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Water resources managementfor part of the lower Gila valley
Item Type Dissertation-Reproduction (electronic); text
Authors Matias Filho, Jose,1927-
Publisher The University of Arizona.
Rights Copyright © is held by the author. Digital access to this materialis made possible by the University Libraries, University of Arizona.Further transmission, reproduction or presentation (such aspublic display or performance) of protected items is prohibitedexcept with permission of the author.
Download date 18/04/2018 16:30:56
Link to Item http://hdl.handle.net/10150/191015
WATER RESOURCES MANAGEMENT FOR PART OF
THE LOWER GILA VALLEY
by
Jose Matias Filho
A Dissertation Submitted to the Faculty of the
DEPARTMENT OF WATERSHED MANAGEMENT
In Partial Fulfillment of the RequirementsFor the Degree of
DOCTOR OF PHILOSOPHY
In the Graduate College
THE UNIVERSITY OF ARIZONA
1974
THE UNIVERSITY OF ARIZONA
GRADUATE COLLEGE
I hereby recommend that this dissertation prepared under my
direction by JOSE MATIAS FILHO
entitled WATER RESOURCES MANAGEMENT FOR PART OF THE LOWER
GILA VALLEY
be accepted as fulfilling the dissertation requirement of the
degree of DOCTOR OF PHILOSOPHY
Date
After inspection of the final copy of the dissertation, the
following members of the Final Examination Committee concur in
its approval and recommend its acceptance:*
Oct /7 /9'74
4,1 /7/ /72z/
&i-19.-t. /7 0'74'
CIO( -7X-
-
This approval and acceptance is contingent on the candidate's
adequate performance and defense of this dissertation at the
final oral examination. The inclusion of this sheet bound into
the library copy of the dissertation is evidence of satisfactory
performance at the final examination.
STATEMENT BY AUTHOR
This dissertation has been submitted in partial fulfillment ofrequirements for an advanced degree at The University of Arizona andis deposited in the University Library to be made available to bor-rowers under rules of the Library.
Brief quotations from this dissertation are allowable withoutspecial permission, provided that accurate acknowledgment of sourceis made. Requests for permission for extended quotation from or re-production of this manuscript in whole or in part may be granted bythe head of the major department or the Dean of the Graduate Collegewhen in his judgment the proposed use of the material is in the in-terests of scholarship. In all other instances, however, permissionmust be obtained from the author.
SIGNED:72-'
ACKNOWLEDGMENTS
It gives me great pleasure to express my sincere appreciation to
my advisor, Professor W. Gerald Matlock, who spared no effort in his
guidance and suggestions throughout this study.
I am particularly thankful to my major professor, Dr. M. M.
Fogel, and the other members of my graduate committee, Dr. D. D.
Fangmeier, Dr. M. J. Zwolinski, and Dr. G. S. Lehman, for their
assistance and time they profferred so generously.
Grateful acknowledgments are expressed to Dr. LeMoyne Hogan for
his interest and cooperation as chief-of-party of the Federal University
of Ceara/University of Arizona/AID Contract LA-145 at the time of my de-
parture to the United States.
I am specially grateful to my wife, Zuleica, and my children,
for their patience, understanding, and assistance.
The author was supported by Ford Foundation and United States
Agency for International Development (USAID), to whom he is deeply
grateful.
TABLE OF CONTENTS
Page
LIST OF TABLES vii
LIST OF ILLUSTRATIONS
ix
ABSTRACT
INTRODUCTION 1
Water Resources Management 1Purpose and Objectives 5
THE LOWER GILA RIVER 7
History 7Physical Features 11
Location and Extent 11Topography 14Vegetation 15Hydrogeology 16Natural Drainage System and Flow Characteristics 20
Climatologic Factors 22Precipitation 22Temperature 24
Hydrologic Characteristics 25Surface Water Hydrology 25Groundwater Hydrology 31
THE WELLTON-MOHAWK IRRIGATION AND DRAINAGE DISTRICT 37
Description 37Soils 37Water Resources 41Water Development 42
Irrigation 42Introduction 42Water Supply 45Irrigation Methods 48Irrigated Acreage 48Irrigated Crops 48Consumptive Use 48
iv
TABLE OF CONTENTS--Continued
Page
Leaching Requirement 50Irrigation Efficiencies 53
Problems of Water Use 54Drainage 55Salinity 57
Economic Status 59Water Management System 63
WATER MANAGEMENT SYSTEM MODEL 65
Description of the Modeling Process 65Phase I Model 65Phase II Model 69
Validation of the Model 79Alternative Management Strategies 79
General 79Change in Irrigation Method 80Increase in Irrigated Area 80Change in Crop Allotment 81Increase in Water Use Efficiency 81Additional Drainage Facilities 82Conjunctive Use of Water Resources 83Phreatophyte Control 84Desalinization 85Summary 86
Model Operation with Alternative Strategies 87Alternative Strategies 88
Strategy I 88Strategies II, III, and IV 89Strategies V and VI 89Strategy VII 89Strategy VIII 89
RESULTS AND DISCUSSION 90
Phase I Strategy I
Phase II Strategy I Strategy II Strategy III Strategy IV Strategy V Strategy VI
9090929497101103106106
vi
TABLE OF CONTENTS--Continued
Page
Strategy VII 108Strategy VIII 111
CONCLUSIONS AND RECOMMENDATIONS 114
Conclusions 114Recommendations 119
APPENDIX A: DESCRIPTION AND LISTING OF THE COMPUTER PROGRAM . 121
SELECTED BIBLIOGRAPHY 126
LIST OF TABLES
Table Page
1. Wellton-Mohawk Irrigation and Drainage District: IrrigatedArea, in Acres 12
2. Wellton-Mohawk Irrigation and Drainage District: CropAcreage 17
3. Mean Annual Precipitation for Representative Stations inthe Lower Gila River Basin 24
4. Lower Gila River Surface Flow, in Acre Feet 28
5. Lower Gila River: Estimated Painted Rock ReservoirReleases Distribution Between the Dam and Dome, Duringthe Spring 1966, in Acre Feet 29
6. Wellton-Mohawk Area: Land Classification, Acreage, andSoil Characteristics 39
7. Wellton-Mohawk Irrigation and Drainage District: WaterSupply Delivered,in Acre Feet 43
8. Wellton-Mohawk Irrigation and Drainage District:Estimated Water Supply Delivered to the Mesa, inAcre Feet 46
9. Wellton-Mohawk Irrigation and Drainage District:Estimated Water Supply Delivered to the Valley, inAcre Feet 47
10. Wellton-Mohawk Irrigation and Drainage District:Estimated Annual Salt Input, in Tons 52
11. Wellton-Mohawk Irrigation and Drainage District:Estimated Salt Output, in Tons 60
12. Yuma Projects: Water Delivered to Farms Per IrrigatedAcre, in Acre Feet 61
13. Yuma Projects: Operation and Maintenance Costs PerIrrigated Acre, in Dollars 62
vi i
LIST OF TABLES—Continued
Table
14. Yuma Projects: Gross Crop Values Per Irrigated Acre,in Dollars
15. Wellton-Mohawk Irrigation and Drainage District:Estimated Land Use 72
16. Wellton-Mohawk Irrigation and Drainage District--Strategy I: No Modification of the Present ManagementPolicy (Phase I) 91
17. Wellton-Mohawk Irrigation and Drainage District:Groundwater Depths for Various Alternative ManagementStrategies, in Feet
93
18. Wellton-Mohawk Irrigation and Drainage District--Strategy I: No Modification of the Present Manage-ment Policy (Phase II) 95
19. Wellton-Mohawk Irrigation and Drainage District--Strategy II: Sprinkler Irrigation on 25 Percent ofthe Mesa Area
98
20. Wellton-Mohawk Irrigation and Drainage District--Strategy III: Sprinkler Irrigation on 50 Percent ofthe Mesa Area
102
21. Wellton-Mohawk Irrigation and Drainage District--Strategy IV: Sprinkler Irrigation on 100 Percent ofthe Mesa Area
105
22. Wellton-Mohawk Irrigation and Drainage District--Strategy V: Reduction by 50 Percent of thePhreatophytes
107
23. Wellton-Mohawk Irrigation and Drainage District--Strategy VI: Reduction by 100 Percent of thePhreatophytes
109
24. Wellton-Mohawk Irrigation and Drainage District--Strategy VII: Sprinkler Irrigation on 50 Percent ofthe Mesa Area and Reduction by 50 Percent of thePhreatophytes
110
25. Wellton-Mohawk Irrigation and Drainage District--
Strategy VIII: Sprinkler Irrigation on 100 Percent of theMesa Area and Reduction by 100 Percent of the Phreatophytes 112
viii
Page
64
LIST OF ILLUSTRATIONS
Figure Page
1. Gila River Downstream from Painted Rock Dam 13
2. Wellton-Mohawk Irrigation and Drainage District 38
3. Flow Diagram for the Hydrologic Model Used in Phase I 70
4. Flow Diagram for Typical Sectors of the HydrologicModel Used in Phase II 78
ix
ABSTRACT
The Wellton-Mohawk Irrigation and Drainage District occupies a
valley and adjoining mesa along the lower Gila River, in the southwestern
part of the State of Arizona. The area has been irrigated for centuries,
and now shows problems which reflect past and present water management.
First, the water supplies came from the Gila River; later, the ground-
water reservoir was used and within about 30 years, groundwater levels
declined and salt accumulation, as a consequence of water recirculation,
put a limit on attempts to maintain irrigated agriculture. Recently,
Colorado River water was brought into the area as the solution to assure
permanent large-scale irrigation development. The application of water
for crops and leaching of salts caused serious drainage problems.
Salinity also caused a problem out of the District as drainage water
from the aquifer with high salt content reached the Colorado River and
became a source of friction between the United States and Mexico.
The water conveyance system in the District is unique in that
irrigation water is pumped up the valley into the distribution system.
During flood flows along the lower Gila River, this leads to the situa-
tion where water is going down the River with little chance to be used,
and goes up the valley through a sophisticated conveyance system.
Flood flows along the lower Gila River are dependent on in-
frequent releases from Painted Rock Reservoir, at the upstream boundary
of the lower Gila River. The few times they have occurred (2 in 15
xi
years), they created high groundwater levels which were damaging to
crop production.
The water problems in the District could have short-run solu-
tions through technically possible and economically feasible management
practices.
The objectives of the study are focused on better use of the
water resources, reduction of risks of flood damages, and decrease of
salt content of water being diverted to Mexico. A mathematical model
was developed to analyze the impact of selected alternatives which could
meet these objectives upon the hydrologic system of the District.
The application of Strategy I, which proposes the increase of
the irrigated acreage by about 5,000 acres, proved to be impracticable
under present management conditions since the amount of drainage water
to be disposed would be greater than the capacity of the disposal system.
Strategies II, III, and IV, which propose increasing levels of
change from flood to sprinkler irrigation (25, 50 and 100 rcent)
showed results that although not economically encouraging, provide,
however, for solution of the internal water problem of the area, and
substantial decrease of drainage flow of high salt content delivered to
the Colorado River.
Strategies V and VI, which proposed reduction by 50 percent or
complete elimination of riparian vegetation also proved to be im-
practicable. Under present management conditions in the District,
phreatophytes are an important auxiliary of the water discharge system
of the area.
xii
Strategies VII and VIII showed that the combination of changes
to sprinkler irrigation and reduction of riparian vegetation at levels
proposed (50 and 100 percent) practically counteract each other in terms
of drainage water to be pumped and does not achieve the proposed
objectives.
Change in the water management system of the Wellton-Mohawk
District would solve its water problems and significantly reduce
salinity of the Colorado River water at Morelos Dam, for which hundreds
of millions of dollars will be expended in a desalting complex.
Drainage from excessive irrigation on the mesa flowing into the valley
aquifer is the main cause of high groundwater levels there. Riparian
vegetation, although increasing flood damages, is indispensable under
the present management system.
INTRODUCTION
Water Resources Management
Man's attitude toward his natural resources was for many
centuries based on the assumption that demand could ever exceed the
supply. This belief led man to consume his natural resources with
little regard to conservation and economy. Population growth and the
consequent need for more food and fiber have proved, however, that man
can no longer retain this selfish and unconcerned attitude toward his
natural resources. Water resources cannot be excluded from the reality
that demand often exceeds supply.
"The possibility of increasing supplies of usable water no
longer exists through the exploitation of new resources but rather an
integration of technological, political, social, and economic factors
will be necessary" (Dvoracek and Peterson 1971, p. 219). The problem of
increasing water supplies becomes, then, more and more a question of
water management to reduce water inefficiency which is characteristic of
high water use developments.
Irrigated agriculture, is and has been, the dominant user in the
allocation of water resources, and has also been accused of being an
inefficient and uneconomical user. A major part of the water used by
irrigated agriculture is lost through the process of evapotranspiration,
in contrast to other uses that do not "consume" water (Jensen 1967).
1
2
In manufacturing, for example, about 98 percent of the water withdrawn
is returned for reuse, but only about 40 percent is returned from irri-
gated agriculture. The remaining 60 percent, termed consumptive use, is
lost through evapotranspiration.
Because irrigated agriculture accounts for a very high percentage
of the water consumed around the world, the greatest opportunity for
saving water through better management is, consequently, through better
management of agricultural water. Management responsibility for an
irrigation system consists essentially of that associated with the
control, movement, and disposal of water or its reuse where possible.
But something more than merely supplying water to the land and removing
the excess as drainage is necessary. An important factor now, and even
more so in the future, will be the impact that the system has on the
quality of the supply and the quality of the drainage. "The most
obvious, or perhaps notorious, examples of man's short-term impact on
the quality of his water resources are found in his manipulation of
water for irrigation" (Orlob and Woods 1967, p. 49).
Reducing evaporation from free water surfaces, controlling
seepage from conveyance channels, artificial replenishment of ground
water, and improvement of structures for water control and management
are some important aspects of water storage and movement which offer
considerable opportunity to increase the availability of our water
resources. Considerable research on evaporation from open water surfaces
and seepage from conveyance channels has been conducted to find
economically feasible techniques which could eliminate or control their
3
effects in depleting the available supplies. Some developed linings
have been shown to be permanent and effective for seepage control.
Research toward controlling evaporation from water surfaces has
centered largely on the use of monomolecular films of long-chain
alkanols. More recently, Myers and Frasier (1970) found that floating
granular materials which cool the water by reflecting incoming shortwave
radiation appear promising as a means of reducing evaporation from water
surfaces. Although substantial evaporation reduction has been observed
in ponds and small reservoirs, the application of these techniques to
larger bodies of water don't produce similar results and much work is
till to be done to justify their use as a practical and economic
measure.
Artificial recharge can be used to store excess water during
flooding periods or through planned "overirrigation," and to dispose of
waste waters. These aspects of artificial recharge have been explored
in theory and in the field, and although many problems are still to be
solved, some techniques have proven both technically and economically
feasible under the conditions where they were developed. Artificial
recharge can also be an important practice in the integrated development
and conjunctive use of surface and groundwaters. This is a very import-
ant aspect in water deficient regions as it provides opportunity for
augmentation of irrigation supplies and a wide range of alternative
decisions for their utilization.
The increasing demand upon available water resources is reaching
levels where agricultural operations cannot be insensitive to wasteful
4
water-use practices. As the competetive pressures from industrial,
recreational, and urban uses increase, agriculture will increasingly
have to justify its high use of water. Of the water delivered to the
farm, the 40 percent not used by plants through evapotranspiration is
lost by surface runoff and deep percolation. Frequently, more agri-
cultural water is wasted by not knowing when to irrigate than by poor
application efficiency (Erie 1968). In many agricultural areas, in-
cluding many modern irrigation projects, farmers continue to use
traditional irrigation practices little influenced by modern science
and technology (Committee on Research of the Irrigation and Drainage
Division, ASCE 1974). Irrigation management services, provided by an
irrigation district to member farmers are being used to supply the
farmers with information that will improve on-farm water management.
Based on more reliable estimates and predictions than the farmers
generally can make of evapotranspiration, soil moisture depletion levels,
and plant nutritional status, these services are producing positive
results. The most significant improvements in water use efficiency,
then, will potentially come from improved water management.
Irrigation practices on the farm are also the primary source of
present return flow quality problems. Historically, water management
has dealt with the distribution of water in time and space, and research
has been directed towards controlling such distribution. Agricultural
water management relates to water quality in a number of ways such as
erosion and sedimentation and through return flows that contain plant
nutrients, animal wastes, and salts. Since all waters contain some
5
dissolved salts, salinity may become a problem when inadequate pre-
cautions are taken to prevent a buildup of salts in the soil. Sub-
stantial progress has been made in developing an understanding of the
physiochemical behavior of salt-affected soils and the movement of
water through them. The tolerance of many plants to salinity has been
determined. An important impact of salt occurrence in irrigated areas
is, however, the concentration of salts in the drainage water being
disposed of downstream that is often too high for safe reuse for
agricultural purposes. A wide range of alternative management practices
have been developed which have shown that it is possible to manage
irrigation water in such a manner that the leaching fraction can be
substantially lower than is now customary or recommended. In this way,
the quantity of drainage water is reduced and its quality increased.
Purpose and Objectives
The purpose of the present work is to develop simple modeling
techniques which can be helpful in applying alternative management
strategies to irrigated agricultural projects and thus to contribute to
better use of the water resources in such areas. The study conducted
refers to many aspects of the field of water resources, and attempts to
analyze irrigation systems as they operate at present. It also seeks
feasible techniques for improving the water management practices being
applied to increase water use efficiency in water deficient areas.
The Wellton-Mohawk Irrigation and Drainage District, one of the
most controversial irrigated areas in the American West was chosen as
the problem area. It is a 75,000-acre irrigable area at the lower reach
of the Gila River, Arizona, in which irrigation practices conducted
for centuries brought salinity, drainage and flooding problems, which
are attracting much attention during the last few years.
The possibilities for alternative management solutions which
could reduce the impact of these problems are various, and for the
present study they were directed to the following proposed objectives.
1. Decrease the volume of drainage water delivered into the
Colorado River.
2. Reduce the salt content of the drainage water returned to the
Colorado River.
3. Reduce the risks of flood damages along the lower Gila River.
4. Make more efficient use of the Gila River flood waters.
6
THE LOWER GILA RIVER
History
The knowledge of man's intense effort for existence in this part
of the southwestern American deserts dates from the Hohokam civilization.
Hohokam means "vanished ones," and their culture extended for a period
of time from about the beginning of the Christian era to A.D. 1400
(Ligner et al. 1969). Although earlier civilizations had been estab-
lished in the lower Gila River basin, the Hohokam are thought to be the
first to learn to manage the meager supply of water and to develop a
productive culture. They built several hundred miles of irrigation
canals that diverted water from the rivers to the cultivated fields
(Ligner et al. 1969). The reasons why the Hohokam vanished are not
well known, but most authorities believe that it was because of severe
drought that lasted for several years. The dependency on a scanty and
sometimes missing supply from the lower Gila River surface flow and the
absence of means to store water during the flow periods left the
Hohokam unable to face such emergencies. From the Hohokam civilization
comes the first evidence of the need to understand and properly manage
the water resources available in this desert region.
The progress of agricultural history in the Lower Gila River
basin follows the Pima Indians, who were irrigating the Gila River
flood plain in the vicinity of the Wellton-Mohawk area in the early
1500's (U.S. Bureau of Reclamation 1950).
