Objectives, Methods, and 

Environment Gila River 

Phreatophyte Project, 

Graham County, Arizona

GEOLOGICAL SURVEY PROFESSIONAL PAPER 655-A

OBJECTIVES, METHODS, AND ENVIRONMENT

GILA RIVER PHREATOPHYTE PROJECT,

GRAHAM COUNTY, ARIZONA
View upstream from the railroad bridge near Calva, Ariz.. showing encroachment of the Gila River flood plain by saltcedar

between 1932 and 1964.
Objectives, Methods, and 

Environment Gila River 

Phreatophyte Project, 

Graham County, Arizona

By R. C. CULLER AND OTHERS

GILA RIVER PHREATOPHYTE PROJECT

GEOLOGICAL SURVEY PROFESSIONAL PAPER 655-A

Contributors to this report are D. E. Burkham, 

M. R. Callings, R. C. Culler, E. S. Davidson, 

R. L. Laney, 0. E. Leppanen, I. S. McQueen, 

N. C. Matalas, R. F. Miller, R. M. Myrick, 

R. M. Turner, and W. G. ff^eist, Jr.

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1970
UNITED STATES DEPARTMENT OF THE INTERIOR 

WALTER J. HICKEL, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 - Price 45 cents (paper cover)
PREFACE

This report is the first of a series of professional papers describing the 

hydrologic studies associated with the Gila Eiver Phreatophyte Project. The 

project plan is described in the report, including the details of observation. 

A sequence of fact finding, estimation, and decision is necessary in planning 

a project of this scope.

First a study was made of the available information. Specific objectives 

were then denned, and the hydrologic problem was identified. Methods of 

measurement were investigated and a primary method was selected. The data 

requirements and statistical problems involved in the application of this 

method were then considered. A site was selected and the hydrologic characteristics investigated. Methods of data collection were determined and the 

project area was instrumented.

The organization of this report follows the general sequence used in 

planning the project. A brief description of the facts considered and analyzed is 

presented to explain the reasons for making the planning decisions. The advice 

and assistance of many scientists were used in planning the project. The 

contributors to this report are the persons having the primary responsibility for 

making decisions concerning the planning and for subsequent reporting of 

results on the various phases of the project.

CONTENTS

Preface..__________________________________________

Abstract.-_________________________________________

Introduction, by R. C. Culler---.________________

Objective.-..____________________

Personnel and acknowledgments __________________

Evapotranspiration: Its measurement and variability, 

by O. E. Leppanen__ _________________________

Introduction. __________________________________

Evapotranspiration variations ____________________

Evapotranspiration measurement.________________

Some aspects of statistical analysis of the water-budget 

method, by N. C. Matalas. ________________________

Introduction. __________________________________

Water-budget period-__----____________--_-_____

Experimental design and analysis_________________

Site selection, by R. C. Culler________________________

Geohydrology, by E. S. Davidson and W. G. Weist, Jr__ 

Introduction. __________________________________

Basin-fill deposits.______________________________

Flood-plain and terrace alluvium _________________

Climate, by M. R. Collings__________________________

Characteristics. ________________________________

Measurement of precipitation ____________________

Surface water, by D. E. Burkham__________________

Purpose and scope_-____-________-______-_-_-___

Physical description of the Gila River drainage 

area.______________________________________

Gila River drainage area above the study 

reach.__________________________________

Tributaries adjacent to the study reach______

Gila River through the study reach ___________

Page

v

Al

1

2

2

3

3

3

5

5

5

6

6

7

8

8

10

10

10

11

11

12

12

12

12

Surface water, by D. E. Burkham Continued Page

Streamflow characteristics----------------------- A13

Gila River__________ __ _ 13

Tributaries .---- _________________________ 13

Data-collection program_________________________ 14

Gila River surface flow___-__---___---__---_- 14

Gila River near Bylas, Ariz______________ 14

Gila River at Calva, Ariz_________-____._ 14

Gila River near Calva, Ariz______________ 14

Gila River above Coolidge Dam, Ariz_____ 14

Tributary surface flow_____________________ 15

Changes in the streamflow conveyance system. _____ 15

Ground water, by R. M. Myrick____________________ 16

Introduction- _________-_____-____--___--__-_-__ 16

Observation-well network ______________________ 17

Water-level records ______________----_--___--_ 17

Soil-moisture observations, by R. M. Myrick__________ 17

Vegetation, by R. M. Turner________ __ __ 19

Characteristics. ________________________________ 19

Plan of study___________.____________ 20

Phreatophyte removal______________________-____ 21

Revegetation __________________________________ 21

Quality of water, by R. L. Laney----_-_-------_--___- 21

Characteristics-________-___-____--__----___-_-. 21

Plan of study..._______________._____- 22

Data analysis__--_____-_----_--------------_--_ 22

Soil-moisture-energy factors influencing evapotranspiration in riparian vegetation, by R. F. Miller and I. S.

