United States
Environmental Protection
Agency
Robert S. Kerr Environmental
Research Laboratory
Ada OK 74820
vvEPA
Research and Development
EPA-600/S2-81-090 Sept. 1982
Project Summary
Controlling Sediment and
Nutrient Losses from Pacific
Northwest Irrigated Areas
Brian L. McNeal, Norman K. Whittlesey, and Vincent F. Obersinner
Environmental protection efforts
dealing with agricultural and nonpoint
sources have been increased since
passage of the Clean Water Act of
1977 and the subsequent implemen-
tation of the Rural Clean Water
Program. As part of the research on
the occurrence, movement, transfor-
mations, fate, impact, and control of
environmental contaminants, data
and analytical methodologies are
developed to assess the causes and
possible solutions of adverse environ-
mental effects of irrigated agriculture.
Efforts to achieve water quality
goals include the identification and
application of best management prac-
tices (BMPs) to control agriculturally
related water pollutants. This report
addresses the physical factors con-
tributing to sediment and nutrient
(phosphorus and nitrogen) losses from
irrigated croplands, methods of char-
acterizing water application to and
losses from such croplands, and the
economic techniques and/or factors
for assessing the costs of selected pol-
lution abatement practices. The meth-
odology and techniques described will
be useful in reaching technically
sound and economically feasible envi-
ronmental management decisions.
This report should especially benefit
environmental managers as they at-
tempt to identify and implement pollu-
tion control strategies relevant to
western irrigated agriculture.
This Project Summary was developed
by EPA's Robert S. Kerr Environ-
mental Research Laboratory. Ada OK,
to announce key findings of the
research project that is fully docu-
mented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
In October of 1 972, the U.S. Congress
passed Public Law (PL) 92-500, the
"Federal Water Pollution Control Act
Amendments of 1972." The most
immediate concerns of this legislation
were obvious point source discharges
of municipal and industrial wastes. On
a more gradual time scale, however.
focus was also to be directed at point
source and nonpoint source urban,
rural and agricultural discharges. Initial
emphasis in the point source agricultural
area was given to livestock and dairy
operations, and to clearly defined
irrigation return flows. Permits were to
be required for each such discharge.
Litigation concerning the minimum size
of irrigated unit requiring a permit
delayed implementation of point source
controls for irrigated areas. Subse-
quently, the Clean Water Act of 1977
(PL 95-217) completely exempted
irrigation return flows from the National
Pollutant Discharge Elimination System
(NPDES) permits and placed them
directly within the responsibility of
Section 208 (b), the area-wide waste
treatment management planning pro-
cess, to be administered by the planning
agencies of each state.
Planning for the control of nonpoint
source discharges from irrigated and
nonirrigated agricultural lands is well
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underway throughout the Pacific North-
west. Such planning, as required by
Section 208 of the Water Pollution
Control Act Amendments, is being
conducted in most cases under the
auspices of county or irrigation district
water quality committees. One purpose
of this report is to assemble and
disseminate information for use by local
groups in evaluating the extent to which
adoption of specific management prac-
tices should decrease the discharge of
sediment and fertilizer nutrients (partic-
ularly nitrogen and phosphorus) from
irrigated areas of the Pacific Northwest.
An equally important purpose is to
provide local planning groups with a
procedure for use in evaluating the
economic costs of management practice
changes, so that such groups can begin
to address the question of how such
costs should be borne for a given degree
of water quality pollution control.
Personnel from the Agricultural
Research Center at Washington State
University have been heavily involved
for several years in water quality
assessment and in evaluating economic
constraints on water quality control. A
detailed survey of nitrogen, phosphorus
and sediment discharge from the
Palouse dryland wheat region was
conducted in 1969-1971. A salt and
nutrient balance was conducted in
1970-1971 for the Wapato Project in
the Yakima Valley, and compared to
results for the same area in 1 940-1941.
