vvEPA
United States
Environmental Protection
Agency
Robert S Kerr Environmental
Research Laboratory
Ada OK 74820
Research and Development
EPA-600/S2-81-034a July 1981
Project Summary
Irrigation Tailwater
Management
Kenneth K. Tanji, James W. Biggar, Robert J. Miller,
William O. Pruitt, and Gerald L. Horner
This investigation was undertaken
to obtain information and data on
irrigation tailwater and other
components of irrigation return flows
from two representative sites in the
Central Valley of California. Field
studies were conducted in the
Sacramento Valley where irrigators
divert water from the Sacramento
River and discharge return flows back
into the river, and in the west side of
the San Joaquin Valley where
irrigators import water from the
Sacramento River Basin and
discharge return flows into the San
Joaquin River.
This report contains extensive data
on the quantity and quality of supply
and drainage waters for the 1975-77
period. The study sites include the 664
km2 (164,076 ac) Glenn-Colusa
Irrigation District and the 113 km (70
mile) Colusa Basin Drain in the
Sacramento Valley, and the 1619 km2
(400,059 ac) Mendota-Crows
Landings Return Flow Group in the
San Joaquin Valley. Within these large
spatial units specific water district and
farm level studies were also
conducted in regard to tailwater
production, irrigation and drainage
practices and extent of reuse of return
flows by agriculture and wildlife areas.
Surface irrigation return flows vary
widely in both quantity and quality.
Site specific conditions and factors
contributing to such variations are
noted.
The results of this investigation
were evaluated to develop
conclusions and recommendations on
the control and management of
irrigation return flows, particularly
tailwater. These findings, which were
reviewed by local, state and federal
water agencies, will contribute to the
Section 208 Water Quality
Management Planning now being
conducted for nonpoint sources of
pollutants. Because irrigation return
flows may be highly variable and their
impacts on receiving waters may be
variable, it is suggested that due
considerations be given to their site
specific nature when developing best
management practices.
This Project Summary was develop-
ed by EPA's Robert S. Kerr Environ-
mental Research Laboratory, Ada,
OK, to announce key findings of the
research project this is fully docu-
mented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
Irrigation tailwater control and reuse
appears to be a deceptively simple
management practice, but in fact may
be a very complex practice because of
the many factors contributing to and/or
affecting tailwater and its quality. To
understand more fully this potential
control technology, field studies were
conducted in association with two of
California's first and largest NPDES
permittees- the Mendota-Crows
Landing Return Flow Group (MCLRFG)
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in the San Joaquin Valley and the
Sacramento Valley Water Quality
Committee in the Sacramento Valley.
These selected operating systems
provide case study information and data
to the public and policy makers for
developing better guidelines for the
management of tailwater.
The objectives of this project were-
(1) to identify and evaluate factors
contributing to or affecting
irrigation tailwater production
and its quality,
(2) to perform field studies in
selected areas in the
Sacramento and San Joaquin
River Basins,
(3) to determine the least-cost
combination of agricultural
production and labor, capital,
irrigation water, and tailwater
management and reuse; and
(4) to integrate scientific, engin-
eering, and economic appraisals
for the recommendation of
guidelines for best practical
technology for irrigation tail-
water management.
Prior to the completion of this report,
PL 92-500 was amended by the Clean
Water Act of 1977 (PL 95-217). The new
amendments affecting irrigated
agriculture include' 1) Irrigation return
flows are reclassified from point to
nonpomt sources of pollutants, and
hence are exempted from NPDES
permits; 2) Irrigation return flows and
their cumulative effects are considered
under Section 208 Areawide Waste
Treatment Management Plans along
with other nonpoint sources of
pollutants; and 3) a cost-sharing
program to be administered by the U.S.
Department of Agriculture (USDA) in
cooperation with the USEPA will be
established to provide technical and
financial assistance to landowners.and
operators in rural areas for
implementing Section 208 manage-
ment plans.
Figure 1 identifies the various
components of irrigation return flow
with a focus on the crop root zone
portion of irrigated lands The
"collected" surface irrigation return
flow may be comprised by both surface
runoffs and collected subsurface
drainage. The former may contain
irrigation water surface runoff
commonly referred to as "tailwater,"
operational spills from irrigation
distribution systems, and runoffs from
precipitation during the irrigation
season. The latter may contain collected
subsurface effluents from tile drainage
and drainage wells, and interception of
subsurface water flows by natural and
man-made open channels.