7
8
Father Kino, the Jesuit missionary, noted agriculture in the
lower Gila River area in 1700. Among his many references to the Gila
River, and talking about the reach near the present town of Wellton
he wrote that all its inhabitants are fishermen and have many nets and
other tackle with which they fish all the year, sustaining themselves
with abundant fish and with their maize, beans, and calabashes.
The earliest agricultural development by white settlers in the
lower Gila River basin began with the establishment of a garrison of
United States troops at Fort Yuma in 1856. Supplies for settlers and
troops were brought in boats that travelled up the Colorado River from
the Gulf of California. With the establishment of the first stage
coach line in 1857, these supplies were distributed by mule team along
the lower Gila River basin, from Fort Yuma to Sacaton, a distance of
about 190 miles.
With the arrival of the white settlers, irrigation farming had
its origin in the Lower Gila River basin. By 1875, a number of homestead
filings had been made in the Wellton-Mohawk area. By 1891, a canal
some ten miles in length and having a concrete heading structure was
located at a narrow section of the valley in the extreme eastern end
of the present Wellton-Mohawk District. A brush dam was constructed
across the river channel to divert water to irrigate a few hundred
acres of land. In this same year, however, a disastrous flood destroyed
everything except the concrete heading structure and ended this attempt
to irrigate that area (Moser 1967). During the following years other
irrigation systems were developed by the people moving to the west,
9
but the severe droughts of 1897, 1898, and 1899 terminated everything
again (Ligner et al. 1969).
In 1908 a new diversion structure was built in another river
section to the west to irrigate 1200 acres of land on the south side of
the valley (Moser 1967). By this time, with the growing development
upstream, the Gila River flow at the Wellton-Mohawk area became even
less dependable. Roosevelt Dam, the first of the storage dams in the
Gila River drainage basin, was completed in 1911 to store flow from the
Salt River, the most important of its tributaries. As other reservoirs
were constructed and additional diversions were being made for agri-
cultural and other purposes, the flow in the lower Gila River basin
became practically nonexistent. This undependable water supply situation
continued for the next few years until about 1920, when groundwater
began to be developed as a new source of irrigation supply. About that
time several small districts were organized to furnish power and to
drill wells that would be pumped for irrigation (Moser 1967). The
Mohawk Municipal Water Conservation District, was formed in 1923 to
supply lands on the north side of the Gila River between the towns of
Wellton and Mohawk. The Gila River Power District was organized at this
same time to serve and develop the area.
This cooperative effort allowed a rapid expansion of irrigation
until a maximum of approximately 11,000 acres were in cultivation by the
early 1930's (Moser 1967). During the ensuing years, however, the rapid
lowering of the water levels, and the deterioration of the water quality
by evapotranspiration and continued recirculation led the farmers to
10
another crossroads in their attempt to expand the irrigation and in-
crease the progress of the lower Gila River agriculture.
By 1934, excessive salts were being pumped from many wells and
the water table decreased to an alarming extent. This situation came
as a result of the growing development in upper Gila River for which
additional reservoirs and wells were constructed, and extensive diver-
sions were being conducted. Spring floods in 1941 gave a short-lived
reprieve from the situation by bringing an additional supply of low
salt flood water that partially replenished the depleted aquifer.
Agriculture flourished again for a period of two years but after that
previous conditions of high salinity levels of soil and water and deep
lifting of the pumped irrigation water returned. One after another,
farms were abandoned as soil and water become too saline for profitable
farming. At this time the transfer of Colorado River water appeared as
the only reasonable solution of continued irrigation water supply which
the Bureau of Reclamation was already seeking to bring to the area.
In 1947, the U.S. Congress re-authorized the Wellton-Mohawk
Division of the Gila Project and provided for the construction of an
irrigation system that would bring water from the Colorado River to
75,000 irrigable acres within the project.
On April 16, 1951, the old power and water districts were
dissolved and their functions were taken over by the newly organized
Wellton-Mohawk Irrigation and Drainage District. The District entered
into a contract with the United States under the Reclamation Act for the
construction of a modern concrete-lined canal and distribution system
11
as well as for a supply of water from the Colorado River (Arizona
Interstate Stream Commission 1967).
The construction of the Wellton-Mohawk Division facilities was
started August, 1949, and by April 21, 1952, Colorado River water was
applied to the Wellton-Mohawk fields for the first time.
With the introduction of water from the Colorado River, the
expanding irrigated acreage (Table 1), the application of large amounts
of surface water, and very little pumping of groundwater, water levels
rose rapidly, and about 1960 a general drainage problem existed in the
area.
The construction of many drainage wells and a conveyance channel
in 1961, and the utilization of wells previously used for irrigation
purposes as drainage wells had by 1964 considerably alleviated the
severity of the drainage problem (University of Arizona 1970).
Later, additional wells were constructed for improving the
drainage conditions and to permit selective well pumping, and at the
present time a condition of practical equilibrium exists.
Physical Features
Location and Extent
The lower Gila River drainage basin is located in the south-
western corner of the State of Arizona and occupies portions of Yuma,
Maricopa, and Pima Counties (Figure 1). It comprises about 7,300 square
miles of which about 2,700 square miles are between Painted Rock Dam
(126 river miles) and Texas Hill (66.5 river miles) (U.S. Army Corps
12
Table 1. Wellton-Mohawk Irrigation and Drainage District: IrrigatedArea, in Acres.*
Year Irrigated Area
1952 14,134
1953 22,396
1954 24,657
1955 30,547
1956 34,939
1957 42,739
1958 45,114
1959 52,813
1960 54,127
1961 52,995
1962 51,735
1963 56,289
1964 58,100
1965 58,040
1966 60,062
1967 61,190
1968 60,758
1969 60,124
1970 60,756
1971 61,152
* Source: Wellton-Mohawk Irrigation and Drainage District, 1952-72.
"••••n
•
L EGEND
••••••11.—.• Boundary of Drainage Area
? Existing Reservoir
5
0
5
10
15flffil
MILES
13
Figure 1. Gila River Downstream from Painted Rock Dam. -- Adapted
from U.S. Army Corps of Engineers, 1962, Plate 1.
14
of Engineers 1962), From Texas Hill to the Gila siphon (8.4 river miles)
where the Gila River flood plain joins the Colorado River Valley, the
river flows for a length of about 58 miles. The Gila River flood plain
throughout this reach is referred to as the Wellton-Mohawk Valley.
The lower Gila River basin consists of broad, flat, low-lying
desert valleys, interrupted by many rugged, but comparatively low and
narrow mountain ridges. The flood plain ranges from less than a mile
to about five miles in width and the river flow meanders over the
generally flat bottom of a shallow channel about 1,000 to 3,000 feet
wide.
Topography
The moderate slopes of the Gila River flood plain have permitted
the development of many irrigation systems which are responsible for
practically all of the agricultural production in Arizona.
The Gila River drainage basin downstream from Painted Rock Dam
consists mostly of gently rolling desert plains ranging in elevation
from 130 to 1500 feet, with elevations of 150 and 325 feet at the Gila
siphon and Texas Hill, respectively. The slope of the river is estimated
to be 3.3 feet per mile from Painted Rock Dam to Texas Hill and 3.0 feet
per mile from Texas Hill to Dome.
The flood plain along the Gila River is only a few feet above
the river bottom. The southern Gila River terrace, known as the Wellton-
Mohawk Mesa constitutes the Mesa section of the Wellton-Mohawk Division.
It has an average elevation of about 70 feet above the adjoining valley.
15
The few minor rugged desert mountains that border part of the
flood plain reach elevations of 3,000 to 4,000 feet (U.S. Army Corps of
Engineers 1962).
Vegetation
The type, density, and distribution of vegetation in the Gila
River basin downstream from Painted Rock Dam reflect the effect of
elevation, temperature, and precipitation. In general the vegetation
between the dam and Texas Hill is cacti, creosote brush, and sagebrush.
Mesquite, saltcedar, and arrowweed grow in dense thickets in most of
the river bottom and in areas where the water table is near the ground
surface. Agricultural development in this area has been limited to a
few isolated ranches (U.S. Army Corps of Engineers 1962).
In the area along the Gila River from Texas Hill to the mouth,
most of the present channel bottom is covered with a heavy mantle of
phreatophytes. This vegetative growth has increased the aggradation of
the river and restricted the channel to such an extent that flows in
excess of 2,500 cubic feet per second would overflow and inundate the
adjoining land (U.S. Army Corps of Engineers 1962).
The 75,000-acre Wellton-Mohawk Division of the Gila Project
occupies most of the irrigable land from Texas Hill to the Colorado
River Valley. That area has been transformed from desert waste to
highly productive farmland. Native vegetation still persists in the
areas not suited to farming.
From a general inventory of the flora in the lower Gila River
conducted by the School of Earth Sciences of The University of Arizona,
16
an approximate estimate of about 16,000 acres of phreatophyte species
stand on the flood plain area between Texas Hill and Dome (University
of Arizona 1970).
The cropping pattern in the irrigated area of the Wellton-
Mohawk District has been practically invariable, although the acreage
for the various growing crops has varied, probably according to market
trends. Alfalfa hay, irrigated pasture, and grasses (all kinds)
accounted for 35 percent of the total crop acreage cultivated in the
District during the period from 1967 to 1972 (Table 2). Alfalfa, a
very high water user, is by far the dominant crop in the area and
accounted for 22 percent of the total crop acreage under irrigation
rotation during the same period.
Although practically all the crops are grown in the valley and
on the mesa, about 50 percent of the irrigated acreage on the mesa in
1972 was cultivated with citrus.
Hydrogeology
The geology of the watershed of the lower Gila River is typically
characteristic of the Basin and Range Physiographic Province, the western
most of the drainage provinces into which the State of Arizona is divided.
The study region consists of three sub-provinces: the dissected block
mountain, the intermountain bajadas and alluvial surfaces, and the Gila
River flood plain.
Because of its much greater importance as a repository to store
and transmit water and because much more information is available within
the limits of the Wellton-Mohawk District, only the flood plain area and
17
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18
adjoining mesa below Texas Hill, referred to as the "Wellton-Mohawk
area," will be considered.
The Wellton-Mohawk area is an irregular alluviated structural
basin bordered in part by north-west trending mountain ranges. It in-
cludes material of Tertiary and Quaternary age. The older of this
series has been designated as "older alluvium" and the younger part as
"Recent alluvium." The older alluvium is composed of two general
lithologic units. The upper unit is about 200 feet thick and is composed
of lenses of silt, sand, and gravel. The lower unit is of much greater
thickness and predominantly clay (Metzger 1952).
The older alluvium underlies the Gila River alluvium and its
thickness is estimated to be as much as 2,000 feet in the center of the
basin. It is a body of earth materials of varied sizes, ranging through
cobbles, coarse gravels, sand, silt, and clay, but it is predominantly
a clay alluvial fill. While part of the unit is considered permeable,
it is said to form the "impermeable" boundary between the river alluvium
and the bedrock floor of the basin.
The geologic unit referred to as Recent alluvium is formed by
the materials filling the broad and shallow trench dug by the Gila River
flow through many erosion cycles. It is composed of clay, silt, sand,
and gravel arranged into many and varied combinations to form a more or
less layered configuration in which a wide range of permeability values
can be found.
The Recent alluvium underlies the flood plain of the Gila River
and the ground surface of the mesa, and contains the principal aquifers
19
in the area. The alluvial deposits in this geologic unit contain highly
permeable gravel horizons with intervening beds of less permeable sand,
silt, and clay. The finer graded materials seriously retard the move-
ment of ground water and are partially responsible for the mesa drainage
problem (dellton-Mohawk Division 1970).
At least three gravel horizons have been recognized in the
Recent alluvial fill. The highest horizon, entirely above the valley
floor is 20 to 40 feet thick but does not extend as a continuous layer
throughout the whole area. It is highly permeable except where cemented,
and where it underlies irrigated areas it can be tapped to provide
drainage.
The second gravel layer in depth contains typical Gila River
gravel and cobbles. Its occurrence is scattered but where present its
thickness ranges from 10 to 20 feet. By its relatively small dimensions
and erratic occurrence this layer has only localized importance as a
pumped aquifer although it can play an important task in the underground
flow from the mesa to the valley. Its elevation is at or near the Gila
River grade.
The third and deeper gravel horizon underlies the mesa and
valley alluvial fill but does not extend to all parts of the mesa. It
contains typical Gila River gravels, and its thickness ranges from 10 to
85 feet. It is tapped by drainage wells in the valley and provides good
hydraulic connection between the mesa and the valley.
The capacity of the various geologic units of the alluvium to
transmit and store water depends on the quality of the alluvial beds and
their thickness, continuity, and location.
20
Measurements of the hydraulic characteristics of the deeper
gravel layer in the Wellton-Mohawk aquifer were obtained by selecting
some wells representatively located, and measuring the water-level
drawdown during field pumping tests. Transmissivity values ranged from
0.26 to 1.29 cubic feet per second per foot of head, and the specific
yield ranged from 10 to 18.5 percent and averaged 15 percent (U.S.
Bureau of Reclamation 1963). It is interesting to note an average
transmissivity value of about 0.33 cubic feet per second was derived from
studies conducted along the Gila River aquifer upstream from San Carlos
Reservoir in a reach of about 15 miles long and about 60 feet deep
(Hanson 1972).
On the basis of an average aquifer depth of about 85 feet, the
effective aquifer underlying the Wellton-Mohawk District could be esti-
mated at about 10,000,000 acre feet. By assuming a porosity of 30
percent (U.S. Bureau of Reclamation 1963), the volume of water in storage
could be three million acre feet, or about 35,300 acre feet per foot
depth of the aquifer.
Natural Drainage System andFlow Characteristics
The Gila River main stream enters the lower Gila River basin at
Painted Rock Dam and flows in a southwesterly direction for a distance
of about 114 miles to a narrow constriction below Dome where it joins
the Colorado River basin. Along this reach the main stream receives
many secondary tributaries the most important of which are:
21
Watershed Drainage Area (square mile)
Palomas Wash 1,360
San Cristobal Wash 1,810
Kofa Wash 575
Rio Cornez Wash 243
Mohawk Wash 710
Coyote Wash 450
Ligurta Wash 30
Castle Dome Wash 410
Fortuna Wash 45
The Gila River, even before the many impoundments and diversions
realized during the present century, was reported to have undependable
flow in its lower portion (Ross 1923). Flow in the lower Gila River
has probably always been seasonal in character and subject to infrequent
and abnormal occurrences. At the present, flow in the lower Gila River
basin is limited to infrequent releases from Painted Rock Reservoir and
flood runoff from the contributing watersheds below the dam, during
periods of heavy precipitation. The channel aggrades during summer
runoff from local washes, and tends toward scouring and meandering when
relatively sediment-free waters are released from Painted Rock Reservoir
during winter months (University of Arizona 1970).
All the tributary washes flowing into the main stream are
ephemeral and discharge both runoff and sediment to the Gila flood plain.
Watersheds such as the San Cristobal, Kofa, and Rio Cornez have poorly
defined channels, and their tributaries disappear into alluvium. Sandy
22
soils are characteristic of these watersheds and contribute to the
apparent lack of heavy runoff in the last several decades.
In contrast to the above, the Coyote and Ligurta washes drain
watersheds with fairly high runoff characteristics. Their combined
areas, however, are considerably less than the tributary watersheds with
low runoff characteristics (University of Arizona 1970).
Climatologic Factors
Precipitation
The climate of the Gila River basin downstream from Painted Rock
Dam is subtropical and arid, characterized by a low annual rainfall, low
humidity, high evaporation, high summer temperatures from June to
September, and high percent of possible sunshine.
The rainfall over the area is biseasonal (July through September
and December through March) in distribution, slightly unbalanced in
favor of winter. Its average annual value has been estimated as less
than four inches (U.S. Army Corps of Engineers 1962).
Practically all moisture for summer rainfall is drawn into the
area from the Gulf of Mexico and Atlantic Ocean, although most of the
recorded summer rains in the past century have been associated with deep
surges of tropical air into Arizona from the Gulf of California and
Pacific Ocean (Green and Sellers 1964). These rains, which occur most
frequently in July, August, and September, are sporadic and likely to
occur at almost any hour, although a nighttime peak has been recorded
at most of the stations. The rains are of high intensity and short
23
duration contributing, in infrequent years, to high peaks of runoff
with devastating effects.
Water from sudden summer thunderstorms does not penetrate deeply
into the soil. Even when the storms are heavy enough to cause surface
runoff, much of the water that is retained in the stream channels either
evaporates or is transpired by river bank vegetation.
Most flood-producing precipitation in the area downstream from
Painted Rock Dam results from showers of short duration and small areal
extent or from general summer storms centering in the area downstream
from the dam. Storms of the thunderstorm type occur separately or in
conjunction with general storms (U.S. Army Corps of Engineers 1962).
Precipitation during the winter usually results from general
winter storms associated with extratropical cyclones of North Pacific
origin. During the months from November to April, such storms move
south over Mexico and result in precipitation over areas of up to
thousands of square miles. Precipitation during general winter storms
may be more or less continuous for several days. Relatively intense
showers near the end of such storms are common. Most precipitation from
these general winter storms would normally occur upstream from Painted
Rock Dam (U.S. Army Corps of Engineers 1962).
Although rainfall amounts may be similar for summer and winter
storms, the summer storms are of short duration with higher intensities
than winter storms.
Precipitation data for representative stations downstream from
Painted Rock Dam are given in Table 3.
24
Table 3. Mean Annual Precipitation for Representative Stations in theLower Gila River Basin.*
Elevation Length of RecordStation(Feet) (Years)
Mean AnnualPrecipitation
(Inches)
Yuma Citrus 191 30 3.47
Yuma 138 90 3.43
Wellton 225 26 4.13
Mohawk 538 64 3.70
Aztec 492 17 4.48
Agua Caliente 516 6 3.50
Sentinel 685 20 4.76
Ajo 1,763 44 8.20
Gila Bend 737 48 5.79
* Source: U.S. Army Corps of Engineers 1962, p. 19.
Temperature
Temperature varies widely over the year from a few degrees below
freezing to a value as high as 120 F (Wishart and Nelson 1963).
During the summer temperature frequently exceeds 100 F. In July
and August the average daily temperature exceeds 90 F with variation from
the middle 70's in the early morning to well over 100 degrees in the
25
early afternoon. Readings above 110 F are quite common during summer
months (University of Arizona 1970).
Temperatures during the coldest part of the year normally rise
into the high sixties in the afternoon, and usually stay above freezing
at night. The average annual frost-free period in the basin is 311 days.
Although the area has a 12-month growing season, temperatures
may drop low enough to damage tender crops any time from November to
February and occasional frosts occur that cause substantial losses.
Hydrologic Characteristics
Surface Water Hydrology
The sources of surface water flowing in the lower Gila River
basin are infrequent releases or uncontrolled flows from Painted Rock
Reservoir, sporadic storm runoff from rainfall over the 7,300 square
mile watershed below Painted Rock Dam, irrigation water diverted from
the Colorado River, and drainage water flowing into the Gila River
channel as return flow from irrigation in the Wellton-Mohawk District
or flowing into the Wellton-Mohawk Main Outlet Drain as groundwater
pumped from the Wellton-Mohawk aquifer.
Runoff records for the Gila River main stream are available for
only two gaging stations: (1) the water-stage recorder gaging station
referred to as "Gila River below Pointed Rock Dam" on the left bank
0.3 mile downstream from the dam, and (2) the water-stage recorder gaging
station ultimately referred to as "Gila River near Dome" on the right
bank three miles west of Dome. The gaging station just below Painted
26
Rock dam was established in October, 1959, and continuous records are
available from that time. The records for the gaging station near Dome
are continuous since 1903.
