&EPA
Rober: imenta
Ada OK 74820
Evaluation of
Measures for
Controlling
Sediment and
Nutrient Losses
From Irrigated
Areas
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL PROTECTION TECH-
NOLOGY series. This series describes research performed to develop and dem-
onstrate instrumentation, equipment, and methodology to repair or prevent en-
vironmental degradation from point and non-point sources of pollution. This work
provides the new or improved technology required for the control and treatment
of pollution sources to meet environmental quality standards.
This document is available to the public through the National Technical Informa-
tion Service. Springfield. Virginia 22161.
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EPA-600/2-78-138
July 1978
EVALUATION OF MEASURES FOR CONTROLLING SEDIMENT
AND NUTRIENT LOSSES FROM IRRIGATED AREAS
by
D. W. Fitzsimmons
0. R. Busch
R. B. Long
K. H. Lindeborg
G. M. McMaster
C. E. Brockway
L. R. Conklin
G. C. Lewis
C. W. Berg
E. L. Michalson
Idaho Agricultural Experiment Station
University of Idaho
Moscow, Idaho 83843
Grant No. R-803524
Project Officer
James P. Law, Jr.
Source Management Branch
Robert S. Kerr Environmental Research Laboratory
Ada, Oklahoma 74820
ROBERT S. KERR ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
ADA, OKLAHOMA 74820
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DISCLAIMER
This report has been reviewed by the Robert S. Kerr Environmental
Research Laboratory, U.S. Environmental Protection Agency, and approved for
publication. Approval does not signify that the contents necessarily reflect
the views and policies of the U.S. Environmental Protection Agency, nor does
mention of trade names or commercial products constitute endorsement or
recommendation for use.
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FOREWORD
The Environmental Protection Agency was established to coordinate
administration of the major Federal programs designed to protect the
quality of our environment.
An important part of the Agency's effort involves the search for informa-
tion about environmental problems, management techniques and new technologies
through which optimum use of the Nation's land and water resources can be
assured and the threat pollution poses to the welfare of the American people
can be minimized.
EPA's Office of Research and Development conducts this search through a
nationwide network of research facilities.
As one of these facilities, the Robert S. Kerr Environmental Research
Laboratory is responsible for the management of programs to: (a) investigate
the nature, transport, fate and management of pollutants in groundwater;
(b) develop and demonstrate methods for treating wastewaters with soil and
other natural systems; (c) develop and demonstrate pollution control tech-
nologies for irrigation return flows; (d) develop and demonstrate pollution
control technologies for animal production wastes; (e) develop and demonstrate
technologies to prevent, control or abate pollution from the petroleum
refining and petrochemical industries; and (f) develop and demonstrate tech-
nologies to manage pollution resulting from combinations of industrial waste-
waters or industrial/municipal wastewaters.
This report contributes to the knowledge essential if the EPA is to meet
the requirements of environmental laws that it establish and enforce pollution
control standards which are reasonable, cost effective and provide adequate
protection for the American public.
William C. Galegar
Di rector
Robert S. Kerr Environmental
Research Laboratory
i i i
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ABSTRACT
The primary objective of this study was to determine the effectiveness
and cost impacts of different measures for controlling sediment and nutrient
losses from surface-irrigated areas. On-farm management practices and pollu-
tant removal systems were emphasized.
Sites in the Boise and Magic Valley areas of southern Idaho were instru-
mented and monitored so that the effects of different irrigation, cropping
and tillage practices on the quality and quantity of surface runoff from
these sites could be determined. In addition, sediment removal devices were
installed at several of the sites and evaluted to determine their effective-
ness in removing sediment, phosphorus and other materials from surface return
flows. Devices evaluated included mini-basins, vegetated buffer strips, small
on-farm sediment retention ponds and large district-type ponds. The results
of the field investigations show that water, sediment and nutrient losses
from surface-irrigated fields can be greatly reduced or even eliminated by the
use of proper management practices and/or sediment retention systems.
Information relative to current crop production, tillage and irrigation
practices, cost of production and income from crop production was collected
from 150 farmers in the two study areas. This information was used to develop
representative farm models for the areas. Estimates of the cost effectiveness
of selected methods for reducing sediment losses from the farms were developed
using linear programming models. Farm income consequences of having to meet
specified restrictions on sediment losses were also determined. The results
show that sediment losses from surface-irrigated fields can be reduced by as
much as 50 percent at modest cost. Elimination of surface runoff and sediment
losses would require the use of sprinkler irrigation which would decrease the
returns to land and management by about 15 percent.
The overall impacts of pollutant losses from irrigated lands in the Boise
Valley study area were evaluated. Sediment losses resulted in annual costs of
about $1.4 million to keep canals and ditches clean in a 68,000-hectare irri-
gated area in the Valley. Water quality in the Boise River was found to be
affected by irrigation activities in the Valley. Boise River water also con-
tributes to pollution problems downstream in the Snake River.
This report was submitted in fulfillment of Grant No. R-803524 by the
University of Idaho under the partial sponsorship of the U.S. Environmental
Protection Agency. This report covers the period from January 15, 1975 to
October 14, 1977.
IV
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CONTENTS
Page
Foreword iii
Abstract iv
Figures vi
Tables .".... ix
Acknowledgments xiv
1. Introduction 1
2. Summary and Conclusions 3
3. Recommendations 5
4. Background Information 7
5. Study Areas 13
6. Boise Valley Field Investigations 23
7. Magic Valley Field Investigations 57
8. Economics of Control Practices 82
9. Overall Impacts of Reducing Pollutant Losses .... 129
References 145
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FIGURES
Number Page
1 Map of the Boise River Basin 14
2 Map of the Magic Valley area 18
3 Major irrigation districts in the Magic Valley area 19
4 On-farm sediment pond under construction 24
5 Large sediment retention pond located in a natural drainageway
near Wilder, Idaho 24
6 T-slot installed at Site 1 in 1976 27
7 Vegetated buffer strip seeded at the lower ends of Sites 2,
3 and 4 in 1976 27
8 Flume and recorder used to obtain a continuous record of
the flow onto a study site 29
9 Flume and automatic sampler used to monitor flow from a site ... 29
10 Rate of runoff from Site 9 during the second irrigation
in 1976 35
11 Sediment concentration in the surface runoff from Site 9
during the second irrigation in 1976 35
*
12 Sediment loss from Site 9 during the second irrigation in 1976 .. 36
13 Sod buffer strip being installed in 1975 44
14 Grain buffer strip following the first irrigation in 1976 .... 44
0
15 Grain buffer strip midway through the 1976 irrigation season ... 45
16 Sediment deposited from furrow runoff backed up by grain
buffer strip in 1976 45
17 T-slot prior to the first irrigation of Site 1 in 1976 47
18 T-slot after the first irrigation of Site 1 in 1976 47
vi
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Number Page
19 Sediment pond at Site 1 prior to the first irrigation in 1976 . . 48
20 Sediment pond at Site 1 after the third irrigation in 1976 .... 48
21 Screen for retaining floating debris in the sediment pond at
Site 5 51
22 Side-outlet pond used to remove sediment from the runoff from
Sites 6, 7 and 8 51
23 Large sediment pond near Melba, Idaho showing the sediment accu-
mulation late in the irrigation season 54
24 Weir and recorder used to measure the flow onto the bean tillage
and mini-basin study sites in 1976 59
25 Leveling device used to set siphon tubes in the bean tillage and
mini-basin studies in 1976 59
26 Lower end of the bean tillage study site showing plastic-lined
furrows 60
27 Lower end of a bean field showing the convex-end syndrome
common in the Magic Valley 60
28 Effect of field slope on sediment yield, 1976 bean tillage
study 64
29 Effect of field slope on water retention, 1976 bean tillage
study 65
30 Relationship between sediment yield and surface runoff 66
31 Mini-basins constructed on the lower end of a bean field 67
32 Mini-basins with grassed overflow sections 67
33 V-notch flume used to measure the flow in check furrows in
the mini-basin study 69
34 Sediment loss rates during a typical irrigation of the
vegetated buffer strip study site in 1976 71
35 Effect of vegetated buffer strip stand density on sediment
yield 73
36 Inlet structure and by-pass channel of the K Lateral wasteway
pond near Jerome, Idaho 79
vn
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Number Page
37 Weir and recorder used to monitor the flow through the K Lateral
wasteway pond near Jerome, Idaho 79
38 Returns to land and management and costs associated with different
levels of sediment loss, Twin Falls small farm model .... 108
39 Returns to land and management and costs associated with different
levels of sediment loss, Jerome small farm model Ill
40 Returns to land and management and costs associated with different
levels of sediment loss, Wilder-Parma small farm model ... 114
41 Returns to land and management and costs associated with different
levels of sediment loss, Nampa-Melba small farm model .... 116
42 Returns to land and management and costs associated with different
levels of sediment loss, Twin Falls large farm model .... 119
43 Returns to land and management and costs associated with different
levels of sediment loss, Jerome large farm model 121
44 Returns to land and management and costs associated with different
levels of sediment loss, Wilder-Parma large farm model. ... 124
45 Returns to land and management and costs associated with different
levels of sediment loss, Nampa-Melba large farm model .... 126
46 Natural flow of the Boise River, canal diversions and return flows
during the 1973 irrigation season 131
47 Specific conductivity of the Boise River near Boise and at Notus,
October 1972 through September 1973 133
48 Dissolved nitrite plus nitrate concentrations in the Boise River
below Lucky Peak Dam and near Caldwell, April 1973 to
September 1976 135
49 Total phosphorus concentrations in the Boise River below Lucky
Peak Dam and near Caldwell, April 1973 to September 1976 . . 136
50 Sediment concentrations in the Boise River below Lucky Peak Dam
and near Cal dwell, April 1973 to September 1976 138
51 Turbidity readings taken in the Boise River below Lucky Peak Dam
and near Cal dwell, April 1973 to September 1976 139
viii
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TABLES
Number Page
1 Number and Size of Irrigated Farms in Canyon County 16
2 Major Field Crops Grown in Canyon County 16
3 Irrigation Water Diversions from the Snake River for Districts
in the Magic Valley, 1976 20
4 Number and Size of Irrigated Farms in Jerome County 21
5 Number and Size of Irrigated Farms in Twin Falls County 21
6 Major Field Crops Grown in Jerome County 22
7 Major Field Crops Grown in Twin Falls County 22
8 Boise Valley On-Farm Study Sites . . 25
9 Descriptions of the Soils Found on the Boise Valley Study Sites . . 26
10 Particle Size Distribution of Surface Layer (Top 30 Centimenters)
of Soils from the Boise Valley Study Sites 28
11 Results of the Boise Valley Furrow Stream Size Study, 1976 .... 31
12 Seasonal Totals for the Boise Valley Furrow Stream Size Study,
1976 32
13 Water Balance Results for the Boise Valley Furrow Stream Size
Study, 1976 32
14 Flow and Water-Use Data for the Furrow Cutback Study at
Site 9, 1976 33
15 Net Sediment, Phosphorus and Nitrate Losses from Cutback and
Non-Cutback Plots at Site 9, 1976 34
16 Effects of Number of Irrigations on Water and Sediment Losses ... 37
17 Effects of Preplant Irrigations on Water and Sediment Losses,
1976 38
IX
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Number Page
18 Comparative Results of Irrigating Alternate Compacted and
Non-Compacted Furrows, 1975 38
19 Average Concentrations of Pollutants in the Surface Runoff from
Sites 1 through 8, 1975 and 1976 40
20 Average Net Losses of Pollutants from Sites 1 through 8, 1975
and 1976 41
21 Average Concentrations of Pollutants in the Surface Runoff from
Sites 6, 7 and 8, 1975 42
22 Flow and Pollutant Loss Data for Sites 6, 7 and 8, 1975 42
23 Comparative Flow and Pollutant Loss Data for Sites 7 and 8, 1975
and 1976 42
24 Effects of Vegetated Buffer Strips on Sediment Losses 46
25 Sediment and Phosphorus Removal by T-Slots and Sediment Pond at
Site 1 During the First Irrigation, 1976 49
26 Seasonal Sediment Balances for the Boise Valley On-Farm Sites and
Sediment Ponds, 1975 and 1976 50
27 Crops Grown in the Wilder Pond Drainage Area, 1976 52
28 Average Pollutant Concentrations and Removal Efficiencies for
Large Sediment Retention Ponds, 1975 and 1976 53
29 Average Pollutant Concentrations and Removal Efficiencies for
Large and On-Farm Sediment Retention Ponds, 1975 and 1976 . . 54
30 Surface Runoff Data, 1976 Magic Valley Bean Tillage Study 61
31 Sediment Yield Data, 1976 Magic Valley Bean Tillage Study 61
32 Total Phosphorus Loss Data, 1976 Magic Valley Bean Tillage Study. . 62
33 Sediment Loss Data, 1976 Mini-Basin Study 68
34 Mini-Basin Sediment Removal Efficiencies, 1976 70
35 Flow and Sediment Yield Data, 1976 Magic Valley Vegetated Buffer
Strip Study 72
36 Flow and Sediment Data, 1975 Sediment Removal by Alfalfa Study . . 74
37 Flow Data, 1975 Furrow Cutback Study 76
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Number Page
38 Sediment Data, 1975 Furrow Cutback Study 77
39 Seasonal Flow and Sediment Removal Data for the K Lateral
Pond near Jerome, Idaho 80
40 Size Classification of Sample Farms in Twin Falls County 83
41 Irrigated Cropland Use on Sample Farms in the Twin Falls Study
Area 84
42 Crops Grown on Model Farms for the Twin Falls Study Area 84
43 Size Classification of Sample Farms in Jerome County 85
44 Irrigated Cropland Use on Sample Farms in the Jerome Study Area . . 85
45 Crops Grown on Model Farms for the Jerome Study Area 86
46 Size Classification of Sample Farms in the Wilder-Parma Study Area. 86
47 Irrigated Cropland Use on Sample Farms in the Wilder-Parma Study
Area 87
48 Crops Grown on Model Farms for the Wilder-Parma Study Area .... 87
49 Size Classification of Sample Farms in the Nampa-Melba Study Area . 88
50 Irrigated Cropland Use on Sample Farms in the Nampa-Melba Study
Area 88
51 Crops Grown on Model Farms for the Nampa-Melba Study Area 89
52 Sediment Loss from Surface-Irrigated Crops Under Typical Farm
Conditions in the Boise and Magic Valley Areas 90
53 Estimated Sediment Loss Reduction for Selected Control Practices. . 90
54 Costs Associated with Using Flow Cutback to Reduce Sediment Loss
on a Typical Farm in the Boise or Magic Valley Areas ...... 92
55 Opportunity Cost of Land Taken Out of Production for Vegetative
Strips (Average for Farm Models) 93
56 Annual Operating Costs Associated with Using Vegetative Strips
on 8.1-Hectare Fields 94
57 Total Annual Costs Associated with Using Vegetative Strips on
8.1-Hectare Fields 95
XI
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Number
58 Sediment Pond Size and Excavation Cost Estimates for Ponds for
8.1-Hectare Fields 96
59 Annual Operating Costs for Sediment Ponds for 8.1-Hectare Fields. . 96
60 Opportunity Cost of Land Taken Out of Production for Sediment
Ponds for 8.1-Hectare Fields 97
61 Total Annual Costs Associated with Sediment Ponds for 8.1-Hectare
Fields 98
62 Cost of Shaping and Seeding Ditch Berms for Mini-Basins 99
63 Basin Construction Costs for Mini-Basins on 8.1-Hectare Fields. . . 100
64 Sediment Spreading Costs for Mini-Basins on 8.1-Hectare Fields. . . 101
65 Total Annual Costs Associated with Mini-Basins on 8.1-Hectare
Fields ..... 102
66 Annual Fixed Costs of a Side-Roll Sprinkler System for
56.7 Hectares of Land 103
67 Labor Cost Savings Resulting from the Conversion of a Surface
Irrigation System to a Side-Roll Sprinkler System 103
68 Costs of Owning and Operating a Side-Roll Sprinkler System
Relative to Sediment Retention 104
69 Cost Effectiveness Summary for Selected Sediment Loss Control
Practices 105
70 Crop Mix, Sediment Loss and Returns to Land and Management Data
for Alternative Control Practices, Twin Falls Small Farm
Model 107
71 Crop Mix, Sediment Loss and Returns to Land and Management Data
for Alternative Control Practices, Jerome Small Farm Model . .110
72 Crop Mix, Sediment Loss and Returns to Land and Management Data
for Alternative Control Practices, Wilder-Parma Small Farm
Model 112
73 Crop Mix, Sediment Loss and Returns to Land and Management Data
for Alternative Control Practices, Nampa-Melba Small Farm
Model 115
74 Crop Mix, Sediment Loss and Returns to Land and Management Data
for Alternative Control Practices, Twin Falls Large Farm
Model 118
xn
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Number Page
75 Crop Mix, Sediment Loss and Returns to Land and Management Data
for Alternative Control Practices, Jerome Large Farm
Model 120
76 Crop Mix, Sediment Loss and Returns to Land and Management Data
for Alternative Control Practices, Wilder-Parma Large Farm
Model 123
77 Crop Mix, Sediment Loss and Returns to Land and Management Data
for Alternative Control Practices, Nampa-Melba Large Farm
Model 125
78 Summary of Sediment Loss and Annual Cost Data 128
79 Cost of Treating Return Flows in Thirteen Major Drains in the
Boise Valley 140
80 Anticipated Performance of Sediment Pond Treatment System for
Boise Valley Drains 140
81 On-Farm Ditch Maintenance Costs, 1975 142
82 Boise Valley Stream Segment Status Relative to Water Quality,
1975 143
xi i i
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ACKNOWLEDGMENTS
The authors are indebted to a number of individuals who contributed to
the success of this study. The cooperation of personnel at the Caldwell,
Kimberly and Parma Research and Extension Centers in carrying out the field
investigations conducted at these centers is gratefully acknowledged. We
would also like to thank Agricultural Research Service personnel at the North-
west Watershed Research Center in Boise and the Snake River Conservation
Research Center in Kimberly for their cooperation. Their cooperation in
allowing us to use some of their recorders and equipment in carrying out this
study is especially appreciated.
We are also indebted to the farmers in the Boise and Magic Valley areas
who participated in the survey of farming practices. Special thanks are
extended to the farmers in the Boise Valley who allowed us to conduct field
investigations on their lands. The assistance and cooperation of irrigation
district personnel in the two study areas is also appreciated.
The help of graduate students in the Agricultural Engineering, Civil
Engineering and Plant and Soil Sciences Departments in achieving the objec-
tives of this project is gratefully acknowledged. The students involved
included R. 6. Allen, M. F. Lindgren and K. L. Pennington.
The assistance and advice given by the EPA Project Officer, Dr. James P.
Law, Jr., is acknowledged. He was helpful in all phases of the work,
including the preparation of the initial proposal and review of the manuscript
for this report.
xiv
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SECTION 1
INTRODUCTION
The importance of irrigation in producing crops in arid and semi-arid
regions of the world is well documented. This practice is particularly impor-
tant to western areas of the United States where irrigation is required for
the production of most crops. While beneficial in many respects, irrigation
can have serious detrimental effects on water quality since irrigation return
flows may contain dissolved salts, sediment, plant nutrients and other mate-
rials. The effects of these materials on the quality of receiving waters are
a major concern in the western states since irrigation return flows constitute
a large portion of the flow in many streams in this region.
Concerns about water quality have led to the passage of legislation
(Federal Water Pollution Control Act Amendments of 1972) designed to alleviate
water pollution problems. The U.S. Environmental Protection Agency is con-
cerned with achieving the goals of this Act; and, as a result, has initiated
comprehensive research, development and demonstration programs designed to
effectively control pollutant discharges. Included are programs to upgrade
the technology for controlling pollutant discharges from irrigated areas.
The major water quality problem in most western irrigated areas is in-
creased salt concentrations in the return flows as a result of the pickup of
minerals from soils and the loss of water through evapotranspiration (Wells,
1974). As a result, a number of studies have been conducted to find ways to
reduce the buildup of salt in return flows in these areas. Salinity is not a
major problem, however, in many irrigated areas. Instead, the major problem
is sediment in the surface runoff from irrigated fields; and, to a lesser
extent, nitrate and other nutrients in ground and surface waters in these
areas.
There are a number of ways in which sediment and nutrient losses from
irrigated areas can be effectively controlled. These include the use of irri-
gation and/or other practices which eliminate or reduce surface runoff and
resulting pollutant losses from individual fields, on-the-farm removal of
sediment and nutrients from surface return flows and removal after the return
flow has entered surface drainage systems or streams. Relatively little is
known,however, about the effectiveness and cost impact of specific control
measures.
The purpose of this study was to further the development of the technology
needed to effectively control sediment and other pollutant losses from surface-
irrigated areas. Primary emphasis was placed on determining the effectiveness
and cost impact of on-the-farm control measures and removal systems. The
specific objectives were to:
1
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1. Determine the effects of different water management, cropping, and
tillage practices and other physical factors on the quality and quan-
tity of surface runoff from irrigated fields.
2. Determine the effectiveness of pollutant removal devices and systems
in controlling sediment and nutrient losses from irrigated areas.
3. Determine the cost effectiveness and aggregate effects of pollutant
removal systems and discharge control measures.
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SECTION 2
SUMMARY AND CONCLUSIONS
The results of field investigations conducted in the Boise and Magic
Valley areas of southern Idaho show that water, sediment and nutrient losses
from surface-irrigated fields are affected by a number of factors and that
these losses can be effectively controlled. For example, the results indicate
that sediment and nutrient losses from furrow-irrigated fields are directly
related to furrow stream size and that it may be possible to completely elimi-
nate these losses by using proper furrow stream sizes. At one of the study
sites, reducing the furrow stream size by 47 percent actually resulted in net
gains of sediment and phosphorus on the site.
Cutting furrow flows back after they reach the end of a field increases
the efficiency of water use and reduces sediment loss. The use of cutback
irrigation on a corn field increased the water-use efficiency from 41 to 78
percent and reduced sediment loss by 93 percent. A 72 percent reduction in the
amount of surface runoff from a potato field resulted in an 87 percent de-
crease in the amount of sediment lost from this field. Phosphorus losses were
also reduced by the use of cutback irrigation.
Preplant irrigation, tillage and cropping practices were found to affect
surface runoff and resulting pollutant losses from furrow-irrigated fields.
Irrigating in non-compacted furrows resulted in less runoff and sediment loss
than irrigating in compacted furrows. However, high infiltration rates in the
non-compacted furrows resulted in excessive deep percolation losses and poor
water distribution efficiencies in these furrows. For corn, over one-third of
the seasonal sediment loss occurred during a preplant irrigation. Wetting
only the seedbed area of a bean field during the preplant irrigation resulted
in less sediment loss than wetting the entire field surface. Reusing sediment-
laden return flows from row crops to irrigate close-growing crops is an effec-
tive way to remove sediment from return flows. Reuse of return flows on an
alfalfa field resulted in removal of 79 percent of the sediment in the flow
entering the field.
Vegetated buffer strips can be used to retard the runoff from surface-
irrigated fields and thereby cause sediment in the runoff to settle out.
Sodded grass and barley strips installed at the lower end of a corn field were
effective in removing about 45 percent of the sediment from the runoff passing
through these strips. Extra plantings of spring wheat seeded across the lower
end of a wheat field reduced the amount of sediment lost from this field by
79 percent.
Mini-basins which collect and detain the runoff from several adjacent
furrows can remove up to 95 percent of the sediment from the runoff from a
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field. Evaluations of twelve mini-basins constructed, on the lower end of a
bean field showed that the basins reduced the seasonal sediment loss from the
field from 14,950 kg/ha to 680 kg/ha. Basins with grassed overflow sections
which collect the runoff from 4 or 5 furrows are recommended.
Properly sized on-farm sediment ponds will remove over 70 percent of the
sediment from incoming runoff, and can be used for at least two years before
they will require cleaning. Large sediment ponds which remove sediment from
return flows in wasteways can be used as an alternative to controlling sedi-
ment losses at their source. The sediment removal efficiences of the large
ponds evaluated in this study ranged from 40 to 70 percent.
The cost effectiveness of control practices considered, in this study
varied widely. In general, cutback irrigation is more expensive than the
other methods of controlling sediment losses from surface-irrigated fields.
On-farm sediment ponds will retain about two-thirds of the sediment loss from
furrow-irrigated fields at a cost of less than two dollars per metric ton of
sediment retained. Vegetated buffer strips compare favorably with sediment
ponds on a cost effectiveness basis. Mini-basins retain more sediment than
ponds or vegetated strips but are more expensive than ponds or strips in terms
of their total cost and their cost per unit of sediment retained.
Converting a surface irrigation system to a side-roll sprinkler system to
eliminate surface runoff and sediment losses from a farm would greatly increase
the costs over those associated with other control practices. Potatoes are an
exception since the amount of sediment loss from surface-irrigated potato
fields is usually much greater than the loss from other surface-irrigated
crops. For other row crops, sprinklers would cost about ten times as much per
unit of sediment retained as would sediment ponds and about four times as much
as mini-basins. On grain, sprinklers would cost about eighteen times as much
as ponds and about six times as much as mini-basins.
The results of an analysis to determine the farm income consequences of
having to meet specified restrictions on sediment losses show that the use of
sediment ponds to meet these restrictions would reduce the returns to land and
management by slightly more than one percent. The use of mini-basins would
reduce the returns by a little more than 2.5 percent. The use of sprinklers,
however, would reduce the returns by about 15 percent.
Some of the overall impacts of surface irrigation in the Boise Valley
were considered in this study. The physical impacts of irrigation were found
to focus about water quality and groundwater levels. During the irrigation
season, specific conductivity levels and nitrogen and phosphorus concentrations
in the Boise River at Notus (near the lower end of the Valley) are from five
to ten times higher than they are at Boise (near the upper end of the Valley).
High groundwater levels, which are primarily due to irrigation, prevent the
use of some valley lands for certain purposes and make it necessary for some
cities to run pumps the year around to reduce groundwater levels. Sediment
losses resulted in annual costs of about $1.4 million to keep canals and
ditches clean in a 68,000-hectare area in the Valley. Boise River water also
contributes to pollution problems downstream in the Snake River.
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SECTION 3
RECOMMENDATIONS
Efforts to disseminate the information now available relative to the
control of sediment and nutrient losses from surface-irrigated lands should be
intensified. Sediment and nutrient losses from many surface-irrigated areas
could be greatly reduced at modest cost by the use of the control technology
now available. Information relative to the cost effectiveness of different
control practices should be included as an integral part of all education pro-
grams on irrigation return flow control.
Criteria for designing and "operating different types of sediment, reten-
tion systems need to be developed. On-farm systems such as vegetated buffer
strips, mini-basins and sediment ponds have been shown to be effective in
removing sediment and certain nutrients from surface return flows. Large
district-type ponds are also effective in this regard. However, criteria for
designing and operating these systems are quite limited at this time.
Work needs to be done to develop a relatively simple and easily used
device for monitoring surface return flows. If such a device were available,
it would enable irrigators to more easily determine the extent and seriousness
of return flow losses from their land. This, in turn, would facilitate imple-
mentation of needed control measures.
Efforts to develop a better understanding of the effects of irrigation,
cropping, tillage and other management practices as well as physical factors
on sediment and nutrient losses from surface-irrigated lands should be conti-
nued. These efforts should include an assessment of the effects of changes
in management practices to meet energy limitations on sediment and nutrient
losses, and an assessment of the cost impacts of such changes. Particular
attention should be given to the effects of reducing the number of tillage
operations, better irrigation scheduling, limiting or changing the use of
sprinkler systems and the use of irrigation methods which have low energy
requirements.
Efforts should be made to improve the data base for estimating the costs
and documenting the benefits of improving sediment and nutrient loss control
practices. The possibility exists that higher crop yields and better crop
quality may help offset the costs of improved management, practices. More work
needs to be done to establish the effects of improved irrigation water manage-
ment and other management practices on crop yield and quality and to document
resulting economic benefits. Accounts of the labor time, machine operating
time and costs associated with the use of different management practices and
devices to control losses should be kept.
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Additional research is needed to more fully determine the overall impacts
of controlling sediment and nutrient losses from surface-irrigated areas.
Improvements in water quality as well as economic benefits occur both on the
farm and downstream as a result of the implementation of effective control
programs. As more detailed information relative to the effectiveness and costs
of control programs becomes available, it will be possible to make better
estimates of the overall impacts of these programs.
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SECTION 4
BACKGROUND INFORMATION
National concerns about water quality problems have focused attention on
the major sources of water pollutants. Agriculture has been accused of being
a major source in many areas; and, as a result, considerable effort and re-
sources have been devoted to determining agriculture's contribution to water
quality problems. According to Viets (1970), the usual approach to the study
of water quality problems in agricultural areas has been to assign certain
inputs of pollutants to identifiable sources and to charge the rest by dif-
ference to agriculture. Possible agricultural inputs include animal wastes,
eroded soil, nutrients washed from dead vegetation, leachate from septic tanks
and fertilizer materials either in solution or adsorbed on sediment particles.
Identifying the source of a particular pollutant found in water in an irri-
gated area is usually extremely difficult.
The purpose of this section of the report is to briefly summarize the
findings of studies which have dealt with sediment and nutrient losses from
agricultural lands. Information obtained from previous irrigation water
quality investigations conducted in the two study areas is included.
GENERAL
Sediment has been described as a primary hazard to water quality (Viets,
1971). Robinson (1971) describes sediment as a pollutant which fills reser-
voirs, lakes and ponds; clogs stream channels; settles on productive land; and
destroys aquatic habitats. It may also act as a scavenger or release nutri-
ents. Nutrient losses from land, particularly phosphorus losses have been
related to sediment losses through soil erosion. Several investigators
(Scarseth and Chandler, 1938; Volk, 1945; and Ensminger and Cope, 1947) have
found that most of the phosphorus added to soils is removed by soil erosion
processes. The soil fraction most subject to detachment and transport by
water has been shown to be higher in total phosphorus than the original soil
(Neal, 1944; Stoltenberg and White, 1953). Stoltenberg and White also found
that the amount of nitrogen in sediments was almost double the amount, in sur-
face soil.
