United States
Environmental Protection
Agency
Robert S. Kerr Environmental
Research Laboratory
Ada OK 74820
Research and Development
EPA-600/S2-82-078 Oct. 1982
Project Summary
Evaluating Furrow Irrigation
Systems for Regional Water
Quality Planning
Wynn R. Walker and Gaylord V. Skogerboe
Field evaluations of furrow irriga-
tion practices at three Colorado loca-
tions were conducted during the 1979
irrigation season. The data were
utilized to assess four alternative field
evaluation procedures and develop
cost effectiveness relationships for
each method. A simulation formu-
lated from volume balance concepts
was also developed and calibrated
using the field data. The model was
used to evaluate the relationships
among furrow hydraulic and perfor-
mance parameters so that proper
alternatives for improving irrigation
efficiency could be determined.
Analysis of spatial and temporal
variabilities in the field indicates that
large errors are likely in field assess-
ments unless the study is comprehen-
sive. Testing should include the first
seasonal irrigation and at least three
later irrigation events. At least six
individual furrows should be studied
on each field.
Relationships among soil proper-
ties, furrow hydraulics, and irrigation
efficiency were not predictable unless
specific intake (infiltration) relations
were utilized as input data. However,
with this information it was possible
to identify the effects of changing
various irrigation practices upon
irrigation efficiencies.
This Project Summary was devel-
oped by EPA's Roberts. 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
Improved irrigation practices have
become increasingly important to
pollution control, water and energy
conservation, and increased food and
fiber production. Sixty-eight percent of
the total irrigated acreage in the United
States is surface irrigated. Furrow
irrigation, comprising a major portion of
this acreage, is characterized by running
water down small channels called fur-
rows located between crop rows. Pro-
perly designed and managed furrow
irrigation systems can result in high crop
production levels while conserving water
and energy resources. However, in-
herent system limitations coupled with
poor management practices can and
often do result in large deep percolation
and tailwater run-off volumes, which
frequently impact downstream water
quality.
Studies of the irrigation return flow
system have been concerned with the
severe problem of collecting data on a
scale large enough to ensure adequate
system characterization. Existing man-
power within planning agencies and the
funding committed to water quality
planning are likely to be insufficient to
facilitate studies of the same detail as
most research field studies. Conse-
quently, the investigative tools appli-
cable at the planning level must be
much simpler in order to accommodate
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the kinds of data that can be realistically
collected. The objective of this project
was to provide such a simplified, usable
computational aid and to concisely
describe the procedures and limitations
of the suggested approaches.
Furrow evaluation data were collect-
ed at six locations in Colorado on fields
with lengths ranging from 175 m to 625
m, slopes of 0.23% to 1.0%, and soils
ranging from loamy sand to clay loam.
These data provided the basis for
comparing four evaluation procedures
and calibrating a furrow irrigation
performance simulation model called
FURSIM.
Field Data Collection
Procedure
Farmers cooperating in the research
efforts were notified several months
prior to the irrigation season of the
nature and objectives of the field work.
An interview with each farmer estab-
lished the history of irrigation and tillage
practices for each field. Following these
initial interviews, groups of three or four
furrows were selected at each site to be
representative of general field condi-
tions.
Furrow lengths were measured and
staked at 25 meter intervals. The field
was surveyed to establish average field
slopes. Soil moisture sampling, furrow
cross-section sampling (with a profil-
ometer), blocked furrow infiltrometer
testing, and the setting of inflow and out-
flow measuring flumes were all accom-
plished on the day just prior to the first
and subsequent irrigations. During the
irrigation event, data collected included
advance times to each 25 m station,
inflow and outflow discharge readings,
and flow depth and top width measure-
ments for selected stations along each
furrow. In addition, recession times
were recorded at each station following
the termination of inflow (time of cutoff).
Two to three days following the irri-
gations, soil moisture and furrow cross-
section sampling was repeated.
Simulation Model
Development
The traditional volume approach for
predicting the distribution of water
under surface irrigation systems was
programmed. The model simulated
furrow irrigation performance as a
function of furrow discharge, time of
cutoff, soil moisture deficit, and number
of previous irrigations. The relations
between hydraulic variables were
described by a series of functions
determined by a regression analysis.
These "state variable" functions in-
clude relations for the advance coeffi-
cient and the basic intake rates. The
primary mathematical elements of the
model included (a) the furrow cross-
sectional flow area and the furrow
wetted perimeter; (b) Manning's rough-
ness factor; (c) a power function used to
characterize the rate of advance; (d) the
modified Kostiakov equation describing
infiltration with extension to incor-
porate wetted perimeter and seasonal
variation effects; and (e)the subsurface
water distribution profile.
