower Gunnison Unit has a few small weather stations that collect data in chips which have to be manually downloaded in the computer. The McElmo Unit obtains data from the Extension 

Office. The collected data is then processed by a micro-computer to determine the effectiveness of the applied irrigation. This document describes the Monitoring and Evaluation (M&E) programs that process the 

information to arrive at the irrigation effectiveness.

There are three discrete functions involved in this process as follows:

1. Collection of data

a) Collection, transformation and storage of

climatological data from weather stations.

b) Collection and storage of individual site parameters.

c) Collection of crop and soil texture characteristics.

d) Collection of irrigation inflow and outflow volumes from individual M&E irrigation sites.
Appendix 2. Natural Resources Conservation Service (NRCS) Evaluation Software and Data Instructions for NRCS staff 109

2. Extraction and storage of inflow and outflow volumes from the 

Omnilogger data storage packs and Datapod storage modules for each

monitored site.

3. Development of an irrigation water budget by event for each 

irrigation site and a seasonal summary for all sites.

Each function and the associated programs are described in the following sections. The program used to perform the function is given in dark 

capital letters enclosed in parenthesis. Refer to “Program Descriptions” section for the required inputs and resultant outputs for each 

program.

1. COLLECTION OF DATA

The data required for irrigati0n monitoring and evaluation study comes 

from three distinct sources: Weather stations, Omnidata Datapod and or 

Easy Logger recorders or both, and site-related information including 

crop and soil texture information.

a) Collection, Transformation and Storage of Climatological 

Data from Weather stations (WSTOEL/RECORDER)

The two weather station sites in the Grand Valley

{Orchard Mesa and Highline) each transmit 

approximately 2 to 4 sets of readings per hour. The

readings are transmitted via microwave to the Grand

Junction field office AT&T microcomputer used as a

recording device which stores the transmitted

weather data on 5 1/4 inch diskettes. At periodic intervals 

(daily from April to September and weekly from October to 

March) the raw weather data on the diskette, is then transmitted to a AT&T PC6300 computer using the “TW” program {See 

appendix D for downloading and processing of weather data). 

The raw data is then processed using the WSTOEL and

RECORDER programs to provide the maximum, average,

minimum and dew point temperatures; in degrees

Fahrenheit; relative humidity; wind run in miles;

precipitation in inches; solar radiation in Langley

minutes; and the potential Evapo-Transpiration in

inches. The RECORDER program scans the data and

prints a warning message if the interval between

readings is over several hours. Additionally, if

there are less than 20 readings per day per site,

the previous day’s readings are projected forward

and another warning message is printed.

A utility program, WSRCOUNT, has been developed to count the 
110 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

readings per hour transmitted from the weather stations to 

the office receiving AT&T computer. It is menu driven.

In the event of a transmission failure, a backup system has 

been developed utilizing the Easy Logger recorder with a data 

storage pack (DSP). The readings recorded on the DSP are 

down-loaded to the CTX computer (monitoring room) using the 

DUMPEL program (see appendix on how to use this program) and 

then processed using the RECORDER program to produce the same 

weather data described above.

In the Lower Gunnison Unit the two weather stations are not 

automated to send data directly to the office. Omnidata datapods are used as recording devices to collect and record data 

on temperature (high/low), and solar radiation. Rainfall data 

is manually read from precipitation gauge. The microchips are 

picked up daily and brought to the office to be downloaded on 

to the CTX computer (monitoring computer) using the DATAPOD 

program. The downloaded raw weather data is then processed 

using the RECORDER program as described above.

b) Collection and storage of Site Parameters (SITEDATA)

Each site participating in this project is assigned

a unique 2-digit identification number (10 through

99). Associated with that site ID is such 

information as crops grown; planting, cover, and

harvest dates; the closest weather station; soil

type and texture; initial soil moisture; number of

acres monitored; field slope in percent; soil intake

family; length of water run; and weir and gage

types. Each site can have up to 2 inflow weirs and

gages, up to 3 outflow weirs and gages, 1 inflow

reduction weir and gage, 1 outflow reduction weir

and gage, and 3 soil moisture probes (currently not

being used).

c) Collection of crop (CROPCOEF) and soil Texture

(SOILDATA) Data

Information about the crops grown in the Grand Valley is required in order to compute the water usage figures. The items 

required include the polynomial factors before and after effective cover has been reached, m1n1mum and maximum allowable 

crop coefficients, rooting depth, days from planting until effective cover is reached, and the management allowed deficit.

In addition to the crop data, soils information is also re-
Appendix 2. Natural Resources Conservation Service (NRCS) Evaluation Software and Data Instructions for NRCS staff 111

quired to calculate the water budget for a site.

Items needed are soil texture, average bulk density, field capacity, wilting point, and the available water holding capacity.

d) Collection of Inflow and outflow Volumes (DATAPOD, LOGGER), 

by Site

Site inflow/outflow volumes are recorded on either Easy Logger Data Storage Packs(DSP)or Datapod Storage Modules (DSM) 

depending on the kind of equipment that has been set up. The 

DSM’s contain only one type of data, either inflow or outflow 

readings. The Easy Logger DSP’s can contain several types of 

information--inflow/outflow and soil moisture probe readings. 

Currently only the inflow or outflow readings are recorded on 

the DSP’s. Both these values are used in the water budget 

calculations. However, the Logger program was constructed so 

that the soil moisture readings can

be extracted and saved if needed.

2. EXTRACTION AND STORAGE OF INFLOW/OUTFLOW VOLUME (LOGGER, DATAPOD 

FOR EACH MONITORED SITE

The DSP’s and DSM’s used on the Omnidata Easy Logger and Datapod Recording devices are periodically replaced; usually after each irrigation. The data contained in these modules is downloaded and stored on 

the CTX computer. The information on the Datapod modules is downloaded - directly by the DATAPOD program. The Lower Gunnison and McElmo units go through one more DATAPOD program to download the data. For 

the Easy Logger packs, the initial extraction is performed by DUMPEL, a 

communications package. The raw data is then processed by the LOGGER 

program. The resultant files from both DATAPOD and LOGGER programs are 

then passed through the EXTRACT program which removes non-significant 

values and breaks the data into discrete irrigation events.

3. DEVELOPMENT OF WATER BUDGET FOR EACH SITE AND SEASONAL SUMMARIES 

(CALCIRRG, IRRIGBAL, SITESMRY AND SEASONAL)

After the irrigation events have been isolated into individual files, 

each event is passed through the CALCIRRG program to obtain the volume of inflow/outflow in inches for inflow and outflow sites, the average flow (in cubic feet per second- cfs), and the total irrigation time. 

The next step is to calculate the water budget by event by site using 

the IRRIGBAL program. The output generated will show the amount of wa-
112 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

ter applied, runoff from the field, crop ET and the resultant soil moisture deficit for the irrigation event. After each irrigation event for a 

site has been processed, the next action is to request a site summary 

through the SITESMRY program. The final step is to ask for a seasonal 

summary of all sites after all the data has been processed for the season. This is accomplished by using the SEASONAL program.

In addition to the above programs, a utility program called FILESCAH

has been developed that allows the operator to display and/or modify 

the water budget information. It is menu driven.

PROGRAM DESCRIPTIONS

More than 16 M&E programs are available to download, process, reduce, 

and evaluate data (irrigation and weather) collected from the fields. 

The final data output will show the effectiveness of applied irrigation.

Each program used by the three project areas (Grand Valley, Lower Gunnison, and McElmo) is described in a logical flow sequence. 

Except where noted, the following conventions are followed: 

M&E

site ID

A 3-digit’number that uniquely identifies a particular site 

and data type. The first two digits represent the cooperator’s 

site identifier and can range from 10 through 99. The last 

digit indicates the type of data under consideration. The 

data types are:

0-10 Inflow data

2-4 outflow data

5-7 Soil moisture blocks 

8 Inflow reduction data 

9 Outflow reduction data

Dates Dates are numeric and must be entered in Month, Day, Year 

format. Use either a period (.), slash(/), comma(,) or a dash 

(-) to separate the Month, Day and Year fields.

Clock

Time

All times are based on a 24-hour clock and must be entered 

in Hour:Minute format. Only the colon is acceptable as a 

separator.
Appendix 2. Natural Resources Conservation Service (NRCS) Evaluation Software and Data Instructions for NRCS staff 113

All programs are menu driven and requested input may be in either upper 

or lower case characters. All programs scan the input data and trap any 

data that does not meet the developed criteria. In addition, any errors 

occurring during execution of any program are also trapped and give the 

operator a choice to either continue execution or to exit to the MS-DOS 

operating system.

COLLECTION OF DATA

Various data such as weather related, site specific, soil characteristics, crop specific, and irrigation inflow and outflow volumes need to be 

collected in order to determine irrigation efficiencies and the amount 

of deep percolation for each monitored site. The programs (right hand 

column in dark bold letters) being used to collect the different kinds 

of data are:

Weather related

Site Specific

Soil Characteristics

Crop Specific

Inflow/Outflow Volumes

DATAPOD, WSTOEL, RECORDER SITEDATA

SOILDATA 

CROPCOEF

DATAPOD, LOGGER

Each program is described in detail, below. 

Weather Related Data:

WSTOEL is the program used in Grand Junction to separate and format the 

raw weather data to Easy Logger format; usable with the RECORDER program. Eight items of raw data are transmitted every 10 to 20 minutes 

from each weather station via a repeater station. The information is 

sent to a receiving AT&T micro computer. Periodically (daily or weekly), the data is transferred to another AT&T micro-computer using the 

TW program (see Appendix D for more details). The raw data is processed 

through the WSTOEL program for formatting.

The initial WSTOEL menu has 3 options. Respond by entering the appropriate number.

1) Convert Cromemco readings to Easylogger format

2) Link to another M & E program

3) Exit to the System

Your choice?

Option 1 solicits the input file name. This is the file name (e.g. 
114 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

mo.et, fr.et etc.) created when the data was transferred from the receiving AT&T PC6300 computer to the AT&T PC6300 computer used for processing weather data. There are two output files created by this program, WSOM##.WYY for Orchard Mesa station and WSHL##.WYY for Highline 

Lake station where “##’’ is the weather - data transfer number and 

“YY’’ is the last two digits of the year.

Option 2 allows linking to any other M&E program.

Option 3 will exit and return control to the MS-DOS operating system.

The DATAPOD program is used in The Lower Gunnison unit to process raw 

weather data rather than the WSTOEL program. The raw weather data collected is downloaded using the DATAPOD program which is menu driven. 

The main menu of the DATAPOD program has five options as follows:

1) Retrieve I/O data from a Datapod

2) Retrieve Weather data from DATAPOD 219

3) Print an existing Datapod file

4) Link to another M&E program

5) Exit to the System

Your choice?

Option 2 needs to be selected for weather data retrieval. When this 

option is selected, the computer asks for the name of the weather file 

and the first day on the chip. At this point, the weather data gets 

transmitted from the DSM (microchip) to the computer through a “reader” 

and then takes you to the main menu again.

Option 4 needs to be selected to link to the RECORDER program. The 

downloaded weather data is then processed using the RECORDER program as 

described below.

The RECORDER program is used to extract, modify and print data collected from the different weather stations. Two at Grand Junction - Orchard 

Mesa and Highline Lake; and two at Lower Gunnison - Cedaredge and -----

----------.

In Grand Junction, the data is then reduced to daily readings for high, 

low, dew point and average temperatures; relative humidity; wind run in 

miles; precipitation in inches; solar radiation in Langley minutes; and 

the Potential Evapo-transpiration in inches (Modified Penman Equation). 

The calculation for Evapotranspiration were taken from a draft manuscript by H. R. Duke, G. W. Buchleiter and D. F. Heerman, USDA Agricultural Research Service, Fort Collins, Colorado.

In Lower Gunnison, the data collected is reduced to daily
Appendix 2. Natural Resources Conservation Service (NRCS) Evaluation Software and Data Instructions for NRCS staff 115

readings for high, low, and average temperatures; solar radiation

in Langley minutes; precipitation in inches (read and entered

manually); and the potential Evapo-transpiration in inches (JensenHayes Equation). Daily ET is calculated by the software program installed in the Omnidata 219 Datapod used for collection of daily data.

The initial RECORDER menu has nine options. The operator responds by 

entering the appropriate number. The options are:

GJFO ONLY! 1) Add data to files

2) Delete the existing files

GJFO ONLY! 3) Discard a portion of the stored data

4) List data stored in files

5) Modify ETp readings

6) Modify Rainfall

7) Change Study Year .

8) Link to another M&E program

9) Exit this program

Your choice?