Most of the sediment in irrigation return flows results from the irriga-
tion of sloping lands by the furrow method. Where irrigation water is applied
on level or nearly level land, erosion is usually light. Likewise, erosion
does not usually occur with a properly designed sprinkler irrigation system
since water is applied no faster than the soil will absorb it. However, when
water is applied on sloping lands by the furrow method, erosion is a constant
threat (Mech, 1959). Land slope, soil conditions, crop cover, furrow stream
size and other factors influence the amount of erosion. As pointed out by
7
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Tovey, et^ al_., (1962), a slight change in one or more of these factors can
significantly change the erosion rate. Methods for reducing erosion rates
have been presented by Mech (1959) and Mech and Smith (1967). Guidelines for
controlling the amount of sediment in irrigation return flows have been pre-
sented by Carter (1976) and Carter and Bondurant (1976).
Studies have been conducted in several areas to determine the concentra-
tions and sources of nitrate and other nutrients in waters in these areas.
In a study of tile drain effluents in the San Joaquin Valley, Johnston et al.,
(1965) found the highest concentrations of nitrogen in areas where heavy
applications of nitrogen fertilizers were made. In another study conducted in
this area, Stromberg (1966) indicates that not all of the nitrate in waters
in the Central San Joaquin Valley can be charged to fertilization practices.
Bower and Mil cox (1969) found that increasing the application of nitrogen
fertilizer to three irrigated areas adjacent to the upper Rio Grande River
did not increase nitrate concentrations in the river. In Nebraska, Muir ejt
al., (1973) found that only at sites of intensive irrigation development and
with irrigation of valley positions of shallow water table has fertilizer
nitrogen contributed substantially to a reduction in groundwater quality.
Return flow from a 203,000-acre tract of calcareous silt loam soils irrigated
with water diverted from the Snake River in Southern Idaho increased the down-
stream total salt and nitrate-nitrogen loads, but decreased the downstream
water-soluble phosphorus load (Carter e_t al_., 1971).
General methods for improving the quality of irrigation return flows have
been summarized by Law and Skogerboe (1972). These include improved on-the-
farm methods of water application, tailwater recovery and reuse, judicious use
of slow-release or other controlled fertilizers and certain specialized cul-
tural practices.
On-the-farm methods of water application affect both the quality and
quantity of irrigation return flows. Furrow irrigation is the most common
method of application because of low installation cost, while sprinkler irri-
gation is used because of its adaptability to a wide range of field conditions.
Two new methods which offer promise are subsurface application, and drip or
trickle irrigation (Wells, 1974). All four systems must be accurately designed
if efficient application and controlled distribution of water are to be ob-
tained. If the systems are correctly designed and used, deep percolation and
surface runoff losses are minimized and the need for control measures is
reduced.
Tailwater recovery and reuse can be achieved by the use of pumpback
systems similar to the one described by Bondurant (1969). Such systems catch
surface runoff at the bottom of a field and pump it back to the head of the
field or to other fields for reuse. Even though field erosion is not elimi-
nated, sediment losses are prevented and the efficiency of water use is
increased. Sediment retention systems used either separately or in conjunc-
tion with pumpback systems effectively remove much of the sediment from
irrigation return flows. As pointed out by Robbins and Carter (1975), sedi-
ment ponds can be built in depressions or on shallow soil areas at minimum
cost to a farmer if he uses his own equipment during slack work periods. The
sediment can be used to improve the land's topography and value. Even so,
8
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trapping sediment in man-made ponds is generally regarded as a temporary or
emergency solution for the sediment loss problem since this practice does not
prevent erosion from occurring.
Costs are an important consideration in selecting alternatives for
improving the quality of irrigation return flows. There must be an economic
incentive for an irrigator to control irrigation return flow (Wells, 1974).
Such an incentive may be either negative or positive. For example, a regula-
tion restricting the quantity of sediment in return flows might force an
irrigator to install on-farm settling basins without any apparent return,
thereby becoming a negative economic incentive. However, if this same irri-
gator improves his practices in such a way that sediment and nutrient losses
are decreased and crop yields are increased to the extent that the combined
benefits are greater than additional costs, he has a positive economic incen-
tive.
Conversion from gravity to sprinkler irrigation has been suggested as one
means of reducing or eliminating irrigation return flows. The economic incen-
tive to a farmer to convert must come from a marked increase in the economic
efficiencies of his farming operation. This involves such factors as the size
of the farm, types of crops grown, and prices of the inputs as well as the
products grown on the farm.
Economic efficiencies were estimated through long-run cost curves for the
Dry Lake area in the Boise Valley (Coffing and Lindeborg, 1966). Costs per
unit of output decreased with increasing size of the farms indicating that for
the larger farms there is an economic incentive to allocate the input factors,
including irrigation water, to the highest economic use.
An economic study of how well irrigation water was used in four areas
along the Snake River was also based on economic efficiences (Lindeborg, 1970).
Prices of irrigation water were estimated. Since water has no free market,
its price in growing crops was estimated by the value of the increase in out-
put resulting from the final unit of water used in producing the output.
PREVIOUS INVESTIGATIONS IN THE STUDY AREAS
Several water quality studies have been conducted in irrigated areas in
southern Idaho. Jensen e_t aJK » (1951) made a detailed study in 1947 and 1948
of the chemical characteristics of surface waters used for irrigation.
Twenty-seven major water sources were systematically sampled and analyzed for
dissolved salts over the two year period. Based on U.S. Department of Agri-
culture standards, all but one of these sources was classified as excellent in
quality for irrigation usage.
A study of the quality of surface and drainage well waters in the Boise
Valley was made by Lewis (1959). Sixty sites, including 50 drainage and
domestic wells and 10 surface water sources, were periodically sampled during
the 1958 irrigation season. The results of this study indicated that most of
the water sources sampled were suitable for irrigation usage and that salinity
is not a major problem in the Boise Valley.
-------
In 1970, a study was started to determine the effects of irrigated agri-
culture on water quality in the Boise Valley. During the first phase of this
study, surface and ground waters in gravity-irrigated areas in the Valley
were systematically sampled and analyzed to determine the kinds and amounts
of pollutants in these waters (Naylor e_t a_K, 1976). Seventy-nine sites,
including 28 headwater sites, 30 surface runoff sites, 12 open ditch drains
and 3 drainage wells, were sampled at two-week intervals during the 1970 irri-
gation season. Twenty-nine gravity-irrigated fields were included in the
sampling program. The water samples were analyzed for nitrate, ammonia,
organic nitrogen, soluble phosphorus, total phosphorus, total solids, elec-
trical conductivity (total salts) and pH.
Data from the 1970 survey indicate that the concentrations of the three
forms of nitrogen were relatively low in all of the water sources
(Fitzsimmons e_t aj_., 1972). Except for isolated instances in which fertilizer
materials were added directly to the irrigation water, the concentrations of
the nitrogen forms in the surface runoff were essentially the same as those
in the incoming irrigation water. In general, the groundwater sources con-
tained the largest concentrations of nitrate-nitrogen and also contained
relatively large concentrations of both soluble and total phosphorus. The
surface runoff contained the largest concentrations of total phosphorus and
total solids (mostly sediment). The concentrations of both of these consti-
tuents varied widely with location and time during the sampling period
(Naylor et al_., 1976).
The results of the first phase of this study showed how the concentra-
tions of several pollutants varied in the Boise Valley as to water source,
location, time of year and other factors. The quantities of pollutants
either lost or gained from fields in the study area were not determined since
flow measurements were not made. Also, the quality and quantity of deep
percolation losses were not determined. To get this type of information, a
60.5-acre tract was monitored during the 1971 irrigation season to determine
the net losses or gains of water, sediment and nutrients on gravity-irrigated
fields in the tract (Busch et_al., 1972). The experiment was repeated in
1972 on 90 acres of land. Sediment retention ponds constructed at the lower
ends of two fields in the tract were included in the 1972 monitoring program.
Sugarbeets and onions were the crops grown in 1971 and a field of beans was
added in 1972.
Data from the 1971 and 1972 studies indicate that the quantity and
quality of the return flows from fields in this tract varied considerably with
the crops grown (Fitzsimmons e_t al_., 1975). Although some of these differ-
ences were attributed to differences in water management practices (Busch
e_t aj_., 1972 and Carlson, 1974). In general, practices which increased
water-use efficiencies tended to reduce sediment and nutrient losses.
Seasonal data for the tract show that more nitrate-nitrogen and ammonia
entered the tract with the incoming irrigation water than was lost in the
surface runoff (Fitzsimmons e_t al_., 1975). There was a net loss of total
phosphorus and total solids from the tract. Factors influencing the loss of
nutrients from this tract have been reported by Busch e_t al_., (1975). These
losses were found to be dependent on several independent variables including
10
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the amount of irrigation water retained on a field, the amount of total
solids in the surface runoff and the amount of fertilizer materials applied
in the irrigation water. Increasing the percentage of applied water retained
on a field and reducing the amounts of fertilizer applied in the irrigation
water would decrease the amounts of all nitrogen forms lost in the surface
runoff.
The sediment retention ponds proved to be very effective in reducing
sediment losses from the tract (Fitzsimmons et^al_., 1975). The data indicate
that as much as 79 percent of the total solids carried from the fields by
surface runoff was retained in the ponds. There was also a small general
decrease in the nutrient load of the water during retention in the ponds
(Bristol, 1973 and Yoo, 1974).
Since the 1970 Boise Valley water quality survey indicated that nitrate-
nitrogen concentrations were greater in groundwater sources than they were in
surface waters, research was initiated in 1973 to determine the quality of
shallow groundwater and its influence on the quality of water in surface drain
systems (Lewis et^ a_l_., 1977). It was found that the complexity of underlying
materials in the Boise Valley makes the interpretation of shallow groundwater
quality data obtained at a given location very difficult. Irrigated agri-
culture appears to have two opposing effects: (1) enrichment of the ground-
water during the crop growing season by the leaching of nutrients through the
soil and (2) dilution of groundwater return flows by surface return flows.
Research was started in the spring of 1974 to determine both the effec-
tiveness and cost impact of measures which might be used to control sediment,
nutrient and other pollutant losses from irrigated lands in the Boise Valley
(Fitzsimmons et al., 1975). Seven sites which were selected to represent the
different soiTsYTield slopes, crops and irrigation practices in the Valley
were instrumented so that water, nutrient and suspended solids mass balances
could be established for each site. These balances were used to determine
the effectiveness of different water management practices and return flow
measures in controlling pollutant discharges. Data relative to the initial
investment costs and operating costs of sprinkler and surface irrigation
systems and sediment retention ponds were gathered and used to prepare
representative farm budgets for four alternative water management plans.
Guidelines for controlling sediment and nutrient losses in the Valley were
presented (Fitzsimmons e_^aj_., 1975).
The results of the 1974 study show how water, sediment and nutrient
losses are influenced by water management practices, tillage and other cul-
tural practices, soil type and field slope. The sediment loss data, for
example, show that sediment losses are influenced more by management practices
than by any other factor. Losses from a seed corn field, which was cultivated
several times, were over fifty times as great as those from an alfalfa field
which was cultivated very little. The loss from a dry bean field whose slope
was about half that of the corn and alfalfa fields was more than three times
the loss from the seed corn field. All three fields were on the same soil
series. The amount of water applied during an irrigation and the associated
stream size also affected sediment losses. Applying a given amount of water
with double the stream size resulted in approximately a two-fold increase in
11
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both surface runoff and sediment losses. Doubling both the amount of water
applied and the furrow stream size resulted in over a four-fold increase in
sediment losses.
Data from the 1974 study show that there was a net loss of total phos-
phorus and suspended solids from the fields where surface runoff occurred
(there was no surface runoff from the sprinkler-irrigated fields). The
coefficient of determination (r2) between the concentrations of total phos-
phorus and suspended solids was found to be 0.62. This indicates that most
of the total phosphorus loss is associated with the loss of suspended solids
and that cultural practices and physical conditions have very little effect
on total phosphorus losses.
There were net seasonal gains of nitrate nitrogen on all of the fields
studied. These gains ranged from 2.8 pounds per acre on a barley field to
15.2 pounds per acre on a hop field. Deep percolation losses on several of
the fields resulted in significant losses of nitrate nitrogen from the root
zones of these fields. Most of these losses were attributed to over irri-
gation and/or over fertilization.
Comparison of the budgets for a 200-acre farm which was assumed to be
representative of the area indicates that the net return per acre using a
gravity irrigation system is about $35 more than the return using a sprinkler
irrigation system. It was concluded, however, that the analysis may have
been biased towards gravity irrigation and that consideration of some of the
advantages of sprinkler irrigation over gravity irrigation would make
sprinkler systems more competitive from an economic standpoint.
Bondurant (1971) measured the quality of applied and runoff water from
surface irrigation of a 536-acre tract on silt loam soil in the Magic Valley.
He concluded that more nutrients were applied to the field in the irrigation
water than were removed in the runoff water. Carter e_t al_., (1974) tabulated
data on total salt, specific ion and fertilizer element concentrations in
the irrigation and drainage waters of the Twin Falls tract in the Magic
Valley. These data were helpful in delineating water quality differences
between surface return flows and subsurface drainage flows.
In connection with sediment pond design studies, Oliver (1974) and
Ballard (1975) measured sediment yields from beans, grain and potatoes grown
on silt loam soils in the Magic Valley. Ballard reported seasonal sediment
yields from potatoes of up to 37 tons per acre and sediment removal efficien-
cies of ponds from 85 to 95 percent. Brockway (1976) reported measured sedi-
ment yields and the results of studies to determine the sediment removal
efficiencies of ponds. He reported that from 82 to 91 percent of the sedi-
ment in the runoff from silt loam soils was removed. Corresponding phosphate
removal efficiencies ranged from 35 to 78 percent.
Bondurant et_al_., (1975) used flow frequency analysis procedures to
determine design flows for sediment ponds in drainageways. These studies in-
dicate that 80 percent of the total seasonal flow in return streams in
southern Idaho occurs at flow rates which are less than 50 percent of the
maximum flow rates in these streams.
12
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SECTION 5
STUDY AREAS
This study was conducted In two major irrigated areas in southern Idaho,
the Boise Valley in southwestern Idaho and the Magic Valley in southcentral
Idaho. Furrow irrigation is the prevalent method of applying water to crop-
lands in these two areas. On some farms, irrigation water is applied so that
there is little, if any, surface runoff and resulting pollutant, losses. On
others, however, the surface runoff and resulting sediment and other pollu-
tant losses are relatively high. Data were gathered in this study to deter-
mine the effectiveness and cost .impact of several methods for controlling
sediment and other pollutant losses from irrigated lands in the two study
areas. The purpose of this chapter is to provide information about the study
areas which will be helpful in interpreting these data.
BOISE VALLEY
For this report, the Boise Valley is considered to include the irrigated
area in the Boise River Basin from the city of Boise west to the Idaho-Oregon
border (Figure 1). Field investigations were conducted in this area at sites
located near the towns of Caldwell and Notus in Canyon County. Canyon County,
with about 88,000 hectares of land under irrigation, is one of the more impor-
tant agricultural counties in the state. Farming and food processing is an
important segment of this county's economy. In 1972, for example, farming
provided 20 percent of all personal income in the county and food processing
accounted for another 9 percent of all personal income. The sale of crops
and crop products accounted for 55 percent of the cash farm receipts in the
county in 1972 and 59 percent of the receipts in 1973. Livestock and live-
stock products accounted for the remainder of these receipts (Bollinger,
1975).
Geology and Soils
The Boise Valley lies in an upland plain of unconsolidated lacustrine and
fluvial materials deposited by the Boise and Snake Rivers. Terraces of these
materials rise stepwise above the Boise River. Relief within the Valley is
generally low. The lowland plain in the vicinity of Boise is about 810 meters
above mean sea level. In the vicinity of Caldwell, local basalt ridges rise
as much as 120 meters above the bottom land. The elevation of the valley
floor at its western edge is slightly less than 670 meters.
The soils in the area are highly variable and complex. Those over the
basalt ridges are generally quite shallow, while those over the lacustrine
deposits are generally quite variable in depth. Duripans in many of the soils
restrict the downward movement of water and plant roots. High water tables
13
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LEGEND
> Basin Boundary
County Lines
~~* Rivers
SCA'.E I* MILES
s
/
Figure 1. Map of the Boise River Basin.
-------
are common in many parts of the Valley.
Climate
The Boise Valley area has a dry, temperate climate which is characterized
by cool, wet winters and warm, dry summers. The mean annual temperature at
Boise is 10.4°C and there is an average of 172 days between killing frosts.
The average annual precipitation varies from about 150 millimeters (mm) in a
strip along the Snake River to over 300 mm in the northeastern part of the
Valley. The annual evaporation from open water surfaces in the area is about
840 mm.
Cropping and Irrigation Practices
Approximately 85 percent of the land in Canyon County is used, for irri-
gated crops. Census of Agriculture figures on the number and size of all
irrigated farms and irrigated farms with annual sales over $2,500 in Canyon
County are given in Table 1. The census includes many part-time and hobby
farms, many of which have annual sales of $2,500 or more.
The principal crops grown in the Boise Valley include sugarbeets, beans,
potatoes, corn, alfalfa, wheat and barley. Hops, onions, mint and a number
of seed crops are also grown in the Valley. Some of the area is used for
orchards. The number of hectares of the major field crops grown in Canyon
County is given in Table 2. Data from two sources are given for wheat,
barley and potatoes. Discrepancies in the data arise from estimation errors
and a difference in tabulation procedures. The Census of Agriculture tabu-
lates farm area according to the location of the farm headquarters, regardless
of whether or not the land actually lies within the same county. The Statis-
tical Reporting Service, on the other hand, attempts to show how much cropland
area is within a county's boundaries.
The surface water used for irrigation in the Boise Valley is'obtained
mainly from the Boise and Payette Rivers. A complex network of lined and
unlined canals is used to distribute the water to over 127,000 hectares of
land in organized irrigation districts in the area. Most of the farms in this
area are gravity irrigated, primarily through the use of siphon tubes and
furrow methods. Although sprinkler irrigation is practiced in the Valley, its
use is not very extensive at present. Surface and subsurface irrigation
return flows are collected by a complex network of open ditch drains. Many
of these drains return all or a portion of their flow to the delivery system
for reuse.
Water-use data for 23 irrigation districts in the Boise Valley show that
deliveries varied from 700 to 2,440 mm (2.3 to 8.0 acre-feet, per acre) in 1970
(Fitzsimmons et al., 1975). The average delivery was 1,300 mm (4.25 acre-
feet per acreJT The consumptive use requirements for the crops grown in the
districts ranged from 551 to 648 mm. The water-use efficiency (percentage
of water delivered to a district used consumptively by the crops grown in the
district) ranged from 24 to 84 percent. The overall average for the valley
in 1970 was 46 percent.
15
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TABLE 1. NUMBER AND SIZE OF IRRIGATED FARMS IN CANYON COUNTY
19691
19742
All Irrigated Farms
Number
Irrigated area (ha)
Average irrigated area per farm (ha)
Irrigated Farms With Sales of
Number
Irrigated area (ha)
Average irrigated area per farm (ha)
11969 Census of Agriculture
21974 Census of Agriculture, Preliminary
(Issued May, 1976)
2,033
87,916
43.2
$2,500 or More
1,594
84,508
53.0
Report, Canyon
1,837
84,888
46.2
1,419
82,220
57.9
County
TABLE 2. MAJOR FIELD CROPS GROWN IN CANYON COUNTY
Census of Agriculture1
Statistical Reporting2
Service
Crop
Alfalfa Hay
Sugarbeets
Wheat
Barley
Corn Silage
Potatoes
Alfalfa Seed
Dry Beans
Sweet Corn Seed
Corn Grain
Hectares Hectares
1969 1974 1969 1974
12,231
14,098
4,183
9,775
4,596
5,097
4,887
2,635
2,473
2,424
13,032
9,423
10,829 7,689
8,629 7,770
5,358
4,941 2,185
NA3
NA
NA
2,296
10,239
10,036
3,035
M969 Census of Agriculture and 1974 Census of Agriculture, Preliminary
Report, Canyon County (Issued May, 1976). Figures are for farms with
sales of $2,500 or more.
21976 Idaho Agricultural Statistics
3Data not available (NA)
16
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MAGIC VALLEY
The Magic Valley is generally considered to include the irrigated area
of the Snake River drainage in southcentral Idaho from the city of Bliss on
the west to Burley and Rupert on the east (Figure 2). It comprises all or
portions of the following counties: Cassia, Gooding, Jerome, Lincoln,
Minidoka and Twin Falls. Field investigations were conducted in this area
at sites located in Jerome and Twin Falls Counties.
Geology and Soils
Most of the land in the Magic Valley lies in an area designated as the
Snake River plain. Land north of the Snake River is underlain by the Snake
Plain aquifer. This aquifer, which consists of intercalated pyroclastic and
sedimentary materials, extends from Bliss eastward nearly to the eastern
border of the state. The Snake Plain aquifer is recharged by natural runoff
from northside streams, precipitation and deep percolation from irrigation
diversions from the Snake River. Well yields are large and the aquifer sup-
plies water for over 230,000 hectares of irrigated land. Land south of the
river slopes northward from foothills and is underlain by basalts and rhyo-
lites at varying depths.
Elevations in the Magic Valley vary from 1,150 meters above mean sea
level at Twin Falls to 1,387 meters at Hollister. Abrupt changes in the
local relief occur near volcanic buttes and cinder cones and along the Snake
River gorge. Near Twin Falls, the gorge is approximately 140 meters deep.
The major soils in the area are silt loam soils of loessal origin with
calcareous loamy subsoils. The silt loams are generally underlain by a
calcareous hardpan at a depth of 60 to 90 centimeters. This cemented layer
is permeable but it does restrict root penetration. Soils in the Gooding-
Wendell area north of the river generally range from sandy loams to loamy
sands. These soils are quite permeable and are highly susceptible to wind
erosion.
Climate
The Magic Valley, like the Boise Valley, has a dry, temperate climate.
The average annual precipitation at Twin Falls is 230 mm. It increases with
elevation to 260 mm north of the Snake River at Shoshone and to 300 mm south
of the river at Hollister. The mean maximum July temperature at Twin Falls
is 33° C. The mean minimum January temperature at this location is 7.5° C.
The average length of the growing season at Twin Falls is 133 days.
Irrigation and Cropping Practices
Irrigation commenced in the Magic Valley about 1910 with the construction
of mutual canal companies under the Carey Act and the 1902 Reclamation Act.
Water for approximately 197,000 hectares of irrigated land in the Valley is
diverted or pumped from the Snake River. Diversions for 1976 for each of the
irrigation districts in the Valley are given in Table 3. The locations of
these districts are shown in Figure 3. The portion of the A and B Irrigation
17
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\
00
*t^^^
i \
i \
/ V-.-T
\ IDAHO
_1.*L-1
; *
LOCATION MAP
LEGEND
County Lines
v ^ Rivers
*
(j
1
i.
i
J^t '
f
u "-
\J=z->-/
TV BLAINE ' r-
V
V
GOODING ft
i i^f
o\G/)^^Sjr LINCOLN
BIJSS Ky !
i^^ [ , | OShoshone
p^jGoodlnq L
t ' "^ ^ ^ h
A_ S/v/i,. Jerome MINIDOKA L y
P^^aS^JEROME *F* ^-fr
c T*F^r%^-t^ /
g\ 5~J if
TWIN (FALLS O] CASSIA K
tn 1 *S t
3| l jl
^ / s ^==ii
Figure 2. Map of the Magic Valley area.
-------
Shoshone
o
Figure 3. Major irrigation districts in the Magic Valley area.
-------
District (25,325 ha) is served by pumping from the Snake Plain aquifer.
Water is conveyed to farms in the Valley through unlined canals and is
distributed through headgates to individual farms or fields. Most of the
deliveries are measured at the headgates. Furrow irrigation, through the use
of siphon tubes, is the predominant method of applying water. The use of
gated pipe is increasing and sprinkler irrigation from groundwater or existing
surface sources is common. The use of pumpback systems is also increasing.
Aerial surveys show that the number of pumpback systems in the Twin Falls
Canal Company area increased from 13 in 1974 to 34 in 1976.
TABLE 3. IRRIGATION WATER DIVERSIONS FROM THE SNAKE RIVER FOR DISTRICTS IN
THE MAGIC VALLEY. 1976
District
Burley
A & B
Twin Falls Canal Company
Norths ide Canal Company
Milner Lowlife
Minidoka
Area
(ha)
19,420
5,875
82,012
64,736
5,450
29,130
Diversion
(1000 m3)
316,763
62,057
1,290,611
1,259,897
73,936
560,665
Unit Diversion
(mm)
1,631
1,055
1,573
1,945
1,356
1,923
Irrigation efficiences have been measured on some of the districts in the
Valley. Data reported by the U.S. Bureau of Reclamation (1971) for the A
Division of the A & B District indicate that on-farm irrigation efficiences
varied from 36 to 44 percent and that attainable efficiencies varied from 51
to 64 percent. Data reported by Claiborn and Brockway (1975) for the A & B,
Northside and Burley Districts indicate that the project efficiencies for
these districts were 42, 23 and 19 percent, respectively, in 1974. The esti-
mated on-farm irrigation efficiences were 62, 39 and 25 percent, respectively.
Drainage problems have occurred in the Twin Falls Canal Company area on
the south side of the Snake River. These have been corrected by installation
of subsurface drainage tunnels into the underlying basalts. Areas of
Minidoka County in the eastern part of the valley have high water tables.
The principal crops grown in the Magic Valley include sugarbeets, beans,
grain, alfalfa and potatoes. The sale and processing of crops is quite impor-
tant to the economy of this area. In Twin Falls County, for example, the sale
of crops accounted for 57 percent of the cash farm receipts in 1972 and 65
percent in 1973. These figures for Jerome County for 1972 and 1973 are 48
and 56 percent, respectively. Livestock and livestock products accounted for
the remainder of the cash farm receipts in each county (Bellinger, 1975). In
1972, farming provided 22 percent of the personal income generated in these
two counties and food processing generated another 5 percent.
20
-------
Figures from the Census of Agriculture on the number and average size of
the irrigated farms in Jerome County are presented in Table 4. Similar data
for Twin Falls County are given in Table 5. Data on the number of hectares
of the major field crops grown in Jerome and Twin Falls Counties are pre-
sented in Tables 6 and 7, respectively. Data from two sources are given for
wheat, barley and potatoes. As explained previously, discrepancies in the
data are probably due to differences in the tabulation procedures used by
the two agencies.
TABLE 4. NUMBER AND SIZE OF IRRIGATED FARMS IN JEROME COUNTY
19691 19742
All Irrigated Farms
Number 801 724
Irrigated area (ha) 49,958 49,648
Average irrigated area per farm (ha) 62.4 58.6
Irrigated Farms With Sales of $2.500 or More
Number 749 674
Irrigated area (ha) 49,465 49,282
Average irrigated area per farm (ha) 66.0 73.1
M969 Census of Agriculture
21974 Census of Agriculture, Preliminary Report, Jerome County
(Issued May, 1976)
TABLE 5. NUMBER AND SIZE OF IRRIGATED FARMS IN TWIN FALLS COUNTY
19691 19742
All Irrigated Farms
Number 1,509 1,405
Irrigated area (ha) 100,790 9*,704
Average irrigated area per farm (ha) 66.8 67.4
Irrigated Farms with Sales of $2.500 or More
Number 1,387 1,276
Irrigated area (ha) 99,892 93,897
Average irrigated area per farm (ha) 72.0 73.6
M969 Census of Agriculture
21974 Census of Agriculture, Preliminary Report, Twin Falls County,
(Issued May, 1976)
21
-------
TABLE 6. MAJOR FIELD CROPS GROWN IN JEROME COUNTY
Census of Agriculture1
Statistical Reporting2
Service
Crop
Alfalfa Hay
Wheat
Dry Beans
Potatoes
Barley
Sugarbeets
Hectares
1969
13,005
4,230
7,917
4,253
2,940
3,066
1974
13,346
10,837
NA3
4,790
2,296
879
1969
4,816
4,452
3,238
Hectares
1974
9,753
5,342
3,238
M969 Census of Agriculture and 1974 Census of Agriculture, Preliminary
Report, Jerome County (Issued May, 1976). Figures are for farms with
sales of $2,500 or more.
21976 Idaho Agricultural Statistics
3Data not available (NA)
TABLE 7. MAJOR FIELD CROPS GROWN IN TWIN FALLS COUNTY
Crop
Alfalfa Hay
Dry Beans
Wheat
Barley
Sugarbeets
Potatoes
Mixed Grain
Field & Seed Peas
Census
1969
21,917
21,345
10,255
5,097
9,343
3,000
4,757
3,268
of Agriculture1
Hectares
1974
23,690
24,822
15,716
5,052
3,323
5,968
1,911
3,389
Statistical Reporting2
Service
1969
11,250
5,747
3,278
Hectares
1974
14,124
4,937
6,677
M969 Census of Agriculture and 1974 Census of Agriculture, Preliminary
Report, Twin Falls County (Issued May, 1976). Figures are for farms
with sales of $2,500 or more.
21976 Idaho Agricultural Statistics
22
-------
SECTION 6
BOISE VALLEY FIELD INVESTIGATIONS
The main purpose of the field investigations conducted in the Boise
Valley was to evaluate the effects of management practices and sediment re-
moval systems on the quality and quantity of the surface runoff from irrigated
fields. On-farm sites were instrumented and monitored so that the effects of
different irrigation, cropping and tillage practices, as well as other fac-
tors, could be determined. In addition, sediment removal devices installed
at the on-farm sites were evaluated to determine their effectiveness in
removing sediment and other pollutants from surface runoff. One of these
devices, a small on-farm pond, is shown under construction in Figure 4. Two
large district-type sediment retention ponds, such as the one shown in Figure
5, were also monitored to determine their effectiveness in improving the
quality of return flows from large irrigated areas.