There are only a few stream-flow records available on the Gila
River tributaries. In the lower reaches their streambeds are dry and
any flow which does occur is very infrequent and erratic (Arizona
Interstate Stream Commission 1967).
Previous to the many impoundments and diversions for agricultur-
al developments and other beneficial uses upstream, the Gila River
surface flow at Painted Rock Dam site was dependent on precipitation
falling over the contributing watershed. Nearly all the major floods
that occurred in the past were winter floods caused by prolonged general
precipitation centering on the Gila River basin upstream from the dam.
The greatest of these floods, in recent years, occurred in January,
1916, with a discharge, adjusted to reflect control at Painted Rock Dam
and other upstream dams constructed since 1916, of about 200,000 cubic
feet per second at Dome (U.S. Army Corps of Engineers 1962).
Flows occurring in the past at the Dome gaging station were
caused in part by winter precipitation falling over the watershed up-
stream from Painted Rock Dam but mostly they are summer runoff from the
contributing watershed below the dam (University of Arizona 1970).
The largest summer flood recorded at Dame occurred in August,
1921, and had a mean daily discharge of 25,000 cubic feet per second.
At the present time, Gila River flow from runoff contributions
upstream from Painted Rock Dam is partially controlled by upstream dams
27
and diversions, and depleted groundwater reservoirs. The lower Gila
River developments are, however, subject to floods caused by rainstorms
falling over the watershed below the dam.
Painted Rock Dam was constructed at the end of the 1950's to
reduce the potential threat of flood damages in the Wellton-Mohawk area,
in the lower Gila River basin, and some areas in the lower Colorado River.
The storage capacity of the reservoir is 2,492,000 acre feet and it was
designed to take a maximum inflow of 300,000 cubic feet per second and
release a maximum outflow of 22,500 cubic feet per second (University
of Arizona 1970).
During the years from 1960 to 1971, about 290,000 acre feet of
water (Table 4) were released from Painted Rock Reservoir. Of this
total, 258,100 acre feet were released in the spring of 1966. This was
the first water stored since the completion of the dam in December,
1959 (Irelan 1971). The flood water was released for a period of three
months--January, February, and March--with a mean daily discharge of
1,430 cubic feet per second. Much of this released flow, about 61
percent, was estimated to dissipate in the dry streambed between the dam
and the east boundary of the Wellton-Mohawk District.
From the estimated 101,300acre feet of released flow reaching
the Wellton-Mohawk area (Table 5), 47,400 acre feet were estimated by
the Bureau of Reclamation Engineers (Irelan 1971) to have infiltrated
into the Wellton-Mohawk aquifer; 16,500 acre feet were pumped into the
Wellton-Mohawk irrigation system, and approximately 37,400 acre feet
were estimated to have reached the gaging station near Dome, near the
28
Table 4. Lower Gila River Surface Flow, in Acre Feet.*
Year Below Painted Rock Dam Near Dome
1960 3,660 17,770
1961 244 11,790
1962 0 3,290
1963 77 7,210
1964 1,320 102
1965 524 323
1966 258,100 39,840
1967 1,590 526
1968 17,370 797
1969 652 1,200
1970 3,050 2,660
1971 3,130 3,760
Total 289,717 89,268
* Source: U.S. Geological Survey, 1960-71.
29
Table 5. Lower Gila River: Estimated Painted Rock Reservoir ReleasesDistribution Between the Dam and Dome, During the Spring1966, in Acre Feet.*
A. Releases from Painted Rock Reservoir
B. Water pumped from the Gila River channel
C. Estimated infiltration volume into theWellton-Mohawk aquifer
D. Estimated volume reaching Dome
E. Estimated volume reaching the Wellton-Mohawkarea (B + C + D)
F. Estimated infiltration volume between PaintedRock Dam and the Wellton-Mohawk area
258,100
16,500
47,400
37,400
101,300
156,800
* Sources: U.S. Geological Survey (1960-71); Wellton-Mohawk Division(1961-71); Irelan (1971).
dividing point between the Wellton-Mohawk and Yuma areas. The precipita-
tion falling over the lower Gila River basin from January to March, 1966,
as usual, probably did not contribute any runoff to the Gila River
surface flow during those months.
A second period of water releases from Painted Rock Reservoir
occurred in 1973, and lasted for more than six months. About 400,000
acre feet of water were released during that period (American Water
Resources Association 1973). The releases began about the middle of
March and by April 12, when about 50,000 acre feet of water had been re-
leased, water flow reached Avenue 51 E, four and one-half miles down-
stream from the east boundary of the Wellton-Mohawk.
30
From April 12 to July 31, 288,000 acre feet reached Avenue 51 E.
About 128,000 acre feet were dissipated through the processes of infil-
tration and evapotranspiration along about 60 miles of river.
During this 112-day period water release rates averaged 1,287
cubic feet per second. During 64 of the 112 days water release rates
were greater than 1,000 cubic feet per second, and for 23 days they
averaged 2,344 cubic feet per second. The maximum release rate was
2,520 cubic feet per second.
Water from Painted Rock Reservoir reached the Colorado River
on May 5 and continued into September. A total of about 100,000 acre
feet of released water reached the Colorado River (American Water
Resources Association 1973). Thus about 300,000 acre feet went into
the ground, was pumped into the Wellton-Mohawk irrigation system, or
was lost to evapotranspiration between Painted Rock Dam and the Colorado
River along about 126 miles of river channel.
Gila River surface flow originating downstream from Painted Rock
Dam could be derived from sporadic storm runoff from the contributing
watershed and from return flow from irrigation in the Wellton-Mohawk
area. Storm runoff can occur in the winter or summer, but predominantly
during the summer.
The flow of the Gila River at its mouth includes the flood water
passing Dome and the normal drainage from irrigation entering the river
between Dome and its mouth.
The annual flow of the Gila River near Dome, in the gap where
the Gila River enters the lower Colorado River Basin has shown
31
considerable decline caused by developments of irrigation within the
basin. Excluding 1966, when releases from Painted Rock Reservoir passed
the gaging station near Dome, the only flow during the period from 1960
to 1971 (Table 4), was surface drainage return flow from irrigation in
the Wellton-Mohawk area or runoff from occasional local storms. During
that period 89,268 acre feet were recorded at Dome, and from this total
37,400 (Table 5) were estimated to be flood water released from Painted
Rock Reservoir.
The difference between these two values averaged for the 12
year record gives an average annual flow of about 4,325 acre feet. This
means that the contribution from precipitation to the Gila River surface
flow in the lower Gila River basin based on these data could be con-
sidered insignificant, since most of this annual flow is drainage return
flow as can be seen from monthly Gila River flows measured at Dome.
Since the confluence of the Gila River and Colorado River is
below all storage reservoirs and below all but one of the main diver-
sions (Alamo Canal), there is little opportunity to use any flood flow
that may occur in the lower Gila River basin.
Irrigation water supply and pumped drainage water flowing in the
Wellton-Mohawk District system account for practically the whole surface
waters flowing in the lower Gila River basin since the introduction of
the Colorado River water into that area.
Groundwater Hydrology
Groundwater occurring in the lower Gila River basin is from
three main sources:(1)Gila River and mountain area underground inflow;
32
(2) Gila River and tributary flood waters that infiltrate and percolate
to the groundwater table; and (3) seepage from excessive irrigation
water applications.
Average annual values for the Gila River underground inflow and
outflow at the boundaries of the Wellton-Mohawk District have been
estimated as 5,000 and 1,000 acre feet respectively (Babcock, Brown and
Hem 1947).
Underground flow from mountain areas could be considered of less
importance.
Storm runoff from the Gila River tributaries could probably
provide at times a considerable volume of recharge to the Wellton-Mohawk
aquifer. Most of the runoff flowing in the smaller washes infiltrates
readily into the coarse, gravel stream bed materials, and the water
either percolates to the water table or returns to the atmosphere by
evaporation and transpiration, but seldom reaches the Gila River channel
(Babcock, Brown and Hem 1947).
Test holes drilled along several tributaries of the Gila River
in April 1968 to see the groundwater recharge effect of winter pre-
cipitation found no water in the alluvium which means that the amount of
underflow along these tributaries is small and probably occurs only
during wet periods (Weist 1971).
On the basis of long-range studies of rainfall and runoff, it is
estimated that 8 to 15 percent of the total precipitation in the mountain
areas becomes runoff, and as much as 50 percent of this runoff may reach
the groundwater reservoir in the pervious zones immediately adjacent to
33
the mountain front and through the recent alluvial fill underlying the
stream channels downstream (Metzger 1952).
In general, more than 95 percent of the precipitation water over
the lower Gila River basin is estimated to be lost by evaporation before
reaching the stream channel (Arizona Interstate Stream Colmuission 1967).
How much of the remaining five percent reaching the stream channel
becomes groundwater recharge is very difficult to estimate in areas such
as the lower Gila River basin, where runoff is of infrequent occurrence.
Groundwater recharge investigations conducted in the Queen Creek
area, Arizona, show that about one-half of the total streamflow occurring
in that area is recharged to the groundwater reservoir (Babcock and
Cushing 1942).
Substantial contributions to groundwater storage occur when re-
leases from Painted Rock Reservoir flow through the lower Gila River
basin. From 658,100 acre feet of water released in 1966 and 1973, more
than 500,000 acre feet were estimated to be lost through infiltration
and deep percolation to the groundwater table, and evapotranspiration
between Painted Rock Dam and the Colorado River. About 70 percent of
this amount was dissipated between the dam and the Wellton-Mohawk area.
During the years from 1940 to 1971, about 1,367,000 acre feet (Arizona
Water Commission 1973) were estimated to have been pumped from this
lower Gila River reach providing for a high storage capacity for in-
frequent releases from Painted Rock Reservoir.
Seepage from excessive irrigation water applications is, however,
the main source of groundwater recharge in the Wellton-Mohawk District.
34
From 1962 to 1971, 2,100,000 acre feet of drainage water was pumped from
the Wellton-Mohawk aquifer, and about 75 percent of this volume, or
1,600,000 acre feet, can be estimated as seepage from excessive irriga-
tion water applications.
Since groundwater levels in the Wellton-Mohawk District during
recent years showed only small average variation, the recharge from
irrigation and other sources to the groundwater reservoir has practically
been counter-balanced by the amount pumped from drainage wells.
The most important source of groundwater in the desert region
of southern Arizona is the alluvial fill. The principal aquifers of the
alluvial fill are permeable lenses of sand and gravel interfingered with
relatively impermeable lenses of silt and clay. Although the alluvial
fill has been separated into older alluvial and Recent alluvial fill,
they are interconnected and the groundwater reservoir is continuous.
Wells in the older alluvial fill are reported to yield 500 to
1,000 gallons per minute from the sand and gravel of the upper 200 feet.
Wells in the Recent alluvial fill yield from 600 to 4,000 gallons per
minute (Babcock and Sourdry 1948). At the present time, the 107 wells
in operation in the Wellton-Mohawk District have an average discharge
of 1,634 gallons per minute with a range from 450 to 4,400 gallons per
minute (U.S. Bureau of Reclamation 1972b).
The general groundwater movement in the lower Gila River basin
is directed from the mountain fronts or the borders of the flood plain
to the Gila River bottom, and westward down the valley gradient. In the
mesa section of the Wellton-Mohawk District some water moves toward the
35
desert area, but predominantly the groundwater movement there is also
directed to the valley following the steep gradients caused by topo-
graphic differences and drainage water pumping at the foot of the mesa.
The continuity and extent of the deeper gravel layer in the Recent
alluvial fill underlying the mesa and the valley is another important
factor in the groundwater movement from the mesa to the valley.
Pumpage of groundwater for irrigation began in the early 1900's
and increased steadily until 1952, when surface water from the Colorado
River entered the Wellton-Mohawk area and groundwater pumping progres-
sively began to decrease.
As a result of the heavy withdrawal of groundwater in the area,
the water table in the farmed areas of the Wellton-Mohawk area had been
declining at an average rate of 0.9 feet a year for the period 1928,-48
(Babcock and Sourdry 1948). By 1950 the Wellton-Mohawk District of the
Gila Project had been reauthorized and a modern irrigation system was
under construction. In April, 1952, Colorado River water entered the
Wellton-Mohawk area.
The application of large amounts of water to cultivated lands
and the decline in pumping of groundwater for irrigation caused the
water levels to rise rapidly. Pumping of groundwater for irrigation
nearly ceased by 1957.
Subsequent recharge by return flow of Colorado River water
caused water levels to rise to within a few feet of the ground surface
necessitating extensive drainage facilities
36
Groundwater is discharged from the lower Gila River basin by
pumping for drainage and by natural means. Natural discharge includes
transpiration and evaporation of groundwater in the areas of cultivated
and natural vegetation along the flood plain, and underflow through the
narrow section of the Gila River valley near Dome.
THE WELLTON-MOHAWK IRRIGATION AND DRAINAGE DISTRICT
Description
The Wellton-Mohawk District occupies an area of about 113,500
acres that extends for a distance of about 45 miles from Avenue 55E,
just upstream from Texas Hill to Avenue 10 E, a few miles below Dome
(Figure 2). The area is bounded on the east by the Mohawk Mountains,
on the west by the Gila Mountains, on the north by the Muggins and
Castle Dome Mountains, and on the south by the Wellton Hills and the
Copper Mountains (Metzger 1952). Its boundaries are established by
Public Law which restricted the irrigable area to be supplied with
Colorado River water to a maximum of 75,000 acres of which approximately
60,000 acres are located in the valley of the Gila River and the remain-
ing 15,000 acres are on the adjacent mesa south of the valley land.
The valley section of the Wellton-Mohawk District includes
practically the whole Gila River flood plain between those avenues.
The mesa section extends for about 21 miles along the river as a strip
of land with an average width of 2.15 miles, which is, on the average,
70 feet above the valley floor.
Soils
One hundred and forty-eight thousand five hundred acres were
classified to determine the 75,000 acres best suited for irrigation
37
39
purposes in the Wellton-Mohawk area. Table 6 gives the soil character-
istics and acreage of the different classes of land.
Table 6. Wellton-Mohawk Area: Land Classification, Acreage, and SoilCharacteristics.*
Mesa Lands Valley Lands
**W.H.C. 3-6 acre-inches/acre 8 acre-inches or more/acre
Texture loamy sand silt loamsandy loam silt clay loam
Class:I none 21,977 acresH 26,896 acres 23,614 acresIII 6,500 acres 7,129 acresIV none 17,586 acresVI non-arable 44,911 acres
* Source: U.S. Bureau of Reclamation (1948, P. 1).
** Water-holding capacity of top 4 feet of soil.
The lands were separated into classes as follows:
Class I--Lands which are considered highly productive and de-
sirable in every respect for permanent irrigated agriculture.
Class II--Lands which are suitable for development, but of
somewhat limited productivity.
Class III--Lands which are marginal and which should be farmed
only in conjunction with lands of better quality.
40
Class IV--Class II except for salinity.
Class VI--Lands which are too low in productivity or which could
not be developed economically, usually considered non-arable.
This detailed land classification was conducted by the Bureau of
Reclamation staff during 1947 and 1948, after the reauthorization of the
Gila Project in July. In this classification, land classes I through IV
were mapped as arable land; class IV land was designated as a limited
arable land, dependent on the correction of the high salinity condition
(U.S. Bureau of Reclamation 1963).
Classes I and IV are found only in the valley. The mesa soils
are almost entirely loamy sand or sandy loam soils while the valley
soils are predominantly silty loam and silty clay loam.
During the period of November 13 through November 21, 1962, a
soil-sampling program was initiated on well cores selected as representa-
tive of both developed land under irrigation and undeveloped land that
would not reflect the effect of leaching by irrigation. The results of
laboratory analysis on the soil samples indicated that most of the salt
content found in previous soil surveys had been removed from the coarse-
to-medium textured soil in the irrigated areas. However, in the finer-
textured soil the salt content was still quite high.
The field and laboratory studies showed that, although the
soluble salts had been leached from the root zone in the developed lands
(in the undeveloped soils, a higher salt content occurs in the surface
soils) of the Wellton-Mohawk Valley, some salts still exist in the sub-
stratum (U.S. Bureau of Reclamation 1963).
41
Both mesa and valley soils were formed from alluvial deposits
of sands, silts, and clays. However, valley soils contain more organic
matter, are more fertile, and have a higher water holding capacity than
the mesa soils. Since the mesa soils drain more rapidly, they require
more irrigation water for crop production (Wishart and Nelson 1963).
Water Resources
Important changes in the hydrologic regimen of the Wellton-
Mohawk area occurred when Colorado River water began to replace the
depleted local groundwater as the irrigation supply, and when drainage
by pumping groundwater began. During almost ten years unused water
percolated into the underlying aquifer which had been depleted by pump-
ing prior to 1952.
Water for the Wellton-Mohawk distribution system (Figure 2)
comes from behind Imperial Dam through desilting basins at its
east abutment and the Gila gravity Main Canal. The canal flows about
15 miles to a "Y" point, just below the siphon under the Gila River,
where it is divided into two branches, one that conducts water to the
Yuma Mesa Division and the other, the Wellton-Mohawk Canal which carries
it up the Gila River valley on a route generally parallel to the Gila
River. The initial capacity of the canal is 1,300 cubic feet per second.
Water flows to a point 19 miles from the origin of the canal where a
pumping plant lifts it into the Mohawk Canal. Ten miles from the "Y"
the Dome Canal branches off to the north and serves the western end of
the Wellton-Mohawk District. The Wellton Canal takes water from the
Wellton-Mohawk Canal about a half mile above its terminus and flows by
42
gravity for 20 miles to a point near the foot of Antelope Hill, six
miles northeast of Wellton. It has an initial capacity of 300 cubic
feet per second, and serves the central area of the District. The
Mohawk Canal flows by gravity from the pumping plant at the terminus of
the Wellton-Mohawk Canal, initially in an eastern direction, turns
north, and then back to the west on the north side of the valley for a
distance of 44 miles. It has an initial capacity of 900 cubic feet per
second, and serves the largest portion of the area. There are three
major pumping plants on the main canal and numerous smaller relifts on
the tributary system.
From 1961 to 1971, 5,074,650 acre feet (Table 7) of Colorado
River water, including 35,698 acre feet from other sources such as flood
water from the Gila River channel, tile drain water, etc., were released
into the Wellton-Mohawk District irrigation system. This means an
average annual diversion of about 461,332 acre feet. About 849,281 acre
feet or about 17 percent of the total diverted water were lost as
seepage from the main and lateral canals and operational spills.
Water Development
Irrigation
Introduction. The establishment of the first civilization in the
Wellton-Mohawk area was made possible only by diverting water from the
Gila River to irrigate the adjoining lands to produce foods which, when
added to the fish catch, would provide the basis for their survival.
43
• Table 7. Wellton-Mohawk Irrigation and Drainage District: Water SupplyDelivered,in Acre Feet.*
YearIrrigated
AcresEstimated
Water Appliedto Farms
WaterLosses
NetSupply
Total Per Acre
1961 52,995 331,804 6.26 51,545 383,349
1962 51,735 348,414 6.73 61,808 410,222
1963 56,289 372,085 6.61 80,008 452,093
1964 58,100 371,197 6.39 91,939 463,136
1965 58,040 374,834 6.46 81,993 456,827
1966 60,062 414,397 6.90 76,061 490,458
1967 61,190 381,678 6.24 69,607 451,285
1968 60,758 396,420 6.52 70,077 466,497
1969 60,124 397,382 6.61 88,224 485,606
1970 60,756 415,269 6.83 81,754 497,023
1971 61,152 421,889 6.89 96,265 518,154
Total 641,201 4,225,369 849,281 5,074,650**
* Source: Wellton-Mohawk Division (1961-71).