Option 1 is used in Grand Junction only. This option solicits the input 

file name for the weather station selected for data addition. This is 

the file name created by WSTOEL (e.g. “from.et” if Orchard Mesa station 

has been selected). If an extent is not provided with the file name, 

the program will append “et”; “et” must be provided as a part of the 

file name. The computer will then check to see if a partial day’s readings are available in files named “WSHLPART.WYY or WSOMPART.WYY”. If so, 

this data is appended to the beginning of the file named above and the 

entire data is processed. If the partial file does not exist, only the 

named file is processed. If the information for a day is either, missing 

or there are less than 20 readings, the previous day’s values are projected and a flag is set to show the projections when the data is printed or used by another program. There are two output files either created 

or modified by this program, ORCHARDM.WYY for the Orchard Mesa site and 

HIGHLINE.WYY for Highline Lake site; where “YY” is the last two digits 

of the year.

If Option 2 is used, the computer will ask if you are sure you

want to delete the files. If the response is “NO,” the program

returns to the main menu. If “YES” is the answer, then the processed 

weather files e.g. ORCHARDM.WYY and HIGHLINE.WYY (Grand Junction) and 

CEDAREDG.WYY (Lower Gunnison) are deleted.
116 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

The third Option (Grand Junction only) allows selective deleting of 

daily events. The computer solicits two dates for each weather station. 

The first is the date to begin deleting or a “S” to begin at the start 

of the data. The second is the date to stop deleting or an “E” to delete to the end of the file.

Selecting Option 4 (Grand Junction and Lower Gunnison) transfers you to 

the print portion of the program. The print menu permits the sub-options on the next page to be selected:

1) Potential E.T. by Date

2) Weather Data by Station by Date

3) Maximum Rainfall intensity and Wind Velocity by Date

4) Return to Main Menu

Your choice?

Sub-option 1 lists the potential Evapo-Transpiration by weather station 

by date.

Sub-option 2 lists the daily information by station by date. Items 

printed are date, high temperature, average temperature, low temperature, solar radiation, and precipitation for all the weather stations. 

For the Grand Junction stations, wind run and relative humidity are 

also listed.

Sub-option 3 will print the maximum hourly precipitation and wind velocity by station by date and the hour these occurred. After the print 

activity described· above is completed, control is returned to the 

print menu.

Sub-option 4 will return control to the Main Menu.

Option 5 of the Main Menu permits the selective modification to the potential Evapo-Transpiration values calculated under Option 1. Either 

those values that were projected from a previous day or for given dates 

can be updated. If the projected values are selected, then the operator is solicited for a new value for each date that was flagged for 

the weather stations. If the date option is selected, the name of the 

weather station is solicited along with the starting date. The program 

will step through the data date by date, allowing the operator to make 

the necessary changes. An “E” will return control to the Main Menu.

Option 7 allows changing of study year.
Appendix 2. Natural Resources Conservation Service (NRCS) Evaluation Software and Data Instructions for NRCS staff 117

Option 6 allows the rainfall values to be modified. The procedure used 

is the same as that used under Option 5.

Option 8 allows linking to any of the other M&E programs.

Option 9 will exit the program and return control to the MS-DOS

operating system.

In Grand Junction there is an Easy Logger backup system at the two 

weather stations in case data transmission through the Popcorn telemetry system fails. The Easy Logger collects and stores data in the 

data storage packs and the data downloaded weekly during the irrigation 

season. Menus, inputs and outputs are identical with those described 

under RECORDER. The raw data output from the Easy Logger (using the 

DUMPEL program) is used with RECORDER.

Site Specific Data:

SITEDATA program is used to collect and. store site specific information. Note that the program uses only the 2-digit cooperator’s farm 

number when it requests the M&E farm number. Output from SITEDATA program consists of 3 random access files SITEGNRL.IYY SITEWEIR.IYYand SITEIRRG.IYY. The Main Menu display for this program is:

1) Add a new Farm

2) Update an existing Farm

3) Delete a Farm

4) Display Farm(s)

5) Print Farm(s)

6) Adj. Farm for next Irrig. Season

7) Change Study Year

8) Link to another program

9) Return to system

Your choice?

Option 1 is used to input information about a new farm. The information 

requested consists of the following:
118 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

1. M&E Farm Number

2. Cooperator’s Name

3. Weather Station

4. Crop Grown

5. Planting Date

6. Cover Date

7. Harvest Date

8. Start SWD (inches)

9. Field Number

10. Monitored Acres

11. Adj. % Cover

12. Soil Depth

13. Total Furrows

14. Texture/AWC(in/ft)

15. Soil Type

16. Slope, %

17. Intake Family

18. Irrigation system

19. Length of Run

20 Inflow/Outflow

to Weir & Gage Types

33.

The cooperator’s unique 2-digit number

Enter an “E” to exit to the Main Menu

The land user’s name, maximum 17 charac- ters

The weather station nearest to this farm

Crop to be monitored

The date that the growing season starts

The date when effective cover is reached

Self-explanatory

The starting soil moisture deficit

before the first irrigation

A numeric identifier of field to be

monitored

The number of acres to be monitored

Crop cover, single digit number (see

appendix ---) 

Self-explanatory

Total number of furrows in the monitored 

field

Enter either soil texture of the field

under study or available water

holding capacity in inches per foot

Soil type of the monitored field

The percent slope of the field in feet

per hundred

A numeric value related to the soil’s

ability to absorb moisture

-- A 3-character abbreviation used to

designate the type of irrigation

system used (Appendix -- provides

codes and descriptions)

The average length that irrigation

water flows from the inlet to

the outlet, in feet

The numbers assigned to the weir

and gage that control and monitor irrigation flows (Appendix -- provides a list of 

weirs and gages).

Additionally, a”?” at the prompt, the

14 weir and 4 gage types are displayed

on the screen
Appendix 2. Natural Resources Conservation Service (NRCS) Evaluation Software and Data Instructions for NRCS staff 119

Note: Planting/cover/harvest dates are entered automatically when a 

crop is entered but may be changed manually if desired.

There are two special weir/gage combinations, one for inflow and one for 

outflow. The “reduction” weirs and gages are used when a portion of the 

irrigation water exits the system before passing through the entire 

field.

Option 2 allows data previously entered and saved farm data to be updated. The computer asks for the 2-digit farm number. A zero or null 

entry at this point returns control to the Main Menu. If the entry is a 

farm number, the information is displayed and the operator is asked to 

enter the line· number of the item to be updated. This action repeats 

until a zero or null entry is entered at which time a new M&E farm number is requested and the process is repeated.

Option 3 deletes a non-active farm from the files. The overall procedure 

is the same as for Option 2 except that after the correct farm number 

is selected, the operator is asked if it is the requested. If the answer is “Yes” then the farm is deleted from the files and a new M&E farm 

number is requested. Again, a zero or null entry terminates this option 

and returns control to the Main Menu.

Option 4 displays the farm information on the computer’s monitor. The 

operator is asked if a single farm or all farms are to be displayed and 

the processing proceeds as directed.

Option 5 is identical to Option 4 except the information is sent to the 

computer’s printer.

Option 6 allows the operator to transfer and adjust site data information from the previous monitoring season to the next season; saves data 

input time.

Option 7 lets the operator change the study year.

Option 8 permits the operator to change to another M&E program without 

going through the system.

Option 9 returns control of the computer to the MS-DOS operating system.
120 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Soil Characteristics Data:

The SOILDATA program allows entry of the necessary data for different 

soils located within the Grand Valley study area. The only file used in 

this system is SOILDATA.DAT, a random access file. The spelling of the 

soil texture must be identical to that given in the SITEDATA program.

The Main Menu options are:

1) Add a soils series

2) List the soil series

3) Modify an existing series

4) Delete a series

5) Link to another M & E program

6) Exit to the System

 Your choice?

Option 1, when selected, will display a screen and request information 

on item numbers 1 to 5 shown below. Items from 6 through 9 are calculated automatically.

1) Soil Texture

2) Avg. Bulk Density

3) Field Cap. % Moist

4) Wilt. Point % Moist

5) Avail. WHC % Moist

6) Wilt. Point/Field cap.

7) Field Cap. Inches

8) Wilt. Point inches

9) Avail. WHC inches

The texture of the soil in the 

rooting zone

Mass per unit volume of soil, 

dried to constant weight

The maximum amount of moisture 

thesoil can hold at full capacity, inpercent

The capacity at which wilting

begins, expressed as a percentage

The available water holding capacity of the soil, in percent

The percent of field capacity at

wilting point

Field capacity in inches per foot

Wilting point in inches per foot

Available water holding capacity 

in inches per foot

When information on items 1 to 5 is obtained, the computer calculates 

the percent of the field capacity at wilting point (item 6). Next the 

computer converts the soil moisture percentages into inches per foot 

and saves the results under items 7, 8, and 9. This process is repeated. To exit back to the Main Menu, enter an “E” for the soil texture.
Appendix 2. Natural Resources Conservation Service (NRCS) Evaluation Software and Data Instructions for NRCS staff 121

Option 2 will list the soil texture information on the screen. The operator is asked if the listing is for all soils or for a single one.

If “All” is entered, the program displays all the soil textures stored 

in the computer. Selecting “Single” lists only the requested texture.

Option 3 permits changes to be made to the existing data for a given 

soil texture. If an “E” is entered when the soil texture is solicited, 

control returns to the Main Menu. If a valid soil texture is entered 

then all information relating to that soil is displayed, the operator 

is then asked for the item number to change. Enter an “E” to end changes and a new soil texture is requested.

Option 4 will delete a soil texture from the file or the whole soildata 

file. Again, entering an “E’’ for soil texture returns control to the 

Main Menu.

Option 5 permits a direct link to another program in the M&E

series.

Option 6 transfers control to the MS-DOS operating system.

Crop Specific Data:

The CROPCOEF program is used to enter the polynomial constants for 

basal crop coefficient curves and other crop specific information. The 

spelling of crop names must be identical with that used in the SITEDATA 

program. The only file used is a random access file named CROPCOEF.DAT. 

The Main Menu is as follows:

1) Add a crop record to the file

2) Display the stored crops

3) Update an existing crop

4) Delete an existing crop

5) Link to another M & E program

6) Exit to the System

Your choice?
122 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Option 1 is used when it is necessary to add a new crop to the existing 

file. The information needed is:

1. Crop Name Crop to be monitored

2. Days to Effective Cover The number of day from planting to reach 

 effective cover

3. Maximum Kcb The maximum coefficient that a crop can 

 have

4. Minimum Kcb The minimum coefficient that a crop can 

 have

5. Rooting Depth Effective rooting depth

6. Mgt. Allowed Deficit percentage of available water which can

 be depleted prior to irrigation - 

generally 50% 

7. ‘A’ Before Effective Cover Items 7 to 14 are polynomial constants 

for use in crop coefficient equation

8. ‘B’ Before Effective Cover

9. ‘C’ Before Effective Cover

10.’D’ Before Effective Cover

11.’A’ After Effective Cover

12.’B’ After Effective cover

13.’C’ After Effective Cover

14.’D’ After Effective Cover
Appendix 2. Natural Resources Conservation Service (NRCS) Evaluation Software and Data Instructions for NRCS staff 123

Inflow/Outflow Volume Data:

The DATAPOD program being used in all three project areas allows downloading of raw inflow/outflow data from the microchip to the computer 

using a “reader”. This program is the same as described earlier under 

“weather related data”. For inflow/outflow volume data downloading, a 

different option is chosen from the Main

Menu. The main menu options are:

1) Retrieve I/O data from a Datapod

2) Retrieve Weather data from Datapod 219

3) Print an existing Datapod file

4) Link to another M&E program

5) Exit to the System

Your choice?

Option 1 will allow retrieval and transfer of raw inflow/outflow data 

from a Datapod microchip to the computer. The computer will request the 

year and the Datapod model being used. The Datapod model (112/312 or 

115) needs to be selected from the sub-menu. The computer then solicits 

information on the three digit site number, and starting date/time of 

the chip. When the requested information is provided, an 8-digit output file name is created consisting of the 3-digit site ID plus the first 

month and day pulled from the stored data and the last digit of the 

year. The extent added to the name is “.iod” (e.g. 13209133.iod- outflow 

site with starting date of September 13, 1993). After the data has all 

been retrieved, the control is returned to the main menu.

Option 3 will print the retrieved data. If no data has been retrieved, 

a file name is requested and the printout is generated. Line numbers are 

printed for each reading for use in the EXTRACT program described in a 

later paragraph. The data is also plotted.

Option 4 allows the operator to link to another M&E program.

Option 5 will transfer control to the operating system.

The LOGGER program is used in Grand Junction only (Lower Gunnison
124 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

?). It allows processing of data from an Easy Logger file. The

Easy Logger file is created when the DUMPEL program is used to

retrieve and transfer raw data from an Easy Logger data storage

pack to the computer using a “reader”. An 8-digit file name with

a “.flo” extent is requested, the first four digit consists of

letters and the last four, the month and day the pack was started

(e.g. mato0913.flo).

The LOGGER program consists of the following menu:

1) Process data from Easy Logger file

2) Print stored data

3) Link to another M&E Program

4) Exit to the System

Your choice?