This study was of particular value
because it provided corresponding data
for a typical Pacific Northwest irrigated
setting before and after commercial
fertilizers had been introduced and used
extensively. Effects of selected manage-
ment practices on nitrate leaching
from irrigated soils of the Columbia
Basin were evaluated during the period
1970-1974. Concurrently, economic
models were being constructed, and
economic evaluations of selected man-
agement practices were being made, in
order to determine the cost per unit of
water quality pollution control. Such
work, coupled with important on-going
research on water quality in other
Northwest states, has produced a timely
need to compile available information
for use by local water quality planning
committees. Objectives of the current
project have been to: (1) assemble,
refine and present to key personnel
from the Pacific Northwest a predictive
procedure for estimating sediment and
fertilizer nutrient losses from irrigated
portions of the area; and (2) present
analyses demonstrating basic approaches
and typical results when assessing the
economic consequences of adopting
selected pollutant control practices.
Study Approach
General cropping pattern information
was assembled for major irrigated
physiographic regions of Washington,
Oregon, and Idaho, as well as irrigation
system characterization data. Sources
of soil survey and landclass information
were identified to aid workers in
establishing model farm characteristics
for comparing physical and economic
effects of proposed management sys-
tems. Background information was
assembled on physical factors leading
to sediment and nutrient (phosphorus
and nitrogen) losses from irrigated
croplands, and on methods of charac-
terizing water application rates and
losses. Economic techniques and/or
factors for assessing the costs of
selected pollution abatement practices
are also discussed.
A relatively simple technique is
proposed for assessing losses of nitrogen
and of sediment (with associated
phosphorus) from Pacific Northwest
irrigated croplands. The technique
attempts to incorporate dominant
factors affecting erosion losses, as well
as the spatial nonuniformity of nitrate
leaching from furrow- and sprinkler-
irrigated lands of the region. Nutrient
loss estimates are generated for model
farms in the Magic Valley area of Idaho
and the Umatilla area of Oregon, along
with an economic analysis of selected
pollution abatement practices. These
results are compared to those from prior
studies in the Yakima Valley of Wash-
ington. The nutrient-loss estimation
technique, and the model-farm approach
to economic analysis, should beof aidto
Section 208 (PL 92-500) planning and
implementation programs in irrigated
portions of the Pacific Northwest.
Presentation of Findings
In Section 4 of the final report,
cropping pattern information is pre-
sented for major irrigated physiographic
areas of the Pacific Northwest, and
cropping pattern and irrigated acreage
trends for the period 1959-1974 are
summarized. These data emphasize the
predominance of relatively nonpolluting
hay and grain crops in many irrigated
areas of the region, and assist in
focusing on more highly erosive and
more heavily fertilized row-crop areas.
Also included are state-wide summaries
of irrigation system information, and
narrative highlights of irrigation system
data for individual physiographic areas.
These data demonstrate that furrow
irrigation still predominates in the
region, despite rapid conversion to
center-pivot sprinkler systems. Because
of the uneven nature and incomplete
coverage of soil survey and land
classification information for physio-
graphic areas of the region, no specific
data are presented in this category.
Sources of such information and their
use in nutrient-loss estimates are
discussed, however.
Section 5 reviews economic concepts
and policies related to the control of
pollution from irrigated agriculture.
Community property rights and private
property rights are contrasted, and costs
of pollution are illustrated via supply
and demand functions for trade goods.
The concepts of externalities and
opportunity costs are introduced priorto
a discussion of benefits and methods of
pollution abatement, and of income
distribution problems. The difficulties of
marketplace solutions to traditional
pollutant abatement problems are
stressed, and the transaction costs
associated with various types of liability
distribution are emphasized. Selected
abatement implementation policies are
reviewed, including effluent standards,
effluent taxes, subsidies, output taxes.
and input taxes and/or limits. The
section closes with a discussion of
various methods and philosophies
related to determining the "correct
amount" of pollution abatement.
In Section 6, the background material
is summarized which relates to sediment
and nutrient loss estimates for irrigated
lands. The determination of irrigation
requirements is included as a part of the
information necessary for nutrient loss
predictions, with major emphasis on the
concept of irrigation efficiency (E),
and on the subdivision of (1-E) values
into runoff, deep percolation, and
evaporative losses. Rooting depths and
water holding capacities are provided
for selected crops and soil types typical
of Pacific Northwest irrigated areas.