A total of nine on-farm sites were monitored during the 1975 and 1976
irrigation seasons. Field, crop and other data for these sites are given in
Table 8. Sites 2, 3 and 4 were located adjacent to each other in a large
field at the CaIdwe11 Research and Extension Center. Site 1 was located in a
cooperator's field which is adjacent to the Caldwell Center. Site 9 was loca-
ted at the Parma Research and Extension Center. The rest of the sites (Sites
5, 6, 7 and 8) were located in cooperators1 fields near Notus. Descriptions
of the soils at each site are given in Tables 9 and 10.
The surface runoff from all but one of the field sites was diverted
through one or more sediment retention devices. In 1976, for example, small
T-shaped basins (T-slots) were dug in the tailwater ditch at the lower end
of Site 1. One of these basins is shown in Figure 6. The runoff from Site 1
flowed through the T-slots before it entered the sediment retention pond at
this site. In 1975, the surface runoff from Sites 3 and 4 passed through a
grass buffer strip before it entered a sediment pond. A densely seeded strip
of barley (Figure 7) was used as a buffer strip at Sites 2, 3 and 4 in 1976.
Several different practices were evaluated at each study site to deter-
mine their effects on the quality of the surface runoff leaving the sites.
These included irrigation scheduling, furrow stream size, run length, culti-
vation practices and fertilization practices. Additional and/or more strin-
gent management practices were imposed on the sites at the Caldwell and Parma
Centers (Sites 2, 3, 4 and 9.) These practices included preplant irrigations;
careful management of the furrow stream size in relation to run length, slope
and soil conditions; cutback streams to minimize runoff; and proper irrigation
scheduling based on soil moisture readings and climatic data.
23
-------
Figure 4. On-farm sediment pond under construction.
Figure 5. Large sediment retention pond located in
a natural drainageway near Wilder, Idaho,
24
-------
ro
en
Site
1
2
3
4
5
6
7
8
9
Year
1975
1976
1975
1976
1975
1976
1975
1976
1975
1976
1975
1976
1975
1976
1975
1976
1976
u
Crop
Corn
Corn
Corn
Corn
Corn
Corn
Corn
Corn
Hops
Hops
Seed Alfalfa
Seed Alfalfa
Barley
Seed Alfalfa
Sugarbeets
Barley
Corn
1I-.I-L. w« u^-.
Area
(ha)
1.76
1.76
1.89.
1.78
1.84
1.74
1.76
1.66
14.45
14.45
8.23
8.23
6.76
6.76
2.00
2.00
0.89
Length
(m)
237
237
345
345
327
327
321
321
383
383
386
386
386
386
386
386
187
Average
Slope
(%)
2.6
2.6
2.7
2.7
2.9
2.9
2.9
2.9
1.1
1.1
1.1
1.1
1.1
1.1
0.7
0.7
1.2
Sediment
Retention
Device(s)
Small Pond
T-Slots & Smal
Sediment Pond
Grain Strip &
Grass Strip &
Grass Strip &
Grass Strip &
Grain Strip &
Sediment Pond
Sediment Pond
Sediment Pond
Sediment Pond
Sediment Pond
Sediment Pond
Sediment Pond
Sediment Pond
None
1 Pond
Pond
Pond
Pond
Pond
Pond
-------
TABLE 9. DESCRIPTION OF THE SOILS FOUND ON THE BOISE VALLEY STUDY SITES
Site
Soil Series
General Characteristics
Purdam Silt
Loam
2,3,4
Purdam Silt
Loam, Vickery-
Marsing Silt
Loams
Greenleaf-Owyhee
Silt Loams,
Power-Purdam
Silt Loams
6,7,8,9
Greenleaf-Owyhee
Silt Loams,
Medium textured soils that have a weakly
cemented duripan at a depth of 50 to 100
centimeters. These soils formed in a
moderately deep loess mantle over medium
textured or moderately coarse textured
alluvium or lacustrine sediments.
These sites are a complex of Purdam and
Vickery-Marsing silt loams. Vickery soils
differ from Purdam soils mostly by having
an indurated or strongly cemented layer
at a depth of 50 to 100 centimeters
instead of a weakly cemented duripan.
Marsing soils are similar to the Purdam
and Vickery soils except they do not have
a duripan or cemented layer.
This site is a complex of soil series.
The Greenleaf series consists of medium
textured and moderately fine textured,
well drained soils formed in laminated
medium textured lacustrine material and
old alluvium that is overlain by loess in
places. Greenleaf soil has a B2t layer
from about 20 to 35 centimeters which is
a light silty clay loam. Owyhee series is
similar to Greenleaf series only without
the heavier textured subsoil. Power and
Purdam soils are similar except the Power
soil lacks the duripan at 50 to 100 centi-
meters .
These sites are a complex of soil series.
The Greenleaf-Owyhee series is the same
as described for Site 5. Nyssaton silt
loam has similar characteristics on the
surface as the Owyhee series but has an
Ap, Clca, C2ca horizon sequence instead
of the Ap, B, Clca horizon sequence of
the Owyhee series.
26
-------
SV «^«
Figure 6. T-slot installed at Site 1 in 1976.
Figure 7. Vegetated buffer strip seeded at the
lower ends of Sites 2, 3 and 4 in 1976.
27
-------
TABLE 10. PARTICLE SIZE DISTRIBUTION OF SURFACE LAYER (TOP 30 CENTIMETERS)
OF SOILS FROM THE BOISE VALLEY STUDY SITES
SiteTotal SandTotal SiltTotal ClayTexture Class
1
2,3,4
5
6,7,8,9
25.11
21.85
26.95
11.07
62.65
63.55
60.20
73.69
12.24
14.60
12.85
15.24
Silt Loam
Silt Loam
Silt Loam
Silt Loam
All study sites were instrumented so that water, nutrient and total sus-
pended solids balances could be established for each site and sediment pond.
Water measurement devices equipped with stage recorders were installed so
that all water entering and leaving each site and sediment pond could be con-
tinuously measured. Two of these installations are shown in Figures 8 and 9.
A modification of the procedure presented by Jensen et_ al_., (1971) was used
to estimate evapotranspiration on a daily basis for the crop on each site.
Samples of head and tailwater flows were taken at frequent intervals
during each irrigation set. Tailwater samples were usually taken at one-hour
intervals as runoff commenced and at two to four-hour intervals during the
remainder of the set. All samples were immediately frozen for storage and
transport to the laboratory for analysis.
The water samples were analyzed for nitrate, ammonia, organic nitrogen,
soluble (ortho) phosphorus, total phosphorus, total suspended solids, turbi-
dity, electrical conductivity and pH. A Technicon Autoanalyzer was used for
determining the nitrogen forms. Samples were filtered through 0.45 y milli-
pore filters to determine soluble phosphorus and digested with sulfuric acid
and ammonium persulfate for total phosphorus. Phosphorus was determined
colorimetrically in the filtrate and digestion mixture by the ascorbic acid-
molybdenum blue method. Suspended solids were measured by drying and weighing
the residue obtained after passing an aliquot of sample through a 0.45 v
millipore filter. Turbidity was obtained using a Model 104 Ecolab Turbidi-
meter. Electrical conductivity was determined with a Solu-Bridge and pH with
a glass electrode.
Water, suspended solids and nutrient balances were established for each
site for the 1975 and 1976 irrigation seasons. Balances were also established
for each irrigation and each set within an irrigation.
MANAGEMENT PRACTICES
Water, nutrient and sediment losses from the study sites were affected
by the water management and cultural practices used at each site. Specific
practices and other factors evaluated in this study included furrow stream
size, irrigation scheduling, alternating furrows, preplant irrigation,
seasonal changes, tillage practices and crops grown.
28
-------
Figure 8. Flume and recorder used to obtain a
continuous record of the flow onto a
study site.
fy
-
Figure 9. Flume and automatic sampler used to
monitor flow from a site.
29
-------
Furrow Stream Size
The plots at Sites 2, 3 and 4 were irrigated five times during the 1976
irrigation season with different sizes of furrow streams. Stream size and
pollutant loss data for each site are given in Table 11. A stream of 0.767
liters per second was used to irrigate Site 2 during the first three irriga-
tions. This stream was reduced to approximately 0.6 liters per second during
the last two irrigations to limit runoff. At Site 3, the furrow stream was
cut back to one-half its initial size after 12 hours during the first three
irrigations. During the last two irrigations, the furrow stream was reduced
to approximately 0.6 liters per second but was not cut back. A stream of
approximately 0.4 liters per second was used to irrigate Site 4. This stream
had to be increased to over 0.6 liters per second during the last two irri-
gations to get the wetting front to advance properly.
The sediment loss during the first irrigation of the season is usually
greater than it is during subsequent irrigations (Mech and Smith, 1967).
This was the case for Sites 2 and 3. However, the sediment loss from Site 3
(with cutback) was almost one-third less than the loss from Site 2 (without.
cutback) during the first irrigation. The sediment losses from both sites
were much less during the last four irrigations than they were during the
first irrigation. The seasonal totals (Table 12) show that the net sediment
loss from Site 3 (with cutback) was over 16 percent less than the net loss
from Site 2 (without cutback). The use of a small stream size on Site 4
resulted in a net gain of sediment on this plot during the first three irri-
gations. However, the sediment losses during the last two irrigations were
nearly the same as those from the other two sites. The overall effect of
using a reduced stream size during the first three irrigations is shown by
the seasonal total which indicates a net sediment retention of over 1,100
kg/ha on this plot.
The runoff from all three plots was sampled after it had passed through
a vegetated buffer strip and had flowed to the sampling point in a ditch
which had a slope of 0.5 percent. As a result, a portion of the sediment
retention shown for these sites occurred in the buffer strip and in the
drainage ditch.
Total phosphorus losses from Sites 2 and 3 were minimal. The net reten-
tion of total phosphorus on Site 4 is related to the net sediment retention,
since total phosphorus losses are associated with sediment losses
(Fitzsimmons e_t al_., 1972 and Naylor e£ aK, 1976). The net retention of
nitrate at all three sites was due to the fact that nitrate moves Into the
soil with the irrigation water. Similar results have been obtained at other
sites in the Boise Valley (Busch e_t al_., 1972 and Fitzsimmons et al_., 1975).
Although reduced stream sizes resulted in significant reductions in pol-
lutant losses from Sites 3 and 4, the overall irrigation efficiencies for the
plots did not vary greatly. The data in Table 13 show that approximately the
same amount of water was applied to each of the three plots; however, the
amounts lost to surface runoff and deep percolation varied considerably. The
water lost to deep percolation could be carrying soluble materials such as
nitrate-nitrogen below the root zone.
30
-------
TABLE 11. RESULTS OF THE BOISE VALLEY FURROW STREAM SIZE STUDY. 1976
Site
2
3
4
2
3
4
2
3
4
2
3
4
2
3
4
Irrigation
1
1
1
2
2
2
3
3
3
4
4
4
5
5
5
Set
Length
(hr)
24
36
48
24
36
24
24
36
48
24
24
24
24
24
24
Stream
Size
(1/s)
0.767
0.767, 0.3841
0.396
0.767
0.767, 0.384
0.407
0.767
0.767, 0.384
0.407
0.599
0.599
0.609
0.599
0.600
0.643
Net Sediment
Loss
(kg/ha)
2456
1647
-6562
395
744
-508
183
155
-140
200
142
69
24
105
123
Net Total
P Loss
(kg/ha)
1.42
1.36
-0.17
0.04
0.60
-0.06
-0.06
0.29
-0.19
0.15
0.01
-0.07
-0.03
0.0
0.01
Net Nitrate
Loss
(kg/ha)
0.09
0.07
-0.18
-0.26
-0.15
-0.33
-0.37
-0.32
-0.35
-0.06
-0.20
-0.45
-0.50
-0.37
-0.40
Stream was cutback to smaller flow rate after 12 hours.
2Negative numbers indicate net gains.
-------
TABLE 12. SEASONAL TOTALS FOR THE BOISE VALLEY FURROW STREAM SIZE STUDY,
1976
Net Sediment
Site Loss
(kg/ha)
2 3,258
3 2,793
4 -1,112
Net Total
P Loss
(kg/ha)
1.52
2.26
-0.48
Net Nitrate
Loss
(kq/ha)
-1.101
-0.97
-1.71
Negative numbers indicate net gains
TABLE 13. WATER BALANCE RESULTS FOR THE BOISE VALLEY FURROW STREAM SIZE
STUDY, 1976
Site
2
3
4
Water
Applied
(mm)
802
692
749
Surface
Runoff
(mm)
218
179
125
Deep
Percolation
(mm)
216
146
257
Water-Use1
Efficiency
(%)
52
61
56
Percentage of water applied going to consumptive use
An in-depth study of a well-managed cutback irrigation system was carried
out at Site 9 in 1976. Two adjacent plots were simultaneously irrigated five
times throughout the season. The control plot was irrigated using constant
stream sizes for 24-hour irrigation sets. The stream size in the cutback
system was reduced an average of five times during each 24-hour set to limit
the runoff per furrow to less than 0.041 liters per second (1/s). A summary
of the initial and final stream sizes for each system is shown in Table 14.
The data in Table 14 also show that the cutback plot received 52 percent
of the amount of water applied to the control plot. The resulting water-use
efficiency of the cutback system was almost twice that of the non-cutback
system.
Careful management of the cutback system reduced the amounts of pollu-
tants lost from the cutback plot. As indicated by the data in Table 15, the
net sediment loss from the cutback plot was less than 7 percent of the loss
from the control or non-cutback plot. The net loss of total phosphorus from
the cutback plot was negligible. Both plots showed a similar net gain of
nitrate-nitrogen because approximately the same amount of water was infiltered
32
-------
TABLE 14. FLOW AND WATER-USE DATA FOR THE FURROW CUTBACK STUDY AT SITE 9, 1976
co
CO
Irrigation
Number
1
2
3
4
5
Totals
Averages
Stream
Cutback
Initial
0.593
0.562
0.498
0.500
0.473
0.525
Final
0.158
0.189
0.177
0.211
0.183
0.184
Size (1/s)
Non-Cutback
Initial
0.347
0.347
0.517
0.505
0.461
0.435
Final
0.322
0.322
0.511
0.511
0.429
0.419
Water Applied (mm)
Cutback
111
106
106
no
101
534
Non-Cutback
151
160
252
254
217
1,034
Water-Use Efficiency U)1
Cutback
81
74
81
77
76
78
Non-Cutback
65
59
38
28
27
41
Percentage of water applied going to consumptive use
-------
TABLE 15. NET SEDIMENT, PHOSPHORUS AND NITRATE LOSSES FROM CUTBACK AND NON-
CUTBACK PLOTS AT SITE 9, 1976
Net Sediment Loss
Irrigation Cutback
Number (kg/ha)
1 411
2 388
3 81
4 34
5 1
Totals 915
Non-Cutback
(kg/ha)
1,603
3,637
5,230
2,327
737
13,534
Net Total P Loss
Cutback Non-Cutback
(kg/ ha) (kg/ha)
0.10
0.27
-0.08
-0.14
-0.08
0.07
0.96
2.70
3.13
0.99
0.47
8.25
Net Nitrate Loss
Cutback
(kg/ha)
-0.76
-0.69
-1.19
-0.95
-0.80
-4.39
Non-Cutback
(kg/ ha)
-0.731
-0.77
-1.79
-0.51
-0.38
-4.18
Negative numbers indicate net gains
into each plot during the season.
During the second irrigation, the initial rate of runoff from the cut-
back plot was approximately the same as that from the control plot. However,
it soon dropped to a much lower level as shown by the data plotted in Figure
10. As a result, the sediment concentration in the outflow dropped after an
initial peak (Figure 11). The plot in Figure 12 shows that there was little
additional loss of sediment from the cutback plot after 120 minutes of run-
off; whereas, the loss from the control plot increased steadily during the
second irrigation.
Irrigation Scheduling
Irrigation scheduling can have an effect on sediment and nutrient losses
from a field as well as an effect on crop yields (Busch e_tal_., 1972). If a
field is over-irrigated or irrigated too frequently, the resulting surface
runoff will be excessive and will carry excessive amounts of sediment and
other pollutants from the field. Reducing the number of irrigations and the
amount of water applied will usually reduce the losses from a particular
field. This was the case for Site 1. The number of irrigations at this site
was reduced from eight in 1975 to six in 1976, partially as a result of a
15 percent decrease in the consumptive use requirements of the crop. As
shown in Table 16, reducing the number of irrigations resulted in a 21 percent
reduction in the amount of water applied, a 31 percent reduction in the amount
of surface runoff, and a 25 percent reduction in the net amount of sediment
lost from the plot.
The water-use efficiences (percentage of water applied used to meet the
consumptive use requirements of the crop) were quite low both years. However,
these efficiencies are about as high as can be expected for a furrow system
34
-------
15
o
0>
10
LJ
5
tr
o
CUTBACK TREATMENT
NON-CUTBACK TREATMENT
30 60 90
TIME (minutes x IO'1)
120
Figure 10. Rate of runoff from Site 9 during the
second irrigation in 1976.
150
CM ISO
b
o»
£100
<
a:
LJ
o
o
50
CUTBACK TREATMENT
NON-CUTBACK TREATMENT
±
30 60 90
TIME (minutes x ICT1)
120
150
Figure 11. Sediment concentration in the surface
runoff from Site 9 during the second
irrigation in 1976.
35
-------
CUTBACK TREATMENT
-- - NON- CUTBACK TREATMENT
X
CO
to
=
S .f
CO /
y
L
30 60 90 \2.0 150
TIME (minutes x 10-')
Figure 12. Sediment loss from Site 9 during the
second irrigation in 1976.
36
-------
TABLE 16. EFFECTS OF NUMBER OF IRRIGATIONS ON WATER AND SEDIMENT LOSSES
Year
1975
1976
Number
of Irri-
gations
8
6
Consump-
tive Use
(mm)
510
432
Water
Applied
(mm)
1,270
1,000
Water-Use1
Efficiency
(%)
40.1
43.2
Surface
Runoff
(mm)
376
261
Net Sedi-
ment Loss
(kg/ ha)
26,565
19,923
1Percentage of water applied going to consumptive use
operating under the soil, slope, run length, and other conditions present at
this site. They could be increased by the installation and use of a pump-
back system.
Prep!ant Irrigation
Many irrigators apply a preplant irrigation regardless of the soil mois-
ture status. In order to evaluate the effects of this practice, preplant
irrigations were applied to Sites 2, 3 and 4 ten days before the 1976 crop
was planted. Water and sediment loss data for these irrigations are summa-
rized in Table 17. The data show that a large amount of sediment was lost
from each plot even though the runoff was not excessive. Over one-third of
the seasonal sediment loss from Sites 2 and 3 occurred during the preplant
irrigation. The amount of sediment lost from Site 4 during the preplant irri-
gation was nearly equal to the net amount retained on that plot during the
remainder of the irrigation season (see Table 12). As a result, the loss
during the preplant irrigation (1,188 kg/ha) was over fifteen times the net
loss (76 kg/ha) from this site.
Tillage Practices
Compacted and Non-Compacted Furrows - In planting and cultivating fields
in the Boise Valley, it is a common practice to compact every other furrow
with planting and tillage equipment. The alternate furrows are never driven
upon during the growing season and are, therefore, not compacted as much as
the other furrows. This difference in compaction can greatly affect the
rates of infiltration and runoff from alternate furrows.
In 1975, tests were conducted on Sites 2, 3 and 4 during the last three
irrigations to determine differences in infiltration, runoff and sediment
losses from alternate non-compacted furrows compared with compacted furrows.
The results of this study are summarized in Table 18. As can be seen, there
was essentially no runoff from the non-compacted furrows while 43 percent of
the applied water ran off the compacted furrows. Due to the minimal amount
of runoff, there was actually a net sediment gain in the non-compacted
furrows.
Although the runoff and sediment losses from the non-compacted furrows
were minimal, high infiltration rates in these furrows resulted in excessive
37
-------
TABLE 17. EFFECTS OF PREPLANT IRRIGATIONS ON WATER AND SEDIMENT
LOSSES, 1976
Site
2
3
4
Water
Preplant
Irrigation
(mm)
41
52
69
Runoff
Percent of
Seasonal
Runoff
16
23
36
Net
Preplant
Irrigation
(kq/ha)
1,773
1,657
1,188
Sediment
Seasonal
Loss
(kg/ha)
5,031
4,450
76
Loss
1 Percent of
Seasonal
Loss
35
37
1,563
Seasonal total includes preplant irrigation loss
TABLE 18. COMPARATIVE RESULTS OF IRRIGATING ALTERNATE COMPACTED
AND NON-COMPACTED FURROWS. 1975
Water Applied Surface Runoff Net Sediment Loss
Furrow Type
Compacted1
Non-Comp'acted2
(mm)
76
132
(%)
43
6
(kg/ha)
179
-1113
Values given are averages for four irrigation sets
2Values given are averages for five irrigation sets
Negative number indicates a net gain
amounts of deep percolation and a low water distribution efficiency. Approxi-
mately 38 percent of the water applied in the non-compacted furrows was lost
to deep percolation. Soluble nutrients were undoubtedly carried below the
root zone by this water. The rate of advance in many of the non-compacted
furrows was so low that the water did not reach the ends of the furrows
during an irrigation set.
Number of Operations - Of all the sites studied in 1975 and 1976, only
four were tilled following the first irrigation. Site 1 was tilled once
following the first irrigation in both 1975 and 1976. Site 5 was tilled
after both the first and second irrigations in 1975 and after the first three
irrigations in 1976.
The additional tillage operations did not significantly increase the
amount of sediment lost from Site 5. In 1975, the amount of sediment lost
during the fifth and last irrigation was twice as great as that lost during
any one of the first four irrigations. In 1976, the largest loss occurred
during the fourth of five irrigations.
38
-------
The sediment loss from Sites 2, 3 and 4, where the soil and slope were
similar to the soil and slope at Site 1, decreased after the first irriga-
tion. This difference may be attributed to the fact that Sites 2, 3 and 4
received no tillage following the first irrigation. The reason that addi-
tional tillage had a negative effect on Site 1 and not on Site 5 may be
attributed to differences in soils and slopes at the two sites (see Tables 9
and 10).
Type of Tillage Equipment - Different types of tillage equipment were
used in forming furrows in the seed alfalfa field (Site 6) during the two
study years. In 1975, a common ditcher shovel was used to form the furrows.
In 1976, a power-driven rotary-type tiller with v-shaped packer wheels was
used. Comparisons of the 1975 and 1976 data show that the average sediment
concentrations decreased from 2,845 mg/1 to 1,278 mg/1 for the first irriga-
tion and from 2,173 mg/1 to 979 mg/1 for the second irrigation. The 1976
concentrations were 45 percent of the 1975 concentrations for both irriga-
tions. This difference indicates that the furrows formed with the packer
wheels were more stable and erosion resistant than those formed with the
ditcher shovel.
The results presented thus far show that management practices associated
with different crops affected sediment and other pollutant losses from the
study sites. The concentrations and amounts of pollutants lost from Sites 1
through 8 during the 1975 and 1976 growing seasons are summarized by crop in
Tables 19 and 20. The values given are averages for all fields for each crop.
In some cases, the range of values 1s quite large.
The data in Table 19 indicate that the average concentrations of nitrate
and ammonia nitrogen and soluble phosphorus in the runoff from all sites are
quite low. The higher values for organic nitrogen and total phosphorus may
be due to the fact that losses of these constituents are associated with
sediment losses. Sediment concentrations and losses point to the fact that
sediment is the main pollutant in the runoff leaving irrigated fields in the
Boise Valley. Although the average concentration of the sediment in the run-
off leaving the hop fields was less than that in the runoff from the barley
fields, the net loss was greater due to more surface runoff from the hops.
The effects of different crops on adjacent fields and of different crops
on the same fields were studied at Sites 6, 7 and 8. In 1975, the crops
grown at the three sites were seed alfalfa, barley and sugarbeets. Average
concentrations and net loss of nitrate-nitrogen, total phosphorus and sedi-
ment from the three sites are tabulated in Tables 21 and 22. The large net
loss of sediment from the sugarbeet field can be attributed to the large
amount of water lost to surface runoff from that field, a management practice
which is related to a particular crop.
After the barley was harvested from Site 7 1n 1975, a crop of seed
alfalfa was established on this site. Barley was planted on Site 8 in 1975.
The data* in Table 23 show that the amount of water applied to Site 7
increased in 1976 as did the amounts of surface runoff and pollutants lost.
39
-------
TABLE 19. AVERAGE CONCENTRATIONS OF POLLUTANTS IN THE SURFACE RUNOFF
Crop
Corn
Sugarbeets
Barley
Hops
Seed Alfalfa
Number
of
Fields
8
1
2
2
3
Nitrate
Nitrogen
(mg/1)
1.34
0.89
0.82
0.38
0.20
Ammonia
Nitrogen
(mg/1)
0.08
0.05
0.04
0.07
0.04
Organic
Nitrogen
(mg/1)
5.16
3.31
2.90
3.52
2.05
Soluble
Phosphorus
(mg/1)
0.10
0.16
0.16
0.38
0.09
Total
Phosphorus
(mg/1)
2.53
3.60
1.63
1.97
1.28
Sediment
(mg/1)
4,006
2,412
2,393
1,757
1,533
Averages for each
Pollutant
1.02
0.07
4.33
0.15
2.39
3,193
-------
TABLE 20. AVERAGE NET LOSSES OF POLLUTANTS FROM SITES 1 THROUGH 8. 1975 AND 1976
Crop
Corn
Sugarbeets
Barley
Hops
Seed Alfalfa
Averages for each
Number
of
Fields
8
1
2
Z
3
pollutant
Nitrate -
Nitrogen
(kg/ha)
7.87
-3.59
0.01
-0.30
-0.54
3.56
Ammonia
Nitrogen
(kq/ha)
-0.291
-0.37
-0.07
0.10
-0.08
-0.17
Organic
Nitrogen
(kq/ha)
8.42
-3.17
-1.09 -
4.65
-1.17
4.28
Soluble
Phosphorus
(kq/ha)
0.10
-0.16
-0.02
0.27
-0.11
-0.05
Total
Phosphorus
(kq/ha)
6.37
9.63
0.45
0.86
0.35
4.00
Sediment
(kg/ha)
8,132
6,636
1,819
4,403
1,228
5,489
Negative numbers indicate net gains
-------
TABLE 21. AVERAGE CONCENTRATIONS OF POLLUTANTS IN THE SURFACE RUNOFF
FROM SITES 6, 7 AND 8, 1975
Site Crop
6 Seed Alfalfa
7 Barley
8 Sugarbeets
Nitrate-
Nitrogen
(mg/1)
0.47
0.64
0.90
Total
Phosphorus
(mg/1)
1.37
2.31
3.63
Sediment
(mg/1)
1,534
2,408
2,433
TABLE 22. FLOW AND POLLUTANT LOSS DATA FOR SITES 6, 7 AND 8. 19751
Site
6
7
8
Crop
Seed Alfalfa
Barley
Sugarbeets
Water
Applied
(mm)
455
385
1,235
Surface
Runoff
(%)
18
18
27
Nitrate-
Nitrogen
Loss
(kg/ha)
-1.502
-1.08
-3.59
Total
Phosphorus
Loss
(kg/ha)
0.59
0.37
9.63
Sediment
Loss
(kg/ha)
926
1,142
6,691
1Pollutant loss values are net values
2Negative numbers indicate net gains
TABLE 23. COMPARATIVE FLOW AND POLLUTANT LOSS DATA
FOR SITES 7 AND 8, 1975 AND 19761
Site
7
7
8
8
Year
1975
1976
1975
1976
Crop
Barley
Seed Alfalfa
Sugarbeets
Barley
Water
Applied
(mm)
385
557
1,235
672
Surface
Runoff
(%)
18
18
27
20
Nitrate-
Nitrogen
Loss
(kg/ha)
-1.082
0.01
-3.59
i.n
Total
Phosphorus
Loss
(kg/ha)
0.37
0.85
9.63
0.54
Sediment
Loss
(kg/ha)
1,142
1,619
6,691
2,496
Pollutant loss values are net values
2Negative numbers indicate net gains
42
-------
Except for nitrate-nitrogen, the converse was true for Site 8.
SEDIMENT RETENTION DEVICES
Vegetated buffer strips and/or sediment retention ponds were installed
at the lower ends of Sites 1 through 8. These devices were evaluated in con-
junction with evaluations of the management practices used at these sites.
Two large sediment ponds located in major wasteways were also evaluated.
These evaluations are discussed in the following paragraphs.
Vegetated Buffer Strips
In 1975, a sodded grass strip which was 1.83 m wide and 61.0 m long was
laid in the drainge ditch at the lower end of Site 3 as shown in Figure 13.
The runoff from Site 3 entered the strip from the side while that from Site 4
entered the strip from the upper end and ran the entire length of the strip.
Samples of the runoff from both sites were collected downstream from the strip.
The runoff from the control plot, Site 2, did not run through the strip.
Dense bluegrass in the strip was well established and approximately 15 cm
high just prior to the first irrigation. The strip did an excellent, job of
reducing the velocity of flow in the drain ditch during the first irrigation.
As a result, it was completely inundated with sediment and was not effective
during the remainder of the irrigation season. The effectiveness of the strip
during the first irrigation is shown by the data in Table 24. About 47 per-
cent of the net seasonal sediment loss from Site 2 (without strip) occurred
during the first irrigation; whereas, only about 19 and 8 percent of the
losses from Sites 3 and 4 (with strip), respectively, occurred during the
first irrigation. Due to the ineffectiveness of the grassed strip, the net
losses during the last four irrigations were essentially the same for all
three sites.