** Includes 35,698 acre feet of water diverted from the Gila River channeland tile drains.
44
This explains why the Wellton-Mohawk area has been irrigated for
centuries, since the settlement of the first inhabitants.
The history of irrigation in the Wellton-Mohawk area can be
described in three stages characterized by different sources of water
supply.
The first stage occurred from the 1800's to about 1908, when
the first power district was established in the area. During this period
thousands of acres were brought under irrigation supplied with water
from the Gila River.
As the Gila River was not a dependable flow, the pioneer agri-
cultural developments were dependent on seasonal flows, and were sub-
jected to critical periods of floods and droughts. By the beginning
of the nineteenth century they had practically been destroyed.
The second stage can be considered from 1920, when the Gila
River Power District was organized to 1952, when Colorado River water
was brought into the area. It marks the beginning of a more intensive
irrigation development supported by a more dependable water supply, the
ground water pumped from many wells drilled throughout the area. The
relatively rapid increases in irrigated acreage and water use reached
their peaks by 1931, when approximately 11,000 acres were under culti-
vation and about 20,000 acre feet of water were pumped from the Wellton-
Mohawk aquifer (Arizona Water Commission 1973, p. 12).
Continued recirculation of irrigation water through deep percola-
tion and evapotranspiration brought an increasing salt concentration to
the land and the groundwater supply which by 1934 led many farmers to
abandon their lands.
45
The third stage, characterized by an adequate water supply,
starts with the introduction of Colorado River water into the Wellton-
Mohawk area. It symbolized increasing progress of the area, which is
today one of the most productive in Arizona and the United States.
Drainage requirements and high salinity are, however, serious problems
in the area and their solution has been a matter of much concern during
recent years.
Water Supply. Imported water from the Colorado River represents
practically the only source of water supply for the Wellton-Mohawk
District at the present time. Total precipitation is not considered
significant. Occasionally flood water released from Painted Rock
Reservoir brings some good quality water, a part of which is pumped into
the Wellton-Mohawk irrigation system.
Construction of the present irrigation system by the U.S. Bureau
of Reclamation in the Wellton-Mohawk area followed the reauthorization
of the Gila Project under Public Law 272 on July 30, 1947. This allowed
diversion of an annual allotment of 300,000 acre feet of water to be
consumptively used in the irrigation of a maximum 75,000 acres.
From the total 4,059,473 acre feet of water diverted from 1961
to 1969 into the Wellton-Mohawk irrigation system, 1,121,743 acre feet
(Table 8) were estimated to be diverted to the mesa section of the
project, and 2,937,730 acre feet (Table 9) to the valley. The amounts
of water applied to the farms were 936,098 acre feet (Table 8) on the
mesa, and 2,452,113 acre feet (Table 9) in the valley.
46
Table 8. Wellton-Mohawk Irrigation and Drainage District: EstimatedWater Supply Delivered to the Mesa, in Acre Feet.*
YearIrrigatedAcres
Estimated
Water Appliedto Farms Water
LossesNetSupplyTotal Per Acre
1961 8,530 88,026 10.32 13,675 101,701
1962 8,784 86,838 9.88 15,405 102,243
1963 8,793 94,170 10.71 20,249 114,419
1964 9,313 103,185 11.08 25,557 128,742
1965 9,313 104,519 11.22 22,863 127,382
1966 9,805 118,237 12.06 21,702 139,939
1967 9,839 109,037 11.08 19,885 128,922
1968 9,500 115,329 12.14 20,387 135,716
1969 9,700 116,757 12.04 25,922 142,679
Total 83,577 936,098 185,645 1,121,743
* Source: Wellton-Mohawk Division (1961-71), Wellton-Mohawk Division(1970).
47
Table 9. Wellton-Mohawk Irrigation and Drainage District: EstimatedWater Supply Delivered to the Valley, in Acre Feet.*
YearIrrigatedAcres
Estimated
Water AppliedTo Farms
Total Per Acre
WaterLosses
NetSupply
1961 44,465 243,778 5.48 37,870 281,648
1962 42,951 261,576 6.09 46,403 307,979
1963 47,496 277,915 5.85 59,759 337,674
1964 48,787 268,012 5.49 66,382 334,394
1965 48,727 270,315 5.55 59,130 329,445
1966 50,257 296,160 5.88 54,359 350,519
1967 51,351 272,641 5.31 49,722 322,363
1968 51,258 281,091 5.48 49,690 330,781
1969 50,424 280,625 5.56 62,302 342,927
Total 519,293 2,452,113 485,617 2,937,730
* Source: Wellton-Mohawk Division (1961-71).
Since estimated irrigated acreage was 83,577 acres (Table 8) on
the mesa, and 519,293 acres (Table 9) for the valley, water application
rates for the two sections during 1961-69 could be estimated as 11.17
and 5.63 acre feet per acre per year, respectively.
48
Irrigation Methods, Although a wide range of soils is found,
all irrigation in the Wellton-Mohawk District is by flooding methods.
In the mesa section of the project, where the soils in general
are coarser textured than those in the valley, losses by deep percola-
tion account for about 70 percent of the applied water.
Irrigated Acreage. Irrigated acreage in the Wellton-Mohawk
District has increased from 14,134 acres in 1952, to 62,351 acres in
1972 (Table 1). In 1972, 9,897 acres of the total 75,000 acres of
irrigable land for service were still out of irrigation rotation.
Irrigated Crops. The principal crops under irrigation rotation
in the Wellton-Mohawk District are wheat, alfalfa hay, cotton, lettuce,
cantaloupes, citrus, grasses, and grain sorghum. During 1972 these
crops accounted for about 91 percent of the total crop acreage under
irrigation (Table 2). The mesa is mostly devoted to citrus which
occupies about 50 percent of the present crop average on the mesa.
Alfalfa occupied 20,294 acres, or 29 percent of all crop acreage in
1972. In 1972 it accounted for 21.3 percent of the total gross revenue
in the Wellton-Mohawk District.
Cantaloupe and lettuce with a total acreage of 6,746 acres in
1972 accounted for 27.4 percent of the total gross income.
Consumptive Use. The term "consumptive use" as applied to an
irrigated area denotes water returned to the atmosphere by evaporation
and transpiration or incorporated in vegetative products. It also in-
cludes evaporation from water surfaces and bare soil and transpiration
49
from native vegetation where these quantities are too small to be con-
sidered separately. In irrigated regions, where an additional amount of
water must be applied to remove excess salts from the soil, the water
required for irrigation of crops exceeds the consumptive use (Hely 1969).
Irrigation is a consumptive use of water inasmuch as an average
two-thirds of the farm delivery is lost by evaporation from water and
land surfaces, and by transpiration of plants (Irelan 1971).
Consumptive use in the Wellton-Mohawk area is relatively high
and some crops such as citrus and alfalfa need water during the entire
year.
Assuming sufficiently similar climate conditions, seasonal
values and seasonal coefficients "K," (for use in the Blaney-Criddle
formula CU = KF) determined at the University of Arizona Experimental
Station farms near Tempe and Mesa (Erie, French and Harris 1965) were
used to estimate the consumptive use of water in the Wellton-Mohawk
District.
An average value of 4.66 acre feet per irrigated acre per year
was found for the valley section of the project and 3.63 acre feet per
irrigated acre per year for the mesa using crop census for the years
from 1965 to 1968. Consumptive use of the phreatophytes was estimated
in previous studies (Young and Blaney 1942; Gatewood et al. 1950;
Robinson 1952, 1958, 1959, 1964, 1965, 1970; McDonald and Hughes 1968;
Culler 1970). A value of 3.0 acre feet per acre per year was decided
upon for this study.
50
Leaching Requirement. Permanent and profitable irrigated agri-
culture requires that salts brought into the root zone of crops by
irrigation water be removed from their zone by applying excess water
which drains from the lower boundary of this zone. The leaching re-
quirement is defined as the fraction of irrigation water that must be
drained from the lower boundary of the root zone to maintain this desired
salt balance.
The simplest expression for salt balance is
D.C. = D C11 dd
(1)
inwhichp.=depthofirrigationwaterapplied;c..salt concentration
of the irrigation water; D d = depth of water draining from the root zone;
and Cd = concentration of the soil water draining from the lower
boundary of the root zone.
The hypothetical fraction of drainage water consisting of dis-
placed soil solution has been called the leaching efficiency, El'
by
Boumans and Van der Molen (in Bouwer 1969). The other complementary
fraction of irrigation water that passes unchanged through the soil
profile is then 1-E1,
and the concentration of the water draining from
the root zone can be calculated as
Cd = El • Cs + (1 - E 1 )Ci (2)
in which Cs = salt concentration of the soil water in the root zone.
E1 appeared to vary from 0.2
for heavy soils to 0.6 for light
soils (Bouwer 1969).
51
The value of Cs should be considered as the maximum permissible
salt concentration of the soil solution for which crop growth and yield
are not inhibited.
Assuming 0.35 and 5,000 parts per million as reliable indexes
for El and Cs, respectively, to be applied to the valley section of the
Wellton-Mohawk District, and taking 900 parts per million (Table 10) as
the average concentration of the irrigation water being applied to the
fields, the value of C d is 2332 parts per million.
The water used by evapotranspiration from cropland is about
4.66 acre feet per irrigated acre per year.
The irrigation water requirement for salt balance is equal to
the amount of water needed for evapotranspiration, De, plus the amount
Dd needed for leaching the profile, or
Di = D
e + D
d
(3)
Solving equation (1) for Di and substituting its corresponding
value in equation (3) we can, with the data available calculate Dd
as
being 2.93 feet.
Thedepthofirrigationwater,D„being applied to the valley
section averages 5.63 feet (Table 9) a year which means that the depth
of water draining below the root zone is about 0.97 feet, about one-
third of the estimated depth of water draining from the root zone, Dd ,
to maintain an efficient salt balance there.
For the mesa section of the Wellton-Mohawk District, where the
soils are coarser than those in the valley, a leaching efficiency index,
52
Table 10. Wellton-Mohawk Irrigation and Drainage District: EstimatedAnnual Salt Input, in Tons.*
YearWater Diverted Dissolved Solidsfrom Main StreamAcre Feet PPm tons/ac-ft tons
1961 338,349 823 1.12 378,951
1962 410,222 814 1.14 467,653
1963 450,268 801 1.09 490,792
1964 461,306 836 1.14 525,889
1965 455,614 914 1.24 564,961
1966 472,344 905 1.23 580,983
1967 450,690 848 1.15 518,294
1968 462,880 835 1.14 527,683
1969 485,606 878 1.26 611,864
1970 492,870 875 1.26 621,016
1971 513,800 933 1.27 652,256
Average 860 1.18
* Source: United States Geological Survey (1961-71).
53
E l , of about 0.45 could be estimated. The depth of irrigation water
being applied in this section averages 11.17 feet (Table 8) a year
and the evapotranspiration requirement was estimated as 3.63 feet a
year.
Using the same reasoning as applied for the valley section, the
depth of water draining from the root zone in the mesa, Dd'
should be
1.77 feet, and the depth of water actually draining to the groundwater
table is 7.54 (11.17 - 3.63) feet. This means that, as an average,
5.77 (7.54 - 1.77) acre feet per irrigated acre per year of the applied
irrigation water in the mesa section has been lost without any beneficial
use.
From the above, irrigation water requirements for the valley
and mesa section of the Wellton-Mohawk District should be, on an average,
7.60 and 5.40 acre feet per irrigated acre per year, and the amounts of
water actually being applied on these areas are 5.63 and 11.17 acre
feet per irrigated acre per year, respectively.
Irrigation Efficiencies. Irrigation efficiencies should not
fall below 60 percent and rarely exceed 80 percent (Hargraves 1968).
A Bureau of Reclamation report for 22 selected irrigation pro-
jects in the western United States shows a water conveyance efficiency
of 62.4 percent and a farm water use efficiency of 57.9 percent. This
means that about 38.0 percent of the water diverted is lost between the
reservoir and the farms, and of the amount delivered to farms, 42.0
percent is lost through irrigation practices. The over-all project
efficiency from the reservoir to the final irrigation process is about
54
36.0 percent (Hely 1969). Of the water flow diverted from the Gila
Gravity Main Canal to the Wellton-Mohawk District, during the period
from 1961 to 1971, 16.7 percent was lost as operational spills and
transportation losses; 83.2 was applied to farms; and 0.1 percent was
delivered for non-irrigational purposes. The conveyance losses from the
Gila Gravity Main Canal in its 18.5 mile reach from Imperial Dam to the
Wellton-Mohawk turnout were estimated, based on previous work (Hely
1969), as about 4.0 percent. The over-all water-conveyance efficiency
in the Wellton-Mohawk District can then be estimated as 79.4 percent
which is a high value compared to the average in the Bureau of Reclama-
tion study.
If one assumes the cropland evapotranspiration as the only water
beneficially used, the efficiency of water utilization in the Wellton-
Mohawk District can be estimated on an annual basis, as averaging 32.0
percent for the mesa (3.63/11.17) and 83.0 percent (4.66/5.63) for the
valley. The low efficiency in the mesa may not be considered the direct
result of inefficient water management since excess irrigation water
must be applied for leaching requirement. The high efficiency in the
valley could, probably, in part be justified by some water contribution
from the groundwater levels, standing at an average depth of about ten
feet from the gound surface.
Problems of Water Use
The application of water for irrigation, as has occurred in other
arid areas of the world, brought serious problems of drainage and high
salinity to the Wellton-Mohawk District.
55
Recently, from the early 1920's to the present time, four facts
disturbed the agricultural activities in the Wellton-Mohawk area. First,
the decline of the water levels from the continued groundwater pumping;
second, the increasing salt concentration from recycling use of water;
third, the rapid rise of the water levels after the introduction of
Colorado River in 1952, mostly because of application of large quantities
of leaching water to reclaim the land; and fourth, the high salt concen-
tration of the drainage water being released into the Colorado River
channel.
These actions combined to give the present drainage and salinity
conditions prevailing in the Wellton-Mohawk District.
Drainage
The continued decline in groundwater pumping, and the application
of large amounts of irrigation water had caused by early 1958 a serious
drainage problem in the Wellton-Mohawk District.
After a detailed study of the situation and proposed alternative
solutions related to the type of drainage facilities to be used, the
District Board of Directors decided on a 73-mile concrete-lined main
conveyance channel, and construction of drainage wells instead of tile
drains to remove the groundwater from the soil zone (Moser 1967). The
construction work began in 1960, and by July, 1961, the last length of
channel was constructed. At that time 67 wells had been drilled and
drainage water was pumped into the new conveyance channel. This channel
has 31 reaches which vary in capacity from a few cubic feet per second
to a maximum of 320 cubic feet per second. The canal and associated
56
drainage wells were constructed to control the rising groundwater levels
in the Wellton-Mohawk aquifer, and initially the canal delivered this
flow to the Gila River channel about 0.6 mile above its confluence with
the Colorado River.
In March, 1962, when the first Depth to Groundwater Map was pre-
pared, about 26,000 acres, almost 50 percent of the irrigable area in
the valley section of the project had a depth to water table of eight
feet or less. By March, 1954, the area with a water table of eight feet
or less had been reduced to 7,250 acres (Moser 1967).
In 1965, a 12-mile extension to the previously constructed
drainage channel, named the "Main Outlet Drain Extension," was built to
permit the Mexican Government to bypass the drain-flow during the period
of low flow in the Colorado River.
From 1965 to 1968 water levels in the valley had an average
decline of about a half foot and the average depths to groundwater on
those dates were 10.38 and 10.82 feet, respectively. With full capacity
pumping, by June, 1970, about 13,000 acres had water levels less than
eight feet from the surface, but only 800 acres had levels less than
four feet. Depth to groundwater on the mesa ranges from 0 to over 100
feet with 1500 acres of land having depth to water of less than ten
feet (Wellton-Mohawk Division 1970).
During the period from 1962 to 1971, the total drainage with-
drawal from the Wellton-Mohawk aquifer and the total supply diverted
from the main stream were 2,084,200 and 4,691,301 acre feet, respec-
tively. This means that as an average for the whole project, about 44
57
percent of the supply diverted from the Gila Gravity Main Canal returns
to the Colorado River through the Main Outlet Drain Conveyance Channel.
At the present, many of the wells in operation in the Wellton-
Mohawk District are for the purposes of drainage and selective pumping
to improve the quality of the mixed flow reaching Morelos Dam, the
Mexican diversion point on the Colorado River.
Releases from Painted Rock Reservoir for two periods, in 1966
and 1973, have aggravated the drainage problem in the Wellton-Mohawk
District by adding thousands of acre feet of water to the aquifer through
the highly permeable materials underlying the Gila River channel.
Salinity
The two major impacts of irrigation on the present salt content
of the drainage water in the Wellton-Mohawk aquifer are the accumulation
of salts when the Gila River water was the only source of water supply,
and the dissolving of the mineral materials underlying the irrigated
areas, during the 30 years in which pumped groundwater was the major
water supply.
Speculation has been made that saline springs are polluting the
aquifer as another source of salts. The results are, however, not con-
clusive since the analyzed salinity anomalies could be caused by past
and present management practices and not by spring inflow (U.S. Bureau
of Reclamation 1972a).
The average salinity of the drainage wells originally was about
6,500 parts per million with the highest well having a salinity of 17,000
parts per million (Moser 1967). In 1961, when intensive pumping of the
58
drainage wells started, salinity became a problem of great concern, be-
cause of the large increase in the salinity of the Colorado River water
reaching the International Boundary and consequently, of the irrigation
water supply diverted at Morelos Dam to the Mexicali Valley.
Although the Mexican Treaty does not specify water of any par-
ticular quality, claims from farmers and the Mexican Government led the
United States and Mexico to an agreement that resulted in many important
measures taken in the interest of international good will to reduce the
salinity of Colorado River water flowing into Mexico.
Construction of additional drainage wells in 1965 for selective
pumping in areas where salinity was lower was an important management
measure. These wells are pumped during the winter months when Colorado
River flows are lower and the opportunities for dilution are reduced.
During the summer months, when flows in the Colorado River reach peak
values, the more saline wells are pumped more intensively.
Although the selective pumping, and a very well-defined scheme of
operation could in the long run bring a satisfactory solution to the
salinity problem in the Wellton-Mohawk District the seriousness of the
international problem required a quick decision upon the problem, and
led to the construction of the Main Outlet Drain Extension.
The dissolved solid concentration of the Colorado River water
reaching the Wellton-Mohawk District averaged 860 parts per million
during the years from 1961 to 1971 (Table 10). The average annual
salt load inflow during this same period can be estimated as 1.18 tons
per acre foot of water, or a total of about six million tons.
59
The average dissolved solid concentration of water from drainage
wells during the period 1962-71 had an almost uniform decline from 6000
to 3650 parts per million (Table 11), or an average improvement of about
235 parts per million per year. During this same period the salt load
discharged to the Colorado River through the Main Outlet Drain Extension
averaged 1.347 million tons per year, or a total of about 13,471,000
tons.