These are combined into values for
depletable soil moisture and numbers of
irrigations for crop-soil combinations
representative of the Magic Valley area
of Idaho and the Umatilla area of
Oregon. Allocation of efficiency, runoff,
and deep percolation values for current
and proposed irrigation systems is
outlined, including correction for varia-
tions in slope class and soil type. Net
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irrigation requirements and seasonal
water application estimates are provided
for the two study areas listed above.
The effects of various factors on
sediment and total phosphorus losses
are also reviewed, including slope,
stream size or percent runoff, tillage,
set length, soil texture, and crop type. A
methodology for predicting sediment
losses is outlined, based upon assign-
ment of a sediment-loss estimate for
prescribed base-level conditions, and
then assignment of multipliers to
account for changes in sediment loss
associated with variations in factors of
the type just described. Total phosphorus
loss is assumed to remain a constant
proportion of sediment loss. This
assumption will require refinement as
sediment and phosphorus loss data
become more widely available for
irrigated areas of the region, but it
serves as a suitable first approximation
at present. Background information on
nitrogen loss estimates (largely from
University of California studies) is
reviewed, and related to prior measure-
ments for irrigated tracts in the Pacific
Northwest. A methodology for predicting
nitrate leaching losses is outlined,
based on the amount of deep percolation
and nitrogen fertilization, with correc-
tions for nonuniformity of water appli-
cation (by dealing with the amounts of
deep percolation and'nitrogen fertiliza-
tion that might reasonably be expected
for tenth-field subunits of each irrigated
field) and for denitrification (as related
to surface-soil texture).
Section 7 summarizes the recom-
mended procedures for sediment,
phosphorus, and nitrogen loss estimates
for Pacific Northwest irrigated croplands.
In Section 8, the procedures for
estimating sediment, phosphorus, and
nitrogen losses are applied to two
Pacific Northwest irrigated areas (the
Magic Valley area of southcentral Idaho
and the Umatilla area of northcentral
Oregon). Model farms are established
for each area. Various irrigation system
and cropping pattern changes are
evaluated with respect to the sediment
and nutrient losses, and associated
economic costs, which each would
produce. For the Magic Valley, the use
of filter strips, sediment ponds, and
pump-back irrigation would all lie on the
"efficiency frontier" curve representing
sediment-loss abatement at minimum
cost. Use of improved furrow manage-
ment, cut-back irrigation systems, and
gated-pipe delivery systems would also
lie only slightly above the efficiency
frontier curve, but conversion to side-
roll sprinklers, multiset irrigation
systems, or alternBtive cropping patterns
would abate sediment loss only at
considerably higher cost.
With respect to nitrogen loss abate-
ment for the Magic Valley, use of
improved furrow management, cut-
back irrigation, or gated-pipe would all
be on the efficiency frontier curve, and
produce approximately 50 percent
abatement (in the case of cut-back
irrigation or use of gated-pipe systems)at
relatively little cost. Further abatement
of losses would require markedly higher
costs per unit of abatement, however.
For the Umatilla area, over 50 percent
abatement of nitrogen losses could be
effected through improved management
of center-pivot systems at relatively
little cost, but conversion to alternative
cropping patterns would abate nitrogen
losses only at considerable cost. The
remainder of this section summarizes
the similar studiesforthe Yakima Valley
of Washington.
The Appendix contains tabular data
required for sediment and nutrient loss
estimates, and economic appraisals, for
the Magic Valley area of Idaho and the
Umatilla area of Oregon.
Conclusions
Though considerable variation exists
between physiographic regions. Pacific
Northwest irrigated croplands have
continued to grow relatively large
amounts of hay, pasture, and small
grains. These crops are relatively
nonerosive and also have relatively low
potentials for nitrate leaching, except
for the initial plow-out period of alfalfa
fields. The greatest potential for soil and
nutrient losses is associated with
smaller amounts of furrow-irrigated,
row-crop acreage (potatoes, corn,
beans, etc.). Highly erosive conditions
also exist on some orchard lands of the
region, if cover crops are not being used.