In 1976, a 2.44 m wide strip of barley was seeded across the lower ends
of the three plots at a seeding rate of approximately 100 kg/ha. The grain
was well established when the irrigation season was started and was effective
in retarding the furrow runoff and causing sediment to settle out of the run-
off before it entered the drain ditch running parallel to the strip. Pictures
of the strip following the first irrigation and midway through the irrigation
season are shown in Figures 14 and 15, respectively. Sediment retained by
the strip is shown in Figure 16. The effectiveness of this strip is shown by
the data presented in Table 24. Site 2 was irrigated nearly the same in 1976
as it was in 1975. Most of the difference in the total net sediment loss
(3258 kg/ha in 1976 as opposed to 7038 kg/ha in 1975) can be attributed to the
effect of the buffer strip used in 1976. Although the net loss from Site 2
during the first irrigation in 1976 was nearly as great as the loss during the
first irrigation in 1975, use of the grain strip resulted in a marked decrease
in the net sediment losses during the last four irrigations. The data in
Table 24 indicate that the grain strip used in 1976 was more effective than
the grassed strips used on Sites 3 and 4 in 1975.
43
-------
Figure 13. Sod buffer strip being installed in 1975.
_ !
'
1
' s
-
'S*~ <
"V*
«
Figure 14. Grain buffer strip following the first
irrigation in 1976.
44
-------
Figure 15. Grain buffer strip midway through the
1976 irrigation season.
!
1
Figure 16. Sediment deposited from furrow runoff backed
up by grain buffer strip in 1976.
45
-------
TABLE 24. EFFECTS OF VEGETATED BUFFER STRIPS ON SEDIMENT LOSSES
Strip
Site Year Type
2 1975 none
3 1975 grass
4 1975 grass
2 1976 grain
Irrigation
Number (s)
1
2-5
total
1
2-5
total
1
2-5
total
1
2-5
total
Net Sediment
Loss
(kg/ha)
3,312
3,726
7,038
740
3,149
3,889
367
4,196
4,563
2,456
802
3,258
Sediment Retention Ponds
Sediment retention ponds were used to remove a portion of the sediment
and phosphorus from the surface runoff from the study sites. In 1976, six
small T-shaped basins (T-slots) similar to the one shown in Figure 17 were
also installed at Intervals of about 20 meters in the drain ditch upstream
from the sediment pond at Site 1. The T-slots were dug with a backhpe with
the top of the "T" perpendicular to the drain ditch. Four of the T-slots had
a capacity of approximately 2 m3 while the other two had a capacity of about
0.5 m3. The six T-slots were filled with sediment during the first irrigation
(Figure 18) and were ineffective thereafter. The effectiveness of the T-slots
and pond during the first irrigation is shown by the data presented in Table
25.
The sediment retention ponds were quite effective in reducing the net
sediment losses from the study sites. Seasonal sediment balances for the
field sites and ponds are given in Table 26. The sediment removal efficiency
of the ponds ranged from 40 to 82 percent. One reason for the low removal
efficiency of the pond at Site 1 in 1975 was the small size of this pond. It
was essentially filled with sediment by the first two irrigations in 1975.
With the added retention of the T-slots in 1976, the pond did not fill with
sediment until after the third irrigation. Pictures of the pond prior to and
after the third irrigation in 1976 are shown in Figures 19 and 20, respecti-
vely. Even though the pond was ineffective for over half of the irrigation
season each year, it did greatly reduce the sediment loss from this site.
All of the runoff from Sites 2, 3 and 4 was diverted through the same
pond. The data in Table 26 show that the sediment removal efficiency of this
46
-------
Figure 17. T-slot prior to the first irrigation of
Site 1 in 1976.
w. a
Figure 18. T-slot after the first irrigation of
Site 1 in 1976.
47
-------
.«..---*. *.
- / >.
'
Figure 19. Sediment pond at Site 1 prior to the
first irrigation in 1976.
*
'
|r
p* v *^\A^f^
Figure 20. Sediment pond at Site 1 after the
third irrigation in 1976.
48
-------
TABLE 25. SEDIMENT AND PHOSPHORUS REMOVAL BY T-SLOTS AND SEDIMENT POND AT
SITE 1 DURING THE FIRST IRRIGATION. 1976
Constituent
Total Phosphorus
Sediment
Into
T-Slots
(kg/ha)
0.73
1055
Into
Pond
(kg/ha)
0.33
504
Out of
Pond
(kg/ha)
0.24
189
Removal
by
T-Slots
(%)
45
48
Removal by
T-Slots
and Pond
(kg/ha)
78
66
pond was quite high both years. This pond was large enough that it did not
require cleaning after the 1975 season and was only about half filled with
sediment at the end of the 1976 season.
During both irrigation seasons, the pond installed at Site 5 removed 64
percent of the sediment from the runoff -from the hop field at this site. This
pond was adequately sized so that it too was only about half filled, with sedi-
ment after two seasons of use. Another problem with hop fields is that a
considerable amount of floating residue is sometimes carried in the runoff.
A screen installed at the outlet of the pond, as shown in Figure 21, was
effective in filtering floating material from the runoff. Downstream irriga-
tors, who reuse the runoff from this field, commented on the improvement in
the quality of the runoff after the screen was installed.
A single pond was used for removing sediment from the runoff from Sites
6, 7 and 8. Water entered each end of the pond and was discharged through an
outlet located near the center of one side of the pond (Figure 22). Since the
outlet was in the center of the pond, the effective length of the pond was
only half of its total length. The pond was smaller than the ponds at the
other study sites; and, as a result, required cleaning at the end of each
irrigation season. This pond, however, was as effective in removing sediment
from runoff as the other two ponds.
The results obtained from these studies indicate that on-farm sediment
retention ponds are effective in removing sediment even when they are parti-
ally filled with sediment. It is necessary that the velocity of the water
moving through the pond be reduced enough to allow sediment to settle. A
small pond, which is cleaned on an annual basis, has the greatest retention
time during the first few irrigations when the sediment loads in the runoff
are the largest.
Large Sediment Retention Ponds
The two large sediment ponds monitored in this study were located in
natural drainageways near Wilder and Melba. Runoff from 325 hectares of land
drain into the Wilder pond. In addition, operational waste from the end of a
supply lateral flows into this pond. The water flowing into the Melba pond is
diverted from a district canal. However, a large portion of the water con-
veyed by the canal at the diversion point is runoff from higher lands which
49
-------
TABLE 26. SEASONAL SEDIMENT BALANCES FOR THE BOISE VALLEY ON-FARM SITES
01
o
_MBMM^»B««
Site
1
2
3
4
5
6
7
8
Year
1975
1976
1975
1976
1975
1976
1975
1976
1975
1976
1975
1976
1975
1976
1975
1976
On Plots
(ka/ha)
621
482
1,051
1,004
1,352
775
1,652
1,787
306
302
365
693
501
553
1,303
742
Off Plots1
(kg/ha)
27,146
20,405
8,088
4,2622
5,241
3,5682
6,215
6752
5,256
4,158
1,291
614
1,643
2,172
7,994
3,238
Out of Pond
(kg/ha)
14,710
6,273
1,425
770
934
888
1,232
261
1 ,864
1,478
453
368
338
655
2,184
951
Removal by
Pond
(%)
46
69
82
82
82
75
80
61
64
64
65
40
79
70
73
71
Net
w/o Pond
(kg/ha)
26,525
19,923
7,038
3,258
3,889
2,793
4,563
-1,112
4,950
3,856
926
-79
1,142
1,619
6,691
2,496
Loss
with Pond
(kg/ha)
14,089
5,791
374
-2343
-418
113
-420
-1,526
1,558
1,176
88
-325
-163
102
881
209
Includes effects of T-slots and vegetated buffer strips where used on Sites 1, 2, 3 and
2Does not include preplant irrigation
Negative numbers indicate a net gain
-------
,
d
:
Figure 21. Screen for retaining floating debris
in the sediment pond at Site 5.
Figure 22. Side-outlet pond used to remove sediment
from the runoff from Sites 6, 7 and 8.
-------
has been collected for reuse on lower lands.
The area draining into the Wilder pond is an intensively farmed area, as
shown by the crop data in Table 27. The average flow rate into the pond was
approximately 0.25 cubic meters per second (m3/sec), and the sediment yield
from the drainage area averaged approximately 5 metric tons/hectare (t/ha).
The canal diverted through the Melba pond had an average flow rate of about
0.55 m3/sec. Return flows entering the canal were from an intensively cropped
area which is similar to the area draining into the Wilder pond except that
hops are not grown in this area.
TABLE 27. CROPS GROWN IN THE WILDER POND DRAINAGE AREA, 1976
Area
Crop (ha)
Alfalfa Hay 9
Alfalfa Seed 2
Barley 29
Dry Beans 7
Sugarbeets 86
Corn 4
Potatoes 38
Hops 87
Onions 37
Orchard 9
Pasture 17
Total 325
The effectiveness of the two ponds in removing sediment and other pollu-
tants is shown by the data in Table 28. The main differences in the removal
efficiencies of the two ponds are for ammonia and sediment. The differences
in ammonia concentrations and removal efficiencies may be attributed to the
fact that considerable amounts of fertilizer were applied by side dressing
during June and July in the Wilder area. The sizing of the ponds affected
their sediment removal efficiencies. Although the average flow rate through
the Melba pond was more than twice that through the Wilder pond, the capacity
of the Melba pond was only half that of the Wilder pond (1,500 m3 versus
52
-------
3,000 m3). As shown In Figure 23, the Melba pond was essentially filled with
sediment by August 20 during both years. Even so, more than 1,200 metric
tons of sediment were removed each year from the water flowing through this
pond. This essentially eliminated downstream canal cleaning operations which
were previously necessary. Sediment cleaned from both ponds was used by the
irrigation district for canal maintenance.
TABLE 28. AVERAGE POLLUTANT CONCENTRATIONS AND REMOVAL EFFICIENCIES FOR LARGE
SEDIMENT RETENTION PONDS, 1975 AND 1976
Wilder Pond
Concentration
Constituent
Nitrate
Nitrogen
Ammonia
Nitrogen
Organic
Nitrogen
Soluble
Phosphorus
Total
Phosphorus^
Sediment
In
(mg/1)
0.870
0.861
2.00
0.113
0.610
852
Removal
Out Efficiency
(mg/1) (%)
0.836
0.491
1.51
0.106
0.440
297
4
40
24
6
27
65
Melba Pond
Concentration
In
(mg/1 )
0.474
0.523
1.27
0.113
0.405
390
Removal
Out Efficiency
(mg/1) (%}
0.451
0.514
0.879
0.103
0.332
235
5
2
31
9
18
40
The average concentrations of the pollutants entering and leaving the
large sediment ponds were generally less than those for the smaller on-farm
ponds monitored in this study. The data in Table 29 indicate that ammonia
is the only exception. The average sediment concentrations in the flows
entering and leaving the large ponds were about one-fifth those for the
smaller ponds. This was due to the fact that much of the sediment in the sur-
face runoff from fields in the drainage areas served by the large ponds
settled out in the drainageways before it reached the ponds. Consequently,
the concentrations of the materials associated with sediment were also reduced
in the flows entering and leaving the large ponds. The average removal effi-
ciencies of the on-farm ponds were higher than those for the large ponds for
all constitutents analyzed.
SUMMARY
Several of the management practices evaluated in the Boise Valley during
the 1975 and 1976 irrigation seasons were found to be effective in reducing
53
-------
Figure 23. Large sediment pond near Melba, Idaho
showing the sediment accumulation late
in the irrigation season.
TABLE 29. AVERAGE POLLUTANT CONCENTRATIONS AND REMOVAL EFFICIENCIES FOR LARGE
AND ON-FARM SEDIMENT RETENTION PONDS. 1975 AND 1976
Large
Concentration
Constituent
Nitrate
Nitrogen
Ammonia
Nitrogen
Organic
Nitrogen
Soluble
Phosphorus
Total
Phosphorus
Sediment
In
(mg/1)
.
.594
.562
.49
.113
.468
530
Out
(mq/1)
0.568
0.507
1.07
0.104
0.367
254
Ponds
Removal
Efficiency
(%}
4
10
28
8
22
52
On -Farm
Concentration
In
(mq/1)
1.02
0.066
4.32
0.153
2.37
3,162
Out
(mg/1)
0.96
0.058
1.88
0.128
0.96
1,052
Ponds
Removal
Efficiency
/(V\
(A)
12
57
16
59
65
54
-------
sediment and nutrient losses from surface-irrigated fields. Sediment reten-
tion devices were also found to be effective in reducing the amounts of sedi-
ment and certain nutrients lost from individual fields as well as large
irrigated areas.
Furrow stream size was found to have a direct influence on the amounts
of sediment and nutrients lost from irrigated fields. On adjacent plots
planted to field corn, the use of a furrow stream size of 0.77 1/s during the
first three irrigations resulted in a net sediment loss of 3,258 kg/ha;
whereas, the use of a furrow stream size of approximately 0.4 1/s resulted in
a net sediment gain of 1,112 kg/ha. There was a net loss of total phosphorus
(1.52 kg/ha) from the plot where the larger furrow stream size was used and a
net gain (0.48 kg/ha) on the other plot. There was a net gain of nitrate
nitrogen on both plots. These results indicate that it may be possible to
completely eliminate sediment and nutrient losses from furrow-irrigated
fields by using the proper furrow stream size.
Cutting furrow flows back after they reach the end of a field increases
the efficiency of water-use and reduces sediment losses, Conventional irri-
gation of a plot planted to field corn resulted in a water-use efficiency of
41 percent and a net sediment loss of 13,534 kg/ha. Cutback irrigation on an
adjacent field corn plot resulted in a water-use efficiency of 78 percent and
a net sediment loss of only 915 kg/ha. In this case, cutting the furrow flows
back resulted in a large increase in the amount of water saved and a 93 per-
cent reduction in the net amount of sediment lost. A,similar reduction was
found in the net amount of phosphorus lost from the cutback-irrigated plot.
The timing of irrigations was found to influence sediment and nutrient.
losses from surface-irrigated fields. Reducing the number of irrigations on
one study site from eight in 1975 to six in 1976 resulted in a 21 percent
reduction in the amount of water applied and a 25 percent reduction in the
amount of sediment lost from the study site. Preplant irrigations may result
in heavy sediment losses. Over one-third of the seasonal sediment loss from
three sites monitored in this study occurred during preplant irrigations.
Tillage practices can have a marked effect on water-use efficiencies and
sediment and nutrient losses. Irrigating in compacted furrows resulted in
more surface runoff and greater sediment losses than irrigating in non-
compacted furrows. However, high infiltration rates in the non-compacted
furrows resulted in excessive deep percolation losses and poor water distri-
bution efficiencies for these furrows. The number of tillage operations
during the irrigation season did not greatly affect sediment losses from a
hop field on a 1.1 percent slope. This was not the case, however, for a corn
field on a 2.6 percent slope. Tilling this field between the first and second
irrigations caused the sediment loss to more than double (from 5,291 kg/ha to
12,705 kg/ha). In contrast, the sediment loss from corn fields which were not
cultivated after the first irrigation decreased.
Vegetated buffer strips can be used to retard the runoff from furrow-
irrigated fields and thereby cause some of the sediment carried by the runoff
to be settled out. Evaluations of a sodded grass strip in 1975 and a grain
(barley) strip in 1976 show that each type of strip removed, about 45 percent
55
-------
of the sediment from the runoff passing through the strips. The grass strip
was more effective than the grain strip during the first irrigation; whereas,
the grain strip was more effective during later irrigations.
On-farm sediment ponds were found to be effective in removing from 40
to 82 percent of the sediment from flows entering the ponds. The variation
in the removal efficiency of the ponds was due to several factors, including
the size of the ponds and the quality of the water entering the ponds.
Sediment-laden water entering one small on-farm pond filled the pond with
sediment after only two irrigations. As a result, the sediment-removal
efficiency of this pond was only 40 percent. Properly sized ponds, on the
other hand, removed over 70 percent of the sediment from incoming runoff and
were only half filled with sediment after two years of use.
Large sediment retention ponds located in natural drainageways can be
used to remove sediment and nutrients from return flows from large irrigated
areas. The results obtained from monitoring two large ponds in the Boise
Valley show that the sediment removal efficiencies of these two ponds were
40 and 65 percent, respectively. Approximately 20 percent of the total
phsophorus and 30 percent of the organic nitrogen entering these ponds was
removed. Overall, the large ponds were not as effective in removing sediment
and nutrients as smaller on-farm ponds. This is due, at least in part, to
the fact that much of the sediment and other materials in the runoff from
surface-irrigated fields settles out in the drainageways before it reaches
the large ponds.
In summary, it may be stated that water, sediment and nutrient losses
from surf ace-irrigated fields can be greatly reduced or even eliminated by
integrating the use of proper management practices with the use of sediment
retention devices. In this study, combining the use of improved water manage-
ment practices with the use of vegetated buffer strips and sediment retention
ponds resulted in net gains of sediment, total phosphorus and nitrate nitrogen
on several of the study sites.
56
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SECTION 7
MAGIC VALLEY FIELD INVESTIGATIONS
Field investigations of several management practices and sediment re-
moval systems were conducted at sites near Kimberly in the Magic Valley. In-
cluded were on-farm studies of (1) tillage and other cultural practices, (2)
mini-basins, (3) vegetated buffer strips, (4) sediment removal by a dense
growing crop and (5) furrow cutback irrigation. In addition, large district-
type sediment removal systems were also studied. Most of these studies were
conducted at the Kimberly Research and Extension Center in cooperation with
Agricultural Research Service personnel at the Snake River Conservation
Research Center located at Kimberly, Idaho.
The on-farm experiments were conducted primarily to determine the effec-
tiveness of different practices and systems in reducing water, sediment and
phosphorus losses from irrigated fields. The district-type sediment removal
systems were monitored to determine their effectiveness in removing sediment
and phosphorus from return flows from large irrigated areas. Other nutrients,
pesticides and chemical constituents were not considered in these studies.
TILLAGE STUDY
A 1.48-hectare field at the Kimberly Center was used to evaluate the
effects of seedbed preparation and cultivation practices on water and sedi-
ment losses from a dry bean field in 1975 and 1976. The soil at this loca-
tion is Portneuf silt loam with field slopes varying from 0.8 to 1.2 percent.
Two methods of prep!ant irrigation were used to prepare the field for
planting. In one case ("broadcast" procedure), a 76-cm furrow spacing was
used to wet the entire field surface. In the other ("banded" procedure),
a 122-cm furrow spacing was used to wet only the seedbed area. After the pre-
plant irrigation, the plots were harrowed and planted with Pinto (UI114) bean
seed in rows which were about 96 meters long. A row spacing of 122 centi-
meters was used and furrows were made in every other row during the planting
process. A total of 30 plots were established in the field.
After planting, the two irrigation treatments were split into three
cultivation treatments. Each treatment was replicated five times. In 1975,
the two irrigation treatments received 1, 2 and 3 cultivations with a stan-
dard 4-row bean cultivator after emergence of the beans. In 1976, the irri-
gation treatments received 0, 1 and 2 cultivations. In 1975, eight irriga-
tions at 8- to 12-day intervals were performed prior to harvest. The 1976
experiment was terminated after a hailstorm destroyed the crop during the
sixth irrigation. Eight-hour sets were used during both years.
During each irrigation, the total flow onto the field was determined by
57
-------
measuring the difference 1n discharge between two weirs in the concrete-lined
head ditch at the upper end of the field. One of these installations is
shown in Figure 24. Siphon tubes from the head ditch were set as accurately
as possible to obtain approximately equal flow in each furrow in 1975. In
1976, each tube was set with a leveling device to insure that the differen-
tial head between the ditch water surface and the end of each tube was exactly
the same (Figure 25).
At the end of the field, two furrows were converged and 6.1 meters of
4 mil thick plastic was laid in the invert leading to a V-notch flume as
shown in Figure 26. The plastic was used to prevent erosion on the lower
ends of the furrows where the slope was significantly steeper than it was in
the rest of the field. This condition of steeper slopes at the lower ends of
fields (convex-end syndrome) is fairly common in the Magic Valley (Figure 27).
The discharge was measured at intervals of 15, 30, 60 and 120 minutes until
the end of each set. One-liter samples were taken from the outlet of the
flumes at the same time intervals.
Sediment concentrations were determined by vacuum filtering the one liter
samples through pre-dried Whatman No. 50, 24-cm diameter filter papers. The
filters were dried and weighed and sediment concentrations determined. Flow
data and sediment concentrations were used as input to a computer program for
determination of the surface runoff and sediment yield from each plot for
each irrigation.
Filtered and unfiltered phosphorus samples were taken at random furrow
locations throughout each irrigation. Filtered samples were obtained in the
field using vacuum filtration through 0.45 ym millipore filters. Filtered
samples were analyzed for ortho and total phosphorus using methods described
by Carter, e_t al_. (1974). Filtered sediment from each sample was scraped
from the filter paper and analyzed for total and bicarbonate extractable
phosphorus. An analysis of variance on sediment yield was performed using
slope, irrigation treatment, and cultivation treatment.
The results of the 1975 study show that there was no significant rela-
tionships between the number of cultivations and sediment losses. For the
preplant irrigation, the banded application resulted in 25 percent less sur-
face runoff than the broadcast application. The sediment yield from the
banded treatment was lower than that from the broadcast treatment. The dif-
ference, however, was not significant. This lack of a significant difference
in sediment yields between the two preplant treatments was attributed to
variations in furrow flow which resulted from the way in which the siphon
tubes were set. For this reason, the experiment was repeated in 1976 with
more accurate control of the furrow stream size.
Sediment yield and surface runoff data for the 1976 study are given in
Tables 30 and 31. The value given for each treatment is the average of five
replications. Surface runoff, which should be influenced by furrow condi-
tions at the Inception of irrigation, was not significantly correlated with
the number of cultivations. Significant differences in sediment yield did
occur between the two preplant irrigation treatments. The yield from the
broadcast treatment, for example, was 1,050 kg/ha while that from the banded
58
-------
\
\ V
Figure 24. Weir and recorder used to measure the
flow onto the bean tillage and mini-
basin study sites in 1976.
Y
£
Figure 25. Leveling device used to set siphon
tubes in the bean tillage and mini-
basin studies in 1976.
59
-------
Figure 26. Lower end of the bean tillage study
site showing plastic-lined furrows.
Figure 27. Lower end of a bean field showing the
convex-end syndrome common in the
Magic Valley.
60
-------
TABLE 30. SURFACE RUNOFF DATA. 1976 MAGIC VALLEY BEAN TILLAGE STUDY
Irrigation
Number
1
2
3
4
5
Average
TABLE 31. SEDIMENT YIELD
Surface Runoff
Cultivation Treatment
1 2 3
18.6 16.5 18.2
35.1 37.1 33.7
42.1 39.5 36.2
46.4 49.2 39.2
40.3 42.1 40.0
36.5 36.9 33.5
DATA, 1976 MAGIC VALLEY BEAN
(%}
Average
17.8
35.3
39.3
44.9
40.8
35.6
TILLAGE STUDY
Sediment Yield (kg/ha)
Irrigation
Number
1
2
3
4
5
Totals
Cultivation Treatment
1 2 3
623 716 619
1,296 1,280 1,209
2,675 2,165 1,812
2,064 2,334 1,646
1,532 2,053 2,469
8,189 10,257 7,754
Average
653
1,261
2,217
2,015
2,018
8,164
61
-------
treatment was only 260 kg/ha. This difference is to be expected since the
furrow spacing for the broadcast preplant irrigation was less than that for
the banded preplant irrigation. For the same furrow flow, the runoff and
resulting sediment loss per unit area would be greater for the broadcast
treatment than for the banded treatment.
In 1975, 869 mm of water were applied to the bean field in eight irri-
gations. Approximately half (50.9 percent) of this water left the field as
surface runoff. The sediment yield for the season was 28,530 kg/ha. The
average discharge per siphon tube for all irrigations was 0.37 I/sec.
In 1976, 343 mm of water were applied during the first five irrigations.
This represents approximately 60 percent of the amount of water that would
have been applied in the normal eight irrigations if the experiment, had been
carried to completion. About one-third (35.6 percent) of the applied water
left the field as surface runoff. The sediment yield for the field for the
five irrigations was 8,164 kg/ha. The average siphon tube discharge was
0.28 I/sec.
The total sediment yield for the five irrigations in 1976 was less than
one-third the yield in 1975. Based on the 1975 results, the expected yield
in 1976 would have been nearly twice the measured yield. The decrease in
yield can be explained by the decrease in furrow flow in 1976 and the corres-
ponding decrease in surface runoff.
Phosphorus loss data for the 1976 study are given in Table 32. There is
no significant difference in phosphorus losses due to cultivation treatments.
The total phosphorus loss from the field amounted to 7.38 kg/ha.
TABLE 32. TOTAL PHOSPHORUS LOSS DATA, 1976 MAGIC VALLEY BEAN TILLAGE STUDY
Total Phosphorus Loss (kg/ha)
Irrigation
Number
1
2
3
4
5
Totals
Cultivation Treatment
1
0.44
1.11
2.47
1.85
1.34
7.21
2
0.50
1.18
2.05
2.21
1.80
7.75
3
0.44
1.01
1.81
1.63
2.28
7.17
Average
0.46
1.10
2.11
1.90
1.80
7.38
The field slopes of the 30 tillage study plots varied from 0.78 to 1.2
percent. The results of the 1976 study show that field slope had a
62
-------
significant effect on sediment yield. This is shown by the regression equa-
tions and plots of field slope versus sediment yield presented in Figure 28.
The units used for sediment yield in this figure are metric tons (tonnes) per
hectare (t/ha). The data presented in this figure also indicate that the
sediment yield increased as the season progressed on the steeper field slopes
(1.2 percent) but stayed nearly the same on the flatter slopes (0.78 percent).
Further experimentation is needed to determine whether these differences are
significant.
Water retention (amount of water applied minus surface runoff) is also
significantly affected by field slope as shown in Figure 29. Except for the
fifth irrigation, the percentage of applied water retained on the field
decreased as field slope increased. More water was retained during the pre-
plant irrigation (Irrigation No. 1) for all slopes than was retained during
any of the later irrigations. This was probably due to antecedent moisture
conditions.
The results of both the 1975 and 1976 experiments indicate that there is
a direct relationship between the seasonal gross sediment yield from the bean
field and surface runoff. A plot of the gross sediment, yield versus percent
runoff for the 13 irrigations performed in 1975 and 1976 is shown in Figure
30. This relationship illustrates one of the basic concepts in reducing
sediment losses from gravity-irrigated fields. Generally, any practice which
V/ill decrease the surface runoff will result in a decrease in sediment and
phosphorus losses.
MINI-BASIN STUDY
In 1976, a mini-basin study was conducted on a 1.38-hectare bean field
adjacent to the tillage study field. The field was preplant irrigated,
harrowed and planted to Pinto (UI114) beans. The beans received three culti-
vations after emergence. A total of 12 basins were installed by constructing
berms perpendicular to the bank of the drain ditch along the lower end of
this field to form small shallow ponds abutting the drain ditch bank (Figure
31). The basins were constructed to collect flow from 3, 4 and 5 furrows and
with either a plastic overflow section on the ditch benk or a grassed overflow
section. Several of basins with grassed overflow sections are shown in
Figure 32. The overflow sections were 0.5 meters wide and were leveled to
provide uniform flow over the section. Bluegrass sod was transplanted onto
the overflow section prior to the first irrigation.
A V-notch flume was installed between each mini-basin as shown in Figure
33 to collect and measure the flow from two check furrows. Plastic was laid
in the furrows for a distance of 6.1 meters upstream from the flume to eli-
minate erosion in the lower part of furrows.
Siphon tubes were set and flows were sampled and measured in the same
way as in the tillage study. One-liter samples were obtained from the outlet
of the mini-basins by integrating the collection along a board installed as
shown in Figure 32 along the downstream side of the overflow sections. Since
the flow from the basins could not be measured, it was assumed that the unit
furrow flow from the basin was the average of the unit furrow flows of the
check furrows on each side of the basin at the same time.
63
-------
Irrigation
Number
1
2
3
4
5
r~
Dates
5/2775/24
6/21
6/30
7/12
7/22
1 ' 1
Regression
Equation
481.6 X - 4.230
696.1 X - 5.809
1,008.9 X - 8.032
1
Level of
Significance
1%
1%
1%
Y = 828.7 X - 6.394
Y = 854.1 X -
8
FIELD SLOPE XKT
II
12
13
Figure 28. Effect of field slope on sediment yield, 1976 bean tillage study.
-------
100
cn
2
z
o
h-
LU
J-
UJ
(T
sr
UJ
75
50
25
Irrigation
Number
1
2
3
4
5
Dates
5/2W24
6/21
6/30
7/12
7/22
Regression
Equation
T= -2,880 X + 111
Y = -5,780 X + 123
Y = -2,580 X + 87
Y = -2,064 X + 76
Y = - 890 X + 68
Level of
Significance
U
1%
V/c
1%
1%
8
9 10
FIELD SLOPE XIO2
II
12
13
Figure 29. Effect of field slope on water retention, 1976 bean tillage study.
-------
o
.c
12
10
8
UJ
UJ
2
0
20 30 40 50 60 70
SURFACE RUNOFF (%)
Figure 30. Relationship between sediment yield
and surface runoff.
Water samples were analyzed for total suspended solids by filtering tech-
niques outlined for the bean tillage study. Four 8-hour irrigations and one
24-hour irrigation were monitored. During the first irrigation, considerable
difficulty was encountered with leakage under the sod and plastic and data
from this irrigation are not reliable. Seven days prior to the fifth irri-
gation a hailstorm caused severe damage to the bean vines and furrows. A
24-hour set was required for this irrigation to adequately irrigate the lower
end of the field.
Sediment loss data for the 12 mini-basins and check furrows are presented
in Table 33 for four irrigations in 1976. The seasonal sediment loss from the
field, as indicated by the average of the check furrow losses, would heve been
14,950 kg/ha. The weighted average loss for the mini-basins was only 680
kg/ha. The average seasonal sediment removal efficiency of the basins was
94.9 percent.