Irrigation tailwater in some quarters,
is considered to be the easiest
component of surface irrigation return
flow to manage and control It is said
that if tailwater is controlled and/or
reused, irrigation application efficiency
would be improved, water and energy
would be conserved, and at the same
time discharge of pollutants would be
substantially reduced Although
tailwater management appears to be a
logical and practical control technology,
it has not been thoroughly evaluated
with regards to economic, legal,
institutional, and physical constraints.
Before a blanket recommendation on
irrigation tailwater management is
made, there is a need to investigate
more fully such a management/control
policy.
Conclusions
The results of this field study can be
presented in three parts. 1) quantity of
tailwater production, 2) quality of
tailwater produced, and 3) control and
management of tailwater quantity and
quality
Tailwater Quantity
Tailwater (irrigation surface runoff) is
only one of several components
Applied Water
and Rainfall
Evapotranspiration
Surface
Return Flow
Collected
Subsurface
Drainage
Deep Percolation
Figure 1. The major water-flow pathways in the root tone portion of irrigated
lands
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comprising surface irrigation return
flows Other components "collected"
surface return flows from irrigated
lands are precipitation runoff,
operational spills from distribution
systems, effluents from tile drainage
and drainage wells, subsurface waters
intercepted by natural and man-made
open channels, and discharges into
irrigation drains by other sectors of
society, for example, municipal storm
water runoffs and treated sewage
effluents Tailwater is not usually
collected in a dram separate from other
collected return flows. In the Central
Valley of California the 2.43 x 103-km2
(0 6 million ac) Westlands Water
District is the only large irrigation
project that is developing a drainage
collection system that separates
surface runoff from tile drainage
Tailwater discharged from irrigated
Ids may not always reach a receiving
surface water body due to evaporation
losses, infiltration into the land surface,
evapotranspiration by phreatophytes
and other vegetation, and recovery and
reuse by downstream irngators and
other sectors of society. In areas where
precipitation occurs during the
irrigation season, it is difficult to
differentiate the magnitudes of runoffs
between rain-fed and applied irrigation
waters. In most instances it is difficult to
accurately measure tailwater
production from a given field because
tailwater is produced intermittently,
coinciding with irrigation schedules.
Unless tailwater is collected in a sump
or drain it is usually discharged diffusely
as a nonpomt source.
The factors contributing to and/or
affecting on-farm tailwater production
are manifold. In areas where water is
scarce or expensive, tailwater is seldom
discharged or, if produced, is generally
reused at or close to the site of
production. Although the price of water
is not the only factor dictating water
reuse, a general observation indicates
that as irrigation water costs increase
tailwater recovery systems become
economically advantageous. Also in
time of drought conditions, such as the
1977 drought in California, irrigation
water is more carefully managed and
reuse is more extensively practiced. In
areas where water is plentiful or
inexpensive, there is a tendency for
large water applications and production
of tailwater. The production of tailwater,
however, does not necessarily mean
inefficient water management since
reuse is commonly practiced.
The tailwater produced is usually
captured and reused, either by plan or
incidentally, at the site of production or
downstream. The reuse of tailwater and
other collected return flows may occur
at several spatial levels, for example,
within an individual irrigated field, on-
farm (i.e., capture and reuse in
downslope field by landowner), district
level (irrigation, drainage, reclamation),
and uptonversubbasm, river basin, and
interbasm levels.
The types of beneficial uses made of
tailwater and other collected irrigation
return flows include irrigation of crops
and pasture, maintenance of
wetland/waterfowl habitats, livestock
water supply, groundwater recharge,
maintenance of summer (low) flows in
stream beds which would otherwise
become dry, repulsion of salinity in tidal
estuaries, fish migration and spawning,
warm water fish habitat, navigation,
recreation and aesthetics, and
municipal/industrial water supply
One of the major factors contributing
to the production of tailwater is
irrigation application method. Surface
flood irrigation methods (basin, border,
furrow), have inherent limitations,
making it difficult to attain high
application efficiencies. The slope of the
irrigated field, length of run, size of
stream used, and water intake
(infiltration) rates are some of the
critical factors affecting tailwater
production. These critical factors must
be balanced within a system to obtain
efficient water application. Tailwater is
less frequently produced in well-
designed and properly managed
sprinkler and drip irrigation systems. In
surface flood irrigation, however, it is
difficult to attain application
efficiencies in excess of 85% for basin
and border methods and 90%forfurrow
method. It is exceedingly difficult to
completely eliminate runoffs from flood
irrigation methods other than from level
borders and basins or level furrows.
These estimated runoffs and attainable
irrigation system efficiencies are
dependent not only upon system design
but also upon technical skills of
irngators.