Despite rapid conversion to sprinkler
(especially center-pivot) systems, furrow
irrigation remains the dominant irriga-
tion technique for most Pacific North-
west areas.
The technique used to estimate
sediment (with associated phosphorus)
losses from furrow-irrigated croplands
of the Pacific Northwest consists of
establishing base-level conditions, with
estimated sediment loss, and then
revising sediment-loss predictions as
physical factors (slope, soil texture, crop
type, stream size or percent runoff, etc.)
are changed for other areas or different
management conditions. Total phos-
phorus is assumed to remain a constant
proportion of eroded sediment. Though
overly simplistic, the technique at least
provides a framework with which to
compare additional sediment loss
values as they become available, and
through which needs for refinement of
the effects of various physical factors
should become apparent.
Nitrate leaching estimates generated
for well-characterized southern Cali-
fornia conditions were modified for the
Pacific Northwest, by incorporating an
estimate of the nonuniformity of water
application and a soil texture-dependent
denitrification multiplier. Such refine-
ment lowered the southern California
estimates, which were two- to three-
fold too large when applied directly to
Pacific Northwest irrigated tracts, to
more realistic levels.
Physical models of nutrient loss from
irrigated croplands have been coupled
to economic appraisals through a
model-farm approach Use of such an
approach for three Pacific Northwest
irrigated areas (the Magic Valley area,
Idaho; the Umatilla area, Oregon; and
the Yakima Valley, Washington) demon-
strates the effectiveness and associated
costs of selected pollution-abatement
practices. For example, a substantial
amount of nitrogen-loss abatement, 50
percent or more, can be achieved
without significantly affecting farm
income. Almost complete sediment-
loss abatement can also be achieved at
costs considerably below those of
conversion to center-pivot sprinkler
systems, an option which is being
adopted with increasing frequency
throughout the irrigated West. It becomes
very costly to achieve nitrogen-loss
abatement levels beyond 50 percent.
however, or beyond those that can be
achieved with managerial improvements,
inexpensive shifts in existing irrigation
systems, and sediment retention devices.
The last increments of combined
abatement, and particularly of nitrogen-
loss abatement, are achieved only at
extremely high cost.
Control practices to abate sediment
losses will generally have little effect on
the abatement of nitrogen losses. In
order to simultaneously achieve the
abatement of pollution from percolated
and runoff waters, it is necessary to
invest in more expensive irrigation
systems and/or to change to substan-
tially less profitable cropping patterns.
The finaf choice of pollution control
practices must be governed by the
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problem(s) to be solved and the available
funds for pollution abatement. There is
little reason to make expenditures for
pollution abatement that substantially
exceed derived benefits.
It must be recognized that edge-of-
field nutrient losses cannot be translated
directly to surface-stream water quality
impairment. Sediments and phosphorus
may be retained in drainage ditches
and/or redeposited on other cropland.
Nitrogen may be utilized by drainage-
ditch vegetation or by other crops
during return-flow reuse. Such redistri-
bution of sediments and nutrients must
be included in basin-wide models of
surface-stream quality.
This study only illustrates a methodology
that can be followed in arriving at
pollution abatement solutions for
irrigation return flows. Each problem
area must be analyzed for its own
characteristics, with specific agronomic,
soils, and economic data collected and
alternative control practices analyzed
for efficiency and effectiveness in
abating pollution. Choices must be
ma- " regarding the level of abatement
to je achieved and the distribution of
c ots for such abatement.
Generally it will be easier to share
costs incurred for capital investments in
items such as new irrigation systems or
ditch lining, for public investment in
capital items is generally assured of a
long-term change in levels of pollution.
An expenditure for implementing an
irrigation scheduling service or an end-
of-field filter strip, however, has no
assured effectiveness beyond the year
of investment. If the objective of federal
subsidies is to compensate the farmer
for income losses, year-to-year variations
in farm income due to changes in crop
prices or yields can raise sizeable
uncertainties about required expendi-
tures.