Economic Status
The evaluation of the economic status of any project requires a
detailed analysis of all factors involved in the production process, and
will be beyond the scope of the present work. Here, only a few aspects
of production will be compared by using six of the irrigation projects
operating in the Yuma area, including the Wellton-Mohawk.
Average annual rates computed for the period 1966-72 ranged from
4.06 to 12.45 acre feet per irrigated acre per year, with the Wellton-
Mohawk District ranking the fourth highest with a water application rate
of about 6.65 acre feet per acre (Table 12) per year.
Average annual operation and maintenance cost in the Yuma area
for the period 1966-71 varied from 7.10 to 42.31 dollars per irrigated
acre (Table 13). The Wellton-Mohawk District ranked again in fourth
highest place with 17.10 dollars per irrigated acre.
The gross crop value per irrigated acre in the Wellton-Mohawk
District is, however, one of the lowest among the Yuma Projects. Average
annual values for the period from 1966 to 1972 ranged from 315.70 to
60
Table 11. Wellton-Mohawk Irrigation and Drainage District: EstimatedSalt Output, in Tons.*
Year Water Pumpage Dissolved SolidsAcre Feet PPm ton/ac-ft Tons
1962 215,100 5,978 8.13 1,748,763
1963 200,700 5,504 7.48 1,501,236
1964 181,000 4,928 6.70 1,212,700
1965 186,100 4,540 6.17 1,148,237
1966 216,900 4,915 6.68 1,448,892
1967 212,600 4,842 6.59 1,401,034
1968 219,800 4,764 6.48 1,424,304
1969 218,300 4,023 5.51 1,202,833
1970 218,400 3,748 5.44 1,188,096
1971 215,300 3,653 5.55 1,194,915
Average 208,420 4,690 6.47 1,347,100
* Source: U.S. Geological Survey (1961-71).
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63
725.01 dollars with the Wellton-Mohawk District ranking the lowest and
the Yuma Auxiliary Project the highest (Table 14).
Water Management System
The water management system used in the Wellton-Mohawk District
generally involves the application of Colorado River water and infre-
quent flood water pumped from the Gila River channel to the irrigated
fields by flooding methods, and the removal of excess water seeping into
the ground through a system of drainage wells and tile drains. Only a
very small amount of water from tile drains returns to the irrigation
distribution system. Other irrigation return flow moves down the river
and mixes with flows returning from other irrigation projects in the
combined flood plain area of the Colorado and Gila Rivers. These waters
are, however, too salty to be reused for irrigation purposes. Drainage
pumping has approximately counterbalanced the groundwater recharge since
groundwater levels during recent years have practically been unchanged.
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COCID I it
WATER MANAGEMENT SYSTEM MODEL
To account for all measurable or estimable interchanges into the
hydrologic system of the Wellton-Mohawk area (Figure 2), a model was
created that would simulate the dynamic behavior of the system under the
conditions of several proposed strategies of operation. From data avail-
able it is impossible to calculate some components of the hydrologic
budget of the area, and therefore they were estimated.
Description of the Modeling Process
The model was created in two basic phases. All the water com-
ponents in the model are taken on an annual basis in units of acre feet.
Phase I Model
The Phase I model is a simple annual accounting of the inflow
and outflow components of the hydrologic system in which the water re-
sources are allocated among their various uses uniformly throughout the
area. The area was assumed to be a regular quadrangle extending along
the Gila River flood plain and adjoining mesa, between the narrow sec-
tions of the valley floor near Texas Hill and Dome. It has a width of
3.7 miles and is 42.0 miles long enclosing an area of about 100,000
acres.
The water flowing into the area is the Wellton-Mohawk Canal in-
flow of Colorado River water, the Gila River surface inflow, the Gila
65
66
River underground inflow, and the contribution to the groundwater re-
charge from precipitation falling on the contributing watersheds along
the Wellton-Mohawk area. Possible groundwater contribution from the
basin fill into the overlying alluvium was considered negligible because
there is no evidence of artesian pressure.
The Colorado River water flowing into the District through the
Wellton-Mohawk Canal is recorded at two water-stage recorder stations,
one above and one below the gates, at the turnout from the Gila Gravity
Main Canal, and reported in U.S. Geological Survey publications (U.S.
Geological Survey 1960-71).
The Gila River surface inflow at the upstream boundary of the
District has been estimated from measurements taken at the gaging sta-
tion "Gila River below Painted Rock Dam," and estimates of the amount of
water released from the reservoir which infiltrates between the dam and
Texas Hill. This estimation does not include evaporation loss during
surface flow, and possible contribution of storm runoff from contribut-
ing watersheds along that reach of the Gila River. Ultimately, more
accurate estimates were substantiated by measurements taken at Avenue
51 E (Figure 2). During the period 1965-68, chosen to test the model by
including a wet season--Spring 1966--the Gila River flow reaching the
Wellton-Mohawk area was estimated from (1) records of the amount of water
released from Painted Rock Reservoir and the amount of released water
pumped from the Gila River channel along the area; and (2) estimates of
the volume of infiltration between Texas Hill and Dome, and the estimated
volume of released water reaching the gaging station near Dome (Table 5).
67
The Gila River underground inflow was computed by applying a
form of Darcy's law:
Q = PIA or PIMW (4)
in which, Q = the Gila River underground inflow in cubic feet per second;
P = the coefficient of permeability in cubic feet per square foot; I =
the hydraulic gradient in feet per foot; M = the thickness of the
saturated aquifer in feet; and W = the width of the flow section in feet.
From hydrologic studies conducted in the study area (U.S. Bureau
of Reclamation 1963) and upstream from San Carlos Reservoir (Hanson 1972)
a value for P of 500 cubic feet per day per square foot was chosen as a
reliable estimate for the lower Gila River basin. Values for I, M, and
W were taken from U.S. Bureau of Reclamation groundwater maps (Wellton-
Mohawk Division 1970). The underground flow crossing the upstream sec-
tion of each sector is logically the underground flow leaving the pre-
ceding sector, as shown in equation Appendix A, line 146.
Precipitation contribution to groundwater recharge directly from
rainfall on the valley floor in the desert region of Arizona, normally
is not appreciable. Its importance, however, is in providing runoff
which is the principal source of recharge in many areas of Arizona
(Metzger 1952). The amount of runoff that becomes recharge to the
groundwater reservoir underlying the valley floor was estimated to be
approximately 55,000 acre feet, or about 4.4 percent of the annual
weighted precipitation falling on the lower Gila River basin below
Painted Rock Dam during the period 1965-68.
68
The water outflow from the Wellton-Mohawk area consists of pumped
drainage water that leaves the area through the Wellton-Mohawk Main
Outlet Drain, the Gila River surface outflow, the Gila River underground
outflow, and evapotranspiration from crops and riparian vegetation.
The Wellton-Mohawk Main Outlet Drain flow is recorded at a water-
stage recorder station located 8.6 miles upstream from the mouth of the
Gila River, and reported in U.S. Geological Survey publications (U.S.
Geological Survey 1960-71).
The Gila River surface outflow is recorded at the gaging station
near Dome, and reported in U.S. Geological Survey publications (U.S.
Geological Survey 1960-71).
The Gila River underground outflow was estimated by applying the
same form of Darcy's law used to estimate the Gila River underground
inflow, previously discussed.
Total crop evapotranspiration was estimated as the weighted
value of 4.42 acre feet per acre per year derived from the values re-
ferred to in the "Consumptive Use" section.
There is practically no surface water impoundment within the
limits of the District. Since the area is under permanent irrigation
which provides for an almost unchangeable long-term soil moisture con-
tent, the difference in water storage could be entirely accounted for
by variation in the groundwater storage.
The difference between inflow and outflow using the mass con-
servation equation is:
I - 0 = AS
(5)
69
or,
TWMINFL + GRSINFL + GRUINFL + TPRECIP -
(TWMOTFL + GRSOTFL + GRUOTFL + TEVPTRN) = AS (6)
where, I = total water inflow; 0 = total water outflow; AS = change in
water storage; TWMINFL = Wellton-Mohawk Canal inflow diverted to the
District; GRSINFL = Gila River surface inflow; GRUINFL = Gila River
underground inflow; TPRECIP = precipitation contribution to the ground-
water recharge in the valley; TWMOTFL = Wellton-Mohawk Main Outlet Drain
flow leaving the District; GRSOTFL = Gila River surface outflow;
GRUOTFL = Gila River underground outflow; and TEVPTRN = crop and
phreatophytic evapotranspiration from the District. AS is a known value
from measurements of changes in groundwater elevations, and the other
factors were determined as discussed above. This is the basis of the
Phase I model flow diagram shown in Figure
Phase II Model
The Phase II model is a more sophisticated water balance struc-
ture that permits a more detailed analysis of the behavior of the hydro-
logic system of the Wellton-Mohawk area. The area is that enclosed
within the boundaries of the Wellton-Mohawk District and contains both
valley and mesa sections. Planes approximately perpendicular to the
general direction of the Gila River flow divide the area into sectors
to make possible the analysis of local effects in the behavior of the
hydrologic system along the area. Nine sectors are located in the valley
and five on the mesa. Irrigation on the mesa area is confined between
Gila RiverSurface Inflow
Gila RiverUndergroundOutflow
Wellton-MohawkOutflow
70
Figure 3. Flow Diagram for the Hydrologic Model Used in Phase I.
71
Avenue 24 E and 46 E (Figure 2) and thus sectors 1, 2, 8, and 9 do not
include a mesa section.
Table 15 gives an estimated allocation of irrigable and total
area for each sector in the District, and also of the estimated surface
area of the groundwater aquifer, which is considered to be limited in
each sector by its imaginary east and west boundaries, the north boundary
of the Gila River Valley and the south limit of the mesa.
For the mesa section of the District the model envisages that
the Colorado River water flowing into the area is the only source of
irrigation water supply. Part of this inflow is consumptively used by
crops while the other part, which percolates deeply into the ground,
flows out of the area as drainage water being pumped into the conveyance
channel; as underground flow moving to the valley aquifer; and as under-
ground flow moving to the desert to the south. The model then considers
that these water components balance the annual water budget of the area,
and other possible components such as change in groundwater storage, are
probably insignificant on an annual basis.
The Wellton-Mohawk Canal inflow of water from the Colorado River
delivered to the mesa was estimated from reported data of the amount of
water applied to farms there and the total water losses occurring in the
District. Because more reliable data were not available, the total
water losses were allocated between the mesa and the valley, proportional
to the amount of water applied to each of them. Total water delivered
to the District and total water losses when plotted on a graph showed a
scattered distribution, indicating that for the District as a whole, the
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72
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correlation between these two water components must be weak. Computed
in this manner, the Wellton-Mohawk Canal inflow delivered to the mesa
was then allocated among sectors proportional to their irrigable areas
(Table 15) according to equation in Appendix A, line 125.
Evapotranspiration was estimated on the basis of the works
previously referred to in the "Consumptive Use" section. A uniform value
of 4.66 acre feet per irrigated acre for the valley and 3.63 acre feet
per acre for the mesa were estimated. Evapotranspiration distribution
among sectors on the mesa was made proportional to their irrigable areas
according to equation in Appendix A, line 130.
Drainage pumped from the wells on the mesa, one in sector 3 and
the other in sector 5, was reported and is the only drainage from the
mesa being released into the conveyance channel. It was estimated as an
average annual discharge of about 6,600 acre feet (Wellton-Mohawk Divi-
sion 1970) and its distribution between sectors 3 and 5 was made accord-
ing to equation in Appendix A, line 132.
Underground flow to the valley, because of the great complexity
in defining hydraulic gradients, the four dimensional (north, south,
west and vertical) flow directions, and possibly incontinuous connection
between the aquifer underlying the mesa and valley sections, was Im-
possible to compute. This flow was then estimated as the difference
between the diverted inflow, and the outflow represented by the under-
ground flow to the desert area, the drainage water pumped into the main
conveyance channel, and the estimated loss through evapotranspiration as
indicated in the following equation:
TMUINFL = MWMINFL - ('INEVPTR + DUTNFL + TMObOTFL) (7)
74
where, TMUINFL = total underground flow leaving the mesa to the valley;
MWMINFL = the Colorado River water delivered to the mesa; TMEVPTR = the
total crop evapotranspiration from the mesa; TDUINFL = the total under-
ground flow from the mesa to the desert area; and TMODOTFL = the total
Wellton-Mohawk Main Outlet Drain flow leaving the mesa. The computation
of the groundwater flow from the mesa to the valley was, consequently,
subject to error in estimating the other water components involved in
the mesa water balance. Its allocation among the sectors was made
proportional to the amount of irrigation water applied on each of them
according to equation in Appendix A, line 134.
The underground flow to the desert area was estimated as about
ten percent of the total groundwater volume flowing to the valley
(Wellton-Mohawk Division 1970), and its allocation among sectors was
assumed to be proportional to the amount of irrigation water applied on
each of them computed according to equation in Appendix A, line 133.
For the valley section of the project the model envisages that
the water supply inflow of Colorado River water, the Gila River surface
inflow, the underground flow from the mesa, the Gila River underground
inflow, and precipitation reaching the Wellton-Mohawk area are used in
part through evapotranspiration from crops and riparian vegetation. A
significant amount is pumped as drainage water and conveyed from the area,
and a relatively small part flows from the area as Gila River surface
outflow and Gila River underground outflow. The difference between
inflow and outflow is accounted for by changes in groundwater storage
estimated from groundwater maps, which balance the annual water budget
of the area.
75
The Wellton-Mohawk Canal inflow applied to the valley was
estimated from the equation
TWMINFL = WMCINAV + WMCINAM + TLOSSES
where, TWMINFL = the Wellton-Mohawk Canal inflow reaching the District;
WMCINAV = the Wellton-Mohawk Canal inflow applied to the valley;
WMCINAM = the Wellton-Mohawk Canal inflow applied to the mesa; and
TLOSSES = the total water losses along the conveyance system within the
District. The Wellton-Mohawk Canal inflow applied to the valley is the
only unknown term of the equation, and the other terms are reported
data from U.S. Bureau of Reclamation publications (Wellton-Mohawk
Division 1961-71; Wellton Mohawk Division 1970) or calculated as dis-
cussed previously.
The Wellton-Mohawk Canal inflow diverted was then computed as the
sum of the applied water plus the water losses occurring along the
conveyance system in the valley and allocated among sectors proportional
to their irrigable areas according to equation in Appendix a, line 124.
The Gila River surface inflow reaching each sector was estimated
to be the Gila River surface inflow plus the return flow from irrigation
reaching the preceding sector, minus the amount of water infiltrated
through the river channel along this preceding sector. It is determined
from equation in Appendix A, line 145.
For normal years, when the Gila River surface flow reaching the
Wellton-Mohawk area is zero, the Gila River surface flow reaching the
other downstream sectors is reduced to return flow from irrigation minus
infiltration occurring through the river channel.
76
Total return flow from irrigation and total infiltrated water
were allocated among sectors proportional to the length of each sector
and the length of river channel, respectively, in each sector. The
corresponding equation are indicated in Appendix A, lines 127 and 126.
The underground flow from the mesa reaching the corresponding
sectors in the valley was previously defined as an outflow component of
the mesa water balance.
The Gila River underground flow reaching each sector in the
Wellton-Mohawk valley was computed by applying the same form of Darcy's
equation previously discussed for the Phase I model.
The direct contribution of the precipitation is considered in-
significant as was done in the Phase I model since most of it is inter-
cepted or detained in a shallow surface layer of the soil and rapidly
evaporated. Its indirect contribution through the amount of runoff that
becomes recharge to the groundwater reservoir underlying the valley
floor was discussed for the Phase I model. Its distribution among
sectors was based on the contribution of the most important tributaries
reaching the Gila River along the Wellton-Mohawk valley or adjusted to
balance the groundwater level changes occurring during the time span
considered and estimated from the equation in Appendix A, line 135.
The water supplies entering the valley section are discharged
as the Wellton-Mohawk Main Outlet Drain outflow, the evapotranspiration
from crop and phreatophytes, the Gila River surface outflow, and the
Gila River underground outflow.
77
The Wellton-Mohawk Main Outlet Drain Outflow leaving the area
and delivered into the lower reach of the Colorado River, as referred to
in the Phase I model, is a measured and reported value. Its allocation
among sectors was made proportional to the total flood plain area within
each sector, and computed by equation in Appendix A, line 128.
Evapotranspiration amounts from crops and phreatophytes were
referred to in the "Evapotranspiration" for the mesa area section.
Their allocation among sectors was made according to equations in
Appendix A, line 129.
The Gila River surface outflow is a measured and reported value
taken as in Phase I model as an average value for the annual flows
measured at the "Gila River near Dome" station during recent years. Its
allocation among sectors was made according to equation in Appendix A,
line 151.
The Gila River underground outflow was estimated by applying the
same form of Darcy's equation, as referred to in Phase I model.
Figure 4 is a diagram of flows occurring in the Wellton-Mohawk
District, as considered in the Phase II model.
Processing the input data into the framework described above, the
net recharge to or withdrawal from each sector on the mesa or in the
valley was determined according to equations in Appendix A, lines 157
and 159. The following step is the determination of the changes in
groundwater elevation for a given recharge or withdrawal for each sector
on the mesa or in the valley according to equations in Appendix A, lines
166 and 162. The groundwater depths expected to be reached in each
78
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79
sector on the mesa or in the valley during a given time span are de-
termined from the equations in Appendix A, lines 167 and 163.
Validation of the Model
To test the model for validity as representative of the hydro-
logic system of the area, the groundwater depths predicted by the model
were checked against field measurements taken from groundwater maps.
The average deviation was .08 feet except in sectors 3 and 6
where larger values were obtained. In these sectors additional research
will be required to determine the cause of the larger error which could
not be reduced by maintaining uniform the criterion for allocation
among all sectors of the groundwater flows from the mesa to the valley
or to the desert area.
Alternative Management Strategies
General
Various water resource management strategies could be applied to
the Wellton-Mohawk District to accomplish the objectives proposed in
the present study. The selection and application of a complete or
optimum alternative management practice requires social, economic, and
legal treatment that would demand much more time and data than are
presently available. Thus some aspects of the existing water resources
management in the area are focused upon, and suggestions that will pro-
vide for a better utilization of the water resources, or will accomplish
the general objectives of the present work are presented.
80
Change in Irrigation Method
A change in irrigation method seems to be advisable for the mesa
section of the Wellton-Mohawk District in which the irrigation method
used is not appropriate for the sandy type of soil dominant there. More
than 50 percent of the water being applied to the mesa fields could be
saved if more suitable methods of irrigation were used.
Since the dominant and ever-increasing crop growing there is
citrus, which can be irrigated by sprinkling with proven advantages
(Gordon 1970), considerable decline in the need for groundwater pumping
could be expected with the introduction of this method. Gordon (1970)
showed that the change from flood to sprinkler irrigation would reduce
the farmers' production costs by a minimum of $4.36 per acre, and the
District would have a net gain of $4.69 per acre.
Trickle irrigation, a relatively new irrigation method from
which high water savings and sizable yield increases have been reported
(De Remer 1970), only recently has been commercially available. From
his economic analysis of the changes in irrigation method on the mesa of
the Wellton-Mohawk District, Gordon (1970) also showed that the change
from flood to trickle irrigation could reduce the farmers' production
costs by $3.98 per acre.