Tailwater Quality
The quality tailwater usually is
similar to that of the applied water but
could be quite variable, sometimes an
improvement and other times a
deterioration in overall quality and/or
specific parameters. The quality of
applied water usually has a strong
influence on the quality of tailwater. In
some instances, tailwater quality may
be considerably degraded because of
the pickup of dissolved mineral salts,
sediments, and agricultural chemicals
In other instances, tailwater quality
may be improved over that of the
applied water. This is possible because
of the deposition of suspended solids
which may contain sorbed agricultural
chemicals as well as the potential
reduction of degradable pollutants as in
flooded rice fields.
Significant changes in tailwater
quality may occur abruptly over a short
time period or over an extended period
For instance, aerial applications of
ammonium sulfate fertilizer in rice
fields may result in a pulse of ammonia
(NHa) and nitrates (NOs) in the runoff
waters over a two-to-four-day period
whereas suspended solids in the flood
waters are significantly reduced by
sedimentation over the rice growing
season.
Suspended matter is frequently the
quality parameter of most concern m
tailwater. Water passing over the land
surface has a tendency to erode the soil
and to transport both mineral and
organic matter in a suspended form
Associated with the suspended matter
are several classes of water quality
constituents such as sorbed pesticide
residue and other toxicants like certain
metals and boron (B), nutrients like
phosphorus (P) and nitrogen (N), and
certain soil minerals like gypsum
(CaS04 • 2H2O)which may laterdissolve
in the water contributing to a rise in
salinity. Thus, the reduction of
sediments in tailwater will not only help
in minimizing the undesirable impacts
of sediment per se, but also decrease
the discharge of pollutants associated
with the sediments.
Other pollution and/or quality
parameters in tailwater may be of
importance for site-specific conditions
and practices. Nitrogen may be picked
up by tailwater in both organic and
inorganic forms as well as dissolved and
particulate forms. In general, runoff
waters from close-growing crops (e g ,
rice and pasture) contain a predomi-
nance of organic nitrogen over that of
inorganic forms (NH3, N03, N02) and
vice versa from widely-spaced crops
(e.g., row crops).
In the reuse or renovation of high
nitrogen-containing wastewaters,
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however, large reduction in nitrogen in
the effluent may be achieved by passing
water overland on grasslands or in
anaerobic ponds. The reduction is
attributed to demtnfication and
assimilation by plants.
Phosphorus, like nitrogen, exists in
many forms. In general, the
concentration of dissolved phosphorus
is low in tailwater due to the low
solubility of phosphorus compounds
However, significant amounts
associated with mineral and organic
matter may be discharged in runoff
Pesticide residue may be present in
tailwater, but the concentrations of
pesticides are highly variable both in
time and location. This is due to the
wide variability in mode of applications,
formulations, soil interactions, and
chemical properties such as solubility,
volatility, and biodegradability.
Tailwater Control and
Management
There appears to be no one universal
control technology for tailwater and
other collected surface irrigation return
flows due to the wide variability in the
quantity and quality of supply waters
and return flows. The various
management practices may include one
or more of the following: improve
irrigation application efficiencies to
attainable levels, capture usable
irrigation return flows, discharge
tailwater only as required by cultural
practices, install sediment retention
sumps or other facilities, install
tailwater recovery system and reuse at
farm site, allow for limited tailwater
discharge under either low stream flow
conditions to augment/maintain flow
when it is desirable or under high
stream flow conditions to minimize
impact of pollutants discharged, and
elimination of discharge of tailwater.
The above technology is available,but in
some, the systems or water controls
needed are so costly that current
conditions do not justify them. For
instance, to allow for limited tailwater
discharge under either low or high
stream flows may require large holding
reservoirs if the timing between
tailwater production and discharge
allowed into streams do not coincide.
The application of the foregoing array
of possible technology should be site-
specific. Although there may be some
that can be broadly applied, there is no
single, universally-applicable control
technology for irrigated agriculture.
Elimination of tailwater at aH sites is not
practical or feasible. These control
technologies also may be viewed in
terms of source control, effluent
treatment, and reuse.
The least-cost combinations of agri-
cultural production and labor, capital,
irrigation water, and tailwater
management and reuse were analyzed
for a variety of alternative on-farm
irrigation systems of varying sizes.