Option 1 will process data from an Easy Logger file. A file name is requested and an Easy Logger file with “.flo” extent needs to be provided 

(e.g. mato0913.flo). After the file name is entered, the M&E site number and the sensor type are requested. once the site number and sensor 

type is known,._ an output file name is created consisting of the 3-digit site ID plus the first month and day pulled from the stored- data 

and the last digit of the year. The extent added to the name is “.IOD” 

for inflow/outflow sites (1320913.iod- outflow, 1300913.iod - inflow) and 

“.SMB” for soil moisture blocks. After the data has all been retrieved, 

control is returned to the Main Menu.

Option 2 will print the stored information. If the previous operation 

pulled information from the blocks, then a printout is given of that 

particular file. If no data has been retrieved, a file name is solicited 

and the printout is generated. Line numbers are printed for each reading for use in the EXTRACT program described in a later paragraph. The 

data is also plotted if the information is inflow or outflow.

Option 3 Allows the operator to load another M&E program directly.

Option 4 return to the computer’s operating system.

When the inflow and outflow readings have been collected, it is necessary 

to isolate the values into discrete irrigation events, calculate the 

inflow or outflow volumes, and produce an irrigation water budget. 

Three programs are used in this process: EXTRACT, CALCIRRG, and IRRIGBAL.
Appendix 2. Natural Resources Conservation Service (NRCS) Evaluation Software and Data Instructions for NRCS staff 125

The EXTRACT program is used to divide the readings into individual irrigation events if there is more than one irrigation event in the input 

data file (*.iod file) and to extract significant values within an irrigation event. This is accomplished by discarding non-significant readings and saving the usable readings in a new -file. Input files are those 

having an extent of “.IOD” described earlier in this document. output 

file names will be identical to the input file names except the extent is 

changed to “.CL#” where “#” is irrigation event number (e.g. 1320913.

cl1).

The Main Menu for the program is:

1) Extract Data for a new site

2) Continue Extraction for this Site

3) Extract Data for a new Event

4) Link to another M&E program

5) Print the Readings

6) Exit to the System

Your choice?

Option 1, when selected, will ask for the M&E Site number and the 

starting date (MO.DA.YR). The site number is the 3-digit number that 

reflects inflow or outflow data. The starting date is the date that the 

DSM module or the DSP pack was installed in the field. This information 

is used to create the input and output file names. The next data items 

requested are the line numbers to begin and end extraction. The line 

numbers are the ones generated during processing through the DATAPOD

and/or LOGGER programs. Next, the computer asks if the data needs to 

be adjusted. If the answer is “No”, extraction begins without any further questions. For a “Yes” answer, the operator is asked if it is an 

adjustment or a replacement. After that query is satisfied, the computer will ask if the adjustment value is to be multiplied or added/subtracted to the readings. The next questions from the computer are for 

the line numbers to begin and end adjustment and the amount of the adjustment. If the ending adjustment line number is less than the ending 

extraction line number, the process is repeated. Enter “C” to end this 

process.

Option 2 is used to add more readings to the output file from the same 

input file and proceeds as Option 1 with the exception that the input 

file name is not requested.

Option 3 is used when more than one irrigation event is stored in the 

same input file. The file name extent, “.CL#”, where “#” is the event 
126 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

number, is incremented by 1 and processing continues as

described in Option 1.

Option 4 will link to another M&E program.

Option 5 will print the extracted readings (with a digital plot) Option 

6 will transfer control to the operating system. After the proper readings have been extracted, the next required step is to compute the volumes and flows for each irrigation event. The program CALCIRRG performs 

this function. The Main Menu is on the next page:

1. Calculate flow for a Site

2. Calculate flow for another Event

3. Change Study Year

4. Link to another M&E program

5. Exit to the System

Your choice?

Option 1 requests the following information:

1) M&E Site Number The 3-digit site ID number

2) Seasonal Irrigation Number The sequential number of this 

 irrigation, starting with 1 for the 

season’s first irrigation and 

 incrementing by one for each 

additional irrigation.

3) Calculate or Enter amount Tells the computer if the flow is to 

 be computed from stored data or will 

be entered through the keyboard.

4) Starting Date (MO.DA.YR) The date that the module was 

installed in the field or the date 

inflow or outflow started if data is 

 to be entered.

Note: The following queries are displayed only if “Enter” in item #3 

was selected

5) starting Time (HR.MN) The time, Based on a 24- hour clock, 

that the inflow or outflow began. Note 

 that a period may be used to 

separate the hours and minutes.
Appendix 2. Natural Resources Conservation Service (NRCS) Evaluation Software and Data Instructions for NRCS staff 127

6) Ending Date (MO.DA.YR) The day that inflow or outflow ceased.

7) Ending Time (HR.MN) The time inflow or outflow stopped.

8) Acre inches or Cfs The type of information to be

 entered.

9) Enter the amount Enter the number in acre inches or 

flow in CFS

10) Total Flow Hours Enter the number of hours that flow 

 actually occurred.

After the above information is entered, the computer asks if the data 

is okay. The operator now has the option of changing any of the line 

information by responding “No”, giving the line number in error when 

asked and entering the new value. This will repeat until a “Yes” response is given to the question.

After a “Yes” is given, the computer wants to know if a printout is 

required for irrigation volume estimates. Answer “Yes” or “No”. If the 

response is “Yes,” the operator is then asked if all the information 

should be printed or only the results. Answer according to needs. The 

computer now calculates the volume and flows. After it has finished calculating, it then asks if the volume is to be modified. If “No”, the 

values are saved and printed as is. If “Yes”, the adjustment value is

requested and is algebraically added to the volume.

If the values have been manually entered, a summary printout is always 

given.

The computed volumes and flows are saved in a random access file named 

“XXWATERB.BYY” where “XX” is the 2-digit site identifier and “YY” is the 

last two digits of the current year (e.g. 13WATERB.B93). In addition, 

the program uses two of the 3 site data files, SITEGNRL.IYY” and “SITEWEIR.IYY”.

Option 2 gives the user the option to continue calculations for another 

seasonal irrigation event if more than one event was extracted from the 

stored data (see EXTRACT program). Option 2 cannot be used if the information was entered manually.

Option 3 links to another M&E program. Option 4 returns control to the 

system. 

After all the irrigation events have been reduced to total volumes, the 
128 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

next step is to run the data through the irrigation water balance program IRRIGBAL. The Main Menu for this program

is:

1) Calculate Water Balance for a Farm

2) Print an additional Water Balance for a Farm

3) Link to another M & E program

4) Change the study year

5) Exit to the System

Your Choice?

Option 1 asks for an M&E site number. Enter the 2-digit site identifier 

and the water balance will run any irrigation event not previously run. 

Input files used in this program are the “SOILDATA.DAT”, ”CROPCOEF.DAT”, 

“SITEGNRL.IYY”, one of the two weather station files, “JIGHLINE.WYY” or 

“ORCHARDM.WYY”, and “XXWATERB.BYY”. The output file is an updated version of “XXWATERB.BYY”. 

Note: If the crop grown is “small grain, winter” and the current date 

is after August lst, the computer will ask if this run is for the current year or for next year.

Option 2 allows printing water balances for sites already processed 

when extra copies are needed.

Option 3 links to another M&E program.

Option 4 allows the operator to change the study year

Option 5 exits to the system.

The next step is to use the SITESMRY program. This program will print 

individual site summary data for each irrigation event that has been 

processed.

The SITESMRY program is menu driven. program is:

The Main Menu for this

1) Print the Summary Report for a Farm

2) Print the Brief Report for a Farm

2) Link to another M&E program

3) Exit to System

If Option 1 is selected, the 2-digit M&E site identifier is solicited 
Appendix 2. Natural Resources Conservation Service (NRCS) Evaluation Software and Data Instructions for NRCS staff 129

and a summarized printout is given of all irrigation events processed 

for that site. Two input files are required by this program. They are 

“SITEIRRG.IYY”, created by the program SITEDATA, and “XXWATERB.BYY” as 

described previously. A summary output file is created or updated for 

use with the program SEASONAL and is named “SITESMRY.SYY”, where “YY” 

is the last 2 digits of the current year. At the conclusion of the 

print, control returns to the Main Menu.

Option 2 gives the option of printing a brief simple report instead of 

the detailed provided by Option 1. This report is primarily for farmer 

use and distribution.

Option 3 permits direct linking with another M&E program. Option 4 returns control to the System. The last step in this whole M&E process is 

to go through the SEASONAL program. This needs to be used only at the 

end of the year after all the data is processed and adjusted. The program SEASONAL is used to print a seasonal summary of selected information extracted by the program SITESMRY and saved in file “SITESMRY.SYY”. 

The Main Menu for this program is:

1) Print the Seasonal Report

2) Change study Year

3) Link to another M&E program

4) Exit to System

Your choice?

Option 1 prints the requested report and returns control to the Main 

Menu. Several different reports can be produced using the sub-menu under this option. The sub-menu is as follows:

1) Report All Sites

2) Report by Crop and Surface Irrigation

3) Report by Crop and Sprinkler irrigation

4) Report by crop and both Irrigation Types

5) Report by surface Irrigation

6) Report by Sprinkler Irrigation

7) Return to Main Menu

Your choice?

Option 2 of the Main Menu allows the operator to change the study year

Option 3 links to any other M&E program. Option 4 exits to the system.

Note:There is no output file created by the SEASONAL program.
130 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Appendix A

Types of Irrigation Systems

(For Input in Sitedata Files)

 Code Description

1. EDF Earth Ditch to Feeder Ditch

2. EDS Earth Ditch to Siphon Tubes

3. CDF Concrete Ditch to Feeder Ditch

4. CDS Concrete Ditch to Siphon Tubes

5. COG Concrete Ditch to Gated Pipe

6. COP Ported Concrete Ditch

7. SGC Skate Gate concrete Ditch

8. PFD Pipeline to Feeder Ditch

9. PGP Pipeline to Gated Pipe

10. GPP Gated Pipe (includes Flextube) 

11. CBG Cablegation

12. TOR Tubing Drip

13. EDR Emitter Drip

14. MIS Microspray

15. SBD Subsurface Drip

16. HMS Hand Move Sprinkler

17. SRS Sideroll Sprinkler

18. CPS Center Pivot Sprinkler

19. SSS Solid Set Sprinkler

20. CGS Concrete Ditch to Gated Pipe (Surge)

21. PCS Ported Concrete Ditch (Surge)

22. PGS Pipeline to Gated Pipe (Surge)

23. GPS Gated Pipe (Surge)

22. (Reserved)

23. (Reserved)

24. (Reserved)

25. (Reserved)
Appendix 2. Natural Resources Conservation Service (NRCS) Evaluation Software and Data Instructions for NRCS staff 131

Appendix B

Weir and Gage Types for Input in Sitedata Files

No. Weir Type

1. 12 inch Broadcrested

2. 18 inch Broadcrested

3. 6 inch Parshall

4. 9 inch- Parshall

5. 8 inch Cutthroat

6. 12 inch Cutthroat

7. 18 inch cutthroat

8. 12 inch Rectangular

9. 12 inch Trapezoidal

10. 8 inch Magnetic Flow Meter

11. 10 inch Magnetic Flow Meter

12. Flowmeter

13. 36 inch S.C. Rectangular

14. 24 inch Rectangular

No. Gage -Type1. Linear Flow Sensor

2. R/H pressure Transducer

3. Potentiometer - Float Sensor

4. Magnetic Flow Meter
132 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

M & E PROGRAMS

Condensed Description)

1. CROPCOEF Input or change crop data

2. SOILDATA Input or change soil data

3. SITEDATA Input or change field data

4. RECORDER Process weather data - calculate E.T.

5. DATAPOD Download and plot: DSM data

6. DUMPEL Download Easylogger data from DSP

7. LOGGER Process DSP data - plot if weir site

8. EXTRACT Extract only the useable data

9. CALCIRRG Calculate the flow volume

10. IRRIGBAL Calculate the soil moisture balance and C.U.

11. FILESCAN View or change the processed data

12. SITESMRY Summarize the seasonal data for a field

13. SEASONAL Report-seasonal data for all fields

14. WSTOEL Convert Cromemco data to Easylogger format

15. WSRCOUNT Count readings I hour from raw weather data

16. GETWETHR Receive weather data from Popcorn receiver to AT&T 

 computer (receiving)

17. TW Transfer/receive raw data to AT&T PC6300 computer

18. ARSSCS Run ET for all crops after processing weather data

Programs have EXE or BAS extension
Appendix 2. Natural Resources Conservation Service (NRCS) Evaluation Software and Data Instructions for NRCS staff 133

M & E FILES

All M&E programs and data files (input and output) need to be backed-up 

initially and then whenever changes are made. The following files are 

created when different programs are used:

CROPCOEF.DAT Output from Cropcoef

SOILDATA.DAT - Output from Soildata

SITEGNRL.IYY

SITEWEIR.IYY - Output from Sitedata

SITEIRRG.IYY

WSS##.DAT - Output from GETWETHR on computer receiving the raw data 

WS###.WYY - Output from TW program 

EL ###.WYY - Output from WSTOEL 

WS PART.WYY

HIGHLINE.WYY - Output from RECORDER

ORCHARDM.WYY

##---.IOD - Output from DATAPOD and LOGGER

##---.SMB - soil moisture output from LOGGER 

(1st 4 LETTERS)(IRR.NO).FLO- Output from DUMPEL 

(for weir or SM)

##---.CL# - Output from EXTRACT

##WATERB.BYY - Output from CALCIRRG

##WATERB.BYY- Output from IRRIGBAL

##WATERB.BYY - View data from Calcirrg and Irrigbal

SITESMRY.SYY - Output from Sitesmry

Note: “YY” - Last two digits of year

SEASONAL and WSRCOUNT programs produce hardcopies only - no files
134 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Appendix C

Sitedata File Data Entry

 Crop Root Depth (ft.)