Sediment removal efficiencies for the basins evaluated in this study
are shown in Table 34. The data presented in this table indicate that there
is no significant difference in the sediment removal efficiency of different
sizes of mini-basins even though the average depth of the larger basins was
less than that of the smaller basins. There is also no apparent benefit to
using a grassed overflow section instead of a plastic section. It is doubtful
that a farmer would spend the time and money required to install plastic sec-
tions. However, grassed overflow sections should be relatively easy to manage.
66
-------
Figure 31. Mini-basins constructed on the lower
end of a bean field.
Figure 32. Mini-basins with grassed overflow sections
67
-------
TABLE 33. SEDIMENT LOSS DATA. 1976 MINI-BASIN STUDY
en
CO
' -
Irrigation
Number
Basin
and
3
3
4
4
5
5
Size*
Type
9
P
9
P
9
P
Basins
0.23
0.16
0.12
0.19
0.22
0.20
2
Check
Furrows
3.24
4.03
4.07
3.30
4.40
3.58
Sediment Loss (t/ha)1
3 4
Basins
0.36
0.11
0.10
0.22
0.18
0.15
Check
Furrows
3.36
4.31
3.60
2.59
3.31
2.41
Basins
0.21
0.20
0.15
0.18
0.20
0.21
Check
Furrows
3.94
5.71
6.43
3.43
5.32
5.26
Basins
0.13
0.21
0.04
0.13
0.04
0.21
5
Check
Furrows
3.94
2.49
0.58
1.76
4.70
4.90
Totals
Basins
0.93
0.69
0.50
0.72
0.63
0.77
Check
Furrows
13.48
16.54
14.67
11.08
17.72
16.18
lMt" is the abbreviation for metric ton (tonne)
2Symbols denote number of furrows (3, 4 or 5) collected by each basin and whether the overflow is
grassed (g) or plastic lined (p)
-------
.*.).
*>
* - -* . ~ -
*,- - . -*-. -
Figure 33. V-notch flume used to measure the flow
in check furrows in the mini-basin study.
The construction and use of simple grassed overflow mini-basins would provide
an economical means of retaining sediment on a field.
One of the 3-furrow basins was filled with sediment after five irriga-
tions. This indicates that the larger 4- or 5-furrow besins are more likely
to remain effective over a full season.
VEGETATED BUFFER STRIP STUDY
An evaluation of the effect of vegetative buffer strips on sediment
losses from a spring wheat field was performed in 1976. A 1.8-hectare field
at the Kimberly Center was divided into three plots, planted at a rate of
78 kg/ha with Twin variety spring wheat, harrowed and then corrugated with
sled corrugators.
One month after the initial planting, a 2.44-meter wide grain drill was
used to band the bottom of the field with multiple plantings of the spring
wheat. Plot 1 was not banded, plot 2 was banded with a single planting and
plot 3 was banded with a double planting. The plots were all the same size
(approximately 0.6 hectares). The slopes of the three plots were 1.2, 1.4
and 1.7 percent, respectively.
Six irrigations were performed on each of the three plots using 6.5-hcur
sets. The water was applied with 19-mm diameter siphon tubes which were set
with a constant differential head of 91 mm. Inlet flows were measured with a
69
-------
Basin Sizez
and Type
3 9
3 P
4 9
4 p
5 g
5 p
Irrigation Number
2
92.92
96.09
97.16
94.15
95.05
94.49
3
89.30
97.36
97.30
91.50
94.54
93.92
4
94.69
96.43
97.66
94.71
96.30
95.93
5
95.68
91.53
93.47
92.80
99.15
95.79
Seasonal
Averaqe
93.15
95.35
96.40
93.29
96.26
95.03
efficiencies are expressed as percentages
2Symbols denote number of furrows (3, 4 or 5) collected by each basin
and whether the overflow is grassed (g) or plastic lined (p)
Cipolleti weir and a 90° V notch weir installed in the head ditch. The sur-
face runoff from the field was measured with a 76-mm Parshall flume. All
measuring stations were equipped with water stage recorders.
Sediment samples were taken at each water measurement station and from a
random sampling of siphon tubes at the beginning, middle and near the end of
each set. Runoff water in the Parshajl flume was sampled at 15, 45, 105, 225
and 285 minutes after the beginning of flow in the flume and 15 minutes before
and after the tubes were pulled at the end of each set.
Sediment samples were analyzed with the same procedure as outlined for
the bean tillage study. Water and sediment flow onto and off the field were
evaluated and plotted with the computer routine for each irrigation. A graph
showing rates of sediment loss from the three plots during a typical irriga-
tion is shown in Figure 34. Prior to harvest and after the sixth and last
irrigation, stand density counts were made in the buffer strips on all three
plots. Two subplots of 0.37 m2 were sampled on each plot.
Flow and sediment yield data for the three plots are presented in Table
35. The average amount of water applied to the three plots during the season
was 516 mm. The average runoff was 157 mm. The average net application was
359 mm. The estimated seasonal consumptive use by the crop was 230 mm.
The data in Table 35 show that, on a seasonal basis, the percent surface
runoff values for the three plots were essentially the same. The seasonal
sediment yields, on the other hand, varied markedlyfrom 1,828 kg/he on the
double-planted plot (plot 3) to 8,618 kg/ha on the check plot (Plot 1). The
effect of the stand density of the wheat in the buffer strip on sediment
yield is shown in Figure 35. Increasing the stand density from 519 to 815
stems/m2 (an increase of 57 percent) resulted 1n over a fourfold decrease in
the sediment yield.
70
-------
PLOT 3
3 4
TIME (hours)
Figure 34. Sediment loss rates during a typical irrigation
of the vegetated buffer strip study site in 1976.
Nonsignificant differences between plots in the total amounts of water
applied and the amounts of surface runoff indicate that retardation of flow
in the buffer strips was sufficient to remove sediment but did not increase
infiltration appreciably. Planting the buffer strips required very little
effort and did not disrupt normal irrigation or other farming operations.
SEDIMENT REMOVAL BY ALFALFA
A 1.52-hectare field of alfalfa at the Kimberly Center was monitored
during 1975 to determine the magnitude of sediment reduction obtainable when
surface runoff is reused for irrigation. The field was 146 meters long and
had an average slope of 1.7 percent. The soil is Portneuf silt loam.
Four irrigations were monitored. The amounts of water and sediment
coming onto and off the field were computed for each irrigation.
The results obtained from this monitoring program are presented in Table
36. The total amount of water applied during the season was 746 mm. Only
71
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TABLE 35. FLOW AND SEDIMENT YIELD DATA, 1976 MAGIC VALLEY VEGETATED
BUFFER STRIP STUDY
Irrigation
1
2
3
4
5
6
Totals
Average
1
2
3
4
5
6
Totals
Average
1
2
3
4
5
6
Totals
Average
Inflow
(mm)
108
92
84
78
87
86
535
108
87
58
81
84
83
501
101
76
84
94
83
76
514
Plot 1, 519 stems/m2
Outflow
(mm)
24
21
28
29
30
30
162
Plot 2, 739 stems/m2
30
26
25
27
26
28
162.
Plot 3, 815 stems/m2
29
23
22
24
24
26
148
Surface
Runoff
(%)
22
23
33
37
34
35
30
28
30
43
33
31
34
32
29
30
26
26
29
34
29
Sediment
Yield
(kq/ha)
2,926
1,625
1,119
1,073
946
929
8,618
1,172
769
458
440
362
210
3,411
600
352
256
274
217
129
1 ,828
72
-------
10
o
-I
fll x»
z
u
5
O 4
CO
500 600 700 800 900
STAND DENSITY (stems/m2)
Figure 35. Effect of vegetated buffer strip stand
density on sediment yield.
73
-------
Irrigation
1
2
3
4
Totals
Average
Inflow
(mm)
172
225
207
142
746
Water
Outflow
(mm)
8
30
31
20
89
Surface
Runoff
(j ocmi'ic.
111 KLrlUVML t
Sedin
Concentrations
Inflow
(ma/1)
73
117
130
359
17(1
Outflow
(ma/1)
667
508
113
72
^An
51 ALrALrA .
SIUUY
Amounts
Inflow
(ka/ha)
125
263
269
509
1,166
Outflow
(kq/ha)
45
152
36
14
247
Amount
Removed
64
42
58
97
70
-------
89 mm or 12 percent of the applied water left the field as surface runoff.
The average sediment concentration of the outflow was 340 mg/1 while that of
the inflow was 170 mg/1. The net sediment removal varied from 42 percent for
the first irrigation to 97 percent for the fourth irrigation, and averaged 79
percent for the season. These results show that utilization of sediment
laden runoff to irrigate a dense growing crop such as alfalfa is a viable
method for improving water quality and retaining sediment on farm fields.
FURROW CUTBACK IRRIGATION STUDY
The effects of furrow cutback irrigation on water and sediment losses
from a potato field were evaluated in 1975. This study was conducted on a
1.69-hectare field at the Kimberly Center which was 146 meters long and had a
slope of 1.0 percent. The field was divided into two equal plots. Each plot
was irrigated 12 times during the season using 19-mm siphon tubes. On alter-
nate irrigations, the irrigator was asked to cut the siphon tube flow back
after the water had reached the ends of the furrows. Each plot received 12
uncontrolled or non-cutback irrigations and 12 controlled or cutback irriga-
tions.
The flow onto the field was determined for each set by measuring the dif-
ference in discharge between two weirs in the head ditch or by calibrating the
siphon tubes to determine their average flow rates. The runoff from the
potato field was measured through a 76-mm Parshall flume equipped with a con-
tinuous recorder. The runoff then entered a sediment pond which was monitored
for sediment removal efficiency. The water sampling and analysis procedures
were the same as those used in the bean tillage study.
Water and sediment budgets for the potato field for both the cutback and
non-cutback sets are given in Tables 37 and 38. On the non-cutback sets,
853 mm or about 57 percent of the applied water (1,487 mm) left the sets as
surface runoff during the season. This resulted in a net application of 634
mm of water to these sets. On the cutback sets, however, only 241 mm or about
20 percent of the applied water (1189 mm) left the sets as surface runoff.
The net application in this case was 948 mm. The estimated seasonal consump-
tive use by the crop was 546 mm. This means that the estimated water-use
efficiencies for the non-cutback and cutback irrigations were 37 and 46 per-
cent, respectively.
The data in Tables 37 and 38 show that sediment losses are directly re-
lated to surface runoff. The non-cutback irrigations, for example, resulted
in 853 mm of surface runoff and a net sediment loss of 92,540 kg/ha. The
cutback irrigations, on the other hand, resulted in only 241 mm of runoff and
a net sediment loss of 12,295 kg/ha. In this case, a 72 percent reduction in
surface runoff resulted in an 87 percent decrease in the net amount of sedi-
ment lost. The utilization of cutback systems on the loessal soils in the
Magic Valley area would be useful in decreasing water use as well as decreas-
ing sediment losses. Additional labor would be required, however, to cut
furrow flows back as was done in this study.
75
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TABLE 37. FLOW DATA, 1975 FURROW CUTBACK STUDY
Irrigation
Number
1
2
3
4
5
6
7
8
9
10
11
12
Totals
Averages
Length
of
Set
(hrs)
10.00
9.50
7.75
7.67
6.50
7.00
7.58
7.42
7.50
7.50
20.67
24.00
11.67
12.00
12.00
13.00
11.58
12.00
7.25
7.00
7.00
7.00
6.00
6.00
Inflow
Cutback
(mm)
97.8
78.6
72.1
80.1
77.7
212.9
120.2
123.5
119.3
73.3
72.1
61.8
1,189.4 1
Non-
Cutback
(mm)
126.7
95.6
79.8
95.0
92.1
294.8
147.3
159.7
147.3
89.0
85.9
73.7
,486.9
Outflow
Cutback
(mm)
15.8
9.9
7.2
12.7
18.2
38.0
42.5
25.1
18.3
13.4
24.6
15.5
241.2
Non-
Cutback
(mm)
40.6
51.4
54.0
46.4
48.6
208.6
85.7
107.1
81.8
36.7
51.7
40.9
853.4
Surface
Cutback
1%)
16.2
12.6
10.0
15.9
23.4
17.8
35.4
21.3
15.3
19.3
34.1
25.1
20.3
Runoff
Non-
Cutback
(%)
32.1
53.7
67.7
48.8
52.7
71.8
58.2
67.1
55.5
41.2
60.2
55.8
57.4
76
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TABLE 38. SEDIMENT DATA, 1975 FURROW CUTBACK STUDY
Irrigation
Number
1
2
3
4
5
6
7
8
9
10
11
12
Totals
Length
of
Set
(hrs)
10.00
9.50
7.75
7.67
6.50
7.00
7.58
7.42
7.50
7.50
20.67
24.00
11.67
12.00
12.00
13.00
11.58
12.00
7.25
7.00
7.00
7.00
6.00
6.00
Inflow
Cutback
(kg/ ha)
78.3
93.5
67.6
384.0
83.5
451.8
54.4
154.5
67.5
30.5
278.4
270.0
2,014.0
Non-
Cutback
(kg/ ha)
194.3
62.9
178.7
94.3
180.5
463. 0
217.0
206.0
127.3
44.6
110.6
321.9
2,201.1
Outflow
Cutback
(kg/ha)
1,238.0
598.3
403.1
2,505.7
2,594.4
3,301.5
2,479.4
685.5
161.1
129.4
135.6
76.5
14,308.5
Non-
Cutback
(kg/ ha)
4,307.0
7,151.3
6,577.7
9,126.6
12,392.0
37,068.9
8,912.0
4,324.4
2,841.0
443.0
1,366.5
240.0
94,740.9
77
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DISTRICT WASTE WATER PONDS
The K Lateral wasteway pond near the Jerome golf course has been moni-
tored since 1972. This pond is 152 meters long, 18.3 meters wide and 1.5
meters deep. The Northside Canal Company constructed inlet and outlet struc-
tures and a by-pass channel at this site in 1972. The inlet structure and
by-pass channel are shown in Figure 36. The outlet structure, which consists
of a weir equipped with a stage recorder, is shown in Figure 37. The pond
was surveyed in 1972, 1973 and 1974 to determine the volume of material
removed by cleaning with a dragline for comparison with the calculated volume
of sediment deposited in the pond. The pond was cleaned again in 1976.
This pond collects return flow from 2,428 hectares of Northside Canal
Company land near Jerome, Idaho. The soils in the area are primarily silt to
sandy silt. The pond discharge is measured with a 2.4-meter rectangular sup-
pressed weir which is equipped with a stage recorder. Water samples were
taken every two weeks throughout each irrigation season by Agricultural Re-
search Service personnel and analyzed for total suspended solids and phos-
phorus.
Two additional large ponds were constructed by the Northside Canal Com-
pany on the J-8 Lateral in 1975. These ponds are 91.5 meters long and were
constructed parallel to each other. One is 21.3 meters wide while the other
one is 39.6 meters wide. Water measurement devices and controls and concrete
overflow sections were installed. Due to low runoff flows in 1976 and diffi-
culties with calibration of the inlet flumes, no meaningful data were ob-
tained from this installation.
Seasonal flow and sediment removal data for the K Lateral pond are given
in Table 39. As can be seen, the seasonal sediment removal efficiency of
this pond varied from 65 to 78 percent in the period from 1972 through 1976.
Total phosphorus measurements indicate that the phosphorus removal efficien-
cies of this pond were from 6 to 10 percent less than the sediment removal ef-
ficiencies during the 5-year monitoring period.
Flow data for the K Lateral pond have been analyzed to determine the
characteristics of the flow into this pond. A frequency analysis of discharge
measurements at 6-hour intervals over the 1975 season indicated an average
discharge of 0.4 m3/sec with a variation of from 0 to 1.1 m3/sec. Ninety-two
percent of the total.seasonal runoff from the K Lateral watershed occurs at
flows which are less than 50 percent of the maximum discharge. Data of this
type have been collected and analyzed for 15 runoff streams in southern Idaho
to develop criteria for designing sediment ponds (Bondurant ejt a]_., 1976).
The data in Table 39 show that large sediment removal ponds are effective
in significantly improving the quality of return flows from large irrigated
areas. Operational sediment removal efficiencies of ponds vary because of
discharge fluctuations and variations in particle size and sediment concen-
tration. Several factors affect the short-term sediment concentration in run-
off streams. Abrupt changes in crop type can significantly affect the sedi-
ment load. For instance, a large conversion from pasture and alfalfa to row
crops due to abrupt commodity price changes would probably result in increased
sediment loads.
78
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Figure 36. Inlet structure and by-pass channel of
the K Lateral wasteway pond near
Jerome, Idaho.
Figure 37. Weir and recorder used to monitor the
flow through the K Lateral wasteway
pond near Jerome, Idaho.
79
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TABLE 39. SEASONAL FLOW AND SEDIMENT REMOVAL DATA FOR THE K LATERAL
POND NEAR JEROME, IDAHO
1972
1973
1974
1975
1976
Total Flow (1000 m3)
Sediment Removal Range (%)
Average Sediment Removal (%)
Total Sediment Retention (t)
4,990 5,280 6,330 3,022 7,900
36-77 20-76 0-90 43-85 31-79
65 67 74 78 68
456 510 735 790 1,284
SUMMARY
The results of the field investigations conducted in the Magic Valley
during the 1975 and 1976 irrigation seasons show that sediment and phosphorus
losses from surface-irrigated lands are affected by a number of factors and
that these losses can be effectively controlled. The results of a tillage
study on beans show, for example, that preplant irrigation practices affect
these losses. A "banded" preplant irrigation where 122-cm furrow spacings
were used to wet only the seedbed area resulted in a 76 percent decrease in
the sediment loss in comparison to a "broadcast" preplant irrigation where
76-cm furrow spacings were used to wet the entire field surface. No signifi-
cant differences in sediment and total phosphorus losses due to cultivation
practices were found in this study. The total sediment loss from the bean
field during five irrigations in 1976 was 8,164 kg/ha with a corresponding
total phosphorus loss of 7.38 kg/ha. Surface runoff was found to be the best
single indicator of sediment losses from this field, with losses increasing
as the runoff (expressed as a percentage of applied irrigation water) in-
creased.
Mini-basins which collect and detain the runoff from several adjacent
furrows prior to discharging the runoff water over a drain ditch berm can
remove up to 95 percent of the total sediment from the runoff from a field.
Evaluations of twelve mini-basins constructed on the lower end of a bean
field showed that the basins reduced the seasonal sediment loss from the
field from 14,950 kg/ha to 680 kg/ha. Basins with grassed overflow sections
which collect the runoff from 4 or 5 furrows are recommended.
Vegetated buffer strips consisting of multiple plantings of wheat across
the lower end of a spring wheat field were found to be effective in reducing
sediment losses from this field. Two extra plantings of a 2.44-meter wide
strip of grain resulted in a 79 percent reduction in the amount of sediment
lost during the season (from 8,619 kg/ha on the single-planted check plot to
1,828 kg/ha on the triple-planted plot). Stand density counts showed that
there is an inverse linear relationship between stand density in the buffer
strips and sediment yield. Increasing the stand density from 519 to 815
stems/m3 (an increase of 57 percent) resulted in over four-fold decrease in
sediment loss. Planting the buffer strip required little extra effort and
presented no inconvenience in normal farming operations. The use of buffer
80
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strips on other crops will require integration of the use of the strips with
other farming practices.
The effectiveness of mature alfalfa stands in removing sediment from
surface runoff which is reused for irrigation was documented in 1975. Moni-
toring of the amounts of water and sediment entering and leaving an alfalfa
field showed that 12 percent of the applied water left the field and that 79
percent of the sediment in the applied water was removed, even though sedi-
ment concentrations in the runoff were double those in the inflow. Using
the sediment-laden runoff from row crops to irrigate alfalfa or other close
growing crops is a viable method for improving the quality of return flows
from surface-irrigated areas.
Furrow cutback irrigation was shown to be effective in reducing water
and sediment losses from a field planted to potatoes. Non-cutback irriga-
tions of this field resulted in 853 mm of surface runoff during the irriga-
tion season (12 irrigations) and a net sediment loss of 92,540 kg/ha. The
cutback irrigations resulted in only 241 mm of runoff and a net sediment loss
of 12,295 kg/ha. These results emphasize the importance of water-use prac-
tices in controlling sediment losses. In this case, a 72 percent reduction
in the amount of surface runoff resulted in an 87 percent decrease in the
amount of sediment lost.
The use of large ponds to remove sediment from the runoff in wasteways
is an alternative to the use of on-farm retention systems or control prac-
tices. The results of five years of monitoring a large pond which collects
the runoff from a 2,340-hectare watershed show that the average sediment and
phosphorus removal efficiencies of this pond were about 70 and 62 percent,
respectively. In 1976, 1,284 metric tons of sediment were retained in this
pond. This is equivalent to a loss of approximately 530 kg/ha from the en-
tire watershed. Data obtained for this and similar ponds are being used to
develop criteria for designing both small on-farm sediment ponds and larger
district-type ponds.
81
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SECTION 8
ECONOMICS OF CONTROL PRACTICES
In this section of the report, cost effectiveness estimates for selected
methods of reducing sediment losses from irrigated farms are described. Farm
income consequences of having to meet specified restrictions on sediment
losses are also discussed. The calculations are based on data from the pre-
viously described field investigations and from a survey of farms in the
Boise and Magic Valley areas.
The balance of this section is organized into three subsections. First,
the farm survey procedure and results are summarized. Then, estimates of
costs associated with selected methods of sediment loss reduction are des-
cribed. The effects of sediment loss restrictions on farm income are dis-
cussed in the third subsection.
FARM SURVEY
The farm survey was conducted after the harvest season in 1975. One-
hundred and fifty randomly selected farm operators were interviewed and asked
to describe their present farming practices, with special emphasis on field
operations and irrigation practices. The study areas were delineated so that
the farms within them had soils, topography, and water supply conditions simi-
lar to those at the sites where the field investigations were conducted. The
study area in Twin Falls County consisted of the irrigated land with predomi-
nantly Portneuf silt loam soil that lies between the Snake River and the irri-
gation canal east of the city of Twin Falls. Field slopes are four percent or
less. All irrigation water is supplied by the Twin Falls Canal Company, which
diverts the water out of the Snake River at Milner Dam.
From the 62 sections of land (1 section = 640 acres or 259 hectares) in
the study area, twelve were selected at random. After the sample sections
were located on a map, the farm interviews were carried out. The goal was to
interview everyone who farmed 16 hectares or more of irrigated land in the
sample sections. Forty-two farmers were contacted and 40 interviews were
conducted.
The study area in Jerome County consisted of 70 sections of irrigated
land lying east and south of Jerome. Most of the soils in this area are silt
loams. Irrigation water is supplied by the Northside Canal Company. Data
collection proceeded just as it did in Twin Falls County. Fourteen sections
were selected at random from the 70 in the study area. Forty-five farmers
were contacted and 40 interviews were conducted.
Two study areas were delineated in Canyon County on the basis of the
82
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soil associations mapped in the soil survey for the county. The Wilder-Parma
area included three tracts of the Green!eaf-Nyssaton-Garbutt Association.
The Nampa-Melba area included areas of the Power-Purdam Association together
with the Minidoka-Marsing-Vickery Association. This is the combination of
soils found on the Caldwell Research and Extension Center. In the southern
part of this area, the Scism-Bahem-Trevino Association predominates. Fifteen
percent of the sections in each of these areas were selected at random.
Interviews were conducted with farm operators according to the procedure used
in the Magic Valley. Twenty-three interviews were conducted in the Wilder-
Parma area. Forty-seven were made in the Nampa-Melba area.
Analysis of Survey Data
The information from the.farm survey was analyzed so that representative
farm models could be constructed for each of the four study areas.
The sample farms in each study area were classified into two size cate-
gories. Then crop rotations and resource combinations (especially machinery
and labor) were studied for the farms in each category to arrive at a typical
or bench mark farm model to represent each size category in each study area.
Typical tillage, cultural, and irrigation practices associated with each crop
were identified from the survey data. This information was combined with in-
put and commodity prices. The Oklahoma State University budget generator was
then used to produce cost-and-return budgets for each crop included in the
farm models.
Farm Models - Magic Valley
Of tdae 40 interviews conducted in the Twin Falls area, only 36 of these
were considered to be representative of this study area. The other four were
with farmers who worked land that lay mostly outside the study area. Based
on 1975 irrigated crop area data, the 36 sample farms were classified into
two size categories as shown in Table 40. The choice of the breakpoint be-
tween the two categories was based mainly on labor requirements. Typically,
only one man is employed on farms of less than 100 hectares. Two or more men
are usually employed on larger farms.
TABLE 40. SIZE CLASSIFICATION OF SAMPLE FARMS IN TWIN FALLS COUNTY
Size Category
(irrigated hectares)
Up to 100
More than 100
Number of
Farms
21
15
Median Farm Size
(irrigated hectares)
56.7
129.7
The principal crops on the sample farms were garden bean seed, alfalfa
hay, commercial beans, garden pea seed and small grains (predominantly wheat),
Irrigated cropland use in the Twin Falls area is summarized in Table 41.
83
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TABLE 41. IRRIGATED CROPLAND USE ON SAMPLE FARMS IN THE
TWIN FALLS STUDY AREA
Crops
Garden Bean Seed
Alfalfa Hay
Commercial Beans
Small Grain
Garden Pea Seed
Sugarbeets
All Corn
All Other
Percent of
Small Farms
42
23
14
10
10
1
1
0
100
Irrigated Cropland
Large Farms Al
24
22
15
12
10
6
9
__2
100
1 Farms
29
23
14
11
10
5
6
2
100
A representative farm was described for each size category. The size of
the representative farm is equal to the median farm size in the corresponding
category. The crop rotations on the two model farms for the Twin Falls area
are shown in Table 42.
TABLE 42. CROPS GROWN ON MODEL FARMS FOR THE THIN FALLS STUDY AREA
__
Crop (ha)
Small Farm Model
Garden Bean Seed 24.3
Commercial Beans 8.1
Garden Pea Seed 8.1
Alfalfa (2-year stand) 16.2
56.7
Large Farm Model
Garden Bean Seed 32.4
Commercial Beans 24.3
Spring Wheat 24.3
Garden Pea Seed 16.2
Alfalfa (2-year stand) 32.4
129.6
84
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Forty Interviews were conducted In the Jerome study area. It was found
that soils in the western part of this area were sandier than those to the
east and south of the town of Jerome. Since the sandy soils were not very
similar to those on which the field investigations were conducted, it was
decided to construct farm models on the basis of the 29 sample farms with
heavier soils. The sample farms for this area were classified into two size
categories in the same way as described for the Twin Falls study area. The
classifications for the Jerome area are given in Table 43.
TABLE 43. SIZE CLASSIFICATION OF SAMPLE FARMS IN JEROME COUNTY
Size Category
(irrigated hectares)
Up to 100
More than 100
Number of
Farms
18
11
Median Farm Size
(irrigated hectares)
56.7
121.5
The principal crops on the smaller sample farms were alfalfa hay, small
grains and commercial beans. The same crops predominated on the larger farms
where potatoes was also a major crop. Table 44 summarizes irrigated cropland
use for the sample farms in the Jerome area. Representative farms were des-
cribed for the two size categories according to the procedure used for the
Twin Falls study. The crop rotations on the two model farms are shown in
Table 45.
TABLE 44. IRRIGATED CROPLAND USE ON SAMPLE FARMS IN THE JEROME STUDY AREA
Percent of Irrigated Cropland
Croo
Alfalfa Hay
Small Grain
Dry Beans
Potatoes
All Corn
Sugarbeets
All Other
Small Farms
44
25
23
2
4
0
2
100
Large Farms
27
23
13
20
10
4
3
100
All Farms
33
24
16
13
8
3
3
100
85
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TABLE 45. CROPS GROWN ON MODEL FARMS FOR THE JEROME STUDY AREA
Area
Crop (he)
Small Farm Model
Commercial Beans 16.2
Spring Wheat 16.2
Alfalfa (5-year stand) 24.3
56.7
Large Farm Model
Potatoes 32.4
Commercial Beans 24.3
Spring Wheat 32.4
Alfalfa (4-year stand) 32.4
121.5
Farm Models - Boise Valley
The 23 sample farms in the Wilder-Parma study area were classified into
two size categories, as shown in Table 46.
TABLE 46. SIZE CLASSIFICATION OF SAMPLE FARMS IN THE WILDER-PARMA STUDY AREA
Size Category Number of Median Farm Size
(irrigated hectares) Farms (irrigated hectares)
Up to 100 15 56.7
More than 100 8 137.7
The principal crops on the sample farms were sugarbeets, alfalfa hay,
potatoes, wheat and barley. Irrigated cropland use in the Wilder-Parma area
is summarized in Table 47. Crop rotations for the two representative farm
models for this area are shown in Table 48.
The 47 sample farms in the Nampa-Melba study area were classified into
two size categories as shown in Table 49. The principal crops on the sample
farms were sugarbeets, corn seed, dry beans and wheat. Alfalfa was an impor-
tant crop on the smaller farms. Irrigated cropland use in this area is sum-
marized in Table 50. Crop rotations for the two representative farm models
are shown in Table 51.