Economic-engineering cost studies of
several field-level (0.688 km2, 170 ac)
alternative irrigation systems indicate
that systems designed to minimize
tailwater discharge will lower annual
irrigation costs compared to a
conventional furrow method These
cost savings a re primarily due to the low
water and labor requirements. These
studies were based on the 1976 interest
rates, input prices, and water applica-
tion ratesfor a 0 688 km2tomatofield m
the San Joaqum Valley study area The
alternatives considered are as follows:
(1) side-roll sprinkler system
(2) furrow irrigation with gated pipe
and a tailwater reuse system
(3) a hand move sprinkler system
(4) variable interest and labor cost
rates
(5) differential water costs
Recommendations
Mitigation of the impacts of irrigation
tailwater can be accomplished by both
technical and managerial methods.
Improved irrigation efficiencies should
be achieved by adopting improved
application methods, irrigation
scheduling and training of irrigators.
Tailwater and other usable collected
irrigation return flows should be
recovered and reused whenever this
practice will be a cost effective method
of improving water quality.
For locations where the collected
subsurface waters are considerably
more degraded in quality than the sur-
face runoff, attempts should be made to
keep these two types of irrigation return
flows separate so that the surface run-
offs will have greater reuse potential for
all sectors of society.
Under certain conditions, it may be
more operationally efficient to capture
and reuse water at larger spatial levels
than field-site and farm-site, e.g., water
district, irrigation project, or basin.
Where there are detrimental impacts
due to the sediment load in tailwater,
sediment source control practices
and/or sediment removal operations
should be considered
(1) Under conditions of moderate to
high erosion hazards, particularly
with surface irrigation methods
such as wildflooding, corruga-
tions and furrows, source control
practices should be implemented,
including better control of water
by reducing the length of run and
slope, or contouring
(2) Where the sediment load in tail-
water is a problem, sediment
retention facilities should be built.
Sediment removal may consist of
sedimentation tanks or ponds,
vegetated buffer strips at the end
of irrigated fields and water
spreading over contiguous grass-
lands and ponds.
The discharge of tailwater should be
minimized during and immediately after
the application of agricultural
chemicals (for instance, injection of
anhydrous ammonia in irrigation water,
aerial top-dressing of fertilizers and (
herbicides on flooded rice fields, etc.) to
prevent pulses of pollutants from being
discharged into receiving waters.
Wherever possible, the resources
and expertise available in line agencies
(USD A-Science and Education
Administration-Agricultural Research,
USDA-Economics, Statistics and
Cooperative Service, Soil Conservation
Service, Water and Power Resources
Services, Agricultural Experiment
Stations and Cooperative Extension
Services, and other state agencies)
should be utilized to develop and
implement Best Management
Practices.
Where there appears to be no
incentives or tangible benefits for
irrigators to implement water
quantity/quality control measures, cost
sharing, low-interest loans,and other
incentive programs should be explored
in order to equitably distribute the
financial burden of maintaining water
quality.
Due to the site variability of receiving
waters,and of tailwater production and
quality, the authors do not recommend
any single universally applicable
control technology. The effect(s) of
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tailwater discharge into surface waters
may be either beneficial, detrimental or
both, depending on the quality
constituents of interest and water flow
A practice that is effective in one
location may not be as effective in
another
Irrigation return flows and the
resulting waste loads range widely in
controllability. Management and
controls should be adopted on the basis
of both cost and technical efficiency
Site-specific factors and conditions
on a case-by-case basis should be con-
sidered in developing regulatory guide-
lines, controls, or standards. Local, as
well as state-wide, standards should be
developed which are in conformance
with the national goals These site-
specific plans and management,
however, should be compatible and
mutually beneficial at the basin and
mterbasm levels.
Additional information on the subject
of irrigation tailwater management is
available through the National Techni-
cal Information Service as.
EPA-600/2-81-034b, "1975-1976
Annual Report on Irrigation Tail-
water Management," (Order No.
PB 81-200545; Cost $17.00)
EPA-600/2-81-034C, "1976-1977
Annual Report on Irrigation Tail-
water Management," (Order No
PB 81-200552; Cost. $18.50)
Kenneth K. Tanji, James W. Biggar, Robert J. Miller, and William 0. Pruitt are
with the Department of Land. Air, and Water Resources; and Gerald L Homer
is with the U.S. Department of Agriculture, all located at the University of
California, Davis. CA 95616.
Arthur Hornsby is the EPA Project Officer (see below).
The complete report, entitled "Irrigation Tailwater Management," (Order No.
PB 81-196 925; Cost: $ 12.50. 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
P.O. Box 1198
Ada. OK 74820
i US GOVERNMENT PRINTING OFFICE 1981-757-01Z/7159
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United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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