Alfalfa 6

Beans 3

Corn 4

Pasture 3

Vegetable 3

Potato 3

Fall Grain(F) 2

Spring s Grain 3

Sugarbeets 3

orchard 6

Grapes 4

Corn Silage 4

Fall Grain{S} 3

Onions 2

Soybeans 4

When entering the starting soil water deficit (SWD) for a crop in the 

SITEDATA program file, it must be the estimated water deficit for the 

total root depth profile. Use the above root depths for this purpose as 

they are installed in the program. In instances where soil is the limiting factor then rooting depth would be the same as the soil depth and 

soil moisture deficit would be based

on this depth.

COVER ADJUSTMENT

Menu item #11 Adj. % Cover (one digit number)

Enter 0 = 100% cover (normal) if mature crop

expected to have full cover

Enter # = # (#*10 = % full cover) e.g. 7 = 70%

of full value

Recommendations:

Use #8 = 80% cover for first year alfalfa

Use #O = 100% cover for annual crops and most

perennial crops after first year of

establishment
Appendix 2. Natural Resources Conservation Service (NRCS) Evaluation Software and Data Instructions for NRCS staff 135

For orchards, use # based on percent canopy cover and cover crop. Measure actual canopy cover in field. Follow the recommendations provided 

on the next page:

Orchard With Cover Without Cover

>70% canopy # = 0 # = 0

70% canopy # = 0 # = 9

60% canopy # = 9 # = 8

50% canopy # = 8 # = 7

40% canopy # = 7 # = 6

Young trees # = 7 # = 5

Cover value numbers affect crop ET estimates. An “O” will estimate full 

ET for the crop; numbers less than a “O” will estimate lower ET.
136 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Appendix 3. Additional NRCS Evaluation Summary Statistics

The report section “Summary Statistics and Charts of Natural Resources Conservation Service (NRCS) Evaluation” 

includes NRCS evaluation summary statistics for all gold standard NRCS evaluation sites. Summary statistics are shown here 

for all usable sites and for all nongold standard sites.

Table 3-1. Discrete variable summary statistics for all usable records collected between 1985 and 2003 in Natural Resources 

Conservation Service evaluation.

[GV, Grand Valley; LG, Lower Gunnison Basin; ME, McElmo Creek Basin; EDF, earth ditch to feeder tube; EDS, earth ditch to siphon tube; CDV, concrete 

ditch to various distribution methods; PCS, ported concrete ditch to surge; CGS, concrete ditch to gated pipe surge; GPP, gated pipe; PGS, pipeline to gated 

surge; SRS, side-roll sprinkler; MIS, microspray.]

Number of Usable 

Site-Year Records 

by Evaluation 

Unit

Number of SiteYear Records 

with Irrigation 

Event Data

Number of SiteYear Records by 

Irrigation System 

Type Codes

Number of SiteYear Records 

by Crop Type

Number of SiteYear Records by 

Irrigation

System Type

Number of Site-Year 

Records by Irrigation Flow Type

Number of SiteYear Records by 

Irrigation

Distribution Type

GV: 211 No: 35 EDF: 4 Alfalfa: 88 Flood: 235 Feeder ditch: 4 Concrete ditch: 99

LG: 51 Yes: 223 EDS: 9 Barley: 1 Microspray: 10 Gated pipe: 80 Ditch: 1

ME: 6 CDV: 92 Beans: 20 Sprinkler: 23 Gated pipe surge: 49 Earth ditch: 13

PCS: 3 Corn: 62 Ported: 7 Pipeline: 155

CGS: 4 Fall grain: 25 Ported surge: 3

GPP: 77 Grain: 3 Side-roll: 23

PGS: 46 Grapes: 10 Siphon tube: 91

SRS: 23 Kenafe: 1 Spray: 10

MIS: 10 Lettuce: 2 Surge: 1

Oats: 2

Onions: 6

Orchard: 36

Pasture: 3

Spelt: 1

Spring grain: 1

Sweet corn: 2

Vegetable: 3

Wheat: 2

Total: 268
Appendix 3. Additional NRCS Evaluation Summary Statistics 137

Table 3-2. Continuous variable summary statistics for all usable records in all evaluation units collected between 1985 and 2003 in 

Natural Resources Conservation Service evaluation.

[All water quantities are in inches; N, number of records; Std Dev, standard deviation; NA, not applicable]

Statistic Field Size

Number of 

Irrigation 

Events

Volume Irrigation Water 

Inflow

Volume

Irrigation 

Water

Outflow

Infiltrated 

Irrigation 

Water Depth

Precipitation Evapotranspiration

Deep

Percolation

Seasonal 

Irrigation 

Efficiency

Minimum 1.4 2.0 11.4 0 3.7 0.4 2.2 0 13.0

1st Quartile 7.0 6.0 39.6 8.6 27.3 2.2 20.3 4.5 33.9

Mean 20.4 7.7 55.9 17.0 38.9 3.5 26.0 14.8 47.6

Median 15.0 7.0 53.6 14.9 37.6 2.8 25.2 12.8 45.0

3rd Quartile 26.0 9.0 70.5 22.7 48.8 4.3 33.3 20.2 60.0

Maximum 327.3 22.0 123.0 80.1 87.9 11.8 41.3 70.7 97.8

Total N 268 268 268 268 268 268 268 268 268

NA 0 0 0 0 0 39 0 0 0

Std Dev 27.7 3.4 22.2 12.04 15.6 2.2 8.06 12.8 17.9

Table 3-3. Discrete variable summary statistics for all nongold standard records, whether usable or not, collected between 1985 and 

2003 in Natural Resources Conservation Service evaluation.

[GV, Grand Valley; LG, Lower Gunnison Basin; ME, McElmo Creek Basin; EDF, earth ditch to feeder tube; EDS, earth ditch to siphon tube; CDV, concrete 

ditch to various distribution methods; PCS, ported concrete ditch to surge; CGS, concrete ditch to gated pipe surge; GPP, gated pipe; PGS, pipeline to gated 

surge; SRS, side-roll sprinkler; MIS, microspray.]

Number of Usable 

SiteYear Records

by Evaluation Unit

Number of

Site-Year Records 

with Irrigation

Event Data

Number of SiteYear Records

by Irrigation System Type Codes

Number of SiteYear Records

by Crop Type

Number of SiteYear Records

by Irrigation System Type

Number of SiteYear Records by 

Irrigation Flow 

Type

Number of SiteYear Records by 

Irrigation Distribution Type

GV: 15 No: 0 EDF: 0 Alfalfa: 15 Flood: 39 Feeder Ditch: 0 Concrete ditch: 11

LG: 24 Yes: 39 EDS: 0 Barley: 1 Microspray: 0 Gated Pipe: 19 Ditch: 0

ME: 0 CDV: 11 Beans: 8 Sprinkler: 0 Gated pipe surge: 8 Earth Ditch: 0

PCS: 0 Corn: 5 Ported: 0 Pipeline: 28

CGS: 0 Fall Grain: 0 Ported Surge: 0

GPP: 19 Grain: 0 Side-roll: 0

PGS: 9 Grapes: 0 Siphon tube: 11

SRS: 0 Kenafe: 1 Spray: 0

MIS: 0 Lettuce: 2 Surge: 1

Oats: 2

Onions: 0

Orchard: 0

Pasture: 0

Spelt: 1

Spring Grain: 0

Sweet Corn: 2

Vegetable: 0

Wheat: 2

Total: 39
138 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Table 3-4. Continuous variable summary statistics for all nongold standard records, whether usable or not, collected between 1985 

and 2003 in Natural Resources Conservation Service evaluation.

[All water quantities are in inches; N, number of records; Std Dev, standard deviation; NA, not applicable]

Statistic Field Size

Number of 

Irrigation 

Events

Volume

Irrigation 

Water Inflow

Volume

Irrigation 

Water

Outflow

Infiltrated 

Irrigation 

Water Depth

Precipitation Evapotranspiration

Deep

Percolation

Seasonal 

Irrigation 

Efficiency

Minimum 2.0 4.0 20.0 4.3 11.3 NA NA 0.2 30.1

1st Quartile 7.5 6.0 45.5 10.9 33.7 NA NA 5.4 42.6

Mean 18.2 7.2 59.4 18.2 41.2 NA NA 12.9 51.3

Median 15 7.0 56.9 14.6 40.6 NA NA 11.9 52.3

3rd Quartile 30.2 8.0 71.2 21.9 50.4 NA NA 19.0 59.4

Maximum 37 12 111.4 54.1 83.9 NA NA 39.0 81.7

Total N 39 39 39 39 39 39 39 39 39

NA 0 9 0 0 0 39 39 0 0

Std Dev 1.1 2.1 22.2 11.6 15.7 NA NA 9.2 11.8
Appendix 4. Additional Box Plot Charts 139

Appendix 4. Additional Box Plot Charts

The report section “Deep Percolation versus Seasonal Irrigation Efficiency” includes box plots of deep percolation and 

seasonal irrigation efficiency grouped by irrigation system improvement order and by crop type. This appendix shows additional 

box plots of deep percolation and seasonal irrigation efficiency grouped by soil type and by crop rooting depth; crop evapotranspiration by soil type, by crop rooting depth, and by irrigation system improvement order; and water infiltrated depth grouped by 

soil type and by irrigation system improvement order.
140 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Figure 4-1. Box plot of deep percolation by soil type1 for all usable evaluation site-years. [1AgFCL, Agua Fria clay loam; 

AvSL, Avalon sandy loam; BarPanComp, Barx-Panitchen complex; FrCL, Fruita clay loam; KiSC, Killpack silty clay; MeCL, 

Mesa clay loam; MiCL, Mikim clay loam; SaL-0-2, Sagerlite loam, 0-2 percent slope; SaL-2-5, Sagerlite loam, slope 2-5 

percent; SaSCL, Sagers silty clay loam; TuCL, Turley clay loam.] AgFCL AvSL BarPanComp FrCL FrFSL KiSC MeCL MeGCL

MiCL

MonDelComp

PeSCL

SaL-0-2SaL-2-5

SaSCL

StSC

TuCL

Soil Type code

0

20

40

60

Deep Percolation (inches)

All Usable Sites Deep Percolation versus Soil Type Code

(5) (2) (1) (22) (2) (54) (47) (2) (5) (1) (2) (37) (4) (41) (1) (42) 

EXPLANATION

Sample size

Data value greater than 1.5 times the

interquartile range outside the box

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

Interquartile range

(11)
Appendix 4. Additional Box Plot Charts 141

AgFCL

AvSL

BarPanComp

FrCL

FrFSL

KiSC

MeCL

MeGCL

MiCL

MonDelComp

PeSCL

SaL-0-2SaL-2-5

SaSCL

StSC

TuCL

Soil Type code

0

20

40

60

80

100

Seasonal Irrigation Efficiency (percent)

All Usable Sites Irrigation Efficiency versus Soil Type Code

(5) (2) (1) (22) (2) (54) (47) (2) (5) (1) (2) (37) (4) (41) (1) (42) 

EXPLANATION

Sample size

Data value greater than 1.5 times the

interquartile range outside the box

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

Interquartile range

(11)

Figure 4-2. Box plot of seasonal irrigation efficiency by soil type1 for all usable evaluation site-years. [1AgFCL, Agua Fria clay 

loam; AvSL, Avalon sandy loam; BarPanComp, Barx-Panitchen complex; FrCL, Fruita clay loam; KiSC, Killpack silty clay; MeCL, 

Mesa clay loam; MiCL, Mikim clay loam; SaL-0-2, Sagerlite loam, 0-2 percent slope; SaL-2-5, Sagerlite loam, slope 2-5 percent; 

SaSCL, Sagers silty clay loam; TuCL, Turley clay loam.]
142 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Figure 4-3. Box plot of crop evapotranspiration by soil type1 for all usable evaluation site-years. [1AgFCL, Agua Fria clay 

loam; AvSL, Avalon sandy loam; BarPanComp, Barx-Panitchen complex; FrCL, Fruita clay loam; KiSC, Killpack silty clay; 