In nearly every case where a reason-
able estimate of the infiltration charac-
teristics of the furrow was used as input
to the model, the predictive results were
satisfactory. Following the verifications
and calibration tests, the model was
used to indicate alternatives for improv-
ing irrigation performance at the local
site. For example, the effects of chang-
ing furrow discharge, time of applica-
tion, and irrigation frequency were
calculated.
Evaluation of Field
Procedures
All field data were reduced, coded in a
computer library, and organized for
each individual field. Then four levels of
field evaluation were devised in which
Procedure 1 is the simplest and Pro-
cedure 4 uses all of the "measured"
field data. The data required for each
procedure were extracted from the files
and used along with appropriate as-
sumptions to predict the actual field
performance of the irrigation, as com-
pared with the complete data set
(Procedure 4). In addition, data from a
single furrow and a single group of
furrows were used to predict the
average field performance. From these
analyses, relationships were developed
which indicated the accuracy of the
various procedures
The projected costs associated with
the use of each procedure were esti-
mated in terms of hours of labor and
equipment needs required for each field
evaluation procedure. Rather than
apportion hourly costs between those of
supervisor and one or two assistants,
the hourly wage was estimated as
seven dollars per hour. Equipment costs
were obtained from catalogs for equip-
ment available in the spring of 1980.
Costs for major items were apportioned
over an estimated useful life on an
annual basis without using a capital
recovery factor. The costs were then
related to the accuracy to yield a cost-
effectiveness function for each pro-
cedure. Examples of the results are
shown in Figures 1 and 2 for tailwater
(surface) runoff and deep percolation,
respectively. Similar plots were made
for cost-effectiveness related to irri-
gation application efficiencies. An
aggregate comparison of the results
indicated that the most detailed ap-
proach was less cost-effective than one
in which a larger number of furrows
were tested.
Conclusions
The accuracy of a field evaluation
procedure is directly proportional to the
cost of conducting the evaluation.
However, a procedure involving a
moderate level of field tests will yield
accurate results if the number of furrow
evaluations is increased. Consequently,
it was concluded that a moderate level
of detail in the field testing procedure,
but a large number of furrows tested,
was the most cost-effective program
(Procedure 3).
A volume balance computer simula-
tion of furrow irrigation performance
was shown to predict the effects of
various irrigation practices so long as
the infiltration rates of the soil are
accurately known Efforts to correlate
furrow and soil parameters with hy-
draulic and management parameters
were only partially successful. Never-
theless, it is concluded that the simula-
tion model can be used effectively on a
site-by-site basis following local calia-
tion
Recommendations
Measurements for evaluating an
existing furrow irrigation system should
include inflow and runoff (tailwater)
discharge, the rate of field coverage
(time of advance), soil moisture prior to
the irrigation, and a typical furrow
cross-sectional shape. At least three
furrows spaced across the field should
be tested during four irrigation events,
including the first irrigation event of the
season.
The basic volume balance analysis
should be used to evaluate the field data
and predict the effects of alternative
irrigation practices. Relating the cost of
improved practices to the level of
improved hydraulic performance will
allow an assessment of Best Manage-
ment Practices to be incorporated into a
water quality implementation program.
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720 r-
i Procedure 4 (Measured) o Procedure 1, & Procedure 2, o Procedure 3
o &
o
2 fi
ao
o
fip
0.7
0.2 0.3
0.4
fa,/ Benson Farm
Figure 1. Cost comparison for tailwater ratios at three farms.
0.5 0.6 0 0.5 1.0 1.5 2.0 0
Average Absolute Fractional Deviation
(b) Printz Farm
• Procedure 4 (Measured),
o Procedure 1, d Procedure 2,
120r
100 -
-§
Uj
o
Cj
0
0
0.1
0.2
0.3 0.4 0.5
Average Absolute Fractional Deviation
fbj Printz Farm
(a) Benson Farm
Figure 2. Cost comparisons for deep percolation ratios at three farms.
0.1 0.2 0.3 0.4
(c) Matchett Farm
D Procedure 3.
0.5
1.0
1.5
(c) Matchett Farm
0 US.GOVERNMENTPRWTINQOFFICE. 1962 -559-017/0843
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Wynn Ft. Walker and Gay lord V. Skogerboe are with Colorado State University,
Ft. Col/ins, CO 80523.
Alvin L. Wood is the EPA Project Officer (see below).
The complete report, entitled "Evaluating Furrow Irrigation Systems for Regional
Water Quality Planning," (Order No. PB 82-255 324; Cost: $13.50, 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
Ada, OK 74820
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business
Penalty for Private Use $300
0000329
ASENC'
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