Increase in Irrigated Area
The design capacity of the main conveyance channel in the
Wellton-Mohawk District, as previously noted, is 320 cubic feet per
second (U.S. Bureau of Reclamation 1972b), or about 231,000 acre feet
per year. In 1971, when 61,152 acres (Table 7) were irrigated, the
81
drainage pumping volume was 215,000 acre feet (Table 11). This means
that the present drainage disposal system is functioning close to its
design capacity. The development of new areas in the District up to
its maximum 75,000 permissible acreage will then require that the
present drainage system be enlarged if water levels are to be kept at
depths required for economic crop production.
Change in Crop Allotment
The reduction in acreage of some crops such as alfalfa and
grasses which occupy a high percentage of the total acreage under irri-
gation and have the highest rates of water use can decrease the total
water requirements of the area, and provide for more flexibility in the
operation of the drainage system. This change in crop allotment could
be done to the benefit of other crops such as cotton with a lower water
requirement and which could compete economically with the substituted
crops. Based on prices and costs prevailing in 1969 (Wildermuth, Martin
and Rieck 1969) substitution of cotton would provide an increase in
returns above the total variable costs of about $157.78 ($258.08 -
$100.30) per acre on a representative general crop farm in Yuma County,
Arizona. To decide upon such a change, however, a more complete analysis
including other assortments of crops should be conducted.
Increase in Water Use Efficiency
Water use efficiency in an irrigated area can be accomplished
through the reduction in canal seepage along the conveyance and distri-
bution systems and by improving the efficiency of water application.
82
With modern technology for construction of irrigation canals and the use
of sealant materials, water losses from canals can be decreased to
acceptable levels. Characteristics of irrigation water applications are,
however, the major cause of low over-all efficiency of the irrigation
projects. In surface irrigation, water application efficiency is in-
fluenced primarily by the amount of water applied, the intake character-
istics of the soil, and the rate of advance of water over the soil
surface (Erie 1968).
Sprinkler and trickle irrigation with practically no conveyance
losses and more uniform distribution of the irrigation water through the
root zone provide higher indexes of water application efficiency and
should be used wherever economically and technically advantageous.
Additional Drainage Facilities
Annual "Depth to groundwater" maps from the U.S. Bureau of
Reclamation show that in many spots within the limits of the Wellton-
Mohawk District the groundwater levels are still very high despite the
number of pumping wells spread over the area. These are areas where
geologic conditions delay the vertical movement of water and create
semi-perched or perched situations, or do not provide for efficient per-
formance of the drainage wells. In such areas additional wells or
complementary tile drains have been proven necessary to lower groundwater
levels to adequate depths. This would result in higher crop yields and,
consequently, greater returns to the farmers.
83
Conjunctive Use of Water Resources
The maximum conservation, utilization, and regulation of the
water resources in an area must be through the conjunctive use of ground
and surface waters. They must be coordinated for maximum regional bene-
fits, and the coordination must not be merely on a physical basis but on
an economic one as well. The problem must also be handled under both
the quantitative and qualitative aspects, although economic guidelines
for water quality have not been well defined. A conjunctive use
system that considers quantity alone might not produce the optimum
results since water salinity will put a constraint on the use of some
water which could be considered available when quality is not considered.
The study of the conjunctive use of the water resources of an
area should be combined with conservation and augmentation practices
which could affect considerably the water balance. Artificial ground-
water recharge, phreatophyte control, and watershed management practices
to increase water yields can, in some cases, make available additional
supplies which will provide for more alternative management opportunities
for the water resources in the area.
As was previously shown, the availability of surface water
supplies other than the imported water from the Colorado River in the
Wellton-Mohawk area is infrequent, and the present condition of a
generally high groundwater table does not afford an opportunity for
storage and later use of the released water from Painted Rock Reservoir
reaching the area. Only a small amount of this water has been pumped
into the irrigation system in the past.
84
The rapid decline of groundwater levels when groundwater was the
only source of irrigation supply showed that the possibility of natural
recharge of the aquifer with good quality water from local storm runoff
is probably insignificant. The opportunity for permanent use of ground-
water available in the Wellton-Mohawk at the present time is practically
limited to the recharge from the percolated irrigation water, if a
balance of the groundwater levels is to be maintained to prevent higher
pumping lifts.
Phreatophyte Control
Inadequate water supply and an increasing demand for water have
made conservation of water essential in irrigated areas. One of the
most important conservation methods, which can save millions of acre
feet of water in western United States today is the eradication of the
phreatophytes or their replacement by beneficial vegetation. Three basic
practices have been suggested (Robinson 1964) to control phreatophytes:
(1) eradication of the plants for which several methods have been pro-
posed: (2) taking the water away from the plants; (3) replacing phreato-
phytic plants by more useful plants.
Because of the complexity of the hydrologic system of the flood
plain of a major river, the measurements of the amount of water saved by
any proposed method is not a simple matter. The application of data
derived from controlled experiments to natural field conditions requires
a complete understanding of the environmental factors and their inter-
relations in the habitat of the phreatophytes (Culler 1970). The
largest losses by phreatophytes in the Southwestern United States have
85
been found in riparian areas dominated by saltcedar as occur in the
Wellton-Mohawk Valley (Robinson 1965).
Phreatophyte control in the Wellton-Mohawk Valley is related to
irrigation practices now being used on the mesa area. These practices
have led to a drainage problem in the valley for which the available
outflow system by itself is insufficient, and the riparian vegetation
can be considered as an important natural disposal method. Reduction of
irrigation applied on the mesa will lower groundwater levels in the
valley and some of the riparian vegetation will be killed. The economic
impact of the reduction in water use will be analyzed as a change in
irrigation method and not as the result of a phreatophyte control
measure.
Desalinization
As previously discussed, drainage water from the Wellton-Mohawk
District has a high salt content, and when mixed with the Colorado River
water it results in a concentration which could be satisfactorily used
for irrigation provided good management is practiced,internal drainage
of the soils is good, and salt sensitive crops are avoided (Smith, Draper
and Fuller 1964). These conditions are not normally found in most irri-
gated areas, and the Colorado River water delivered at Morelos Dam has
been a source of disagreements between the United States and the Republic
of Mexico. The agreement (Minute No. 242) signed between the two
countries on August 30, 1973, for a "permanent" solution of the problem
provides for the construction by the United States of a desalting complex
near Yuma, Arizona, at a capital cost of $111 million (Martin 1974).
86
This plant, as part of the agreement, will reduce the salinity of water
at Morelos Dam to 115 parts per million above the salinity of the water
at Imperial Dam. If the very high investment of this decision were
applied to eliminate or reduce to desired levels, the causes of the
problem, instead of focusing on the results, its objectives could be
achieved and important additional benefits could derive to the problem
areas. The change from flood irrigation to sprinkler or trickle irri-
gation, which are recognized as advantageous management practices to the
solution of the problem, could be accomplished at a much lower cost and
the expected benefits would have a much wider amplitude.
Summary
From the alternative management strategies suggested above for a
better utilization of the water resources in the Wellton-Mohawk District,
only change in irrigation method, increase in irrigated acreage, and
change in crop allotment were applied to the model. These are considered
basic alternatives which would meet the logical desire to increase the
irrigated acreage in the District to its maximum permissible level and
present management practices through which this could be accomplished.
The other alternatives, although possibly important to the solution of
the drainage, salinity, and flood control problems in the District, were
not applied to the model, although they might be. The ultimate solution
of the problem will likely involve parts of several alternatives.
87
Model Operation with Alternative Strategies
The model developed in the "Description of the Modeling Process"
was programmed in Fortran IV language and was solved using the CDC 6400
computer available at The University of Arizona, A description of the
computer program and the program itself are included as Appendix A.
After testing the model and considering its operation satis-
factory, alternative management strategies thought socially and tech-
nically viable were developed and applied to it. Because of the im-
possibility of estimating groundwater levels for the mesa section from
the available "depth to groundwater" maps, the testing of the model was
limited to the valley section of the District.
As was previously mentioned, the Wellton-Mohawk District project
was designed to beneficially use some 300,000 acre feet of water per year
on a maximum 75,000 acres of irrigable land within the District. Another
limitation to the project is the capacity of the drainage channel which
is designed to carry 320 cubic feet per second, or 231,300 acre feet a
year.
Based on these limitations and the stage of development reached
by 1971, when 61 152 acres (Table 1) were irrigated, it was assumed
that the present irrigated acreage, about 50,000 acres in the valley and
10,000 on the mesa, will increase to a maximum of 65,000 acres of which
52,000 will be in the valley and 13,000 on the mesa. The remaining
10,000 acres will be occupied by miscellaneous roads, buildings, etc.,
or be fallow or idle.
88
Three further assumptions were made when applying the model to
this projection of the irrigation development of the Wellton-Mohawk
District. First, the Gila River surface inflow as an infrequent com-
ponent of the hydrologic budget was assumed to be zero, although some-
times it can add a substantial contribution to the irrigation supply or
to the groundwater storage, as occurred in 1966 and 1973. Second, the
drainage flow to be pumped and disposed of through the Wellton-Mohawk
Main Outlet Drain was assumed to be the design capacity of the disposal
channel. Third, the Gila River surface outflow was derived as an
approximate value from the last flows measured near Dome.
Alternative Strategies
The alternative management strategies to be applied to the model
were selected from those which seemed technically possible, and which
could more efficiently meet the objectives proposed for the present
study.
Strategy I. No modification of the present management policy.
The objective of including this strategy was to evaluate what
would be the impact upon the hydrologic system of the area of increasing
the present irrigated acreage up to the level proposed for the irriga-
tion project without change of the operational management being used.
The amounts of water to be delivered were based on rates now being used,
and the crop pattern is that prevailing in 1971.
Because the other strategies refer to changes specific to the
valley or mesa, this will be the only one that will be analyzed under the
assumptions described for the two model phases, I and II.
89
Strategies II, III, and IV. Sprinkler irrigation on 25, 50, and
100 percent, respectively, of the mesa area.
Sprinkler irrigation was shown to be beneficial to both farmers
and the District (Gordon 1970), and could be a solution to many problems
affecting the area. The change in irrigation method from flooding to
sprinkler at the proposed rates, will substantially increase the water
use efficiency on the mesa and alleviate the drainage problem in the
corresponding sectors of the valley. It is supposed that the crop to be
irrigated with the new method will be citrus.
Strategies V and VI. Reduction by 50 and 100 percent of the
phreatophytes.
Riparian vegetation could be partially or totally eradicated in
order to save substantial amounts of water, and improve the conveyance
capacity of the Gila River channel below Painted Rock Dam, limited at
the present time to a nondamaging flood flow of probably less than 2,500
cubic feet per second.
Strategy VII. Sprinkler irrigation on 50 percent of the mesa
area and reduction by 50 percent of the phreatophytes.
Strategy VIII. Sprinkler irrigation on 100 percent of the mesa
area and reduction by 100 percent of the preatophytes.
The combination of sprinkler irrigation and eradication of the
riparian vegetation at the proposed levels could add their advantages
and provide management practices for better use of the water supply
available in the District.
RESULTS AND DISCUSSION
The results of the present study were analyzed from the view-
point of the proposed objectives and other aspects that became important
during the progress of the study. It is important to keep in mind when
comparisons are made between the results from application of a given
strategy and figures derived from the present management conditions,
that the model is being applied to a projection of the irrigation de-
velopment in the Wellton-Mohawk District, characterized by a 5,000-acre
increase in the present irrigated area.
Phase I
Strategy I
Table 16 shows the hydrologic budget for Strategy I when applied
to the Phase I model. The 29,105 acre feet imbalance could account for
change in groundwater storage, underground flow to the desert, and a
relatively lower drainage water pumping. The drainage flow pumped from
the Wel1ton-Mohawk aquifer for recent years has averaged about 44 percent
of the total Wellton-Mohawk Canal flow diverted to the District. The
delivery of 545,000 acre feet of water as proposed in the Phase I model,
Table 16, would then require about 240,000 acre feet of water pumpage,
9,000 acre feet greater than the capacity of the drainage conveyance
channel, taken as the pumping rate in the application of the various
strategies to the model.
90
91
Table 16. Wellton-Mohawk Irrigation and Drainage District--Strategy I:No Modification of the Present Management Policy (Phase I).
Water Component*InflowAcre Feet
OutflowAcre Feet
TWMINFL 545,000GRUINFL 500TPRECIP 55,000
VODOTFL 231,300GRSOTFL 3,000GRUOTFL 1,600
TEVPTRN 335,495IMBALAN 29,105
Total 600,500 600,500
* Definitions:TWMINFL--Total Wellton-Mohawk Canal inflow diverted to the District.
GRUINFL--Gila River underground inflow.TPRECIP--Total precipitation contribution to groundwater recharge
in the valley.VODOTFL--Total Wellton-Mohawk Main Outlet Drain flow leaving the
District.GRSOTFL--Gila River surface outflow.GRUOTFL--Gila River underground outflow.TEVPTRN--Total evapotranspiration from the District.
IMBALAN--Imbalance.
92
Phase II
Table 17 shows the groundwater depths which are the most im-
portant model characteristics resulting from the present study. The
initial water table depths (INWATD) are average values obtained from
"depth to groundwater" maps of the U.S. Bureau of Reclamation for July,
1973. They reflect the dynamic behavior of the various components of
the hydrologic system in the Wellton-Mohawk area under the present
management conditions and will be compared to the groundwater depths
generated by operation of the Phase II model under the various proposed
alternative management strategies.
The highest elevations in the sectors 1, 2, 3, 6, and 9 coincide
with the confluence of the most important tributaries of the Gila River
along the Wellton-Mohawk area, and probably reflect the effect of some
underground water contribution through these secondaries to the ground-
water reservoir underlying the valley floor. Examining average depths
to groundwater, also derived from U.S. Bureau of Reclamation maps for
1968, the same coincidence is observed, but for 1965 this coincidence
is not in evidence.
The drainage water pumping is an artificial discharge system
which controls the groundwater elevations at maximum acceptable values
and masks, to some extent, the effects of aquifer characteristic which
could be seen under natural flow conditions . It creates so many draw-
down cones that groundwater movement can be observed in every direction,
and underground flow from one sector to another is probably of minor
importance. From these considerations it can then be concluded that the
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94
groundwater depths reflect much more a pumping operations condition than
the dynamic behavior of the hydrologic system of the area as a natural
drainage unit.
Strategy I
Column (I) in Table 17 shows the results from the application of
Strategy I to the model. The increase in water supply diverted to the
area from about 515,000 acre feet (Table 10) in 1971 to 545,000 acre
feet (Table 18) as a consequence of the proposed increase in irrigated
acreage,and the increase in drainage pumping from about 215,000 acre
feet (Table 11) in 1971 to the design capacity of the disposal channel,
are the only modifications from the conditions prevailing in 1971. Most
of the sectors showed a decline in groundwater levels but the average
depth for the whole area was raised from 9.47 to 8.90 feet since the
recharge to the aquifer is greater than the withdrawal from it (Table 18).
Sectors 3 and 6 showed a significant rise because of the low ratio be-
tween their corresponding valley and mesa areas, and the relatively high
increase in irrigated acreage and water application on the mesa had an
adverse effect on the valley groundwater levels.
The amount of water beneficially used is 313,760 acre feet per
year, greater than the 300,000 acre feet established by law. The amount
of drainage water to be pumped to balance the annual water budget of the
area would be about 241,500 acre feet (Table 18), a little larger than
the design capacity of the disposal channel available. Some small ad-
justment should then be made if Strategy I is to be applied.
95
Table 18. Wellton-Mohawk Irrigation and Drainage District--Strategy I:No Modification of the Present Management Policy (Phase II).
Water Component* Inflow OutflowAcre Feet Acre Feet
Mesa:MWMINFL 187,952TMODOTF 6,600TMUINFL 123,797TDUINFL 12,380TMEVPTR 45,175
187,952 187,952
Valley:VWMINFL 357,108TMUINFL 123,797GRUINFL 500TPRECIP 55,000TOVINFL 536,405
VODOTFL 231,300TVEVPTR 242,320TPEVPTR 48,000GRSOTFL 3,000GRUOTFL 1,600TOVOTFL 526,220TWMINFL 545,060UNBALAN 10,185WATCUSE 313,760PUMP BAL 241,485
* Definitions:GRSOTFL =GRUINFL =GRUOTFL =MWMINFL =PUMPBAL =
TDUINFL =
TMEVPTR =TMODOTF =
Gila River surface outflow.Gila River underground inflow.Gila River underground outflow.Wellton-Mohawk Canal inflow diverted to the mesa.(VODOTFL UNBALAN)--Drainage water pumping to balancethe annual water budget.Total underground flow leaving the mesa area to thedesert.Total crop evapotranspiration from the mesa.Total Wellton-Mohawk Main Outlet Drain flow leavingthe mesa area.
96
Table 1, Continued.
TMUINFL = Total underground flow leaving the mesa area to thevalley.
TOVINFL = Total water inflow reaching the valley.TOVOTFL = Total water outflow leaving the valley.TPEVPTR = Total phreatophytic evapotranspiration from the valley.TPRECIP = Total precipitation contribution to groundwater recharge
in the valley.TVEVPTR = Total crop evapotranspiration from the valley.TWMINFL = (MWMINFL + VWMINFL)--Total Wellton-Mohawk Canal inflow
diverted to the District.UNBALAN = (TOVINFL - TOVOTFL)--Amount of water to balance the
annual water budget in the valley.VODOTFL = Total Wellton-Mohawk Main Outlet Drain flow leaving the
District.VWMINFL = Wellton-Mohawk Canal inflow diverted to the valley.WATCUSE = (TWMINFL - VODOTFL)--The amount of water consumptively
used in the District.
97
Strategy I is by itself then an impracticable management alterna-
tive since the recharge is greater than the withdrawal and a progressive
rise of the groundwater levels will occur. No protection is provided
against floods occurring along the area since groundwater levels will
stay high and could assume critical elevations even with small addi-
tional recharge from infrequent flood flows along the lower Gila River.
The drainage flow would have to be increased by about 16,000 acre feet
per year from the present values, increasing by about 90,000 tons the
salt load to the Colorado River.
Strategy II
Column (II), Table 17, shows the average groundwater depths
expected to be reached in the valley from the application of Strategy II
to the model. Most of the sectors show a decline in their groundwater
levels compared to the present levels, but the average annual drop is
only about 0.70 feet. If the annual pumping rate of 231,000 acre feet
were maintained for ten years, it would result in an average decline of
about seven feet, if no flood flow occurs along the lower Gila River.
Sectors 3 and 6, however, would have their groundwater levels progres-
sively raised and would require an intensification of the pumping rates
now being applied there.
The amount of water delivered to the District is about 522,000
acre feet (Table 19), a little higher than that presently used (Table 10).
The amount of water lost by evapotranspiration is practically the same
since no change in crop allotment occurred, and the management practice
change proposed will not substantially affect the evapotranspiration
98
Table 19. Wellton-Mohawk Irrigation and Drainage District--StrategyII: Sprinkler Irrigation on 25 Percent of the Mesa Area.
Water Component* Inflow OutflowAcre Feet Acre Feet
Mesa:MWMINFL 164,458TMODOTF 6,600TMUINFL 102,439TDUINFL 10,244TMEVPTR 45,175
164,458 164,458
Valley:VWMINFL 357,108TMUINFL 102,439GRUINFL 500TPRECIP 55,000TOTINFL 515,047
VODOTDL 231,300TVEVPTR 242,320TPEVPTR 48,000GRSOTFL 3,000GRUOTFL 1,600TOTOTFL 526,220
TWMINFL 521,566UNBALAN 11,173WATCUSE 290,266
PUMP BAL 220,127
* See Table 18 for definitions.