MeCL, Mesa clay loam; MiCL, Mikim clay loam; SaL-0-2, Sagerlite loam, 0-2 percent slope; SaL-2-5, Sagerlite loam, slope 2-5 

percent; SaSCL, Sagers silty clay loam; TuCL, Turley clay loam.] AgFCL AvSL BarPanComp FrCL FrFSL KiSC MeCL MeGCL

MiCL

MonDelComp

PeSCL

SaL-0-2SaL-2-5

SaSCL

StSC

TuCL

Soil Type code

0

10

20

30

40

Evapotranspiration (inches)

All Usable Sites Evapotranspiration versus Soil Type Code

(5) (2) (1) (22) (0) (54) (47) (0) (5) (1) (0) (37) (4) (41) (0) (42) 

EXPLANATION

Sample size

Data value greater than 1.5 times the

interquartile range outside the box

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

Interquartile range

(11)
Appendix 4. Additional Box Plot Charts 143

Figure 4-4. Box plot of irrigation water infiltrated depth by soil type1 for all usable evaluation site-years. [1AgFCL, Agua Fria 

clay loam; AvSL, Avalon sandy loam; BarPanComp, Barx-Panitchen complex; FrCL, Fruita clay loam; KiSC, Killpack silty clay; 

MeCL, Mesa clay loam; MiCL, Mikim clay loam; SaL-0-2, Sagerlite loam, 0-2 percent slope; SaL-2-5, Sagerlite loam, slope 2-5 

percent; SaSCL, Sagers silty clay loam; TuCL, Turley clay loam.] AgFCL AvSL BarPanComp FrCL FrFSL KiSC MeCL

MeGCL

MiCL

MonDelComp

PeSCL

SaL-0-2SaL-2-5

SaSCL

StSC

TuCL

Soil Type code

0

20

40

60

80

Infiltrated Depth (inches)

All Usable Sites Infiltrated Depth versus Soil Type Code

(5) (2) (1) (22) (2) (54) (47) (2) (5) (1) (2) (37) (4) (41) (1) (42) 

EXPLANATION

Sample size

Data value greater than 1.5 times the

interquartile range outside the box

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

Interquartile range

(11)
144 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Figure 4-5. Box plot of deep percolation by crop rooting depth for all usable evaluation site-years. [DP, deep percolation.]

12 18 24 30 36 42 48 54 60

Crop Rooting Depth (inches)

0

20

40

60

Deep Percolation (inches)

All Usable Sites Deep Percolation (DP) versus Crop Rooting Depth

 (8) (0) (22) (6) (107) (0) (5) (0) (22)

EXPLANATION

Sample size

Data value greater than 1.5 times the

interquartile range outside the box

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

Interquartile range

(11)
Appendix 4. Additional Box Plot Charts 145

Figure 4-6. Box plot of seasonal irrigation efficiency by crop rooting depth for all usable evaluation site-years. [SIE, seasonal 

irrigation efficiency.]

12 18 24 30 36 42 48 54 60

Crop Rooting Depth (inches)

0

20

40

60

80

100

Seasonal Irrigation Efficiency (percent)

All Usable Sites Seasonal Irrigation Efficiency (SIE) versus

Crop Rooting Depth

 (8) (0) (22) (6) (107) (0) (5) (0) (22)

EXPLANATION

Sample size

Data value greater than 1.5 times the

interquartile range outside the box

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

Interquartile range

(11)
146 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Figure 4-7. Box plot of irrigation water infiltrated depth by soil type for all usable evaluation site-years. [ETc, crop 

evapotranspiration.]

12 18 24 30 36 42 48 54 60

Crop Rooting Depth (inches)

0

20

40

60

80

Infiltrated Depth (inches)

All Usable Sites Soil Infiltrated Depth versus Crop Rooting Depth

EXPLANATION

Sample size

Data value greater than 1.5 times the

interquartile range outside the box

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

Interquartile range

(11)
Appendix 4. Additional Box Plot Charts 147

Figure 4-8. Box plot of crop evapotranspiration by crop rooting depth for all usable evaluation site-years. [ETc, crop 

evapotranspiration.]

12 18 24 30 36 42 48 54 60

Crop Rooting Depth (inches)

0

10

20

30

40

Crop Evapotranspiration (inches)

All Usable Sites Crop Evapotranspiration (ETc) versus Crop Rooting Depth

 (8) (0) (22) (6) (107) (0) (5) (0) (22)

EXPLANATION

Sample size

Data value greater than 1.5 times the

interquartile range outside the box

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

Interquartile range

(11)
148 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Figure 4-9. Box plot of crop evapotranspiration by irrigation system type in improvement order for all usable evaluation siteyears. [ETc, crop evapotranspiration.]

12345678 9

0

10

20

30

40

Crop Evapotranspiration (inches)

All Usable Sites Crop Evapotranspiration (ETc) versus Improvement Order

EDF EDS CDV PCS CGS GPP PGS SRS MIS

 (4) (9) (92) (3) (4) (77) (46) (23) (10)

EXPLANATION

Sample size

Data value greater than 1.5 times the

interquartile range outside the box

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

Interquartile range

(11)

Irrigation System Type in Order of Improvement

EDF Earth Ditch to Feeder Ditch

EDS Earth Ditch to Siphon Tubes

CDV Concrete Ditch to Various Distribution

PCS Ported Concrete Ditch to Surge

CGS Concrete Ditch to Gated Pipe Surge

GPP Gated Pipe

PGS Pipeline to Gated Pipe Surge

SRS Sideroll Sprinkler

MIS Microspray

Irrigation System Types
Appendix 4. Additional Box Plot Charts 149

Figure 4-10. Box plot of irrigation water infiltrated depth by irrigation system type in improvement order for all usable 

evaluation site-years. [EDF, earth ditch to feeder tube; EDS, earth ditch to siphon tube; CDV, concrete ditch to various 

distribution methods; PCS, ported concrete ditch to surge; CGS, concrete ditch to gated pipe surge; GPP, gated pipe; PGS, 

pipeline to gated surge; SRS, side-roll sprinkler; MIS, microspray.]

12345678 9

0

20

40

60

80

Infiltrated Depth (inches)

All Usable Sites Infiltrated Depth versus Improvement Order

EDF EDS CDV PCS CGS GPP PGS SRS MIS

 (4) (9) (92) (3) (4) (77) (46) (23) (10)

EXPLANATION

Sample size

Data value greater than 1.5 times the

interquartile range outside the box

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

Interquartile range

(11)

Irrigation System Type in Order of Improvement

EDF Earth Ditch to Feeder Ditch

EDS Earth Ditch to Siphon Tubes

CDV Concrete Ditch to Various Distribution

PCS Ported Concrete Ditch to Surge

CGS Concrete Ditch to Gated Pipe Surge

GPP Gated Pipe

PGS Pipeline to Gated Pipe Surge

SRS Sideroll Sprinkler

MIS Microspray

Irrigation System Types
150 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Appendix 5. Additional Multiple Comparison Tables

The report section “Multiple Comparison Statistics” includes two tables of multiple comparison statistics for seasonal 

irrigation efficiency by irrigation system improvement order and for deep percolation by irrigation system improvement order. 

Appendix 5 shows additional multiple comparison tables for both seasonal irrigation efficiency irrigation and deep percolation 

by crop type, by soil type, by evaluation unit, and by crop rooting depth. Also shown are multiple comparison tables for crop 

evapotranspiration by Natural Resources Conservation Service (NRCS) evaluation unit, by gold standard evaluation year, and by 

crop rooting depth. Finally, a multiple comparison table for irrigation water infiltrated depth is shown by NRCS evaluation unit. 

For reference, a reference table of irrigation system improvement order, system type codes, and descriptions is shown.

Table 5-1. Table of irrigation system improvement order, type codes, and descriptions.

[EDF, earth ditch to feeder tube; EDS, earth ditch to siphon tube; CDV, concrete ditch to various distribution methods; PCS, ported concrete ditch to surge; 

CGS, concrete ditch to gated pipe surge; GPP, gated pipe; PGS, pipeline to gated surge; SRS, side-roll sprinkler; MIS, microspray.]

Improvement Order Irrigation System Code Description

1 EDF Earth Ditch to Feeder Ditch

2 EDS Earth Ditch to Siphon Tubes

3 CDV Concrete Ditch to Various Distribution

4 PCS Concrete Ditch Ported Surge

5 CGS Concrete Ditch to Gated Pipe Surge

6 GPP Gated Pipe

7 PGS Pipeline to Gated Surge

8 SRS Sideroll Sprinkler

9 MIS Microspray

Table 5-2. Multiple comparison table of seasonal irrigation efficiency by crop type.

Crop Type Difference in Median Seasonal Irrigation Efficiency of Column Crop Type Over Row Crop Type (Percent)

Alfalfa Beans Corn Fall Grain Grapes Onions Orchard Pasture Spring Grain Vegetable

Alfalfa

Beans +17 +40 +27

Corn +14 +20

Fall grain +21 +44 +29

Grapes

Onions +48 +35

Orchard

Pasture

Spring grain

Vegetable +41
Appendix 5. Additional Multiple Comparison Tables 151

Table 5-3. Multiple comparison table of deep percolation by crop type.

Crop Type Difference in Median Deep Percolation of Column Crop Type Over Row Crop Type (Percent)

Alfalfa Beans Corn Fall Grain Grapes Onions Orchard Pasture Spring Grain Vegetable

Alfalfa

Beans

Corn

Fall grain

Grapes

Onions -36 -31

Orchard

Pasture

Spring grain

Vegetable +41

Table 5-4. Multiple comparison table of crop evapotranspiration by crop type.

Crop Type Difference in Median Crop Evapotranspiration of Column Crop Type Over Row Crop Type (Percent)

Alfalfa Beans Corn Fall Grain Grapes Onions Orchard Pasture Spring Grain Vegetable

Alfalfa

Beans +16 +13 +15

Corn +12 +11

Fall grain +16 +12 +15

Grapes

Onions +16

Orchard

Pasture

Spring grain

Vegetable +16 +14
152 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Table 5-5. Multiple comparison table of seasonal irrigation efficiency by soil type.

[AgFCL, Agua Fria clay loam; AvSL, Avalon sandy loam; BarPanComp, Barx-Panitchen complex; FrCL, Fruita clay loam; KiSC, Killpack silty clay; MeCL, 

Mesa clay loam; MiCL, Mikim clay loam; SaL-0-2, Sagerlite loam, 0-2 percent slope; SaL-2-5, Sagerlite loam, slope 2-5 percent; SaSCL, Sagers silty clay 

loam; TuCL, Turley clay loam.]

Soil Type

Code Difference in Median Seasonal Irrigation Efficiency of Column Soil Type Over Row Soil Type (Percent)

AgFCL AvSL BarPanComp FrCL KiSC MeCL MiCL SaL-0-2 SaL-2-5 SaSCL TuCL

AgFCL +44 +53 +28

AvSL

BarPanComp

FrCL +35

KiSC +38

MeCL

MiCL

SaL-0-2 +38

SaL-2-5

SaSCL +26 +40

TuCL

Table 5-6. Multiple comparison table of deep percolation by soil type.

[AgFCL, Agua Fria clay loam; AvSL, Avalon sandy loam; BarPanComp, Barx-Panitchen complex; FrCL, Fruita clay loam; KiSC, Killpack silty clay; MeCL, 

Mesa clay loam; MiCL, Mikim clay loam; SaL-0-2, Sagerlite loam, 0-2 percent slope; SaL-2-5, Sagerlite loam, slope 2-5 percent; SaSCL, Sagers silty clay 

loam; TuCL, Turley clay loam.]

Soil Type

Code Difference in Median Deep Percolation of Column Soil Type Over Row Soil Type (Percent)

AgFCL AvSL BarPanComp FrCL KiSC MeCL MiCL SaL-0-2 SaL-2-5 SaSCL TuCL

AgFCL

AvSL

BarPanComp

FrCL

KiSC

MeCL -45 -48

MiCL -58 -62

SaL-0-2

SaL-2-5

SaSCL

TuCL
Appendix 5. Additional Multiple Comparison Tables 153

Table 5-7. Multiple comparison table of irrigation water infiltrated depth by soil type.

[AgFCL, Agua Fria clay loam; AvSL, Avalon sandy loam; BarPanComp, Barx-Panitchen complex; FrCL, Fruita clay loam; KiSC, Killpack silty clay; MeCL, 

Mesa clay loam; MiCL, Mikim clay loam; SaL-0-2, Sagerlite loam, 0-2 percent slope; SaL-2-5, Sagerlite loam, slope 2-5 percent; SaSCL, Sagers silty clay 

loam; TuCL, Turley clay loam.]

Soil Type 

Code

Difference in Median Irrigation Water Infiltrated Depth of 

Column Soil Type Over Row Soil Type (Percent)

AgFCL AvSL BarPanComp FrCL KiSC MeCL MiCL SaL-0-2 SaL-2-5 SaSCL TuCL

AgFCL

AvSL

BarPanComp

FrCL +17

KiSC

MeCL

MiCL +33 +25 +23

SaL-0-2

SaL-2-5

SaSCL

TuCL

Table 5-8. Multiple comparison table of seasonal irrigation efficiency by evaluation unit.