86
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TABLE 47. IRRIGATED CROPLAND USE ON SAMPLE FARMS IN THE WILDER-PARMA
STUDY AREA
Crop
Sugarbeets
Alfalfa Hay
Potatoes
Wheat
Barl ey
Onions
Corn Silage
Alfalfa Seed
Dry Beans
All Other
Percent
Small Farms
30
15
14
13
10
1
5
0
6
6
100
of Irrigated Cropland
Large Farms
28
16
14
10
11
7
3
6
0
5
100
All Farms
29
15
14
11
11
5
4
4
2
5
100
TABLE 48. CROPS GROWN ON MODEL FARMS FOR THE WILDER-PARMA STUDY AREA
Area
Crop (ha)
Small Farm Model
Sugarbeets 16.2
Potatoes 16.2
Winter Wheat 16.2
Alfalfa Hay (3-year stand) 8.1
56.7
Large Farm Model
Sugarbeets 40.5
Potatoes 32.4
Winter Wheat 32.4
Alfalfa Hay (3-year stand) 32.4
137.7
87
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TABLE 49. SIZE CLASSIFICATION OF SAMPLE FARMS IN THE NAMPA-MELBA STUDY AREA
Size Category
(irrigated hectares)
Up
More
to 100
than 100
Number of
Farms
29
18
Median Farm Size
(irrigated hectares)
64.8
129.6
TABLE 50. IRRIGATED CROPLAND USE ON SAMPLE FARMS IN THE NAMPA-MELBA STUDY
AREA
Crop
Sugarbeets
Corn Seed
Dry Beans
Wheat
Bar! ey
Alfalfa Hay
Potatoes
Alfalfa Seed
Vegetables
Vegetable Seed
All Other
Percent
Small Farms
23
14
15
11
3
12
1
2
3
7
9
100
of Irrigated Cropland
Large Farms
31
11
8
10
10
3
8
5
9
3
2
100
All Farms
28
12
11
10
8
6
6
4
7
5
3
100
-------
TABLE 51. CROPS GROWN ON MODEL FARMS FOR THE NAMPA-MELBA STUDY AREA
Area
Crop (ha)
Small Farm Model
Sugarbeets 24.3
Corn Seed 16.2
Dry Beans 16.2
Alfalfa Hay (3-year stand) 8.1
64.8
Large Farm Model
Sugarbeets
Corn Seed
Dry Beans
Winter Wheat
COST EFFECTIVENESS OF SELECTED SEDIMENT CONTROL PRACTICES
The surface irrigation method under consideration in this section in-
volves tJie use of furrows or corrugates to distribute water over a field.
However, even with just one method of water application, the sediment loss
from a surface-irrigated field is a function of many parameters. Included in
these parameters are soil characteristics, field topography and the rate and
time of water application.
Irrigation water supply, return flow and sediment loss were estimated
for typical crop and field conditions in the study areas. The estimates of
annual sediment loss are presented in Table 52. These estimates assume silt
loam soils with slopes varying from one-haIf to four percent, and are based
on data obtained from field investigations conducted in the study areas over
the past five years (Ballard, 1975; Fitzsimmons et_ al_., 1977 and Watts et al.,
1974).
The physical effectiveness of the sediment reduction practices consid-
ered in this chapter was estimated on the basis of field experiments conduc-
ted by Fitzsimmons et^al_. (1977). These estimates are presented in Table 53
and are expressed in terms of the percentage reduction in the sediment, loss
that could be achieved by using a particular practice. The sediment loss
reduction practices are described in the following paragraphs.
89
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TABLE 52. SEDIMENT LOSS FROM SURFACE-IRRIGATED CROPS UNDER TYPICAL FARM
CONDITIONS IN THE BOISE AND MAGIC VALLEY AREAS
Annual Sediment Loss
Crops (kg/ha)
Potatoes 40,340
Corn, Beans and Sugarbeets 8,070
Small Grain and Peas 3,140
Alfalfa 900
TABLE 53. ESTIMATED SEDIMENT LOSS REDUCTION FOR SELECTED CONTROL. PRACTICES
Control Practice Sediment Loss Reduction
Flow Cutback 30
Vegetative Buffer Strip 50
Sediment Pond 67
Mini-Basins 90
Sprinklers 100
Sediment Loss Reduction Practices
Flow cutback involves running the usual amount of water down a furrow or
corrugate until the water is through to the lower end, then cutting the
stream size back for the remainder of the irrigation set. This reduced flow
results in less erosion and less soil transport in the furrows. However,
more labor is required to perform the cutback operation. In this study, it
was assumed that the irrigation labor requirement would be doubled because,
in essence, the water must be set and then reset. Based on the estimates in
Table 53, flow cutback would reduce the sediment loss from a field by 30 per-
cent. On a typical bean field, the total loss would be reduced from 8,070
kg/ha to 5,650 kg/ha.
Vegetative buffer strips are strips of close growing crops such as grass
or grain which are established across the lower end of a field to slow the
velocity of the water running off the field, causing it to deposit some of
its sediment. Crops that are normally planted with a drill can be double or
even triple-planted in a buffer strip across the lower end of a field.
90
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A sediment pond is a pond dug into a waterway for the purpose of reducing
flow velocity and retaining sediment. The effectiveness of such a pond de-
pends on its shape and size and on the volume of flow going through it. The
results presented previously (Table 28) show that on-farm ponds retain about
two-thirds of the sediment coming into them.
Mini-basins are small shallow ponds constructed at the lower end of a
field by putting in a low berm or dike along the bank of the drain ditch.
Other berms are constructed perpendicular to the drain ditch so that each
basin retains the runoff from a small number of furrows. Since the berm along
the drain ditch also serves as a spillway when necessary, it should be seeded
with grass to minimize erosion of the berm.
Sprinklers are in use. in many western areas, mainly in areas that do not
have facilities for surface irrigation or that have soils that are difficult
to surface irrigate. Some land is being converted to sprinkler irrigation
using power-move systems, largely for the sake of labor saving and field con-
solidation. It is usually possible to design and operate sprinkler systems so
that the water application rate is less than the soil intake rate. When this
is done, surface runoff and resulting sediment losses are eliminated.
Economic Analysis
The assumptions and calculations involved in determining the cost effec-
tiveness of selected sediment loss control practices are described in the
following paragraphs.
Flow Cutback - The irrigation labor that is typically involved in growing
a crop was computed on the basis of the farm survey data. For each crop, the
median number of irrigations was multiplied by 1.0 hour/hectare/irrigation to
compute the hours of irrigation labor used per hectare over the irrigation
season. This time does not include pre-season ditch work on the farm which
was computed separately for the crop budget.
It was assumed that the cutback procedure would double irrigation labor
time, which was valued at $3.00 per hour. Costs associated with the use of
the flow cutback method are presented in Table 5^. For purposes of compari-
son, the cost per metric ton ($/t) of sediment retained on the field is com-
puted on the basis of both a 30 percent and an 80 percent retention of the
sediment that would be lost under typical present management conditions. The
results of the previously discussed field investigations show a large vari-
ability in percentage retention achieved by cutting furrow flows back --
from 16 to nearly 100 percent.
Vegetated Buffer Strips - For row crops,the use of a grass or grain buf-
fer strip at the end of a field would probably entail taking some land out of
production. In order to estimate the area of land involved, it was necessary
to make some assumptions regarding field size and shape. From the farm survey
data, and from air photos in the Canyon Area Soil Survey, it was noted that
the majority of fields in the study area were either 4.05- or 8.1-ha tracts.
The 8.1-ha fields were usually rectangular, with dimensions of 201 by 402
meters. Water may run across either the short or the long side of the field
91
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TABLE 54. COSTS ASSOCIATED WITH USING FLOW CUTBACK TO REDUCE SEDIMENT LOSS ON A TYPICAL FARM IN THE
10
ro
Crop
Dry Beans
Bean Seed
Corn
Sugarbeets
Potatoes
Pea Seed
Winter Wheat
Spring Wheat
Alfalfa Hay
Number
of
Irrigations
7
8
7
10
12
5
5
4
6
Irrigation Labor
Normal
(hr/ha)
7
8
7
10
12
5
5
4
6
Cutback
(hr/ha)
14
16
14
20
24
10
10
8
12
Added
Labor
Cost
($/ha)
21.00
24.00
21.00
30.00
36.00
15.00
15.00
12.00
18.00
Sediment
30%
Retention
(t/ha)1
2.42
2.42
2.42
2.42
12.10
0.94
0.94
0.94
0.27
Retained
80%
Retention
(t/ha)
6.45
6.45
6.45
6.45
32.27
2.51
2.51
2.51
0.72
Cost
Sediment
30%
Retention
($/t)
8.68
9.92
8.68
12.40
2.98
15.96
15.96
12.77
66.67
of
Retained
80%
Retention
($/t)
3.26
3.72
3.26
4.65
1.12
5.98
5.98
4.78
25.00
't" is the abbreviation for tonne or metric ton (1000 kg)
-------
depending on the field slope. For the sake of standardization, it was as-
sumed that all field are 8.1 hectares in size and that the lower ends of the
fields are 300 meters in length. If the seeded strip is 2.44 m wide, then
732 m2 or 0.0732 hectares of land would be taken out of production.
It was further assumed that, for row crops, the lower ends of fields are
less productive per unit area than the rest of the field; that is, the land
taken out of production would have yielded 80 percent, of the field average
used in the crop budgets. For grain and peas, it was assumed thet a normal
harvest would be taken from the overplanted strip. No overplant procedure
was used with alfalfa.
The costs of taking row crop land out of production for vegetative
strips, based on opportunity cost or the value of production given up, are
presented in Table 55. "Calculations have not been included for potatoes
since a vegetative strip would probably be obliterated by the first irriga-
tion of the potatoes.
TABLE 55. OPPORTUNITY COST OF LAND TAKEN. OUT OF PRODUCTION FOP. VEGETATIVE
STRIPS (AVERAGE FOR FARM MODELS)
Net Return to Land
and Management
Crop
Dry Beans
Bean Seed
Corn Seed
Sugarbeets
Field
Average
($/ha)
529
988
806
875
Strip Area
(20% Lower Yield)
($/ha)
334
688
477
504
Opportunity Cost for
Taking 0.0732 ha of Land
Out of Production
m
24.45
50.36
34.92
36.90
The operating costs include the costs associated, with planting the strip
and spreading deposited sediment back on the field after harvest. For row
crops, the time involved in getting the drill set up to plant a strip, driving
to the field, planting the strip, driving back to the farmstead and putting
the drill away is difficult to estimate. In calculating labor and machinery
variable costs, the actual field time was multiplied by four in an attempt to
include all the steps in the operation. For grain and pea fields, only the
time involved in making another pass over the lower end of the field was used
in computing costs.
Machine field time and variable costs per hour of operation came from
the model farm budgets for grain enterprises. It was assumed that the farmer
already had the machinery and that machinery fixed costs had already been
allocated to crop enterprises. Therefore, no fixed costs were charged to the
strips. Table 56 shows the calculation of operating costs for row crops,
93
-------
grain and peas. Total annual costs for vegetative strips are shown in Table
57.
TABLE 56. ANNUAL OPERATING COSTS ASSOCIATED WITH USING VEGETATIVE STRIPS ON
8.1-HECTARE FIELDS
Row Crops
Machine variable costs for drill and tractor:
$3.88/hr x 0.86 hr/ha x 0.0732 ha x 4 = $ 0.98
Labor cost of seeding:
$3.00/hr x 0.86 hr/ha x 0.0732 ha x 4 = 0.76
Wheat or barley seed:
100 kg/ha x 0.0732 ha x $0.24/kg = 1.76
Sediment spreading:
$3.70/ha x 8.1 ha = 29.97
$33.47
Corrugated Crops Grain Peas
Machine variable costs for drill and tractor:
$3.88/hr x 0.86 hr/ha x 0.0732 ha = $ 0.24 $ 0.24
Labor cost of seeding:
$3.00/hr x 0.86 hr/ha x 0.0732 ha =0.19 0.19
Seed wheat = 1.76
Seed peas = 6.40
Sediment spreading:
$3.70/ha x 8.1 ha x .05 = 14.98 14.98
Total annual operating costs $17.17 $21.81
Sediment spreading could be accomplished by making an extra pass over the
field with a land plane. This would probably have to be done every year for
row crops and every other year for grain and peas. Based on figures from the
cost budgets, this operation would cost $3.70 per hectare.
Sediment Ponds - In determining the cost effectiveness of sediment ponds,
it was assumed that a pond would be used for each 8.1-ha field. Pond size
and excavation costs depend on the volume of sediment to be handled. The
figures used in this study are shown in Table 58. Since sediment spreading
costs are usually about equivalent to excavation costs, excavation costs were
doubled to arrive at the annual operating costs for sediment ponds (Table 59).
94
-------
TABLE 57. TOTAL ANNUAL COSTS ASSOCIATED WITH USING VEGETATIVE STRIPS ON 8.1-HECTARE FIELDS
Crop
Dry Beans
Bean Seed
Corn Seed
Sugarbeets
Pea Seed
Grain
Opportunity Cost of
Land Taken Out of
Production
($)
24.45
50.36
34.92
36.90
0
0
Total Costs
Operating
Costs
($)
33.47
33.47
33.47
33.47
21.85
17.17
Whole
Field
($)
57.92
83.83
68.39
70.37
21.85
17.17
Per
Hectare
($)
7.15
10.35
8.44
8.69
2.70
2.12
Sediment
Retained
(t/ha)
4.03
4.03
4.03
4.03
1.57
1.57
Cost of
Sediment Retained
($/t)
1.77
2.57
2.10
2.16
1.72
1.35
-------
TABLE 58. SEDIMENT POND SIZE AND EXCAVATION COST ESTIMATES FOR PONDS FOR
8.1-HECTARE FIELDS
Excavation Cost
Pond Size (@ $0.75/m3) Percent of Pond
Crop
Beans, Beets,
Corn Seed
Potatoes
Grain, Peas
Alfalfa Hay
(m3)
72
200
45
17
($)
54.00
150.00
33.75
12.75
Filled in One
50
100
30
25
Year
TABLE 59. ANNUAL OPERATING COSTS FOR SEDIMENT PONDS FOR 8.1-HECTARE FIELDS
Crop
Beans, Beets,
Corn Seed
Potatoes
Grain, Peas
Alfalfa Hay
Excavation and
Spreading Costs-Pond
Filled with Sediment
($)
108.00
300.00
67.50
25.50
Percent of
Pond Filled
in One Year
50
100
30
25
Annual
Operating
Costs
($)
54.00
300.00
20.25
6.38
To compute the costs associated with taking land out of production for a
sediment pond, the surface area of the pond was tripled to allow for margins
around it. This area was then multiplied by the value of output given up on
a cropped area of that size. Once again, row crop yields on these areas were
assumed to be 20 percent below field averages. Table 60 shows the opportunity
costs of the land taken out of production. The total annual costs for sedi-
ment ponds are presented in Table 61.
Mini-Basins - In this analysis, it was assumed that the land area taken
out of production for mini-basins would be the same as the area taken out by
vegetative strips. Thus, the opportunity cost for the two cases would be the
same. It was also assumed that the berm along the drain ditch bank would have
to be shaped and seeded every five years. The cost of this operation for a
96
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TABLE 60. OPPORTUNITY COST OF LAND TAKEN OUT OF PRODUCTION FOR SEDIMENT
PONDS FOR 8.1-HECTARE FIELDS
Crop
Dry Beans
Bean Seed
Corn Seed
Sugarbeets
Potatoes
Pea Seed
Winter Wheat
Spring Wheat
Alfalfa Hay
Net Return
Given Up
($/ha)
334
688
477
504
714
592
381
331
257
Land Opportunity Cost of
Area Land Taken Out
Lost of Production
(ha) ($)
0.018
0.018
0.018
0.018
0.038
0.010
0.010
0.010
0.006
6.00
12.38
8.59
9.07
27.13
5.92
3.81
3.31
1.54
300-m length of ditch bank is given in Table 62.
Maintaining mini-basins would involve spreading deposited sediment and
rebuilding the field berms every year on row crops and every other year on
grain and peas. For alfalfa, basins put in before establishment of the alfalfa
would serve for the duration of the stand. Basin construction costs are shown
in Table 63. The machine labor and shovel work costs shown in this table are
based on machine labor and shovel work times of 0.1 and 0.2 hours per basin,
respectively, and a labor cost of $3.00 per hour.
Since mini-basins retain 1.8 times as much sediment as vegetative strips
do for a given field and crop, sediment spreading costs for the basins were
assumed to be 1.8 times those for strips. Sediment spreading costs for the
basins are shown in Table 64. Total annual costs for the mini-basins are
given in Table 65. The operating costs are the sum of the cost of shaping and
seeding the ditch berm (Table 62), the basin constructions costs (Table 63)
and the sediment spreading costs (Table 64).
Sprinkler Irrigation - Any large scale conversion of surface-irrigated
lands to sprinklers would have many impacts that are beyond the scope of this
paper. The availability of power for pumping could be a major constraint in
some areas. Even so, it might be useful to look at the costs of installing
and operating a sprinkler system for comparison with the costs of other
methods of reducing sediment loss. In making this analysis, it was assumed
97
-------
TABLE 61. TOTAL ANNUAL COSTS ASSOCIATED WITH SEDIMENT PONDS FOR 8.1-HECTARE FIELDS
1C
oo
Crop
Dry Beans
Bean Seed
Corn Seed
Sugarbeets
Potatoes
Pea Seed
Winter Wheat
Spring Wheat
Alfalfa Hay
Opportunity Cost
of Land Taken Out of Operating
Production Costs
($) m
6.00
12.38
8.59
9.07
27.13
5.92
3,81
3.31
1.54
54.00
54.00
54.00
54.00
300.00
20,25
20.25
20.25
6.38
Total Costs
Whole
Field
($)
60.00
66.38
62.59
63.07
327.13
26.17
24.06
23.56
7.92
Per
Hectare
($)
7.41
8.20
7.73
7.79
40.39
3.23
2.97
2.91
0.98
Sediment
Retained
(t/ha)
5.38
5.38
5.38
5.38
26.89
2.10
2.10
2.10
0.60
Cost of
Sediment
Retained
($/t)
1.38
1.52
1.44
1.45
1.50
1.54
1.41
1.39
1.63
-------
TABLE 62. COST OF SHAPING AND SEEDING DITCH BERMS FOP. MINI-BASINS
Labor: 5 hr x $3.00/hr T 5 years = $3.00/year
Machine variable costs for tractor,
"V" ditcher and blade: 2.5 hr x $2.00 hr * 5 years = $1.00/year
Grass seed:
(area seeded - 300 m x 0.08 m = 240 m2)
240 m2 T 61.5 m2/kg of seed = 4.0 kg
4.0 kg x $2.20/kg * 5 years = $1.76/year
$5.76/year
that sprinkler systems would be designed and operated so as to eliminate run-
off and sediment losses from fields.
Cost estimates were computed for a side-roll sprinkler system, as shown
in Table 66. The system consists of a pump taking water out of a pond, a
mainline and six laterals for 56.7 hectares of irrigated crops on a quarter
section of land. Depreciation was calculated on a straight-line basis, with
a useful life of 15 years for all components and a salvage value of 10 per-
cent per year on the average investment, which is defined by the formula:
. T ... New Price + Salvage Value
Average Investment = - z
The annual depreciation and interest cost of the system would be $69.00 per
hectare. The costs of power and repairs amount to $3.70 and $2.50 per irri-
gation per hectare, respectively.
Table 67 shows the labor cost savings that would result from converting
the surface irrigation system to a side-roll sprinkler system. Ditch main-
tenance work would be reduced to one-third its present level (the remaining
time would be spent on the pond and supply ditch and on maintaining the pipe
system and controlling weeds along the mainlines). Irrigation labor, which
is valued at $3.00 per hour, would be reduced by 0.25 hours per hectare per
irrigation. Machine labor savings result from the elimination of operations
like land planing and corrugating that do not have to be performed with sprin-
kler irrigation. There would be no savings in the case of potatoes since they
are hilled under both methods of irrigation.
In Table 68, the total costs (net of labor savings) of owning and opera-
ting the sprinkler system are presented for each crop. The cost of sediment
retention is also shown.
99
-------
TABLE 63, BASIN CONSTRUCTION COSTS FOR MINI-BASINS ON 8.1-HECTARE FIELDS
o
o
Crop
Beans, Beets
Corn
Potatoes
Grain, Peas
Alfalfa Hay
Furrow
Spacing
(m)
1.12
0.76
0.91
0.76
0.76
Number
of
Furrows
per
Basin
4
4
4
6
6
Number of
Basins on
300 m of
Ditch
67
99
82
66
66
Machine
Labor
Cost
($)
20.10
29.70
24.60
19.80
19.80
Shovel
Work
Cost
($)
40.20
59.40
49.20
39.60
39.60
Machine
Variable
Cost
($)
13.40
19.80
16.40
13.20
13.20
Total Berm
Construction Costs
Each Time Annual
($) ($)
73.70 73.70
108.90 108.90
90.20 90.20
72.60 36.20
72.60 --1
Annual Cost = $72.60 + years of stand
-------
TABLE 64. SEDIMENT SPREADING COSTS FOR MINI-BASINS ON 8.1-HECTARE FIELDS
Crop Cost
Beans, Beets, Corn $53.95
Potatoes 74.92
Grain, Peas 26.96
Alfalfa Hay 7.74
Summary
The sediment loss reduction practices considered, in this study showed a
wide variation in cost effectiveness. Total annual costs per metric ton of
sediment retained are shown in Table 69 for each of the practices analyzed.
Flow cutback is the most expensive method associated with surface irri-
gation of retaining a given amount of sediment if the sediment loss can be ~
reduced by only 30 percent. Even with an 80 percent reduction, flow cutback
is less cost effective than mini-basins on all crops except potatoes and corn
seed.
On-farm sediment ponds can retain about two-thirds of the sediment loss
from all of the crops considered, at a cost of less than two dollars per
metric ton. On grain crops, a vegetative buffer strip compares favorably
with sediment ponds on a cost effectiveness basis. However, vegetative
strips generally retain less total sediment than ponds do.
Mini-basins retain more sediment than ponds or vegetative strips on a
given field. However, they are also more expensive both in terms of total
cost and the cost per metric ton of sediment retention.
Converting a surface irrigation system to a side-roll sprinkler system
would eliminate surface runoff and sediment losses from a farm but would in-
volve a large increase in costs over those associated with the use of other
control practices. Potatoes are an exception since the amount of sediment
loss from surface-irrigated potato fields is usually much greater than the
loss from other surface-irrigated crops. For other row crops, sprinklers
would cost about ten times as much per unit of sediment retained as would
sediment ponds and four times as much as mini-basins. On grain, sprinklers
would cost about eighteen times as much per unit of sediment, retained as
ponds and about six times as much as mini-basins.
FARM INCOME IMPLICATIONS OF SEDIMENT LOSS REDUCTION
The costs of employing practices such as those considered in this study
to reduce sediment losses from irrigated fields can also be discussed in
terms of their effects on farm income. In this sub-section, the previously
discussed farm models are used to describe how sediment loss control would
101
-------
TABLE 65. TOTAL ANNUAL COSTS ASSOCIATED WITH MINI-BASINS ON 8.1-HECTARE FIELDS
c
of
Crop
Dry Beans
Bean Seed
Corn Seed
Sugarbeets
Potatoes
Pea Seed
Winter Wheat
Spring Wheat
Alfalfa Hay (2-yr stand)
Opportunity Cost
Land Taken Out of
Production
($)
24.45
50.36
34.92
36.90
52.26
50.65
27.89
24.23
18.81
Operating
Costs
m
133.46
133.41
168.61
133.41
170.88
69.02
69.02
69.02
37.70
Tota'
Whole
Field
($)
157.86
183,77
203.53
170.31
223.14
119.67
96.91
93.25
56.51
1 Costs
Per
Hectare
($)
19.49
22.69
25.13
21.03
27.55
14.77
11.96
11.51
6.98
Sediment
Reta i ned
(t/ha)
7.26
7.26
7.26
7.26
10. 091
2.82
2.82
2.82
0.81
Cost of
Sediment
Retained
($/t)
2.68
3.13
3.46
2.90
2.73
5.24
4.24
4.08
8.62
Because of the large volume of sediment Involved, basins on a potato field would probably
1 Lup,before the season ended. For purposes of comparison, it was assumed that 25 percent
of the Incoming sediment would be retained.
-------
TABLE 66. ANNUAL FIXED COSTS OF A SIDE-ROLL SPRINKLER SYSTEM FOR
56.7 HECTARES OF LAND
Item
Lateral s
Mainline
50 HP Pump
Pond
Investment
Cost
($)
27,000
6,600
3,500
500
37,600
Annual
Depreciation
($/yr)
1,620
396
210
33
2,259
Annual
Interest
($/yr)
1,188
290
154
20
1,652
TABLE 67. LABOR COST SAVINGS RESULTING FROM THE CONVERSION OF A SURFACE
IRRIGATION SYSTEM TO A SIDE-ROLL SPRINKLER SYSTEM
Labor Cost Savings
Crop
Dry Beans
Bean Seed
Corn Seed
Sugarbeets
Potatoes
Peas
Winter Wheat
Spring Wheat
Alfalfa Hay
Number
of
Irrigations
7
8
7
10
12
5
5
4
6
Ditch
Maintenance
($/ha)
7.25
7.25
7.25
7.25
7.25
7.25
7.25
7.25
7.25
Irrigation
($7ha)
5.25
6.00
5.25
7.50
9.00
3.75
3.75
3.00
4.50
Machine
Labor
($/ha)
7.62
7.62
5.74
8.34
0
3.60
3.60
3.60
3.60
Total
($/ha)
20.12
20.87
18.24
23.09
16.25
14.60
14.60
13.85
15.35
103
-------
TABLE 68. COSTS OF OWNING AND OPERATING
RETENTION
A SIDE-ROLL SPRINKLER SYSTEM RELATIVE TO SEDIMENT
Crop
Dry Beans
Bean Seed
Corn Seed
Sugarbeets
Potatoes
Peas
Winter Wheat
Spring Wheat
Alfalfa Hay
Number
of
Irrigations
7
8
7
10
12
5
5
4
6
Power
Cost
($/ha)
25.90
29.60
25.90
37.00
44.40
18.50
18.50
14.80
22.20
Repair
Cost
($/ha)
17.50
20.00
17.50
25.00
30.00
12.50
12.50
10.00
15.00
Labor
Cost
Savings
($/hal
20.12
20.87
18.24
23.09
16.25
14.60
14.60
13.85
15.35
Depreciation
and
Interest
($/ha)
69.00
69.00
69.00
69.00
69.00
69.00
69.00
69.00
69.00
Net
Annual
Cost
($/ha)
92.28
97.73
94.16
107.91
127.15
85.40
85.40
79.95
90.85
Sediment
Retained
(t/ha)
8.07
8.07
8.07
8.07
40.34
3.14
3.14
3.14
0.90
Cost of
Sediment
Retained
($/t)
11.43
12.11
11.67
13.37
3.15
27.20
27.20
25.46
100.94
-------
TABLE 69. COST EFFECTIVENESS SUMMARY FOR SELECTED SEDIMENT LOSS CONTROL PRACTICES1
o
en
Crop
Dry Beans
Bean Seed
Corn Seed
Sugarbeets
Potatoes
Pea Seed
Winter Wheat
Spring Wheat
Alfalfa
Vegetative
Strip
1.77
2.57
2.10
2.16
1.72
1.35
1.35
--
Sediment
Ponds
1.38
1.52
1.44
1.45
1.50
1.54
1.41
1.39
1.63
Flow Cut-Back
Mini -Basins
2.68
3.13
3.46
2.90
2.73
5.24
4.24
4.08
8.62
30% Retention
8.68
9.92
8.68
12.40
2.98
15.96
15.96
12.77
66,67
80% Retention
3.26
3.72
3.26
4.65
1.12
5.98
5.98
4.78
25.00
Side-Roll
Sprinkler
11.43
12.11
11.67
13.37
3.15
27.20
27.20
25.46
100.94
XA11 figures are in dollars per metric ton of sediment retained
-------
affect the net returns to land and management (used as a measure of net farm
income) on representative farms in each study area.
Small Farm Models
Relationships between the level of sediment loss and the net returns to
land and management for the small farm models are presented in Figures 38,
39, 40 and 41. Points A through E in each of these figures correspond to the
sediment loss control practices or devices used on that particular farm model.
In each case, the points represent the data given in Tables 70, 71, 72 and
73, respectively, for the basic crop rotation (first row of data for each
practice). The sediment loss and net returns to land and management with
typical current management practices and crop mixes is shown as point A in
each figure. Adjustments to a sediment loss constraint set at some level
lower than point A are different for each farm model and are described in the
following paragraphs.
The cost curves presented in Figures 38 through 41 (right ordinate) show
the annual cost of sediment loss control for each farm model. In this case,
points A through E represent the reductions in net returns to land and manage-
ment resulting from the use of the corresponding sediment loss control prac-
tices or devices.
The data in each table indicate what happens to the net returns to land
and management as the crop mix is adjusted to meet a sediment loss constraint.
In each case, it was assumed that no land is retired from irrigated crop
production. Two of the small farm models include a grain crop on which a
vegetative strip could be used instead of a sediment pond to control losses.
On grain, vegetative strips are more cost effective than sediment ponds even
though they do not remove as much sediment. Since it was assumed that there
would be no runoff or sediment loss from sprinkler-irrigated fields, it was
not necessary to change the crop mix for sprinklers.
Twin Falls Area - As shown in Table 70, the total sediment loss from the
small farm model for the Twin Falls area with present management practices is
300 metric tons. This corresponds to point A in Figure 38. If a sediment
loss limit were set at a level between points A and C, the farm operator's
most efficient response (from a sediment loss control standpoint) would be
to put in enough sediment ponds to meet the constraint. All fields would
have sediment ponds at point C.
If the sediment loss were to be limited to a level between points C and
D, the farmer would have to use sediment ponds on some fields and mini-basins
on others. At point D, all fields would have mini-basins.
A sediment loss constraint set below 30 metric tons (point D) would
cause some crop mix adjustment. For example, changing the crop mix to in-
clude only alfalfa hay would reduce the sediment loss to 5 metric tons for
the mini-basin control practice (see Table 70). To reduce the sediment loss
below about 20 metric tons, the least-cost method would be to convert the
farm to sprinkler irrigation and go back to the original crop mix. For each
of the farm models, it was assumed that the conversion to sprinklers would
106
-------
TABLE 70. CROP MIX, SEDIMENT LOSS AND RETURNS TO LAND AND MANAGEMENT DATA
FOR ALTERNATIVE CONTROL PRACTICES. TWIN FALLS SMALL FARM MODEL
Control Dry
Practices Beans
No Sediment 8.1
Control
Vegetative 8.1
Strips
Sediment 8.1
Ponds
Mini-Basins 8.1
Crop Mix
Bean
Seed
24.3
24.3
24.3
24.3
24.3
24.3
24.3
24.3
(Hectares)
Pea Alfalfa
Seed Hay
8.1
8.1
8.1
8.1
8.1
8.1
8.1
8.1
8.1
8.1
8.1
8.1
16.2
24.3
48.6
56.7
16.2
24.3
48.6
56.7
16.2
24.3
48.6
56.7
16.2
24.3
48.6
56.7
Sediment
Loss
(t)
300
245
70
50
160
135
55
50
100
80
25
17
30
25
7
5
Net Returns
to Land and
Management
(!)