This study has shown that the most
cost-effective measures of pollution
abatement are those of a temporary or
nonstructural nature. These temporary
measures will be difficult to administer,
however. In the past, agencies such as
the Soil Conservation Service have
been reluctant to share costs of nonper-
manent soil conservation practices.
These and other problems must be
solved before widespread pollution
abatement programs can be implemented
for irrigated agriculture. This report
provides a current estimate of technical
knowledge and abatement alternatives
which can be applied to problems of
return-flow pollution. Knowledge will
change as experience is gained. The
information herein is only a suggested
foundation on which to build.
Recommendations
This study has illustrated a method-
ology for assessing the costs and
benefits of selected pollution abatement
practices for irrigation return flows The
methodology has intentionally been
kept simple to permit its usage and/or
visualization by relatively nontechnical
groups. It is hoped that this report will
encourage prior assessment of proposed
management changes by Section 208
(PL 92-500) personnel in order to
quantify probable abatement and cost
effects of planning efforts.
Management plans should be devel-
oped with a specific view toward the
elements to be abated and the desired
level of abatement to be achieved. It is
not useful to abate pollutants unless
derived benefits equal or exceed incurred
costs. This report shows that modest
levels of nutrient and sediment losses
can be abated rather inexpensively
through management improvements or
small capital expenditures. These
approaches should be considered prior
to employment of more effective, but
more costly or energy-intensive, irriga-
tion systems. Expensive and energy-
intensive sprinkler systems should not
be subsidized for abating nitrate losses,
for example, if realistic management of
fertilizer and water with present furrow-
irrigation systems can achieve adequate
abatement. On the other hand, it
sometimes will be necessary to turn toa
practice that is more expensive and/or
more energy-intensive than others in
abating a single pollutant, becauseof its
combined effectiveness in abating more
than one pollutant, such as leached
nutrients and eroded sediments.
Abatement plans should emphasize
education programs that will inform
parties about their potential role in
environmental improvement. Significant
quality improvements probably can be
achieved by some farmers without
costly investments or reductions in net
income. These efforts should be empha-
sized and implemented prior to the use
of subsidy programs that may also
affect subsequent freedom of decision
making.
This study primarily provides an
assessment of current knowledge for
estimating effluent quantities and
evaluating alternative abatement con-
trol measures. To achieve the desired
level of generality for this report, data
specific to all major irrigated regions of
the Pacific Northwest could not be
included. Hence, the data presented are
intended only as a foundation upon
which to build in solving problems for a
particular region. Similarly, the meth-
odology suggested for project assess-
ment is only an example of that which
might be useful or necessary in any
specific situation. It is recommended
that persons responsible for pollution
abatement planning obtain the assis-
tance of professional scientists (par-
ticularly in the areas of soils, agricultural
engineering, and agricultural economics)
to help build and evaluate alternative
programs. The costs of such assistance
are likely to be far less than the costs of
programs improperly perceived and
implemented.
Finally, it is recommended that
abatement programs be developed with
a careful view of the problems to be
solved and the benefits to be derived
from such resolution. It is not useful to
expend scarce capital or to reduce
agricultural outputs merely to reduce
effluents that are causing virtually no
problem. Similarly, there is no reason to
expend large sums to abate one compo-
nent, such as nitrates, if another such
as water temperature is really limiting
the quality of receiving waters. We must
not focus on the abatement of one
effluent pollutant simply because we
know how to reduce its level, if other
pollutants actually limit waterquality. In
short, we must be careful not to allow
the level of program costs to escalate
beyond the level of perceived and
measurable program benefits.
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Brian L. McNeal, Norman K. Whittlesey. and Vincent F. Obersinner are with
Washington State University, Pullman, WA 99164.
James P. Law, Jr. is the EPA Project Officer (see below).
The complete report, entitled "Controlling Sediment and Nutrient Losses from
Pacific Northwest Irrigated Areas." fOrder No. PB 82-255 357; Cost: $18.00,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Robert S. Kerr Environmental Research Laboratory
U.S. Environmental Protection Agency
P. O. Box /198
Ada. OK 74820
. S. GOVERNMENT PRINTING OFFICE: 1982/559-092/0516
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