[GV, Grand Valley Unit; LG, Lower Gunnison Unit; ME, McElmo Creek Unit]

Evaluation Unit 

Code

Difference in Median Seasonal Irrigation 

Efficiency of Column Evaluation Area 

Over Row Evaluation Area (Percent)

GV LG ME

GV +32

LG +16 +47

ME

Table 5-9. Multiple comparison table of deep percolation by evaluation unit.

[GV, Grand Valley Unit; LG, Lower Gunnison Unit; ME, McElmo Creek Unit]

Evaluation Unit 

Code

Difference in Median Deep Percolation of Column Evaluation Area 

Over Row Evaluation Area (Percent)

GV LG ME

GV -65

LG -63

ME
154 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Table 5-10. Multiple comparison table of crop evapotranspiration by evaluation unit.

[GV, Grand Valley Unit; LG, Lower Gunnison Unit; ME, McElmo Creek Unit]

Evaluation Unit 

Code

Difference in Median Crop Evapotranspiration of Column Evaluation 

Area Over Row Evaluation Area (Percent)

GV LG ME

GV

LG +7

ME

Table 5-11. Multiple comparison table of irrigation water infiltrated depth by evaluation 

unit.

[GV, Grand Valley Unit; LG, Lower Gunnison Unit; ME, McElmo Creek Unit]

Evaluation Unit 

Code

Difference in Median Irrigation Water Infiltrated

Depth of Column Evaluation Area Over

Row Evaluation Area (Percent)

GV LG ME

GV

LG

ME +17 +16

Table 5-12. Multiple comparison table of crop evapotranspiration by Natural Resources Conservation Service evaluation gold 

standard years.

Evaluation 

Year

Difference in Median Crop Evapotranspiration of Column Evaluation

Year Over Row Evaluation Year (Percent)

1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995 +14 +13 +11

1996
Appendix 5. Additional Multiple Comparison Tables 155

Table 5-13. Multiple comparison table of seasonal irrigation efficiency by crop rooting depth.

Difference in Median Seasonal Irrigation Efficiency of Column Rooting

Depth Over Row Rooting Depth (Percent)

Crop Rooting Depth 

(Inches) 12 24 36 48 60

12 +35 +26

24 +27 +17

36 +19 +13

48

60

Table 5-14. Multiple comparison table of deep percolation by crop rooting depth.

Difference in Median Deep Percolation of Column Rooting

Depth Over Row Rooting Depth (Percent)

Crop Rooting Depth 

(Inches) 12 24 30 36 48 60

12 -31 -23

24 -11

30

36

48

60

Table 5-15. Multiple comparison table of crop evapotranspiration by crop rooting depth.

Difference in Median Crop Evapotranspiration of Column Rooting

Depth Over Row Rooting Depth (Percent)

Crop Rooting Depth 

(Inches) 12 24 30 36 48 60

12 +11 +11

24 +15 +16

30 +15 +12

36 +11 +12

48

60
156 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Appendix 6. Columns in the soil moisture balance deep percolation worksheet

Appendix 6 shows a table of columns used in the soil moisture balance deep percolation worksheets. The table lists the 

category, column heading, and a descriptive note for each column. This explanation is to aid in the understanding of the various 

model parameters included in the soil moisture balance spreadsheets.

Table 6-1. Columns in the soil moisture balance deep percolation worksheet.

[Ref ET, reference evapotranspiration; ETc, crop evapotranspiration; Kc, crop coefficient; SMB, soil moisture balance; precip, precipitation; SWD, soil water 

deficit; FAO-56, United Nations Food and Agricultural Organization Irrigation and Drainage Paper No. 56; NRCS, Natural Resources Conservation Service; 

RAW, readily available water; TAW, total available water; WP, wilting point.]

Category Column Heading Note

Date Date Microsoft Excel date format mm/dd/yyyy

Note Note Planting, harvest, ETc

Ordinal Date Ordinal Date The day number of the year

Water Applied Net application quantity inches From reported total value apportioned equally over the days 

of event

Crop ET Ref ET Selects from Fruita or Orchard Mesa weather station ET

Crop ET Crop cycle days Count of crop growth cycle days

Crop ET Crop coefficient Kc Selects from various models of Kc

Crop ET Crop ET Ref ET * Kc

Crop ET Total ET between & during events Reported on chart page

Crop ET Total ET per month Used to calculate monthly consumptive use on chart page

Crop ET Plant date (-1) Harvest date (+1) flag Used in chart to flag planting & harvest(s)

Precipitation Ref precipitation Selects from 4 weather station sources

Precipitation Effective precipitation Ref precip—effective threshold

Precipitation Total precip between & during events Reported on chart page

Reported Soil Moisture Reported soil water deficit (SWD) NRCS reported values at beginning and ending of each 

irrigation event

Reported Soil Moisture Soil moisture Field capacity minus SWD

Reported Soil Moisture Crop cycle Kc Selects from among several models of Kc

Preliminary Soil Moisture Balance Daily soil moisture = previous soil moisture balance + water applied + local 

precipitation – ETc

Trial balance before ET stress correction and deep percolation determination

Preliminary Soil Moisture Balance Kc

 stress correction factor Uses FAO-56 stress model in VBA macro program

Preliminary Soil Moisture Balance Stress corrected ETc Output from VBA macro

Deep Percolation Calculation Soil water deficit (SWD) Repeated from above

Deep Percolation Calculation Daily accumulated soil moisture balance 

without ET stress correction

Previous day ending SMB + net irrigation applied + effective precip – stress corrected ETc

Deep Percolation Calculation Daily deep percolation = soil moisture balance greater than field capacity

Deep Percolation Calculation Daily net available soil moisture balance (max=field capacity, min=0)

Irrigation event total deep percolation Reported on chart page

Field Capacity Total FC for rooting depth Constant

Wilting Point Total WP for rooting depth Constant

Total available water (TAW) = Field capacity – wilting point

ET stress point = ((1-SWD)*TAW) + WP

Readily available water (RAW) TAW * readily available water constant
Appendix 7. All Soil Moisture Balance Charts 157

Appendix 7. All Soil Moisture Balance Charts

In the report section “Soil Moisture Balance Charts” 5 of the 12 soil moisture balance charts created for this report are 

discussed in detail. Appendix 7 includes all 12 of the soil moisture balance charts for completeness, including the five already 

discussed. All soil moisture balance charts in appendix 7 were created using Natural Resources Conservation Service (NRCS) 

reported precipitation, no ET stress correction, and NRCS reported ETp.

Figure 7-1. Soil moisture balance chart for Grand Valley Unit 1989 site 12, an alfalfa site with a concrete ditch to siphon tube irrigation 

system. [NRCS, Natural Resources Conservation Service; GV, Grand Valley; SWD, soil water deficit; SMB, soil moisture balance; DP, 

deep percolation; Kc

, crop coefficient; ETc, crop evapotranspiration.]

17.2

20.9

17.2

20.9

15.0

20.9

17.1

20.9

14.8

20.9

17.4

20.9

14.1

20.9

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

-6

-4

-2

0

2

4

6

8

10

12

14

16

18

20

22

24

3/15/893/22/893/29/89

4/5/89

4/12/894/19/894/26/89

5/3/89

5/10/895/17/895/24/895/31/89

6/7/89

6/14/896/21/896/28/89

7/5/89

7/12/897/19/897/26/89

8/2/898/9/89

8/16/898/23/898/30/89

9/6/89

9/13/899/20/899/27/8910/4/89

10/11/8910/18/8910/25/89

11/1/8911/8/89

11/15/8911/22/8911/29/89

Precipitation & Etc (inches)

SWD, SMB, DP, Net Irrigation

(Inches of water), Cutting Dates (unitless)

Date

NRCS Evaluation Site GV-12 1989 Soil Moisture Balance

Net Irrigation Deep Percolation (DP) Net Precipitation

Field Capacity Soil Moisture Balance (SMB) Soil Water Deficit (SWD)

Wilting Point ETc Stess Point Cutting Dates

Crop Evapotranspiration (ETc) Crop Coefficient (Kc)

Permanent

Wilting

Point

Field 

Capacity

ET Stress 

Point
158 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Figure 7-2. Soil moisture balance chart for Grand Valley Unit 1989 site 21, a newly-fall-seeded alfalfa site with a pipeline to gated 

pipe irrigation system. [NRCS, Natural Resources Conservation Service; GV, Grand Valley; SWD, soil water deficit; SMB, soil moisture 

balance; DP, deep percolation; Kc

, crop coefficient; ETc, crop evapotranspiration.]

15.8

20.9

18.2

20.9

18.7

20.9

14.1

20.9

18.2

20.9

15.1

20.9

19.1

20.9

16.6

20.9

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

-6

-4

-2

0

2

4

6

8

10

12

14

16

18

20

22

24

3/15/893/22/893/29/89

4/5/89

4/12/894/19/894/26/89

5/3/89

5/10/895/17/895/24/895/31/89

6/7/89

6/14/896/21/896/28/89

7/5/89

7/12/897/19/897/26/89

8/2/898/9/89

8/16/898/23/898/30/89

9/6/89

9/13/899/20/899/27/8910/4/89

10/11/8910/18/8910/25/89

11/1/8911/8/89

11/15/8911/22/8911/29/89

Precipitation & Etc (inches)

SWD, SMB, DP, Net Irrigation

(Inches of Watetr), Cutting Dates (unitless)

Date

NRCS Evaluation Site GV-21 1989 Soil Moisture Balance

Net Irrigation Deep Percolation (DP) Net Precipitation

Field Capacity Soil Moisture Balance (SMB) Soil Water Deficit (SWD)

Wilting Point ETc Stess Point Cutting Dates

Crop Evapotranspiration (ETc) Crop Coefficient (Kc)

Permanent

Wilting

Point

Field 

Capacity

ET Stress 

Point
Appendix 7. All Soil Moisture Balance Charts 159

Figure 7-3. Soil moisture balance chart for Grand Valley Unit 1989 site 33, a newly-fall-seeded alfalfa site with a side-roll sprinkler 

irrigation system. [NRCS, Natural Resources Conservation Service; GV, Grand Valley; SWD, soil water deficit; SMB, soil moisture 

balance; DP, deep percolation; Kc

, crop coefficient; ETc, crop evapotranspiration.]

19.7

21.1

20.2

21.3

19.8

21.1

19.2

20.3

17.4

18.8

17.6

18.6

17.5

18.5

17.3

18.3

17.1

17.7 17.4

18.5

17.6

18.7

17.8

18.9

17.2

19.4

18.3

20.4

18.7

20.9

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

-4

-2

0

2

4

6

8

10

12

14

16

18

20

22

24

26

3/15/893/22/893/29/89

4/5/89

4/12/894/19/894/26/89

5/3/89

5/10/895/17/895/24/895/31/89

6/7/89

6/14/896/21/896/28/89

7/5/89

7/12/897/19/897/26/89

8/2/898/9/89

8/16/898/23/898/30/89

9/6/89

9/13/899/20/899/27/8910/4/89

10/11/8910/18/8910/25/89

11/1/8911/8/89

11/15/8911/22/8911/29/89

Precipitation & Etc (inches)

SWD, SMB, DP, Net Irrigation

(Inches of Water), Cutting Dates (unitless)

Date

NRCS Evaluation Site GV-33 1989 Soil Moisture Balance

Deep Percolation (DP) Net Precipitation Net Irrigation

Field Capacity Soil Moisture Balance (SMB) Soil Water Deficit (SWD)

Wilting Point ETc Stess Point Cutting Dates

Crop Evapotranspiration (ETc) Crop Coefficient (Kc)

Permanent

Wilting

Point

Field 

Capacity

ET Stress 

Point
160 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Figure 7-4. Soil moisture balance chart for Grand Valley Unit 1993 site 33, an alfalfa site with a side-roll sprinkler irrigation system. 

[NRCS, Natural Resources Conservation Service; GV, Grand Valley; SWD, soil water deficit; SMB, soil moisture balance; DP, deep 

percolation; Kc

, crop coefficient; ETc, crop evapotranspiration.]