38,400
38,000
18,700
16,200
38,100
36,800
18,600
16,200
38,100
36,800
18,600
16,200
37,500
36,200
18,200
15,800
Sprinklers 8.1
24.3
8.1
16.2
33,100
107
-------
39
O
O
O
38
X
»
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D
I
- -NET RETURNS I -
ANNUAL COSTS 1
8 0
Q
X
7 ^
i
O
o:
6 Z
o
o
1 E J 0*
A -NO SEDIMENT CONTROL \ J
B- VEGETATIVE STRIPS I /
C -SEDIMENT PONDS \ /
D -MINI- BASINS I'
E -SPRINKLERS l/-
1
/
I
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, I
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300 200 100 0
SEDIMENT LOSS (metric tons)
Figure 38. Returns to land and management and costs
associated with different levels of sediment
loss, Twin Falls small farm model.
108
-------
not be gradual; that is, that either none of the fields would be sprinkler
irrigated or all of them would be.
Assumptions regarding the crop mix affect the results obtained for each
farm model. In this case, the maximum allowable area devoted to bean seed
was assumed to be 24.3 hectares. It was further assumed that the maximum for
pea seed would be 8.1 hectares and that the minimum allowable area for alfal-
fa hay would be 16.2 hectares.
The annual cost of sediment loss control (reduction in net farm income)
versus the level of sediment loss for this farm model is shown as a cost
curve in Figure 38. The annual sediment loss from this farm model could be
reduced from about 300 to 100 metric tons at a rather modest cost ($300 per
year) by using sediment ponds. It could be reduced by 90 percent by using
mini-basins at a cost of $900 per year. Reducing the annual loss below about
20 metric tons would require the use of sprinkler irrigation which would be
quite costly. In this case, the use of side-roll systems would reduce the
return to land and management by $5,300 per year, a reduction of about 14 per-
cent.
Jerome Area - The data in Table 71 show that farm income and sediment
loss values for the Jerome farm model are less than those for the Twin Falls
farm model. With present management practices, the sediment loss from the
Jerome farm is 205 metric tons (point A in Figure 39).
If a sediment loss constraint were set at a level between points A and
C, the farm operator could put in sediment ponds (or vegetative strips on the
spring wheat) to meet the constraint. Sediment ponds would have to be used
on all fields to meet a limit of 65 metric tons (point C). To meet a sedi-
ment loss limit set between points C and D, some fields would have sediment.
ponds and others would have mini-basins. At point D, all fields would have
mini-basins.
A sediment loss limit set below 20 metric tons (point D) would cause
some crop mix adjustment, or force a conversion to sprinklers. As shown in
Table 71, the sediment loss could be reduced to 5 metric tons if the only
crop grown with mini-basins is alfalfa. Further reductions in sediment loss
might be attained by retiring land from production, but the farm operator
would be more likely to install sprinklers or sell his farm (depending on his
financial situation). For this farm model, beans were constrained to a maxi-
mum area of 16.2 hectares and the minimum alfalfa area was set at 24.3 hec-
tares.
The reduction in farm income associated with sediment loss control for
the Jerome farm model is shown by the cost curve in Figure 39. Starting at
the present level of sediment loss (point A), the first increments of reduc-
tion have a relatively low cost. Reducing the loss to less than 5 metric
tons would imply a reduction in net farm income of $5,000, a decrease of
about 27 percent.
Wilder-Parma Area - Data for the small farm for the Wilder-Parma area
are given in Table 72. As can be seen, potatoes are included in the crop
109
-------
TABLE 71. CROP MIX, SEDIMENT LOSS AND RETURNS TO LAND AND MANAGEMENT DATA
FOR ALTERNATIVE CONTROL PRACTICES, JEROME SMALL FARM MODEL
Crop Mix (Hectares)
Control
Practice
No Sediment
Control
Vegetative
Strips
Sediment
Ponds
Mini-Basins
Dry Spring
Beans Wheat
16.2 16.2
32.4
16.2 16.2
32.4
16.2 16.2
32.4
16.2 16.2
32.4
Alfalfa
Hay
24.3
24.3
56.7
24.3
24.3
56.7
24.3
24.3
56.7
24.3
24.3
56.7
Sediment
Loss
(t)
205
125
50
115
75
50
65
40
17
20
13
5
Net Returns
to Land and
Management
($)
18,400
17,300
14,700
18,200
17,200t
14,700
18,200
17,200
14,700
17,700
16.700
14,300
Sprinklers 16.2
16.2
24.3
0
13,400
110
-------
i y
8 '8
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4fr
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35
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CD
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1 l5
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i i i 1
A
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i
*.if*r r+ffi ii-ikiM 1
-ANNUAL COSTS \
\E-
\
A NO SEDIMENT CONTROL \
B -VEGETATIVE STRIPS \ j
C -SEDIMENT PONDS \ 1
D -MINI -BASINS \i
E -SPRINKLERS 1
t
i
| \
1 \
I
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tft-
5 JE
O
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4o
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33
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-------
TABLE 72. CROP MIX, SEDIMENT LOSS AND RETURNS TO LAND AND MANAGEMENT DATA
FOR ALTERNATIVE CONTROL PRACTICES. WILDER-PARMA SMALL FARM MODEL
Control
Practice
Crop Mix
Sugar-
Potatoes beets
(Hectares)
Winter
Wheat
Alfalfa
Hay
Sediment
Loss
(t)
Net Returns
to Land and
Management
($)
No Sediment
Control
Vegetative
Strips
Mini -Basins
Sediment
Ponds
16.2 16.2
16.2
16.2
16.2 16.2
16.2
16.2
16.2 16.2
16.2
16.2
16.2 16.2
16.2
16.2
16.2
32.4
16.2
32.4
16.2
32.4
16.2
32.4
8.1
8.1
40.5
56.7
8.1
8.1
40.5
56.7
8.1
8.1
40.5
56.7
8.1
8.1
40.5
56.7
840
240
165
50
750
125
100
50
510
25
17
5
280
80
55
17
41,900
27,800
24,500
14,600
41,700
27,600
24,300
14,600
40,900
27,000
23,800
14,200
40,900
27,500
24,300
14,600
Ponds for Pota
toes, Basins
for Others
- 16.2
16.2
16.2
8.1
235
40,800
Sprinklers
16.2
16.2
16.2
8.1
0
35,900
112
-------
mix for this model. Since the large volume of sediment loss from potato
fields would probably fill mini-basins before the end of the irrigation
season, a relatively low sediment retention efficiency (25 percent) was
assumed for mini-basins for potatoes. As a result, the sediment loss for the
mini-basin practice is greater than the loss for sediment ponds when potatoes
are included in the rotation. The loss when sediment ponds are used for pota-
toes and mini-basins are used for the other crops (beets, wheat and alfalfa)
is shown as point D1 in Figure 40.
The unconstrained sediment loss for this farm model is 840 metric tons
(point A in Figure 40). If a sediment loss constraint were set at a level
between points A and C, the farm operator would have to put in sediment ponds
(or vegetative strips on the wheat) in order to comply. Sediment ponds would
have to be installed on all fields to meet a limit of 280 metric tons (point
D). To meet a sediment loss limit between points D and D1, some fields would
have mini-basins and some (including all of the potato fields) would have
sediment ponds. At point D1, all fields except the potato fields would have
mini-basins.
A sediment loss limit below 235 metric tons (point D1) would cause the
farmer to change the crop mix. If the farmer was required to reduce the
sediment loss below about 160 metric tons, the least-cost alternative would
be to install sprinklers and go back to the original crop mix. For this farm
model, beets and potatoes were constrained to a maximum area of 16.2 hectares
each and the minimum alfalfa area was set at 8.1 hectares.
The cost of sediment loss control for this farm model is also shown in
Figure 40. The cost of reducing the loss to about 28 percent of its present
level would be $1,100 which is about 2.5 percent of the present return to
land and management. It would cost the farm operator $6,000 per year to
reduce the loss to less than 160 metric tons through the use of sprinklers.
This would result in a 15 percent reduction in the net farm income.
Nampa-Melba Area - The crop mix and other data for the small farm model
for the Nampa-Melba area are given in Table 73. Although different crops
are involved, the graphs of farm income and sediment control costs for this
farm model (Figure 41) are similar in shape to those for the Twin Falls model.
The unconstrained sediment loss for this model is 465 metric tons (point A
in Figure 41). The farm operator would have to use sediment ponds to meet a
sediment loss constraint of 155 metric tons (point C) and would have to use
mini-basins if the constraint was set between 155 and 45 metric tons (point
D).
To meet a sediment loss constraint set between points D and E, the farm
operator could adjust his crop mix. As shown in Table 73 for the mini-basin
practice, substituting alfalfa for the other crops would reduce the sediment.
loss to less than 45 metric tons for this farm model. If the sediment loss
limit was set below about 30 metric tons, the farm operator's least-cost
alternative would be to convert to sprinkler irrigation and go back to his
original crop mix. For this model, sugarbeets and seed corn were constrained
to maximum areas of 24.3 and 16.2 hectares, respectively. The minimum alfalfa
area was set at 8.1 hectares.
113
-------
42
4 I
_ 40
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CD 39
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Z
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z
oc
38
37
36
<>
8
NET RETURNS
ANNUAL COSTS
A -NO SEDIMENT CONTROL
B -VEGETATIVE STRIPS
C -MINI-BASINS
D -SEDIMENT PONDS
D'-PONDS FOR POTATOES, BASINS
FOR OTHER CROPS
E -SPRINKLERS
E-
I
u
I
X
C Dji
i
J_
1
1000
Figure 40.
80O 600 400 2OO
SEDIMENT LOSS (metrictons)
Returns to land and management and costs
associated with different levels of sediment
loss, Wilder-Parma small farm model.
114
-------
TABLE 73. CROP MIX, SEDIMENT LOSS AND RETURNS TO LAND AND MANAGEMENT DATA
FOR ALTERNATIVE CONTROL PRACTICES. NAMPA-MELBA SMALL FARM MODEL
Control Dry
Practices Beans
No Sediment 16.2
Control
Vegetative 16.2
Strips
Sediment 16.2
Ponds
Mini-Basins 16.2
Crop Mix
Corn
Seed
16.2
16.2
16.2
16.2
16.2
16.2
16.2
16.2
(Hectares)
Sugar-
beets
24.3
24.3
24.3
24.3
24.3
24.3
24.3
24.3
24.3
24.3
24.3
24.3
Alfalfa
Hay
8.1
24.3
40.5
64.8
8.1
24.3
40.5
64.8
8.1
24.3
40.5
64.8
8.1
24.3
40.5
64.8
Sediment
Loss
(t)
465
350
230
60
235
200
135
60
155
115
75
20
45
35
25
6
Net Returns
to Land and
Management
m
41,300
39,300
30,900
16,700
40,900
38,900
30,700
16,700
40,900
39,000
30,700
16,700
40,000
38,200
30,100
16,300
Sprinklers
16.2
16.2
24.3
8.1
0
35,000
115
-------
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o 4I
8
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1-
2
UJ
V
2
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^w 1
-NET RETURNS >v '
. ANNUAL COSTS ^ ^
1 1
1
A -NO SEDIMENT CONTROL 1 '
B- VEGETATIVE STRIPS 1 l_
C- SEDIMENT PONDS ll"
D - MINI - BASINS U
E- SPRINKLERS if
I
1
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ll
1 *
1 1
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6tr
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-------
Reducing the sediment loss from this farm model to less than 30 metric
tons would require the use of sprinkler irrigation. This would result in a
15 percent or $6,300 reduction in net farm income (Figure 41).
Large Farm Models
Data and figures similar to those for the small farm models are presented
and discussed in the following paragraphs. The points in Figures 42, 43, 44
and 45 correspond to the same sediment control practices or devices used on
the small farm models. Each of the large farm models includes a grain crop
on which a vegetative strip could be used to effectively control some of the
sediment loss. The data for the four large farm models considered in this
study are presented in Tables 74, 75, 76 and 77.
Twin Falls Area - Crop mix, sediment loss and returns to land and manage-
ment data for the large farm model for the Twin Falls area are presented in
Table 74. The total sediment loss from the farm with present management
practicies is 615 metric tons. This loss corresponds to point A in Figure 42.
If a sediment loss limit were set at a level between points A and C, the farm
operator's most efficient response would be to use sediment ponds to meet the
constraint. Mini-basins would have to be used if the limit were set between
points C and D.
A sediment loss constraint set below 60 metric tons (point D) would
cause some crop mix adjustments. Alfalfa would have to be substituted for
wheat to reduce the loss to 55 metric tons, for dry beans to reduce the loss
to 40 metric tons and for bean seed to reduce it to 15 metric tons. To re-
duce the loss below about 35 metric tons, sprinkler irrigation would have to
be used along with the original crop mix.
For this farm model, pea seed was constrainted to a maximum area of 16.2
hectares, bean seed to a maximum area of 32.4 hectares and dry beans to a
maximum area of 24.3 hectares. A minimum alfalfa area of 32.4 hectares was
also specified.
The reduction in returns to land and management associated with sediment
loss control for this farm model is shown by the cost curve in Figure 42.
The first increments of sediment loss reduction are rather inexpensive. For
example, the loss can be reduced to about one-third its present level at a
cost of $600 per year. However, reducing the sediment loss to less than
about 35 metric tons would involve a reduction in net farm income of $11,700
or 17 percent.
Jerome Area - Data for the large farm model for the Jerome area are
presented in Table 75. Under present management practices, 32.4 hectares of
sprinkler-irrigated potatoes are included in the crop mix. The other crops
are surface irrigated.
The sediment loss from this farm under present conditions is 325 metric
tons (point A in Figure 43). Adoption of sediment ponds would reduce the
loss to 110 metric tons (point C). The use of mini-basins would reduce it to
35 metric tons (point D). The crop mix would have to be changed to reduce
117
-------
TABLE 74. CROP MIX, SEDIMENT LOSS AND RETURNS TO LAND AND MANAGEMENT DATA
FOR ALTERNATIVE CONTROL PRACTICES, TWIN FALLS LARGE FARM MODEL
Control Spring
Practice Wheat
No Sediment 24.3
Control
Vegetative 24.3
Strips
Sediment 24.3
Ponds
Mini -Basins 24.3
Sprinklers 24.3
Crop Mi
Dry
Beans
24.3
24.3
24.3
24.3
24.3
24.3
24.3
24.3
24.3
x (Hectares)
Bean
Seed
32.4
32.4
32.4
32.4
32.4
32.4
32.4
32.4
32.4
32.4
32.4
32.4
32.4
Pea
Seed
16.2
16.2
16.2
16.2
16.2
16.2
16.2
16.2
16.2
16.2
16.2
16.2
16.2
16.2
16.2
16.2
16.2
Alfalfa
Hay
32.4
56.7
81.0
113.4
129.6
32.4
56.7
81.0
113.4
129.6
32.4
56.7
81.0
113.4
129.6
32.4
56.7
81.0
113.4
129.6
32.4
Sediment
Loss
(t)
615
560
385
155
115
320
305
230
125
115
205
185
125
50
40
60
55
40
15
12
0
Net Returns
to Land and
Management
($)
70,500
69,500
65,500
40,900
36,100
69,900
68,900
65,100
40,900
36,100
69,900
68,900
65,100
40,700
36,000
68,600
67,600
63,900
39,900
35,200
58,800
118
-------
( £
O 70
0
O
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S 68
H
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3
0
«- 60
CO
QC
^
j- 58
Ul
i i I i i i
A
_ __ B C
»\ tm
.D
i
-ANNUAL COSTS \ £
_ i
A - NO SEDIMENT CONTROL I ,
B -VEGETATIVE STRIPS 1 J
C - SEDIMENT PONDS \ /
D -MINI -BASINS 1,
E - SPRINKLERS V
A
l\
I6g
O
X
A ^^^^F
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8 Ul
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0
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^t
2 i
z
600 500 40O 3OO 200 100
SEDIMENT LOSS (metrictons)
Figure 42. Returns to land and management and costs
associated with different levels of sediment
loss, Twin Falls large farm model.
119
-------
TABLE 75. CROP MIX, SEDIMENT LOSS AND RETURNS TO LAND AND MANAGEMENT DATA
FOR ALTERNATIVE CONTROL PRACTICES. JEROME LARGE FARM MODEL
Control
Practice
No Sediment
Control
Vegetati ve
Strips
Sediment
Ponds
Mini-Basins
Potatoes
32.4
32.4
32.4
32.4
32.4
32.4
32.4
32.4
32.4
32.4
32.4
32.4
Crop Mix (Hectares)
Dry Spring
Beans Wheat
24.3 32.4
56.7
24.3 32.4
56.7
24.3 32.4
56.7
24.3 32.4
56.7
Alfalfa
Hay
32.4
32.4
89.1
32.4
32.4
89.1
32.4
32.4
89.1
32.4
32.4
89.1
Sediment
Loss
(t)
325
205
90
180
120
90
110
70
25
35
20
8
Net Returns
to Land and
Management
m
69,500
67,600
61 ,700
69,200
67,500
61 ,700
69,200
67,400
61 ,600
68,400
66,700
61 ,000
Sprinklers
32.4 24.3
32.4
32.4
61,700
120
-------
70
69 -
2 68
X
z 67
LU
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O
5 65
O
§
-------
the loss below 35 metric tons. Sprinkler irrigation would have to be used
along with the original crop mix to reduce the loss to less than about 10
metric tons.
For this model, potatoes were limited to a maximum area of 32.4 hectares
and beans were limited to 24.3 hectares. A minimum alfalfa area of 32.4
hectares was also used.
The costs of sediment loss control for this model are shown in Figure 43.
These costs are low relative to the costs shown for the other farm models
because part of the farm is already sprinkler irrigated. Elimination of
sediment loss would cost $7,800 per year or 11 percent of the present net
returns to land and management.
Wilder-Parma Area - Crop mix and other data for the large farm model for
the Wilder-Parma area are given in Table 76. The crop mix for this model is
almost the same as the mix for the small farm model for this area. The rela-
tionships between farm income and sediment loss control shown in Figure 44
are also very similar to those for the small farm model. Again, point D'
represents the case where sediment ponds are used for potatoes and mini-basins
are used for the other crops.
The sediment loss from this farm under current management practices is
1,750 metric tons (point A in Figure 44). The use of sediment ponds would
reduce this loss to 580 metric tons (point D). To meet a sediment loss
constraint between points D and 0', some fields would have mini-basins and
some (including all of the potato fields) would have sediment ponds. At
point D1, all fields except the potato fields would have mini-basins. A
sediment loss limit set at less than 475 metric tons (point D') could be met
by substituting wheat for potatoes. A limit set below about 300 metric tons
would require the installation of sprinklers and a return to the original
crop mix (point E).
In this case, potatoes were constrained to a maximum area of 32.4 hec-
tares and sugarbeets were limited to 40.5 hectares. The minimum area for
alfalfa was set at 32.4 hectares.
The costs of sediment loss control for this model are shown by the cost
curve in Figure 44. Sediment loss could be reduced to about 28 percent of
its present level at a cost of $3,100 or about three percent of the present
net returns to land and management by using ponds for potatoes and mini-
basins for other crops. Reducing the loss below about 300 metric tons
through the installation of sprinklers would reduce the returns by about 14
percent.
Nampa-Melba Area - Data for the large farm model for the Namp-Melba area
are given in Table 77. This model differs from the others in that it in-
cludes no alfalfa. The lowest sediment yield, among the crops in the model,
comes from wheat.
The total sediment loss from this farm under present management prac-
tices is 925 metric tons (point A in Figure 45). This loss could be reduced
122
-------
TABLE 76. CROP MIX, SEDIMENT LOSS AND RETURNS TO LAND AND MANAGEMENT FOR
ALTERNATIVE CONTROL PRACTICES. WILDER-PARMA LARGE FARM MODEL
Crop
Control
Practice Potatoes
No Sediment 32.4
Control
Vegetative 32.4.
Strips
Mini -Basins 32.4
Sediment Ponds 32.4
Mix (Hectares)
Sugar-
beets
40.5
40.5
40.5
40.5
40.5
40.5
40.5
40.5
40.5
40.5
40.5
40.5
Winter
Wheat
32.4
64.8
32.4
64.8
32,. 4
64.8
32.4
64.8
Alfalfa
Hay
32.4
32.4
97.2
137.7
32.4
32.4
97.2
137.7
32.4
32.4
97.2
137.7
32.4
32.4
97.2
137.7
Sediment
Loss
(t)
1750
560
410
120
1540
290
250
120
1020
55
40
12
580
185
135
40
Net Returns
to Land and
Management
(I)
98,300
71,300
62,700
36,900
97,900
70,800
62,400
36,900
95,900
69,400
61 ,200
35,900
96,200
70,800
62,400
36,800
Ponds for Pota
toes, Basins
for Others
- 32.4
40.5
32.4
32.4
475
95,200
Sprinklers
32.4
40.5 32.4
32.4
84,100
123
-------
98
O
O
2 96
94
92
90
88
86
UJ
UJ
O
<
Q
Z
O
<
-I
O
CO
UJ
UJ
84
-NET RETURNS
ANNUAL COSTS
A-NO SEDIMENT CONTROL
B VEGETATIVE STRIPS
C -MINI-BASINS
D- SEDIMENT PONDS
D'PONDS FOR POTATOES, BASINS
FOR OTHER CROPS
E - SPRINKLERS
D.
2 Z
I80O 1500 I20O 900 600 300
SEDIMENT LOSS (metric tons)
Figure 44. Returns to land and management and costs
associated with different levels of sediment
loss, Wilder-Parma large farm model.
124
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TABLE 77. CROP MIX, SEDIMENT LOSS AND RETURNS TO LAND AND MANAGEMENT DATA
FOR ALTERNATIVE CONTROL PRACTICES. NAMPA-MELBA LARGE FARM MODEL
Control Dry
Practices Beans
No Sediment 24.3
Control
Vegetative 24.3 -
Strips
Sediment 24.3
Ponds
Mini-Basins 24.3
Crop Mix
Corn
Seed
24.3
24.3
24.3
24.3
24.3
24.3
24.3
24.3
(Hectares)
Sugar-
beets
56.7
56.7
56.7
56.7
56.7
56.7
56.7
56.7
56.7
56.7
56.7
56.7
Winter
Wheat
24.3
48.6
72.9
129.6
24.3
48.6
72.9
129.6
24.3
48.6
72.9
129.6
24.3
48.6
72.9
129.6
Sediment
Loss
(t)
925
805
685
405
465
405
345
205
310
270
230
135
95
80
70
40
Net Returns
to Land and
Management
($)
90,700
90,400
79,700
51 ,800
89,900
89,600
79,000
51 ,700
89,900
89,700
79,000
51 ,500
88,100
88,000
77,600
50,300
Sprinklers 24.3
24.3
56.7
24.3
78,000
125
-------
92
^90
O
O
O
X
40-88
UJ
UJ
O 86
O
Z 8 4
CO
cr
8 2
80
A
B
C
D
E
-NET
-ANNUAL COSTS
NO SEDIMENT CONTROL
VEGETATIVE STRIPS
SEDIMENT PONDS
MINI-BASINS
SPRINKLERS
12
o
^M
O
o
CO
I-
z
Ul
6 5
UJ
CO
CO
o
o
1000
8OO 600 400 200
SEDIMENT LOSS (metric tons)
Figure 45. Returns to land and management and costs
associated with different levels of sediment
loss, Nampa-Melba large farm model.
126
-------
to 310 metric tons by the use of sediment ponds (point C) and to 95 metric
tons by the use of mini-basins (point D). The farm operator would have to
change the crop mix to reduce the loss below 95 metric tons. If the farm
operator were required to reduce the loss below about 70 metric tons, the
least-cost method would be to convert to sprinkler irrigation and go back to
the original crop mix.
For this model, sugarbeets were constrained to a maximum area of 56.7
hectares and seed corn was constrained to an area of 24.3 hectares. The
minimum area of wheat was set at 24.3 hectares.
The costs of sediment loss control are shown by the cost curve in Figure
45. Like the cost curves for the other farm models, it shows that modest
costs are associated with the first 70 percent decrease in sediment loss and
that the costs to eliminate losses would be quite high. To reduce the sedi-
ment loss below about 70 metric tons would reduce the returns to land and
management by $12,700, a decrease of 14 percent.
SUMMARY
Based on the assumptions of this study concerning the physical effective-
ness of different control practices and devices, sediment losses from surface-
irrigated fields can be reduced to between one-half and one-third of their
present levels at a modest cost. This could be done by using on-farm sedi-
ment ponds (or vegetative buffer strips on grain) to remove the sediment from
the surface runoff from fields. The costs of ponds would average $475
annually on the small farm models and $950 annually on the large farm models.
As shown in Table 78, the reduction in net returns to land and management for
ponds is slightly more than one percent.
Compared with sediment ponds, mini-basins increase the amount of sedi-
ment retained on the model farms for all crops except potatoes. They also
increase the costs. For both sizes of farm models, the average sediment loss
reduction for the mini-basins is 82 percent (from 452 to 82 metric tons for
the small farm models and from 906 to 166 metric tons for the large ones).
The annual costs average $1,000 and $2,175, respectively, for the two sets of
farm models. These costs would lower the net returns to land and management
by slightly more than 2.5 percent.
Elimination of surface runoff and sediment losses would require the use
of sprinkler irrigation. This would cost an average of $5,650 annually on
the small farm models and $11,600 annually on the large farm models. The
resulting decrease in the net returns to land and management would be about.
15 percent in both cases.
127
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TABLE 78. SUMMARY OF SEDIMENT LOSS AND ANNUAL COST DATA
ro
oo
Sediment Loss (metric tons)
Base Ponds Basins Sprinklers
Small Farm Models
Twin Falls
Jerome
Wilder-Parma
Nampa-Melba
Average
Average decrease
Large Farm Models
Twin Falls
Jerome
Wilder-Parma
Nampa-Melba
Average
Average decrease
300
205
840
465
452
in net returns
615
325
1,750
925
906
in net returns
100
65
280
155
150
to
205
110
580
310
300
to
30
20
2351
45
82
land and
60
35
4751
95
166
land and
0
0
0
0
0
management (%)
0
0
0
0
0
management (%)
Annual Costs (dollars)
Ponds
300
200
1,000
400
475
1.4
600
300
2,100
800
950
1.2
Basins
900
700
1,100
1,300
1,000
2.8
1,900
1,100
3,100
2,600
2,175
2.6
Sprinklers
5,300
5,000
6,000
6,300
5,650
16.1
11,700
7,800
14,200
12,700
11,600
14.1
Pediment ponds on potatoes, mini-basins on other crops
-------
SECTION 9
OVERALL IMPACTS OF REDUCING POLLUTANT LOSSES
The general purpose of this phase of the study was to determine the over-
all effects of reducing pollutant losses from irrigated lands. The specific
purpose was to evaluate the aggregate effects of reducing the loss of sediment
and other pollutants from surface-irrigated fields in the Boise Valley. Bene-
fits may be derived both on the farm and further downstream by programs which
effectively reduce these losses. Pollutant losses from irrigated lands may
result in both a physical change in water quality and an actual reduction in
the well being of society. Water quality may decline, however, without an
immediately apparent impact on society.
METHODOLOGY
The approach used in this phase of the study was to first identify the
impacts of sediment and other pollutant losses on water quality and then to
identify and quantify the economic losses (if any) that result from these
losses. On-farm impacts of pollutant losses were determined by interviewing
irrigators in the Boise Valley and obtaining costs incurred because of sedi-
ment and other pollutant losses. The same approach was used for irrigation
districts and canal companies. Expenditures are necessary to clean and main-
tain canals and ditches where sedimentation occurs.
The impacts of pollutant losses on water quality were determined by
studying parameters associated with irrigation (specific conductivity, suspen-
ded solids, nitrogen and phosphorus). Comparisons were made of the level of
these parameters above Boise (before the water was used for irrigation or
other purposes) and at Notus or Parma which are near where the Boise River
flows into the Snake River. Changes in the quality of water in the Boise
River due to irrigation have detrimental impacts in the Boise Valley itself as
well as in the Snake River below its confluence with the Boise River. Asses-
sing these impacts in the Snake River becomes more difficult as one moves
further downstream and other streams enter the river.
WATER QUALITY
In the Boise Valley, surface water is used primarily for irrigation while
groundwater supplies individual, urban and industrial needs. Some groundwater
is also used for irrigation in the area.
Groundwater
Water departments in three Boise Valley cities (Boise, Meridian and Cald-
well) were contacted to determine if seepage from irrigation has affected
129
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groundwater quality in the area. At the date of this report, no major ground-
water users in the area have reported previous contamination of wells. The
state chemist for the Idaho Department of Water Resources reported that some
shallow wells had poor water quality because of poor construction. A study
of groundwater quality in the Boise Valley based on 200 samples found no dif-
ference in quality between 1953 and 1970 (Dion, 1972). Consequently, it was
concluded that surface irrigation has not affected groundwater quality except
in the case of a few poorly constructed shallow wells. Based on the sample
size and analytical methods used, one may question whether or not this study
is conclusive.
Irrigation has had a major impact on water table elevations in the Boise
Valley. An especially high water table exists in the lower downstream por-
tions of the Valley. Irrigation raises groundwater levels in many valley
areas in the latter part of the irrigation season. Because of this, it is
necessary for the city of Meridian to run four pumps year round to reduce high
groundwater levels. High groundwater levels are also a problem in the Cald-
well area.