99
rates. The amount of water used consumptively is about 290,000 acre
feet per year, a little smaller than the limit imposed by law, and the
drainage pumping to balance the annual water budget is about 220,000
acre feet, smaller than the capacity of the disposal channel and
approximately the same as observed in 1969 and 1970 (Table 11).
The amount of irrigation water to be applied on the mesa area
by the sprinkler method could be estimated as the sum of the water re-
quirement for this area (5.40 feet) referred in the previous section
plus ten percent (0.6 foot) of the total amount to be applied, or
6.0 feet. The change from flood to sprinkler irrigation would reduce
the amount of water used on the mesa area by about 6.0 (from 12.0 to
6.0) acre feet per acre. If 3,250 acres (25 percent of the projected
irrigated area on the mesa) are changed to sprinkler irrigation, an
annual saving of 19,500 (3,250 x 6.0) acre feet of water could be ob-
tained. This would be the reduction in the amount of water to be
lifted to the mesa, and also the reduction in the amount of drain water
to be pumped from the valley aquifer. Since the cost involved in these
operations would be $2.00 per acre foot and $1.00 per acre foot,
respectively, (Gordon 1970), the savings to the District would amount to
$58,500 (19,500 x $3.00).
In 1969 the cost of water to the farmers was a minimum of $9.00
per acre for the first four acre feet plus supplemental charges of $3.00
per acre for the first acre foot above the minimum, $3.50 per acre for
each of the next two acre feet, and then $4.50 per acre for each addi-
tional acre foot of water thereafter (Gordon 1970).
100
Based on total annual fixed and total variable costs developed
by Gordon (1970) and the prices of water in effect in 1969 in the Wellton-
Mohawk District, the total annual production costs to farmers from flood
and sprinkler irrigation would be $56.50 and $53.14, respectively. This
means a net gain to farmers of $3.36 per irrigated acre, or $10,920 for
the 3,250 acres proposed in Strategy II.
The 6.0 acre feet per acre of water which would not be sold
could be scheduled according to price charges as follows:
2 acre feet per acre x 3,250 acres = 6,500 acre feet
2 acre feet per acre x 3,250 acres = 6,500 acre feet
2 acre feet per acre x 3,250 acres = 6,500 acre feet
Total
The decrease in the annual income
6,500 acre feet x $4.50/acre feet
6,500 acre feet x $3.50/acre feet
6,500 acre feet x $3.00/acre feet
Total
19,500 acre feet
of the District would then be:
= $29,250
= $22,750
= $19,500
$71,500
The change to sprinkler irrigation would require additional
electricity to push the water to the desired pressure at the sprinkler
nozzles. Estimating its value as $6.35 per irrigated acre (Gordon 1970)
the income to the District from the sale of power for the sprinkler
irrigation would be a total annual amount of $20,637 ($6.35 x 3,250).
The net gain to the District would then be:
$58,500 - 71,500 + 20,637 = $7,637.
101
Since farmers and the District form a cooperative enterprise
their benefits could be added and the gain per acre foot of water saved
would be $0.95 [($10,920 + 7,637) 19,500) and the total gain per acre
$5.71 ($10,920 + 7,637) ; 3,250].
Although beneficial to farmers and to the District Strategy II
will not meet important objectives of the present study and only on a
long-term basis would provide the desired levels of flood protection by
eliminating some of the riparian vegetation, and providing additional
storage space for groundwater recharge from eventual flood flows occur-
ring along the lower Gila River.
Strategy III
Column (III), Table 17, shows the average groundwater depths in
the valley expected from the application of Strategy III to the model.
In most of the sectors they are deeper than the present levels, but in
sector 3 are a little higher, and will progressively rise with the con-
tinued application of the Strategy requiring increases in the pumping
rates now being applied there. The average annual decline is about 1.8
feet which could lead to a total decline of nine feet in five years, if
pumping rates are maintained at full capacity of the disposal channel.
The amount of water delivered is about 15,000 acre feet per year
lower than the amount presently used (Table 10), but the amount lost
through evapotranspiration remains practically the same. The amount of
water used consumptively, and the amount of drainage water to be pumped
to balance the annual water budget are about 266,800 and 198,800 (Table
20) acre feet,respectively,much lower than the limits imposed on them.
102
Table 20. Wellton-Mohawk Irrigation and Drainage District--StrategyIII: Sprinkler Irrigation on 50 Percent of the Mesa Area.
Water Component*InflowAcre Feet
OutflowAcre Feet
Mesa:MWMINFL 140,964TMODOTF 6,600TMUINFL 81,081TDUINFL 8,108TMEVPTR 45,175
140,964 140,964
Valley:VWMINFL 357,108TMUINFL 81,081GRUINFL 500TPRECIP 55,000
TOTINFL 493,689
VODOTDLTVEVPTRTPEVPTR
231,300242,32048,000
GRSOTFLGRUOTFLTOTOTFL
3,0001,600
526,220
TWMINFL 498,072
UNBALANWATCUSEPUMPBAL
32,531266,772198,769
* See Table 18 for definitions.
103
The results of identical economic analysis (as was done in
Strategy II) on an annual basis, are as follows:
Water saving in acre feet $ 39,000
Saving to the District 117,000
Decrease in income to the District 143,000
Sale of power to the District 41,275
Net gain to the District 15,275
Net gain to farmers 21,840
Total net gain 37,115
As in Strategy II, the direct impact of Strategy III within the
District, measured in terms of the total net gain, is insignificant as
compared to the investment. Indirect benefits related to flood protec-
tion and the opportunity for saving flood water could be estimated as
hundreds of thousands of dollars.
Strategy IV
Column (IV), Table 17, shows average groundwater depths in the
valley expected from the application of Strategy IV to the model. They
are, in most of the sectors, substantially greater than the present
levels from which they dropped by an average annual value of about 3.90
feet. If drainage pumping rates are maintained at their highest levels
for three years, groundwater depths could be dropped to levels which
could inhibit growth of phreatophytes and provide enough storage space
for groundwater recharge from occasional flood flows occurring along the
lower Gila River. At the same time that the riparian vegetation is being
104
eliminated, the pumping rates would be adjusted to compensate for the
decrease in evapotranspiration losses and the drain water pumping rate
to balance the annual water budget therefore would be higher than 158,700
acre feet (Table 21).
The amount of water delivered to the District is about 451,000
acre feet a year, about 65,000 acre feet less than the amount presently
used (Table 10). The evapotranspiration losses show a small decline as
a consequence of the minor change in about 50 percent of the mesa area.
The amount of water used consumptively and the amount of drain water to
be pumped to balance the annual water budget are about 220,000 and
160,000 (Table 21) much lower than the limits imposed on them.
The economic analysis for Strategy IV shows the following results:
Water saving, in acre feet $ 78,000
Saving to the District 234,000
Decrease in income to the District 286,000
Sale of power by the District 82,550
Net gain to the District 30,550
Net gain to farmers 43,680
Total net gain 74,230
Strategy IV retains all the advantages from Strategy III and
furthermore is the only one under which an increase in crop acreage
beyond the proposed expansion of the irrigation development could be
possible.
105
Table 21. Wellton-Mohawk Irrigation and Drainage District--StrategyIV: Sprinkler Irrigation on 100 Percent of the Mesa Area.
Water Component*InflowAcre Feet
OutflowAcre Feet
Mesa:MWMINFL 93,976TMODOTF 6,600TMUINFL 41,024TDUINFL 4,102TMEVPTR 42,250
93,976 93,976
Valley:VWMINFL 357,108TMUINFL 41,024GRUINFL 500
TPRECIP 55,000TOTINFL 453,632
VODOTDLTVEVPTRTVEVPTR
231,300242,32048,000
GRSOTFLGRUOTFLTOTOTFL
3,0001,600
526,220
TWMINFL 451,084
UNBALANWATCUSEPUMPBAL
72,588219,784158,712
* See Table 18 for definitions.
106
Strategy V
Column (V), Table 17, shows the average groundwater depths in the
valley expected from the application of Strategy V to the model. The
decrease in phreatophytic coverage brought the groundwater levels to
unacceptable depths for continued crop production with an average annual
rise of about 2.2 feet from the present levels. The phreatophytic
evapotranspiration is 24,000 acre feet (Table 22) per year, assumed to
decrease proportionally to the acreage reduction.
Economically, Strategy V implies the saving of 24,000 acre feet
of water which would not be charged against the District because it
returns as drain flow to the Colorado River, but it would cost $24,000
to be pumped into the conveyance channel.
The application of Strategy V, however, also implies the neces-
sity of increasing the drainage pumping rates to about 265,000 acre feet
per year to maintain the present groundwater levels, which is greater
than the capacity of the disposal channel. It is then a technically
impossible solution under the present drainage disposal facilities and,
therefore, not deserving of much consideration.
Strategy VI
Column (VI), Table 17, shows the average groundwater depths in
the valley expected from the application of Strategy VI. The total
elimination of the phreatophytes brought groundwater to unacceptable
levels in most of the sectors with an expected average annual rise of
about four feet.
107
Table 22. Wellton-Mohawk Irrigation and Drainage District--StrategyV: Reduction by 50 Percent of the Phreatophytes.
Water Component* Inflow OutflowAcre Feet Acre Feet
Mesa:MWMINFL 187,952TMODOTF 6,600TMUINFL 123,797TDUINFL 12,380TMEVPTR 45,175
187,952 187,952
Valley:VWMINFL 357,108TMUINFL 123,797GRUINFL 500TPRECIP 55,000TOTINFL 536,405
VODOTDL 231,300TVEVPTR 242,320TPEVPTR 24,000GRSOTFL 3,000GRUOTFL 1,600TOTOTFL 502,220TWMINFL 545,060UNBALAN 34,185WATCUSE 313,760PUMPBAL 265,485
* See Table 18 for definitions.
108
Economically, Strategy VI implies the saving of 48,000 acre feet
of water which would be not charged against the District since it re-
turns as drain flow to the Colorado River, but it would cost $48,000 to
be pumped into the conveyance channel.
Assuming that the elimination of the riparian vegetation could
reduce to zero the evapotranspiration of the corresponding area, the
drainage pumping rate to balance the annual water budget would increase
to 290,000 acre feet (Table 23) which is impossible because of the
present drainage disposal capacity. As in Strategy V, Strategy VI does
not bring any chance to improve the present management of the Wellton-
Mohawk District, but rather aggravates the drainage problem.
Strategy VII
Column (VII), Table 17, shows the average groundwater depths in
the valley expected from the application of Strategy VII to the model.
Although they have dropped in most of the sectors, the rise in the other
sectors show the impossibility of a continued use of Strategy VII with-
out increasing the present drainage pumping rates being applied in these
sectors.
The amount of water delivered to the District (Table 24) is less
than the amount now being used (Table 10). The amount of water con-
sumptively used is about 267,000 acre feet, much lower than 300,000 acre
feet, the annual limit imposed by law, and the drainage water to be
pumped to balance the annual water budget is about 223,000 acre feet,
slightly lower than the capacity of the drainage disposal channel.
109
Table 23. Wellton-Mohawk Irrigation and Drainage District--StrategyVI: Reduction by 100 Percent of the Phreatophytes.
Water Component* Inflow OutflowAcre Feet Acre Feet
Mesa:MWMINFL 187,952TMODOTF 6,600TMUINFL 123,797TDUINFL 12,380TMEVPTR 45,175
187,952 187,952
Valley:VWMINFL 357,108TMUINFL 123,797GRUINFL 500TPRECIP 55,000TOTINFL 536,405
VODOTDL 231,300TVEVPTR 242,320TPEVPTR 0GRSOTFL 3,000GRUOTFL 1,600TOTOTFL 478,220TWMINFL 545,060UNBALAN 58,185WATCUSE 313,760PUMPBAL 289,485
* See Table 18 for definitions.
110
Table 24. Wellton-Mohawk Irrigation and Drainage District--StrategyVII: Sprinkler Irrigation on 50 Percent of the Mesa Areaand Reduction by 50 Percent of the Phreatophytes.
Water Component*InflowAcre Feet
OutflowAcre Feet
Mesa:MWMINFL 140,964TMODOTF 6,600TMUINFL 81,081TDUINFL 8,108TMEVPTR 45,175
140,964 140,964
Valley:VWMINFL 357,108MMUINFL 81,081GRUINFL 500
TPRECIP 55,000493,689TOTINFL
VODOTDL 231,300
TVEVPTRTPEVPTR
242,32024,000
GRSOTFLGRUOTFLTOTOTFL
3,0001,600
502,220
TWMINFL 498,072
UNBALANWATCUSE
8,531266,772222,769
PUMP BAL
* See Table 18 for definitions.
111
According to the economic analysis for Strategy III, the total
annual gain from the change in irrigation method would be $37,115 and
according to Strategy V, the cost for pumping the 24,000 acre feet of
water saved from the reduction in the riparian vegetation would amount to
$24,000. A total annual gain of $13,115 would then accrue from the
application of Strategy VII.
Strategy VII provides limited opportunity for meeting the pro-
posed objectives in the present work since the drainage flow is about
the same as now being pumped and, consequently, the salt load to the
Colorado River is the same. The opportunity for flood and groundwater
recharge control could only be achieved in the long term.
Strategy VIII
Column (VIII), Table 17, shows the average groundwater depths in
the valley expected from the application of Strategy VIII to the model.
Five of the nine sectors showed substantial decline in their groundwater
levels, but sectors 1, 2, 8, and 9, which are not influenced by the re-
duction in water application to the mesa area, show a substantial rise
in their groundwater levels from the elimination of the riparian vege-
tation. As an average for the whole valley an annual decline of about
0.70 feet in the groundwater levels is observed. As in Strategy VII,
the continued use of Strategy VIII could be possible only by increasing
the present pumping rates in sectors 1, 2, 8, and 9.
The amount of water delivered to the District is about 451,000
(Table 25) or about 65,000 acre feet lower than the amount now being
used. The evapotranspiration from the area occupied by the riparian
112
Table 25. Wellton-Mohawk Irrigation and Drainage District--StrategyVIII: Sprinkler Irrigation on 100 Percent of the Mesa Areaand Reduction by 100 Percent of the Phreatophytes.
Water Component* Inflow OutflowAcre Feet Acre Feet
Mesa:MWMINFL 93,976TMODOTF 6,600TMUINFL 41,024TDUINFL 4,102TMEVPTR 42,250
93,976 93,976
Valley:VWMINFL 357,108TMUINFL 41,024GRUINFL 500TPRECIP 55,000TOTINFL 453,632
VODOTDL 231,300TVEVPTR 242,320TPEVPTR 0GRSOTFL 3,000GRUOTFL 1,600TOTOTFL 478,220
TWMINFL 451,084
UNBALAN 24,588
WATCUSE 219,784
PUMPBAL 206,712
* See Table 18 for definitions.
113
vegetation was considered to be zero with the assumption that it would
be proportional to the reduction in the phreatophytes. The amount of
water used consumptively is much lower than the limit established by
law which means a large amount of water could be allocated for other
beneficial uses. The amount of drainage water to be pumped to balance
the annual water budget is about 10,000 acre feet less than the present
pumping rate.
According to the economic analysis for Strategy IV, the total
amount gained from the change in irrigation would be $74,230 and accord-
ing to Strategy VI, the cost of pumping the 48,000 acre feet of water
saved from the eradication of the riparian vegetation would amount to
$48,000. A total annual net gain of $26,230 would then accrue from
application of Strategy VII.
Although it provides for the saving of large amount of water,
Strategy VIII reduces the drainage flow from the present rates by only
an insignificant amount which means that the reduction in the salt load
to the Colorado River will also be insignificant. Improvement of the
present drainage conditions and increase of the storage space for
groundwater recharge from eventual flood flows occurring in the lower
Gila River could be obtained only in the long term.
CONCLUSIONS AND RECOMMENDATIONS
Conclusions
In this study, the past and present water management practices
used in the Wellton-Mohawk District and their problems were outlined.
The widespread drainage well pumping and the need for more information
on the groundwater movement from the mesa to the valley and the pre-
cipitation contribution to the groundwater recharge made the understand-
ing of the dynamic behavior of the hydrology system of the area a diffi-
cult matter. Crop maps would have been useful in allocating the applied
water supplies and estimating the drainage withdrawal from each sector.
A mathematical model which represents as closely as possible
the physical hydrology of the area was developed. The objective of
using the model was to generate information which would reflect the
dynamic hydrologic behavior of the area from the application of selected
alternative management strategies. Following are the major conclusions
drawn from the study.
1. New irrigation developments in the District, as proposed in
Strategy I, are legally and technically impracticable under the
present management conditions and drainage disposal facilities
available.
2. Strategy II is shown to be beneficial to farmers and to the
District, but only in the long term would it provide desired
114
115
levels of flood protection and enough storage space for ground-
water recharge from occasional flood flows occurring along the
lower Gila River. The drainage flow and, consequently, the salt
load to the Colorado River would be always higher than the
present levels.
3. Strategy III is shown to be beneficial to farmers and to the
District, and after a few years of full drainage water pumping,
desired levels of flood protection and enough storage space for
groundwater recharge could be obtained. After that drainage
water pumping could drop to about 200,000 acre feet per year,
which would reduce the present annual pumping costs by about
$15,000. The annual salt load to the Colorado River would be
reduced by about 83,250 (15,000 x 5.55) tons.
4. Strategy IV is shown to be beneficial to farmers and to the
District. In a short period of two or three years of full
drainage water pumping desired levels of flood protection and
enough storage space for groundwater recharge could be obtained.
After that, drainage pumping could drop to about 160,000 acre
feet per year, which could reduce the present annual pumping
costs by about $55,000. The annual salt load to the Colorado
River would be reduced by about 305,250 (55,000 x 5.55) tons.
5. Strategy V would bring a net gain to the District resulting from
the difference in the price of 24,000 acre feet of water which
would not be charged against the District because it returns to
the Colorado River, and the costs for pumping this amount of
116
water, which would be $24,000. However, this strategy is im-
practicable as it requires an annual drainage pumping of about
265,000 acre feet, much greater than the design capacity of the
drainage disposal system.
6. Strategy VI would provide a net gain to the District resulting
from the difference in the price of 48,000 acre feet of water
which would not be charged against the District because it re-
turns to the Colorado River, and the costs for pumping this
amount of water, which would be $48,000. As in Strategy V,
Strategy VI is an impracticable management alternative since it
requires an annual drainage pumping of about 290,000 acre feet,
much greater than the capacity of the drainage disposal system.
7. Strategy VII would bring a total annual gain of $37,115 from the
change in irrigation method plus the difference between the
price of 24,000 acre feet of water not charged against the
District, and the costs to pump it into the conveyance channel,
which would be $24,000. Since the drainage flow requirement
would be about the same as now being pumped, this strategy
would not provide any opportunity for achieving the objectives
proposed in the present study.
8. Strategy VIII would provide a total gain of $74,230 from the
change in irrigation method, plus the difference between the
price of 48,000 acre feet of water not charged against the
District, and the costs to pump it into the conveyance channel.
Since the drainage flow to balance the annual water budget is
117
only a little less than the present rate, little opportunity to
meet the objectives proposed in the present study could be found.
9. The present phreatophytic coverage on the Gila River bottom
along the Wellton-Mohawk Valley is an important auxiliary of the
drainage disposal system of the area, although it increases the
opportunity for flood damages along the developed area. Its
substantial reduction or elimination would considerably aggra-
vate the drainage problem now existing there.