20.1

23.4

21.8

23.9

18.9

21.6

19.7

22.2

19.6

22.1

19.0

21.6

19.8

22.8

21.7

23.9

22.1

23.9

20.5

23.1

21.9

23.9

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

-4

-2

0

2

4

6

8

10

12

14

16

18

20

22

24

26

3/15/893/22/893/29/89

4/5/89

4/12/894/19/894/26/89

5/3/89

5/10/895/17/895/24/895/31/89

6/7/89

6/14/896/21/896/28/89

7/5/89

7/12/897/19/897/26/89

8/2/898/9/89

8/16/898/23/898/30/89

9/6/89

9/13/899/20/899/27/8910/4/89

10/11/8910/18/8910/25/89

11/1/8911/8/89

11/15/8911/22/8911/29/89

Precipitation & Etc (inches)

SWD, SMB, DP, Net Irrigation

(inches of water), Cutting Dates (unitless)

Date

NRCS Evaluation Site GV-33 1993 Soil Moisture Balance

Deep Percolation (DP) Net Precipitation Net Irrigation

Field Capacity Soil Moisture Balance (SMB) Soil Water Deficit (SWD)

Wilting Point ETc Stess Point Cutting Dates

Crop Evapotranspiration (ETc) Crop Coefficient (Kc)

Permanent

Wilting

Point

Field 

Capacity

ET Stress 

Point
Appendix 7. All Soil Moisture Balance Charts 161

Figure 7-5. Soil moisture balance chart for Grand Valley Unit 1989 site 36, an alfalfa site with a side-roll sprinkler irrigation system. 

[NRCS, Natural Resources Conservation Service; GV, Grand Valley; SWD, soil water deficit; SMB, soil moisture balance; DP, deep 

percolation; Kc

, crop coefficient; ETc, crop evapotranspiration.]

16.9

22.2

19.2

21.7

16.4

18.8

17.1

20.0

17.8

20.4

17.3

19.8

18.4

20.3

18.9

20.8

17.0

19.2

17.9

20.1

18.1

20.4

17.6

19.8

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

-4

-2

0

2

4

6

8

10

12

14

16

18

20

22

24

26

3/15/893/22/893/29/89

4/5/89

4/12/894/19/894/26/89

5/3/89

5/10/895/17/895/24/895/31/89

6/7/89

6/14/896/21/896/28/89

7/5/89

7/12/897/19/897/26/89

8/2/898/9/89

8/16/898/23/898/30/89

9/6/89

9/13/899/20/899/27/8910/4/89

10/11/8910/18/8910/25/89

11/1/8911/8/89

11/15/8911/22/8911/29/89

Precipitation & Etc (inches)

SWD, SMB, DP, Net Irrigation

(inches of water), Cutting Dates (unitless)

Date

NRCS Evaluation Site GV-36 1989 Soil Moisture Balance

Net Irrigation Deep Percolation (DP) Net Precipitation

Field Capacity Soil Moisture Balance (SMB) Soil Water Deficit (SWD)

Wilting Point ETc Stess Point Cutting Dates

Crop Evapotranspiration (ETc) Crop Coefficient (Kc)

Permanent

Wilting

Point

Field 

Capacity

ET Stress 

Point
162 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Figure 7-6. Soil moisture balance chart for Grand Valley Unit 1993 site 36, an alfalfa site with a side-roll sprinkler irrigation system. 

[NRCS, Natural Resources Conservation Service; GV, Grand Valley; SWD, soil water deficit; SMB, soil moisture balance; DP, deep 

percolation; Kc

, crop coefficient; ETc, crop evapotranspiration.]

19.3

21.5

19.6

21.7

18.0

18.8

20.2

21.0

18.3

20.4

18.0

20.1

18.5

21.1

19.3

21.9

19.1

22.1

20.2

22.8

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

-4

-2

0

2

4

6

8

10

12

14

16

18

20

22

24

26

3/15/893/22/893/29/89

4/5/89

4/12/894/19/894/26/89

5/3/89

5/10/895/17/895/24/895/31/89

6/7/89

6/14/896/21/896/28/89

7/5/89

7/12/897/19/897/26/89

8/2/898/9/89

8/16/898/23/898/30/89

9/6/89

9/13/899/20/899/27/8910/4/89

10/11/8910/18/8910/25/89

11/1/8911/8/89

11/15/8911/22/8911/29/89

Precipitation & Etc (inches)

SWD, SMB, DP, Net Irrigation

(inches of water), Cutting Dates (unitless)

Date

NRCS Evaluation Site GV-36 1993 Soil Moisture Balance

Deep Percolation (DP) Net Precipitation Net Irrigation

Field Capacity Soil Moisture Balance (SMB) Soil Water Deficit (SWD)

Wilting Point ETc Stess Point Cutting Dates

Crop Evapotranspiration (ETc) Crop Coefficient (Kc)

Permanent

Wilting

Point

Field 

Capacity

ET Stress 

Point
Appendix 7. All Soil Moisture Balance Charts 163

Figure 7-7. Soil moisture balance chart for Grand Valley Unit 1993 site 53, an alfalfa site with a pipeline to gated surge irrigation 

system. [NRCS, Natural Resources Conservation Service; GV, Grand Valley; SWD, soil water deficit; SMB, soil moisture balance; DP, 

deep percolation; Kc

, crop coefficient; ETc, crop evapotranspiration.]

19.2

23.3

20.8

23.3

14.7

22.3

18.7

23.3

21.0

23.3

18.7

23.3

20.3

23.3

16.9

23.3

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

-4

-2

0

2

4

6

8

10

12

14

16

18

20

22

24

26

3/15/893/22/893/29/89

4/5/89

4/12/894/19/894/26/89

5/3/89

5/10/895/17/895/24/895/31/89

6/7/89

6/14/896/21/896/28/89

7/5/89

7/12/897/19/897/26/89

8/2/898/9/89

8/16/898/23/898/30/89

9/6/89

9/13/899/20/899/27/8910/4/89

10/11/8910/18/8910/25/89

11/1/8911/8/89

11/15/8911/22/8911/29/89

Precipitation & Etc (inches)

SWD, SMB, DP, Net Irrigation

(inches of water), Cutting Dates (unitless)

Date

NRCS Evaluation Site GV-53 1993 Soil Moisture Balance 

Net Irrigation Deep Percolation (DP) Net Precipitation

Field Capacity Soil Moisture Balance (SMB) Soil Water Deficit (SWD)

Wilting Point ETc Stess Point Cutting Dates

Crop Evapotranspiration (ETc) Crop Coefficient (Kc)

Permanent

Wilting

Point

Field 

Capacity

ET Stress 

Point
164 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Figure 7-8. Soil moisture balance chart for Grand Valley Unit 1993 site 58, an alfalfa site with an earth ditch to siphon tube irrigation 

system. [NRCS, Natural Resources Conservation Service; GV, Grand Valley; SWD, soil water deficit; SMB, soil moisture balance; DP, 

deep percolation; Kc

, crop coefficient; ETc, crop evapotranspiration.]

15.1

20.9

13.1

19.2

14.5

20.9

14.0

20.9

12.3

19.8

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

-4

-2

0

2

4

6

8

10

12

14

16

18

20

22

24

3/15/893/22/893/29/89

4/5/89

4/12/894/19/894/26/89

5/3/89

5/10/895/17/895/24/895/31/89

6/7/89

6/14/896/21/896/28/89

7/5/89

7/12/897/19/897/26/89

8/2/898/9/89

8/16/898/23/898/30/89

9/6/89

9/13/899/20/899/27/8910/4/89

10/11/8910/18/8910/25/89

11/1/8911/8/89

11/15/8911/22/8911/29/89

Precipitation & Etc (inches)

SWD, SMB, DP, Net Irrigation

(inches of water), Cutting Dates (unitless)

Date

NRCS Evaluation Site GV-58 1993 Soil Moisture Balance

Net Irrigation Deep Percolation (DP) Net Precipitation

Field Capacity Soil Moisture Balance (SMB) Soil Water Deficit (SWD)

Wilting Point ETc Stess Point Cutting Dates

Crop Evapotranspiration (ETc) Crop Coefficient (Kc)

Permanent

Wilting

Point

Field 

Capacity

ETc Stress 

Point
Appendix 7. All Soil Moisture Balance Charts 165

Figure 7-9. Soil moisture balance chart for Grand Valley Unit 1989 site 17, a wine grapes site with a microspray irrigation system.

[NRCS, Natural Resources Conservation Service; GV, Grand Valley; SWD, soil water deficit; SMB, soil moisture balance; DP, deep 

percolation; Kc

, crop coefficient; ETc, crop evapotranspiration.]

10.0

11.9

11.2

13.9

12.8

13.9

13.3

13.9

12.6

13.9

13.4

13.9

12.5

13.4

11.6

12.6

11.3

13.2

9.2

10.2

8.3

9.3

6.8

8.2

7.6

8.9

7.5

8.6

8.0

9.5

5.7

7.97.9

10.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

-4

-2

0

2

4

6

8

10

12

14

16

3/15/893/22/893/29/89

4/5/89

4/12/894/19/894/26/89

5/3/89

5/10/895/17/895/24/895/31/89

6/7/89

6/14/896/21/896/28/89

7/5/89

7/12/897/19/897/26/89

8/2/898/9/89

8/16/898/23/898/30/89

9/6/89

9/13/899/20/899/27/8910/4/89

10/11/8910/18/8910/25/89

11/1/8911/8/89

11/15/8911/22/8911/29/89

Precipitation & ETc (inches)

SWD, SMB, DP, Net Irrigation

(inches of water), Cutting Dates (unitless)

Date

NRCS Evaluation Site GV-17 1989 Soil Moisture Balance

Net Irrigation Deep Percolation (DP) Net Precipitation

Field Capacity Soil Moisture Balance (SMB) Soil Water Deficit (SWD)

Wilting Point ETc Stess Point Plant Date / Harvest Date

Crop Evapotranspiration (ETc) Crop Coefficient (Kc)

Permanent

Wilting

Point

Field 

Capacity

ET Stress 

Point
166 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Figure 7-10. Soil moisture balance chart for Grand Valley Unit 1989 site 26, a grain corn site with a pipeline to gated pipe irrigation 

system. [NRCS, Natural Resources Conservation Service; GV, Grand Valley; SWD, soil water deficit; SMB, soil moisture balance; DP, 

deep percolation; Kc

, crop coefficient; ETc, crop evapotranspiration.]

6.9

10.4

7.3

9.7

5.7

8.3

5.8

7.3

4.9

5.9

4.2

5.4

3.3

4.5

2.6

4.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

-10

-8

-6

-4

-2

0

2

4

6

8

10

12

3/15/893/22/893/29/89

4/5/89

4/12/894/19/894/26/89

5/3/89

5/10/895/17/895/24/895/31/89

6/7/89

6/14/896/21/896/28/89

7/5/89

7/12/897/19/897/26/89

8/2/898/9/89

8/16/898/23/898/30/89

9/6/89

9/13/899/20/899/27/8910/4/89

10/11/8910/18/8910/25/89

11/1/8911/8/89

11/15/8911/22/8911/29/89

Precipitation & ETc (inches)

SWD, SMB, DP, Net Irrigation

(inches of water), Cutting Dates (unitless)

Date

NRCS Evaluation Site GV-26 1989 Soil Moisture Balance

Net Irrigation Deep Percolation (DP) Net Precipitation

Field Capacity Soil Moisture Balance (SMB) Soil Water Deficit (SWD)

Wilting Point ETc Stess Point Plant Date / Harvest Date

Crop Evapotranspiration (ETc) Crop Coefficient (Kc)

Permanent 

Wilting

Point

Field 

Capacity 

ET Stress 

Point 
Appendix 7. All Soil Moisture Balance Charts 167

Figure 7-11. Soil moisture balance chart for Grand Valley Unit 1989 site 27, a grain corn site with a pipeline to gated pipe irrigation 

system. The corn crop was cut for silage. [NRCS, Natural Resources Conservation Service; GV, Grand Valley; SWD, soil water deficit; 

SMB, soil moisture balance; DP, deep percolation; Kc

, crop coefficient; ETc, crop evapotranspiration.]

12.9

13.9

10.1

13.9

10.4

13.9

9.8

13.9

10.2

13.9

12.1

13.9

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

2

4

6

8

10

12

14

16

18

3/15/893/22/893/29/89

4/5/89

4/12/894/19/894/26/89

5/3/89

5/10/895/17/895/24/895/31/89

6/7/89

6/14/896/21/896/28/89

7/5/89

7/12/897/19/897/26/89

8/2/898/9/89

8/16/898/23/898/30/89

9/6/89

9/13/899/20/899/27/8910/4/89

10/11/8910/18/8910/25/89

11/1/8911/8/89

11/15/8911/22/8911/29/89

Precipitation & ETc (inches)

SWD, SMB, DP, Net Irrigation 

(inches of water), Cutting Dates (unitless)

Date

NRCS Evaluation Site GV-27 1989 Soil Moisture Balance

Net Irrigation Deep Percolation (DP) Net Precipitation

Field Capacity Soil Moisture Balance (SMB) Soil Water Deficit (SWD)

Wilting Point ETc Stess Point Plant Date / Harvest Date

Crop Evapotranspiration (ETc) Crop Coefficient (Kc)

Permanent 

Wilting

Point

(-24.6)

(25.5)

Field 

Capacity

ETc Stress 

Point
168 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Figure 7-12. Soil moisture balance chart for Grand Valley Unit 1991 site 49, a fall grain site with a concrete ditch to gated pipe irrigation 

system. [NRCS, Natural Resources Conservation Service; GV, Grand Valley; SWD, soil water deficit; SMB, soil moisture balance; DP, 

deep percolation; Kc

, crop coefficient; ETc, crop evapotranspiration.]