High groundwater levels also create problems when basements are dug for
houses. When they become too high, sewage treatment plants may be ineffective,
resulting in raw sewage being dumped back into the Boise River. Also, septic
tank drainfields in the area do not function properly when groundwater levels
are too high. On the other hand, high groundwater levels may result in lower
pumping costs and may provide a flushing effect in drainage systems in the
Valley.
Surface Water
River Flows - The purpose of the storage system on the Boise River is to
spread the water supply over the growing season. The natural flow of the
Boise River, monthly canal diversions and return flows from drains in the area
(Musselman, 1973) are shown in Figure 46 for the 1973 growing season. The
natural flow of the river rises in April, peaks in May and then declines
throughout the summer months. Canal diversions are essentially constant from
May through August.
Based on the data shown in Figure 46, it would be expected that the pol-
lution from irrigation would be highest in the May through August period when
canal diversions are highest. The flow in the Boise River drops off drasti-
cally as water is diverted for irrigation. This, of course, would tend to
increase the concentrations of pollutants in the river.
The river water above Lucky Peak Dam (just upstream from Boise) is rela-
tively unspoiled by human activity and consequently provides a high quality
source of irrigation water for use further down the Valley. At several points
in the Valley, irrigation return flows are diverted again for irrigation
purposes. When the sediment load carried by these return flows is high, down-
stream users may suffer economic loss in order to either remove the sediment
before the water is used or to clean their ditches after the irrigation sea-
son. Prevention of sediment losses on the farms where they originate would
benefit downstream users.
130
-------
500
-------
Specific Conductivity - As a measure of the salt content of water, speci-
fic conductivity offers one of the better indicators of the impact of irriga-
tion on the quality of the water in the Boise River. Natural increases in
salt concentrations are to be expected as water flows toward the sea. Since
seepage and return flows from irrigated lands carry soluble salts into receiv-
ing ditches and streams, they can substantially increase salt concentrations
over natural levels.
Specific conductivity readings taken at Boise and Notus during 1973
(USDI, Geological Survey, 1973) are compared in Figure 47. The average
reading at Boise was 87.7 micromhos/cm as compared to an average reading of
499 micromhos/cm at Notus which is downstream from Boise. The higher average
reading at Notus indicates that the salt concentration in the Boise River
increases as one goes downstream. Also, the standard deviation about the mean
reading was much higher at Notus than at Boise. The monthly readings shown in
Figure 47 for Notus indicate that the specific conductivity is higher during
the fall and winter months than it is during the irrigation season. This may
be due to the fact that the river flows are lower during this period than they
are during the irrigation season and groundwater contributions are relatively
higher.
There is no evidence to support whether or not the salts in the Boise
River water cause any economic loss in the Boise River Valley or further down-
stream in the Snake River. The average specific conductivity of the water at
Notus, while being over five times as high as the average conductivity at
Boise, is not any higher than the conductivity of water samples taken from
wells in the area used for drinking water. The higher salt concentrations at
Notus during the growing season are probably due to irrigation. However, they
cause no known problems.
Data are available on a daily basis for the specific conductivity of
Boise River water at Notus (USDI, Geological Survey, 1973). Also, data on
stream discharges, diversions for irrigation and return flows from drains are
available. Using a model which makes specific conductivity a function of
stream discharges, diversions and return flows gave statistically significant
results for all three independent variables (all three are significant at the
one percent level). The results of this analysis for the 1973 irrigation
season were as follows:
Y = 450.121 - 8.971 X] - 0.801 X2 + 8.226 X3
where
Y = specific conductivity in micromhos/cm
X-j= discharge in cubic meters per second
Xg= diversions in cubic meters per second
X_= return flow in cubic meters per second
O
All variables are for the Boise River at Notus. The standard error for the
three independent variables are 0.8566, 0.1357 and 0.9174, respectively. The
corresponding t-values are -10.4734, -5.9024 and 8.9670, respectively. The
132
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o
8 60°
o
£
50°
O 40O
1
£
> 300
00
O
8
O
y=
I
CO
200
100
NEAR BOISE
AT NOTUS
_L
_L
OCT
NOV
DEC
JAN
FEB
MAR
APR
MAY
JUNE
JULY
AUG
SEPT
Figure 47. Specific conductivity of the Boise River near Boise and at Notus,
October 1972 through September 1973.
-------
multiple correlation coefficient for this analysis is 0.770 and the standard
error of estimate is 37.847.
Essentially, the preceding equation indicates that the specific conducti-
vity of the Boise River water at Notus increases as return flows increase and
decreases as diversions and discharge increase. The conclusion that can be
drawn from this analysis is that it is necessary to reduce return flows or in-
crease discharge and diversions in order to reduce salt concentrations in the
Boise River at Notus. Since the latter two variables are fixed for a given
year, the control or reduction of return flows seems to be the most logical
way to achieve this. This may not be entirely practical since a certain
amount of salts must be leached out of the soil to keep it productive.
Nitrogen - Various forms of nitrogen may be present in water due to numer-
ous human activities including farming. The data plotted in Figure 48 show
monthly variations in dissolved nitrite plus nitrate concentrations in the
Boise River below Lucky Peak Dam and near Caldwell from April 1973 to November
1976.l The dissolved nitrite plus nitrate concentrations below Lucky Peak Dam
are substantially lower than the concentrations near Caldwell. The average
concentration near .Caldwell was over seven times greater than that below Lucky
Peak Dam (1.09 versus 0.14 mg/1) which leads one to the conclusion that consi-
derable nitrogen is added to the Boise River as it flows from Lucky Peak Dam
to its mouth. It should not be concluded, however, that irrigation return
flows are the only source of the nitrogen in the river. Sewage, feedlots,
large dairy operations and pastures located adjacent to the river are also
possible sources of this nitrogen.
The data presented in Figure 48 indicate that nitrite plus nitrate concen-
trations are higher after the irrigation season (October through March) than
they are during the irrigation season (April through September). As in the
case of specific conductivity, the larger flows in the river during the irri-
gation season probably have a dilutive effect on the groundwater that enters
the stream. Nitrogen concentrations in the river water near Caldwell are not
any higher than they are in many of the groundwater observations wells in the
Valley. It was not determined that the nitrogen per se in the Boise River
caused any economic losses in the Boise Valley or further downstream. If the
population in the area continues to increase and to put additional demands on
the water supply, greater controls on the sources of nitrogen in the Boise
River may be necessary. Effective control measures could be very expensive.
Total Phosphorus - Total phosphorus concentrations below Lucky Peak Dam
and near Caldwell are shown in Figure 49 by months from 1973 to 1976. As with
the other constituents, the concentrations of total phosphorus near Caldwell
were higher than those just below Lucky Peak Dam (0.28 versus 0.04 mg/1).
Phosphorus concentrations in the river water were considerably higher than
those of water samples taken from area wells. However, data for comparisons
are scarce. There is no evidence of economic loss as the result of the in-
crease in the concentration of total phosphorus in the Boise River between
Lucky Peak Dam and Caldwell. However, nutrients and chemicals may be causing
Unpublished data, Northwest Region, U.S. Bureau of Reclamation, 1976.
134
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set
DISSOLVED NITRITE PLUS NITRATE (mg/L)
o ro i»
w o « o o»
n n
i
1
BELOW LUCKY PEAK DAM *
II
HIGHWAY 30 BRIDGE NEAR CALDWELL (I
i i
' i i
/ ' /^ A '
/ 1 . /VNJ
i '. / ' ' \
i / 7 / N
* A /- * ' « / \
\ / V 1 / t / i
\ / t / , / \
V I / /" \ /
; ', / ;
/ i ; 'i <
h- > / . \ ;
k -s/ \ ' \ '
x -^ ' >...' X '
*~ ^ s 1 ^'** ^-~~ 1 ^ ^*-~*-*' 1 ^ ~~'
1 1 1 1 1 1 t 1 1 1 1 t 1 1 1 'I 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1974
1975
1976
Figure 48. Dissolved nitrite plus nitrate concentrations in the Boise River below
Lucky Peak Dam and near Caldwell, April 1973 to September 1976.
-------
BELOW LUCKY PEAK DAM
9£L
TOTAL PHOSPHORUS (mg/L)
DO o o p o o
D l» W & Ol Jj>
HIGHWAY 30 BRIDGE NEAR CALDWELL
» i
f, I!
M M . , t
/'./'' /' '"'
, / M , / " ! .\ / i i :
r /\ / \ \ ._..' l ' \ .-' i ' '/"N
"\ / \' i / \/ i i 'V
1 ' 1 < '
1 ' 1 1 1 1
- ' 1 1 1 ,\ '
' i ; "
' -" -; A
A'-'" /\
^_x..^\._.^-x/ /Vv ^X /\/^ ^
~i i i i i i i i 1 i i I i i i i I i i i 1 i i i i i i i i i i i ii L i i i^i i i
1974
1975
1976
Figure 49. Total phosphorus concentrations in the Boise River below Lucky Peak Dam
and near Caldwell, April 1973 to September 1976.
-------
adverse downstream effects in Brownlee Reservoir on the Snake River (EPA,
1975).
Changes in the quality of the Boise River are apparently the result of:
(1) operations which result in the addition of various materials to the river
water and (2) diversions which reduce flows in the river to the point where
the concentrations of nutrients and other chemical constituents become detri-
mental. These factors may also encourage the growth of algae which results in
a loss of oxygen in the river water and less wildlife. Economic losses from
these factors are not known nor have values been estimated.
Sediment - Soil losses from fields are one of the greatest pollution
problems associated with surface irrigation. Both the individual farmer who
loses the soil and downstream water users suffer economic losses as a result
of these soil losses. Sediment concentrations in the Boise River below Lucky
Peak Dam and near Caldwell are shown in Figure 50. In general, sediment con-
centrations below Lucky Peak Dam are lower than they are near Caldwell. How-
ever, the data show instances where the reverse is true. In 1975 and 1976,
the concentrations near Caldwell were consistently higher than those below
Lucky Peak Dam. During the 1975 and 1976 irrigation seasons, the sediment
concentrations near Caldwell were 8 to 10 times higher than those below Lucky
Peak Dam. Most of this increase is due to irrigation return flows.
As shown in Figure 51, turbidity readings taken near Caldwell are higher
than those taken below Lucky Peak Dam. The readings, which are in Jackson
Turbidity Units (JTU), are a measure of the amount of suspended matter in a
sample of water which causes light to be scattered or absorbed rather than
transmitted through a sample. Most of the peaks in the readings shown in Fig-
ure 51 for^Caldwell occur during the latter part of the irrigation season.
Other peaks occur at other times which indicates that irrigation is not the
only source of suspended matter in the Boise River.
Treating Boise Valley Return Flows
The Corps of Engineers has studied the cost of treating drain water in
the Boise Valley (Corps of Engineers, 1976). Costs have been reported for
treating 13 major drains in the valley. The costs of the three levels of
treatment considered are summarized in Table 79.
Based on the costs given in Table 79, sediment ponds apparently pose the
only realistic alternative. According to the Corps of Engineers' report, the
pond system will not meet zero discharge standards for all constituents. The
anticipated performance of the sediment pond system is shown in Table 80. The
annual cost of this system was estimated at $17.50 per hectare. However, it
is open to question as to whether or not the results would be worth the costs.
It might be more effective to control the surface runoff from individual
fields rather than wait until the water is in the drains. In any event, the
ultimate treatment system (filtration-ion exchange) considered by the Corps of
Engineers is completely unreasonable from the standpoint of annual costs.
137
-------
200
BELOW LUCKY PEAK DAM
HIGHWAY 30 BRIDGE NEAR CALDWELL
130-
<
tr
z 100
n w
& o
LU
5
Q
UJ
CO
50
1974
1975
1976
Figure 50.
Sediment concentrations in the Boise River below Lucky Peak Dam and
near Caldwell, April 1973 to September 1976.
-------
40
^ 30
I-
~3
to Q
CD
(T
I- 10
BELOW LUCKY PEAK DAM
HIGHWAY 30 BRIDGE NEAR CALDWELL
1974
1975
1976
Figure 51. Turbidity readings taken in the Boise River below Lucky Peak Dam
and near Caldwell, April 1973 to September 1976.
-------
TABLE 79. COST OF TREATING RETURN FLOWS IN THIRTEEN MAJOR DRAINS IN THE BOISE
VALLEY (Corps of Engineers. 1976)
Cost of Items
Capital Investment
Annual Operation and
Maintenance
Capital Cost ($/ha)
Operation and Maintenance
Cost ($/ha)
Total Annual Cost ($/ha)
Sediment
Ponds
$1,500,000
190,000
15.00
2.50
17.50
Type of Treatment
Flocculation-
Sedi mentation
$67,000,000
6,700,000
642.00
64.00
706.00
Filtration-
Ion Exchange
$620,000,000
46,000,000
5,930.00
445.00
6,375.00
TABLE 80. ANTICIPATED PERFORMANCE OF SEDIMENT POND TREATMENT SYSTEM FOR BOISE
VALLEY DRAINS (Corps of Engineers. 1976)
Water Quality Improvement
Percent Removal
Suspended Solids
Turbidity
BOD
COD
Nutrients
Total Dissolved Solids
50 - 75
70
35
60
40
0
140
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IMPACT OF SEDIMENT LOSSES
In the Boise Valley, sediment from surface-irrigated fields may be depo-
sited in canals and drain ditches in the area or in the Boise River itself.
When canals and ditches receive large amounts of sediment, costs may be incur-
red to remove and transport the sediment to keep the canals and ditches oper-
ational. These costs are usually incurred by downstream farms who use return
flows for irrigation, irrigation districts and whoever maintains the drainage
systems. When fertile soil is washed from fields, both the landowner and
society suffers a loss in terms of future agricultural production. Conse-
quently, it is preferable to prevent erosion where it initially occurs.
Farm Ditch Maintenance Costs
Data on farm production costs were collected from 93 irrigated farms in
southern Idaho in the fall of 1975. Eighty-six of these farms had equipment
which was used for removing sediment from ditches and for spraying and burning
weeds growing on ditch banks. As shown in Table 81, the costs associated with
performing these operations varied from $9.99 per hectare for ISO-hectare
farms to $11.74 per hectare for 57-hectare farms. Higher costs would be
incurred by farmers, such as those in the lower parts of the Boise Valley,
using return flows which carry large quantities of sediment for irrigation.
Irrigation District Ditch Maintenance
Several organized irrigation districts in the Boise Valley supply water
from the Boise River to farmers in the area. These districts are managed by
the Boise Board of Control with offices in Boise. The Board of Control
manages the water distribution for 67,585 hectares of irrigated land in the
Valley. Independent irrigation districts manage the distribution for the rest
of the irrigated land in the area (about 59,500 hectares). In 1975, the oper-
ation and maintenance costs of the Boise Board of Control were about $24.00
per hectare or $2.20 per thousand cubic meters of water delivered. These
costs include costs for maintaining and cleaning canals and ditches in the
Valley in addition to costs for operating the water distribution system. The
Board of Control reported that considerable sediment enters their water dis-
tribution and drainage systems from grazing lands above the Valley and from
sprinkler-irrigated lands in the Dry Lake area south of Nampa. The costs of
ditch and canal maintenance for the Board of Control have been estimated to
be from $8.03 to $9.88 per hectare depending on the seriousness of erosion in
any one year.
Assuming a farmer cost of $11.74 per hectare and an irrigation district
cost of $8.03 per hectare, approximately $1,336,155 ($19.74/ha times 67,585
ha) is being spent each year in the area managed by the Boise Board of Control
to clean and maintain ditches and canals. Controlling sediment losses to a
greater extent would help reduce these costs.
IMPACTS OF NUTRIENTS AND OTHER POLLUTANTS
Not all of the pollution in the Boise River is due to irrigation. Other
sources include urban areas, industries and livestock operations. Even
141
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TABLE 81. ON-FARM DITCH MAINTENANCE COSTS. 19751
Costs ($/ha)
57-Hectare Farm 130-Hectare Farm
Ditching-All Costs
V-Ditcher2 $58.50 = . , $58.50 _ n .,
v mtcner 57 i.ud 13Q - o.4b
Tractor3 0.62 0.62
Labor (0.49 hr x 3.00/hr) 1.47 1.47
Total 3.12 2.54
Burning and Spraying-All Costs
Machinery (burner and sprayer)2 2x$58.50 , n7 2x$58.50 n Qn
57 " ^'u/ 130 ~ °'90
Tractor 0.62 0.62
Labor and Maintenance
(0.3 hr x 3.00/hr)
Materials (fuel and spray)
Total
Total Maintenance Cost
2.22
3.71
8.62
11.74
2.22
3.71
7.45
9.99
Equipment costs - equipment includes a V-ditcher, weed burner and
sprayer. Each costs about $600 new, has a 20-year life and a salvage
value of about $60.
2Fixed costs - depreciation ($540 * 20) plus interest of investment
(0.08 x $330) plus annual repair cost ($5.00) = $58.40 for each piece
of equipment (V-ditcher, burner and sprayer)
3Tractor and fuel costs - fixed costs for tractors, weed burners and
sprayers are allocated to their major uses (crop production). A very
small portion of their use is for ditch maintenance.
Ditching: 0.66 1/hr x 0.49 hr/ha =0.33 1/ha
Burning and Spraying: 0.53 1/hr x 0.62 hr/ha = 0.33 1/ha
The fuel cost (with gasoline @ $1.89/1) = $0.62/ha for ditching and
for burning and spraying.
142
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flooding of pasture lands contributes to the overall problem. The water qual-
ity status of the Boise River and two area drains is summarized in Table 82.
In the reach of the river above the irrigation drains (above Middleton), bac-
teria and turbidity are problems. Below this reach, temperature, dissolved
oxygen and aesthetics are also problems. Bacteria, turbidity, nutrients,
dissolved oxygen and aesthetics are local problems in the Ten Mile, Five Mile
and Indian Creek drains. Irrigation return flows probably contribute to the
temperature, nutrient, bacteria and turbidity problems in the river and the
drains.
TABLE 82. BOISE VALLEY STREAM SEGMENT STATUS RELATIVE TO WATER QUALITY, 1975
_ (Idaho Department of Health and Welfare. 1975) _
Segment Water Quality Stream
Description _ Standard Problems _ Classification _ Status
Boise River - Lucky Bacteria, occasional A1 WQL2
Peak to Middleton turbidity
Boise River-Mi ddleton Bacteria, turbidity, A WQL
to mouth temperature, dis-
solved oxygen and
aesthetics
Ten Mile and Five Bacteria, nutrients A WQL
Mile Creeks - and aesthetics
source to mouth
IndiaruCreek - source Bacteria and occa- A WQL
to mouth sional turbidity
A - primary contact recreational waters are for uses where
the human body may come in direct contact with the raw water to
the point of complete submergence
2WQL - water quality limiting
In all of the areas shown in Table 82, water quality is limiting. In
other words, water quality limiting (WQL) refers to any segment of a stream
where it is known that water quality does not meet applicable water quality
standards even after the application of effluent limitations required by regu-
latory agencies. Evidently the pollution problems of the Boise River are not
going to be solved by current legislation and the problems will continue, even
after some control measures are implemented, with present standards. A com-
prehensive water management plan may be needed for all competing wa^er uses in
the Boise Valley.
Pesticides
Although not caused by irrigation per se, pesticide contamination may be
143
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spread by surface irrigation return flows, especially in intensively cropped
areas. Bodhaine (1966) observed that about seven pounds of pesticide,
chiefly dieldrin and lindane, passed the Notus station each day during the
latter part of July, 1965.
A paper on the quality of water in the upper middle Snake River indi-
cates that the pesticide problem in the Boise River still existed in 1974
(EPA, 1975). In this paper, it is indicated that the highest pesticide level
was in the Boise River west of Parma. Data from this study indicated a sub-
stantial input of DDT into the area between Boise and Notus. It appears that
pesticides are still a problem in the Boise River and that they will continue
to be a problem as long as pesticides are used and surface return flows occur.
Return flows will have to be reduced or eliminated in order to reduce pesti-
cide levels in the river and still gain the benefits of their use. Again,
this could be accomplished by the introduction of water management, programs
which would reduce water use for irrigation and consequently reduce or elimi-
nate surface return flows. Sprinkler irrigation or much more closely managed
surface irrigation could help solve the problem.
Brown!ee Reservoir
In the paper on the quality of water in the upper Snake River (EPA,
1975), it was stated that:
The reservoir behind Brownlee Dam stores waters of the Snake
River which come partially from the Boise River. By the time
the Snake River leaves Brownlee Dam, it is a river of high
nutrient and pesticide levels and has a low dissolved oxygen
content. The station with the highest pesticide level was the
Boise River west of Parma. The dissolved oxygen standards are
violated at Brownlee Dam throughout most of the year. The
main problem areas of the upper Snake River are: (1) the
Portneuf River, (2) the Owyhee, Malheur, Boise and Weiser
Rivers and (3) the Milner Reach.
It was noted that, in comparison to the other tributaries and reaches of the
Snake River, the Boise River had the highest levels of phosphorus, nitrogen
and pesticides. Obviously the Boise River is not the only contributor to
problems in the Snake River, although it is probably a major contributor in
the Brownlee Reservoir area. What additional impacts the Boise River itself
has on downstream water users is unknown. No evidence has been found to indi-
cate direct economic losses. Where pollution problems from irrigation are
concerned, it is probably best to control pollutant inputs at the sources of
the problem rather than at downstream locations. It would seem that improving
on-farm management practices to reduce sediment losses and the introduction of
nutrients, pesticides and other chemicals into return flows would be the best
approach to solving these problems.
144
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Bower, C. A. and L. V. Wilcox. 1969. Nitrate content of the upper Rio Grande
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Brockway, C. E. 1976. Settling basins for irrigation return flows and fresh
pack effluent. Research Technical Completion Report, Idaho Water Re-
sources Research Institute, University of Idaho, Moscow.
Bristol, Andrew L. 1973. Phosphorous chemistry of some drainage water and
sediments from Irrigated land in the Boise River Valley. Unpublished
M.S. Thesis (Soils), University of Idaho, Moscow.
Busch, J. R., D. W. Fitzsimmons, G. C. Lewis and D. V. Naylor. 1972. Cultural
influences of irrigation drainage water. Proceedings, ASCE Irrigation and
Drainage Specialty Conference, Spokane, Washington.
Busch, J. R., D. W. Fitzsimmons, G. C. Lewis, D. V. Naylor and K. H. Yoo.
1975. Factors influencing the loss of nitrogen and phosphorus from a
tract of irrigated land. Paper 75-2543 presented at the ASAE Winter
Meeting, Chicago, Illinois.
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Carlson, Ronald D. 1974. A water, nutrient and sediment budget for an irri-
gated farm in the Boise Valley. Unpublished M.S. Thesis (Agricultural
Engineering), University of Idaho, Moscow.
Carter, D. L. 1976. Guidelines for sediment control in irrigation return
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Carter, David L. and James A. Bondurant. 1976. Control of sediments, nutri-
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Research and Development, U.S. Environmental Protection Agency, Ada,
Oklahoma.
Carter, D. L., J. A. Bondurant and C. W. Robbins. 1971. Water-soluble N03-
nitrogen, PO^-phosphorus, and total salt balances on a large irrigation
tract. Soil Sci. Soc. Amer. Proc. 35: 331-335.
Carter, D. L., M. J. Brown, C. W. Robbins and J. A. Bondurant. 1974. Phos-
phorus associated with sediments in irrigation and drainage waters for
two large tracts in southeastern Idaho. J. Environ. Quality 3: 287-291.
Claiborn, B. A. and C. E. Brockway. 1975. Impact of changes in irrigation
water management in eastern Idaho. Technical Completion Report, Idaho
Water Resources Research Institute, University of Idaho, Moscow.
Coffing, Arthur and Karl H. Lindeborg. 1966. Relationship between farm size
and ability to pay for irrigation water. University of Idaho Agricul-
tural Experiment Station Progress Report No. 112.
Dion, N. P. 1962. Some effects of land use changes on the shallow groundwater
system in the Boise-Nampa area, Idaho. Idaho Department of Water Admini-
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Ensminger, L. E. and J. T. Cope, Jr. 1947. Effect of soil reaction on the
efficiency of various phosphates for cotton and loss of phosphorus by
erosion. Agronomy J. 39: 1-11.
Fitzsimmons, D. W., C. E. Brockway, J. R. Busch, G. C. Lewis, G. M. McMaster
and C. W. Berg. 1977. On-farm methods for controlling sediment and
nutrient losses. Proceedings, National Conference on Irrigation Return
Flow Quality Management, Fort Collins, Colorado, May 16-19.
Fitzsimmons, D. W., J. R. Busch, G. C. Lewis, D. V. Naylor and R. D. Carlson.
1975. Establishing water, nutrient and total solids mass budgets for a
gravity-irrigated farm. Paper 75-2544 presented at the ASAE Winter
Meeting, Chicago, Illinois.
Fitzsimmons, D. W., G. C. Lewis, D. V. Naylor and J. R. Busch. 1972. Nitro-
gen, phosphorus and other inorganic materials in waters in a gravity-
irrigated area. Transactions of the ASAE 15: 292-295.
146
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Fitzsimmons, D. W., 6. C. Lewis, K. H. Lindeborg, J. R. Busch, D. V. Naylor
and D. H. Fortier. 1975. Effects of on-farm water management, practices
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(Walla Walla, Washington) Boise Valley Regional Water Management Study.
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irrigation waters in Idaho. University of Idaho Agricultural Experiment
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depletion from climate, crop and soil data. Transactions of the ASAE
14: 954-959.
Johnston, W. R., F. Ittihadich, R. M. Daum and A. F. Pillsbury. 1965. Nitro-
gen and phosphorous in tile drainage effluent. Soil Sci. Soc. Amer. Proc.
29: 287-289.
Law, James P.and Gaylord V. Skogerboe. 1972. Potential for controlling qual-
ity of irrigation return flow. J. Environ. Quality 1: 140-145.
Lewis, G. C. 1959. Water quality study in the Boise Valley. University of
Idaho Agricultural Experiment Station Bulletin No. 316.
Lewis, G. C., D. V. Naylor, J. R. Busch and D. W. Fitzsimmons. 1977. Ground-
water Quality in the Boise Valley. Report prepared for the Pacific North-
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Lindeborg, Karl. 1970. Economic values of irrigation water in four areas
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Mech, Stephen J. 1959. Soil erosion and its control under furrow irrigation
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Mech, Stephen J. and Dwight D. Smith. 1967. Water erosion under irrigation.
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Muir, J., E. C. Seim and R. A. Olsen. 1973. A study of factors influencing
the nitrogen and phosphorus contents of Nebraska waters. J. Environ.
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Musselman, Daniel L. 1973. Water distribution of Boise River, District 63,
1973. Boise River Board of Control Report.
147
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Naylor, D. V., G. C. Lewis, J. R. Busch and D. W. Fitzsimmons. 1976. Quality
of irrigation and drainage waters in the Boise Valley. University of
Idaho Agricultural Experiment Station Bulletin No. 97.
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Agron. Journal 36: 601-607.
Oliver, A. E. 1974. Analysis of settling basins. Unpublished M.S. Thesis
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Robbins, C. W. and D. L. Carter. 1975. Conservation of sediment in irriga-
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Stoltenberg, N. L. and J. L. White. 1953. Selective loss of plant nutrients
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149
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/2-78-138
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
EVALUATION OF MEASURES FOR CONTROLLING SEDIMENT
AND NUTRIENT LOSSES FROM IRRIGATED AREAS
5. REPORT DATE
July 1978 issuing date
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
D. W. Fitzsimmons, C. E. Brockway, J- R- Busch, L. R.
Conklin and R. B. Long (See Section 15)
8. PERFORMING ORGANIZATION REPORT NO.
. PERFORMING ORGANIZATION NAME AND ADDRESS
Idaho Agricultural Experiment Station
University of Idaho
Moscow, Idaho 83843
10. PROGRAM ELEMENT NO.
1BB770
11. CONTRACT/GRANT NO.
R-803524
12. SPONSORING AGENCY NAME AND ADDRESS ... nv
Robert S. Kerr Environmental Research LaboratoryAda»UK
Office of Research and Development
U.S. Environmental Protection Agency
Ada, Oklahoma 74820
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
EPA/600/15
IS. SUPPLEMENTARY NOTES
Other Authors: G. C. Lewis, K. H. Lindeborg, C. W. Berg, G. M. McMaster and
E. L. Mi dial son
16. ABSTRACT
Field studies were conducted in two southern Idaho areas to determine the effects
of different management practices on the quality and quantity of the runoff from
surface-irrigated fields. Pollutant removal systems (primarily mini-basins, vege-
tated buffer strips and sediment retention ponds) were installed at some of the study
sites and evaluated to determine their effectiveness in removing sediment and other
materials from return flows. The results indicate that water, sediment and nutrient
losses from surface-irrigated areas can be greatly reduced or eliminated by the use
of certain types of management practices and/or pollutant removal systems.
Linear programming models were used to determine the economic 'impacts of using
different types of practices to control surface runoff and sediment losses from model
farms. The results indicate that sediment losses from surface-irrigated fields can
be reduced by as much as 50 percent at modest cost. Elimination of surface runoff
and sediment losses would require the use of sprinkler irrigation systems and would
decrease net income by about 15 percent.
Some of the overall impacts of pollutant losses from surface-irrigated areas
were evaluated. The annual cost of removing sediment from canals and ditches in the
Boise Valley was found to be about $20 per hectare. Irrigation return flows contri-
bute to water quality problems in the Boise River and downstream in the Snake River.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/GlOUp
Irrigation, soil conservation, water
quality, salinity, economic analysis,
management
Boise Valley, Magic Val-
ley, irrigation return
flow, irrigation prac-
tices, nutrient and sedi-
ment loss control, econo-
mic impacts of control
measures
98C
3. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)
UNCLASSIFIED
21. NO. OF PAGES
164
20. SECURITY CLASS (Thispage)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
150
h 11.1 GOVnNMBIT nuniNG OfFKt 1978-757-140/1367 Region No. 5-11
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