10. The amount of water applied to the soil for irrigation on the
mesa area exceeds by large amounts the requirements for crops,
including the amount needed for leaching requirements. Although
it has only about 16 percent of the present irrigated area in
the District, the mesa is the main area responsible for the
serious drainage problem in the valley and, consequently, the
water quality problem in the lower reach of the Colorado River.
It receives about 28 percent of the total water delivered to the
District and about 70 percent of this water reaches the ground-
water reservoir and moves to the valley.
11. The infrequent releases of stored flood water from Painted Rock
Reservoir and sporadic runoff from contributing watersheds below
the dam can, at times, provide good quality water which can be
used to supply part of the irrigation requirements in the Wellton-
Mohawk District. Since Painted Rock Reservoir is a flood con-
trol reservoir with its method of operation directed to this only
purpose, the largest possible utilization in the District of
118
water released from the reservoir could be accomplished through
the scheme of simultaneous pumping from the river channel, as
already has been done, and storage as groundwater recharge of
some part of the flow volume. The assumption of considering as
zero the surface flow contribution from the upstream reach of
the Gila River did not cause any impact on the water balance
defined in the model. It is an abnormal event whose effect on
the groundwater levels can be counterbalanced by increasing the
drainage pumping rates and the increased opportunity for natural
discharge through evaporation and transpiration.
12. Much more information about crop and water distribution is
needed to allocate water supplies and estimate pumpage with-
drawal more precisely among the various sectors. Groundwater
levels in the mesa, and transmissivity and specific yield esti-
mates for the Wellton-Mohawk aquifer are not sufficient to evalu-
ate the underground flow movement and changes in groundwater
levels resulting from given recharge or withdrawal. More pre-
cipitation data are needed for the mountain areas, where practi-
cally all runoff contributing to groundwater recharge originates.
The establishment of streamflow measuring stations in the lower
reaches of the major runoff-contributing watersheds would be
useful in estimating the precipitation contribution to the sur-
face and underground flows of the Gila River. Evapotranspiration
from phreatophytes is largely influenced by groundwater depth
and will require research for its reliable estimate.
119
13. The proposed desalting complex will treat water for irrigation
at a cost of $114.00 per acre (considering all irrigation
districts involved in the problem) compared to estimates of the
marginal value of water in the Yuma area of $2.00 to $12.00 per
acre foot (Martin 1974). It would then seem much more reasonable
for the United States Government to subsidize the investment
costs, and possibly other costs, of sprinkler or trickle irriga-
tion systems which could conveniently reduce the excessive
drainage flow from the Wellton-Mohawk District and, consequently,
the salt content of the Colorado River water at Morelos Dam.
14. The economic impact of water saving from the application of the
various strategies to the model, based on the expected returns
to farmers and to the District, is insignificant and probably
would not encourage them to change from their present management
practices. However, the social returns of some of these strate-
gies, although not specifically evaluated here, would contribute
to the good will between the United States and Mexico and save
money that would be drawn from taxpayers. Their total value
might amount to millions of dollars.
Recohmlendations
The following recommendations are made for future consideration
in the Wellton-Mohawk District.
1. The prevention of any new irrigation development on the mesa
area until more efficient water management practices are applied.
120
2. The change to sprinkler irrigation on the mesa area at least at
the level proposed in Strategy III (50 percent of area).
3. Studies to define an engineering and management structure for a
better utilization of water from flood flows occurring along
the lower Gila River, and greater protection against flood
damages.
4. Further analysis of the data available to better define the
groundwater movement in the area.
5. Studies for more accurate estimation of evapotranspiration losses.
6. The establishment of a more intensive net for collection of pre-
cipitation and stream flow data.
APPENDIX A
DESCRIPTION AND LISTING OF THE COMPUTER PROGRAM
121
30
35
40
45
50G
55
60
zo
25
5
to
15
122
PROGRAM H2OBAL f INPUT, OUTPUTOUINFL = UNDERGROUND FLOW LEAVTNG EACH SECOTR ON THE MESA TO THE
'DESERTFACTOR = pRoPoRTIoNALITy FACTOR WHICH ALLOCATES THE WATER COMPCNE
ANTS AMONG SECTORSGRSINFL r GILA RIVER SURFACE INFLOW REACHING EACH SECTOR IN THE
1V ALLEYGRSOTFL = GILA RIVER SURFACE OUTFLOW LEAVING EACH SECTOR IN THE
1VALLEYGRUINFL GILA RIVER UNDERGROUND INFLOW REACHING EACH SECTOR IN1THE VALLEYGRUOTFL = GILA RIVER UNDERGROUND OUTFLOW LEAVING EACH SECTOR IN
AVALLEYINFILTR = GILA FLOW INFILTRATEO THROUGH ITS BED IN EACH SECTOR IN
1THE VALLEYHr ESTIMATED AVERAGE SATURATED THICKNESS AT EACH CROSSASECTION LIMITING THE SEcTDRS, IN FTMDELTwL = NET CHANGE IN WATER TABLE LEVEL FOP EACH SECTOR ON THE
1MESAHESAREA = TOTAL AREA FOP EACH SECTOR ON THE MESAmEVPTRN = COP EVAPOTRANSPIRATfCN FROM CACH SECTOR ON THE MESAmNRCHAO = NET RECHARGE TO OR WITHDRAWAL FROm FOR EACH SECTOR ON1THE MESAMODINFL r HELLION-m0HAwK MAIN OUTLET DRAIN. INFACw REACHING EACH1SECTOR ON THE MESAMOOOTFL HELLION-m0HAWK HAIN OUTLET DRAIN OUTFLOW LEAVING EACH1SFCTOR ON THE MESAmpERc0 r PORTION OF THE HATER DELIVERED To THE MESA THAI BECOMESAGPoUNOWATER RECHARGEmUINFL UNDERGROUND FLOW LEAVING EACH SECTOR ON THE MESAMwMINFL = HELLION-m0HAwK CANAL INFLOW REACHING EACH SECTOR ON THE
1MESAMwmOTFL wELLTON-m0HAWK CANAL OUTFLOW LEAVING EACH SECTOR ON THE
AMESANRCHAO = NET RECHARGE TO OD WITHDRAWAL FROM FOR EACH SECTOR IN THE10ISTRICT
= ESTIMATED AVERAcE ALLUVIUM FILL PERMEABILITY, IN SO FTIPEP DAYPEVPTRN = pHREATopHyTES EVAPDTRANtRIRATIOn FROM EACH SECTOR IN THE1VALLEYPPECIP LOWER GILA RIVER BASIN PRECIPITATION CONTRIBUTION TO GROUANOwATZR RECHARGE REACHING SamE SECTORS IN THE VALLEYRETFLOw = RETURN FLOW FROM IRRIGATION AND DIRECT RUNOFF FROM'RAINSTORMS REACHING EACH SECTOR IN THE VALLEY
ESTIMATED AVERAGE HyDRAULIC GFAOIENT FOR EACH SECTOR,UN FT PER FTTnuINFL = TOTAL UNDERGROUND FLOW LEAVING THE MESA TO THE DESERTTINFILT TOTAL GILA RIVER FLOW INFILTRATED THROUGH ITS BED ALONG
1THE WELLTON-HOHAwK DISTRICTTHE VPTR = TOTAL CROP EVAPOTRANSPIRATION ON THE MESATmOnoTF = TOTAL wELLTON-moHARK MAIN OUTLET DRAIN OUTFLOW LEAVING
ITHE MESATmUINFL = TOTAL UNDERGROUND FLOW LEAVING THE MESA TO THE VALLEYTOTINEL r TOTAL INFLOW REACHING EACH SECTOR IN THE DISTRICTTOTOTFL = TOTAL OUTFLOW LEAVING EACH SECTOR IN THE DISTRICTTPEVDTR TOTAL PHREATOPHYTES EVAPOTRANSPIRATION IN THE VALLEYTPRECIP = TOTAL LOWER GILA RIVER PRECIPITATION CONTRIBUTION TO GRO
1UNOwATER RECHARGE REACHING THE HELLION-m0HAwK VALLEYTRETFL TOTAL RETURN FLOW FROM IRRIGATION AND DIRECT RUNOFF FROMiRAINSTOPms REACHING THE GILA RIVER CHANNEL ALONG THE DISTRICTTVEVDTR = TOTAL CROP EvApoT0ANSPIRATION IN THE VALLEY
123C VALAREA = TOTAL AREA FOR EACH SECTOR IN THE VALLEYC " VOELTWL = NET CHANGE IN WATER TABLE LEVEL FOR EACH SECTOR IN THEC ** 'VALLEY
65 C " VEVPTRN = CROP EVAPOTRANSPIRATION FROM EACH SECTOR IN THE VALLEYC ** VFHATO = WATER TABLE DEPTH AT THE ENO OF THE PERIOD FOR EACH SECTOC " 1R IN THE VALLEYC ** VINwATO = INITIAL WATER TABLE DEPTH FOR EACH SECTOR IN THE VALLEYC ** VNRCHAO = NET RECHARGE TO 0-2 wITHORAWAL FROM FOR EACH SECTOR IN
70 C ** lfHE VALLEYC VODINFL = wELLTON-MOHAwK MAIN OUTLET DRAIN INFLOW REACHING EACHC ** ISFCTOR IN THE VALLEYC VOBOTFL = HELLION-m0HAWK MAIN OUTLET DRAIN OUTFLOW LEAVING EACHC ** 1SECTOR IN THE VALLEY
75 C ** VHMINFL = HELLTON-MOHAWK CANAL INFLOW REACHING EACH SECTOR IN THEC ** 1VALLEYC ** VWMOTEL = wELLTON-M0mANK CANAL OUTFLOW LEAVING EACH SECTOR IN THEC ** 1VALLEYC ** X = NUMBER OF YEARS FOR THE STUDY PERIOD
AO C W = WIDTH or THE CROSS SECTIONS LIMITING THE SECTORS, IN FTC ** ALL WATER COMPONENTS ABOVE ARE CONSICERFD IN ACRE FEET
REAL MwmINFL, mODOTEL, mwMOTEL. mEVIDTRN, NRCHAO. MNRCHAO, HOELTWL,1MINWATO, MFwATO, INFILTR, mESAREA, m, mPERCO, MUINELDIMENSION VWMINFL (9), mwmINFL (9). GRSINFL (9), GRUINEL (9), VODI
85 'NFL (9), PPECIP (9), VWHOTFL (9), MwMOTFL J91, GRSOTEL(9), GRUOTFL2 (9), VODOTFL (9 ) . MODOTFL (9), VEVPTRN (9), mEVPTRN (9), PEVPTRN3(9). TOTINFL (9), TOTOTEL (9), NRCHAO (9), mNRCHAO (9), VNRCHAQ (94): HOELTWL (9), VDELTHL (9), mFwATO (91, VEHATO (9), mINwATO (9),4VINWATO (91, INFILTR (9), RETELOw (9), VALAREA (9), MESAREA (9),
90 5p (10 ) ,.S (10 ) , m (10), 14 (10 ) , X (10), MUINFL (91, DUINFL (9).6FACTORI, (S), FACTOR? (9), FACTOR3 (9), FACTOR). (9), EACToR5 (9),7FACTOR6 (9). FAOTOR7 (9), FACTOR8 (9), FACTOR9 (9), FATORIO (9),AFAT0711 (9), FATOR12 (9)INTEGER 0
95 C ** READ IN INPUT DATAREAD 103, VWWINFL (9), HWMINFL (9), GRSINFL (1), TINFILT, IRETEL,1V000TEL (9), TVEVPTP, TmEVPTR, TPEVPTR, TPRECIP, TmOOOTF
100 FORMAT ( 1E8.0. 8E7.0, 2F7.0 )PRINT 200, VwMINFL(9), mwmiNFL(9), GRSINFL(1),TINFILT,TRETFL. VODO
100 1TFL(9), TVEV 0 TR, TmEVRTR, TPEVPTR200 FORMAT ( IX. F9.0, 8(1X, F4.0)1
00 1 1=1,9READ 101, VINHATO (/), mINwATD (I), VALAREA (I). HESAREA (I)
101 FoRmAT ( 2F5.2, 2F6.0 1105 PPINT 201, VINWATO(I), MINwATO(I), VALAREA(I), MESAREA(I)
201 FORMAT (2(1X, F5.2), 2(1X, F7.0111 CONTINUEDO 2 I = 1,10RUA') 102, P(I), S(t), M(I), W(I), X(I1
110 102 FORMAT ( 3E4.0, 1E7.0, 1E3.0 )PRINT 20 7 . 0 (I), S(I), M(I), W(I), X(I)
702 FORMAT ( 3(1x, F5.0), lx, F8.0, 'X, F4.0)
2 CONTINUEMRERCO = (MWMINFL(9)-TMEVPTR)
115 TOUINEL = ( mPERCO - 5600 1/11.0TmUINFL = 10.0 * TOuINFLREA3 103, FAcToR1, FACTOR?, FAcTOR3, FACTOR',. FACTORS, FACTOR6, FA1CTOR7, FACTOR8, FACTOR9, FATORIO, FATOR11, FATOR12
103 FORMAT ( 9E5.0 1120 PRINT 203, FACTOR', FACTOR?, FACTOR3, FACTOR'., FACTORS, FACTORS, ' F
1ACTOR7, FACTORS, FACTOR9, FATOR10, FATOP11, FATOR12
203 FORMAT ( 9(1X. F12.4 )1DO 3 1=1,9VWHINFL(I) = FACTOR1(I) • VWMINFL(9)
125 MWMINFL(I) = FACTOR2(I) * MWMINFL(91INFILTR(I) = FACTOR3(1) * TINFILTRETFLCW(I) = FACTOR4(I) * TRETFL
124
0000TFL(I) = RACTOR5(I) * V000TFL(9)0EVRTRN(II = FACTOR6(I) * TVEvRTR
130 ME0RTRN(I) = FACTOR7(I) • T4EVRTRPEVRTRN(I) = FACTOREI(I) • TREVRTRMODOTEL(I ) = FACTORqIII * TAOOOTEDUINF1(I) = FATOR10(I) * TqUINE1MUINFL(I) = FA1ORI1(I) * T 9 UINFL
135 PRECIP(I) = FATOR12(I) * TPRECIP3 CONTINUE
GRUINE1(1)=W(1)*S(11*m(11*W(II*X(11)/(119.6E+05,DO 4 n=1,9L=0+1
140 GRUOTFI(0)=0,(0)S(0)*M(L)*W(L)*X(1)1/(119.6E+05)L. CONTINUE
DO 5 0=20i=n-1vwmorFi(o).vwmINFL(L)
145 GRSINFLIDI = GRSINEL(L)+RETRLOW(1)-INFILTR(L)GRUINF1(0)=GRUOTFL(L )VODINF1(0I=V000TFL(L)
MWMOTFL(D)=mwmINFL(LI
5 CONTINUE150 DO 6 I=1,q
GRSOTFL(I)=ORSINEL(I)-INFILTR(I)+RETFLOw(I)TOTINFL(I)=OIMINFL(I)+mwmiNFL(I)+GRSINFL(I)+GRUINF1(I)+VODINFL(I) 4
1PRECIR(I)TOTOTFL(I)=VWNOTFL(I14-mw4OTL(I)+GRSOTEL(I)+GRUOTFL(I)+VOOOTFL(I ) .
155
1MOD3TFL(WvEVRIPN(I)+t1EV2TRN(I)+REvRT0N(I)+OUINFL(I)NRCHAO(I)=ToTINF1(II-TcToTEL(IIMNRC4Arl(I) = mrimINRL(I)-(mwmoTFL(I)4m000TFL(I).-MEVRTRN(I)+MUINR1(1
1)4-nuINFL(1 ))
VNRCHAQ(I)= VwMINFL(I)+GRSINFL(I)+GRuINFL(I)+VODINFL(I)+PRECIP(Ii•
160 1MUINEL(I)-(01,4MOTFL(I)+GRSqTEL(I)+GRuOTFL(I)4VODOTEL(II+VEvRTRN(II+
2PEYRTRN(I)IVTIELTwL(II=VNRCHAO(I)/IVALADEACII*.1 81
11FWATO(I)=VINwATO(I)-VnELTrIL(II
6 CONTINUE165 DO 7 I=3,7
MOELTwL(I)=MNRCH0I(I)/(MESAREA(I )* . 18)
MFWATO(Il=mINwATO(I ) -NDELT ,IL(I)
7 CONTINUEPRINT 204
170 204 F 0 RmaT(1H1,6X,*SECTOR*,7X,*VALLET W-m*,10X,*NESA 14-m*,13x,*GILA*,111X,*GIL4',14X,*GILA*,12x,*GILA*,/.18Y,*CANAL INFLoW.,7X,*CANAL IN
?FLOw*,10X,*SuRFACE*0x,*SUREAGE*,9X.*UNDERGROuN 0*,5 X. * UNDERGRouN 93
3,/,5qx,*INFLON.,10X,*OUTFLOW*,iix, * INFLoW *,10 x ,* OuTFLCIA *, / )
00 A I=1,q
175 PRINT 205,I,V4MINFL(I), NwMINFL(I), GRSOTFL(I), GRUINF
11M. GRUOTFL(I)205 FORNAT(//,AX,I1,11x,FA.0,11X,F7.0,13X,F7.00X,F7.0,11x,F7.0,9X,F7.
10,1 )8 CONTINUE
150 PRINT 206206 FORmAT(//,6x,*SECTOR*,7x,*VALLEY w-M*,10x, 441EsA w-M*,9x,*PRECIPITA
1TION,Ax,*vALLEY*,11x,*rESA* , 11X ,* T 0 T 01*,12XT 0 TAL *, / ,18 X ,* OU T LET
20RAIV*,7x,*OUTLET ORAIN*,26X,*EVAPOTRANS*,6X,*EVAPOTRANS*,8X,*INFL
30w*.10X,*OUTELOW*,/,20X,*DUTELOR*,12x,*OuTFLOW *,30 X ,* PIRATION *03 X ,
185 4*PIRATI0N*,/)00 9 I=10PRINT 207.1,0000TFL(I),NO0OTFIAII , PRECIP ( I ), VEVRTRN 4 I ), MEVRT R N( I ),
ITOTINrL(I ) ,TOTOTFL(I )207 FORMAT(//.8X,I1,11X,F8.0,11X.,F7.0.13X,F7.0,10X,F7.0,10X,E7.0,8X,
190 1F8.3.)X.F8.0,/)9 CONTINUE
PRINT 235
. 208 FORMAT(//,3WSECTOR*,6X,*NET RECNARGE*,10X,I,VALLEY*,14X,,MESA.,
125
113WVALLEY*.11X,* MESA *11X1*VALLEY FINAL*.FIXt*MESA FINAL*,/,15X,195 2•OR WITRORAWA1*,6X.*NET RECHARGE!,7YONET RECHARGE*,7XO'NET CHANGE
3*.6X,*NET CHANGV.7Xv*W.T. OEPTMS,7x,*W.T. DEP111 1 ,/,34Xl*OR NITHOR4ANA1TIbX,*09 NITHDRAWAL',7Yg'IN W.T. L.*117X.*I4 W.T.LavalDO 10 I=1,9
. PRINT 209,I,NRCHAQ(DIVNRCHAO(I)01NRCHAOIDsVIELTNL(I),MOELTWL(I),200 INFWATO(11.MFWATO(I)
209 FORmAT(//OIX,I1,11X,F8.0.12X.F7.0.12X,F8.0,11X,F6.2, 9X,F6.2,11X,1F6.2.1/X,F6.2,/)
10 CONTINUESTOO
205 END
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