9.9

13.8

10.1

13.8

9.6

13.8

11.0

13.8

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

-10

-8

-6

-4

-2

0

2

4

6

8

10

12

14

16

18

3/15/913/22/913/29/91

4/5/91

4/12/914/19/914/26/91

5/3/91

5/10/915/17/915/24/915/31/91

6/7/91

6/14/916/21/916/28/91

7/5/91

7/12/917/19/917/26/91

8/2/918/9/91

8/16/918/23/918/30/91

9/6/91

9/13/919/20/919/27/9110/4/91

10/11/9110/18/9110/25/91

11/1/9111/8/91

11/15/9111/22/9111/29/91

Precipitation & ETc (inches)

SWD, SMB, DP, Net Irrigation

(inches of water), Cutting Dates (unitless)

Date

NRCS Evaluation Site GV-49 1991 Soil Moisture Balance

Net Irrigation Deep Percolation (DP) Net Precipitation

Field Capacity Soil Moisture Balance (SMB) Soil Water Deficit (SWD)

Wilting Point ETc Stress Point Plant Date / Harvest Date

Crop Evapotranspiration (ETc) Crop Coefficient (Kc)

Permanent 

Wilting

Point

Field 

Capacity 

ETc Stress 

Point

(20.5)

(-16.6)
Appendix 8. Derivation of NRCS Evaluation Crop Coefficient Curves 169

Appendix 8. Derivation of NRCS Evaluation Crop Coefficient Curves

The ZETA.wks spreadsheet was obtained from the few Natural Resources Conservation Service (NRCS) evaluation 

records preserved at CSU Extension Orchard Mesa Research Station. This spreadsheet was used by the NRCS evaluation staff to 

calculate one day’s ETc for a selected crop to be made available to the agricultural community for use in irrigation management 

decisions. The crop coefficient equation in the ZETA.wks spreadsheet was published in the booklet “Scheduling Irrigation” by 

the Agricultural Research Service (ARS) in Fort Collins, Colo. (U.S. Department of Agriculture, 1987).

The ZETA.wks spreadsheet is designed to only calculate ETc for one day and one crop type at a time. The user enters the 

crop and current date as an ordinal date (the number of the day of the year). The code then calculates Kc and ETc for that day of 

the year for that crop. The ZETA.wks spreadsheet is organized into several sections. The leftmost section shows the ETc data 

for the selected crop for all Julian days of the year. The center section shows two tables of daily potential ETp covering 1989 

through 1999—one table for Grand Junction and a separate table for Fruita. Presumably these came from data collected at the 

two NRCS evaluation weather stations. The code to calculate ETp from raw weather data must have resided in a separate program, probably written in Basic, which no longer exists. 

The right-hand section of the spreadsheet contains a data table containing emergence, cover, maturity, and harvest dates for 

27 crop types. The dates are stated as ordinal dates. Below that table is the code to calculate the crop coefficient Kc for each crop 

type, given the current Julian date.

There is an error in the coding of the crop coefficient equation in ZETA.wks. This causes the Kc

 crop coefficient curve from 

ZETA.wks to jump suddenly from about midpoint in the rising limb of the equation up to the steady state value. Former ARS 

employees have identified the ZETA.wks spreadsheet as having been developed by CSU Extension, and it is presumed that they 

coded the spreadsheet independently from the NRCS evaluation team(Clay Gibson, National Park Service, former ARS Grand 

Valley staff, oral commun., August 20, 2013). For this reason, it may further be assumed that the implementation error in ZETA.

wks for the Kc equation did not necessarily exist in the Basic software used by the NRCS evaluation.

The ZETA.wks spreadsheet calculates an R value based on the current Julian date desired as follows:

BEFORE FULL COVER—R is a fraction of time from planting date to full cover date (0.0 to 1.0)

AFTER FULL COVER—R is days after full cover date

The crop coefficient Kc is then calculated with this equation:

Kc= A R^3 + B R^2 + C R + D

Where A, B, C, and D are constants in the table below which are selected for the crop in question. 

Table 56 shows the various dates associated with crops in the ZETA.wks spreadsheet. Table 56 gives the A, B, C, and D 

coefficients for the Kc equation when the crop stage is before full cover, and table 57 gives the coefficients for after full cover is 

achieved. Table 56 and table 57 were extended in the ZETA.wks spreadsheet to more crop types than the Scheduling Irrigations 

- A guide for improved irrigation water management through proper timing and amount of water application booklet published. 

Sample crop data from NRCS evaluation crop evapotranspiration spreadsheet “ZETA.wks” from 1999.
170 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Table 8-1. Sample crop data from Natural Resources Conservation Service evaluation 

crop evapotranspiration spreadsheet “ZETA.wks” from 1999.

[EMERG, crop emergence date; Ordinal date, the day number of the year; COVER, crop full cover; 

MATURE, crop maturity date; QUIT, end of irrigation season; R, multiplier; Kc, crop coefficient]

Crop Emerge Cover Mature Quit

Ordinal date Ordinal date Ordinal date Ordinal date

Alfalfa 70.00 96.00 156.00 304.00 

Turf grass 70.00 90.00 164.00 304.00 

Pasture 80.00 111.00 227.00 304.00 

Corn 136.00 181.00 242.00 260.00 

Silage corn 136.00 181.00 246.00 260.00 

Beans 154.00 194.00 232.00 258.00 

Onion 94.00 152.00 254.00 254.00 

Small grain spring 91.00 147.00 199.00 199.00 

Smalll grain fall 70.00 111.00 189.00 189.00 

Sorghum 142.00 216.00 261.00 261.00 

Apple w/cover 100.00 167.00 270.00 304.00 

Peach/pear w/cover 100.00 167.00 250.00 304.00 

Apple 100.00 167.00 270.00 304.00 

Cherry/cot 100.00 167.00 175.00 304.00 

Peach/pear 100.00 167.00 250.00 304.00 

Young tree 90.00 140.00 304.00 

Grapes 100.00 130.00 250.00 300.00 

Conifer 70.00 150.00 300.00 330.00 

Asparagus 70.00 160.00 164.00 194.00 

Broccoli 89.00 112.00 183.00 183.00 

Cabbage 110.00 137.00 244.00 245.00 

Cantaloupe 110.00 137.00 270.00 290.00 

Carrots 97.00 137.00 257.00 257.00 

Cauliflower 110.00 137.00 183.00 185.00 

Cucumber 130.00 137.00 250.00 250.00 

Lettuce 100.00 130.00 170.00 170.00 

Squash 130.00 137.00 284.00 285.00 

Tomatos 130.00 137.00 279.00 280.00
Appendix 8. Derivation of NRCS Evaluation Crop Coefficient Curves 171

Table 8-2. Sample before full cover constant values from Natural Resources Conservation 

Service evaluation crop evapotranspiration spreadsheet “ZETA.wks” from 1999.

[COVER, crop full cover; R, multiplier; Kc, crop coefficient]

Constants for use in the crop coefficient equation Kc= A R^3 + B R^2 + C R+ D

Before full cover—R is a Fraction of Time from Planting to Full Cover (0.0 to 1.0)

Crop A B C D

Alfalfa 0.33 -1.19 1.51 0.25 

Turf grass 0.00 0.00 1.51 0.25 

Pasture 0.00 0.00 1.51 0.25 

Corn -1.58 2.76 -0.43 0.21 

Silage corn -1.58 2.76 -0.43 0.21 

Dry beans -1.35 2.56 -0.35 0.21 

Onion -1.46 2.58 -0.74 0.43 

Small grains spring -2.89 4.84 -1.14 0.23 

Small grains winter -2.89 3.83 -0.15 0.23 

Sorghum -1.58 2.76 -0.43 0.21 

Apple w/cover -2.87 4.64 -1.02 0.45 

Peach/pear w/cover -2.44 3.95 -0.86 0.45 

Apple -0.65 1.28 0.00 0.27 

Cherry/cot -0.80 1.45 -0.02 0.27 

Peach/pear -0.63 1.17 0.00 0.20 

Young tree 0.67 -0.73 0.19 0.27 

Grapes -0.82 1.13 0.08 0.32 

Conifer 0.00 0.00 0.38 0.67 

Asparagus 6.61 -2.24 0.21 0.29 

Broccoli -0.45 0.86 0.12 0.27 

Cabbage -1.06 1.56 -0.07 0.09 

Cantaloupe -1.24 2.24 -0.64 0.21 

Carrots -0.98 1.69 -0.33 0.21 

Cauliflower -4.52 5.42 0.46 0.15 

Cucumber -1.35 2.45 -0.69 0.22 

Lettuce -1.23 3.20 -0.44 0.31 

Squash -1.24 2.24 -0.64 0.21 

Tomatoes market -11.27 11.21 -0.71 0.25 

Tomato canned -14.21 12.82 -0.82 0.20 
172 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Table 8-3. Sample after full cover constant values from Natural Resources Conservation 

Service evaluation crop evapotranspiration spreadsheet “ZETA.wks” from 1999.

[COVER, crop full cover; R, multiplier; Kc, crop coefficient]

After full cover—R is days after full cover

Crop A B C D

Alfalfa 0.00 0.00 0.00 0.90 

Turf grass 0.00 0.00 0.00 0.87 

Pasture 0.00 0.00 0.00 0.87 

Corn 0.00 0.00 0.02 0.95 

Silage corn 0.00 0.00 0.02 0.95 

Dry beans 0.00 0.00 0.00 1.05 

Onion 0.00 0.00 0.00 0.80 

Small grains spring 0.00 0.00 0.01 1.02 

Small grains winter 0.00 0.00 0.01 1.02 

Sorghum 0.00 0.00 0.00 0.92 

Apple w/cover 0.00 0.00 0.00 1.21 

Peach/pear w/cover 0.00 0.00 0.00 1.10 

Apple 0.00 0.00 0.02 0.90 

Cherry/cot 0.00 0.00 0.00 0.94 

Peach/pear 0.00 0.00 0.00 0.75 

Young tree 0.00 0.00 0.00 0.41 

Grapes 0.00 0.00 0.01 0.72 

Conifer 0.00 0.00 0.01 0.81 

Asparagus 0.00 0.00 0.03 0.94 

Broccoli 0.00 0.00 0.00 0.75 

Cabbage 0.00 0.00 0.00 0.51 

Cantaloupe 0.00 0.00 0.00 0.64 

Carrots 0.00 0.00 0.00 0.59 

Cauliflower 0.00 0.00 0.01 1.03 

Cucumber 0.00 0.00 0.00 0.63 

Lettuce 0.00 0.00 0.02 0.92 

Squash 0.00 0.00 0.00 0.57 

Tomato market 0.00 0.00 0.02 1.12 

Tomato canned 0.00 0.00 0.01 
Appendix 9. 1988 Colorado Irrigation Guide Consumptive Use Tables for Grand Junction and Fruita 173

Appendix 9. 1988 Colorado Irrigation Guide Consumptive Use Tables for Grand 

Junction and Fruita

In the report section “Crop Consumptive Use Discrepancies,” the use of published crop consumptive use for the Grand 

Valley Unit is discussed. The Grand Valley Unit primarily consists of the towns of Grand Junction and Fruita. The two tables 

in this appendix (fig. 9-2 for Grand Junction and 9-3 for Fruita) are reproduced from the 1988 Colorado Irrigation Guide (U.S. 

Department of Agriculture, 1988) to provide a more complete understanding of how crop consumptive use data were derived for 

this report. The Colorado climate zone map (fig. 9-1), also from the 1988 Colorado Irrigation Guide, shows the various Colorado 

climate zones, including those which are required in the Grand Junction table in the Perennials row for alfalfa. The soil moisture 

balance sites which have a crop type of alfalfa were geo-located on the climate zone map to determine the correct climate zone 

and crop consumptive use from the Grand Junction table. The Fruita table does not require a climate zone for alfalfa.
Figure 9-1. Map of Colorado climate zones for crop consumptive use of water (1988 Colorado Irrigation Guide, U.S. Department of Agriculture, 1988)
Appendix 9. 1988 Colorado Irrigation Guide Consumptive Use Tables for Grand Junction and Fruita 175

Figure 9-2. Table of estimated seasonal crop consumptive use for Grand Junction, Colo. (1988 Colorado Irrigation Guide, U.S. 

Department of Agriculture, 1988). 
176 Analysis of Historic Agricultural Irrigation Data, Western Colorado, 1985 to 2003

Figure 9-3. Table of estimated seasonal crop consumptive use for Fruita, Colo. (1988 Colorado Irrigation Guide, U.S. Department of 

Agriculture, 1988).
Mayo—Historic Agricultural Irrigation Data, Natural Resources Conservation Service, Western Colorado, 1985–2003—Open-File Report 2014–1261