McQueen__________________________ 22

The energy budget for evapotranspiration measurement,

by O. E. Leppanen.________________________ 23

Summary, by R. C. Culler__________________ 24

References cited______________--___--_-_------___--_ 25

ILLUSTRATIONS

Page 

FBONTISPIECE. Photographs near Calva, Ariz., showing encroachment of the Gila River flood plain by saltcedar between

1932 and 1964____________________________________________________ n

FIGUBE 1. Map showing Gila River Phreatophyte Project area and instrumentation location. ____________________ A9

2. Photograph of the central part of the project area.

3. Photograph showing exposure of basin fill in the lower part of the project area__________

4. Schematic block diagram showing geology and ground-water movement in the project area. 

5-10. Photographs showing:

5. Lower part of project area during high water and the natural levees______________

6. Log jam and sediment accumulation below section 23____-______-___--_------__-

7. Water-level observation welL___-_-_________-_______________--__---_--_---__-

8. Hydraulic rotary vacuum drill used to install soil-moisture wells..____--___----_-_

9. Typical observation site_____________________________________________________

10. Energy-budget station in operation at section 19_____________________________

10

10

11

13

13

17

18

18

24

vn

GILA RIVER PHREATOPHYTE PROJECT

OBJECTIVES, METHODS, AND ENVIRONMENT GILA RIVEP 

PHREATOPHYTE PROJECT, GRAHAM COUNTY, ARIZONA

By R. C. CULLER and others

ABSTRACT

An inadequate water supply and an increasing demand for 

water have made conservation of water essential in the arid 

Southwest. One conservation method, which has been used in 

several places and which has been proposed for others, is replacement of phreatophytes by useful vegetation. Nonbeneficial 

plants infest areas of shallow ground water, such as flood plains 

of major rivers. Tank studies have shown that phreatophytes 

use more water than beneficial grass in the same location. However, many hydrologic variables in nature are not duplicated in 

tank studies.

The most obvious need in phreatophyte-control research is 

evaluation of water conservation on a flood plain typical of 

many areas of existing and proposed application. Hydrologic 

and ecologic variables must be defined by the evaluation so that 

the data may be applied to other sites. The Gila River Phreatophyte Project was begun in 1962 by the U.S. Geological Survey 

in order to make this evaluation.

The project area is a 24-kilometer (15-mile) reach of the 

Gila River flood plain in the San Oarlos Indian Reservation 

which has been divided into three subreaches. About 2,400 

hectares (6,000 acres) are covered by phreatophytes, principally 

saltcedar and mesquite. Phreatophyte removal was started on 

the upper subreach in 1966; the middle and lower subreaches 

were undisturbed until 1967. The period of preclearing measurement of evapotranspiration extended from 1963 to 1966 for 

the upper subreach and from 1964 to 1967 for the other two 

subreaches. Postclearing measurement will extend to July 1972.

A water budget is being used to compute evapotranspiration 

as a residual. The water budget includes surface and subsurface inflow and outflow in the Gila River and its tributary 

inflow to the reach, precipitation on the flood plain, and changes 

in ground-water storage in the saturated and unsaturated 

zones of the study reach. The vegetation, chemical quality of 

water, sedimentation, and climate also are being studied. The 

water budget will be the basic method of evaluation, but other 

methods will be applied and tested. All data are being collected 

for analysis by digital computer and will be subjected to 

rigorous statistical tests.

INTRODUCTION

By R. C. OULLEB

Phreatophytes are plants that depend on ground 

water within reach of their roots for their water supply. 

More than 70 species of plants have been classified as 

phreatophytes (Kobinson, 1958, p. 1). The consumptive 

use of water differs greatly among species, but, in 

general, phreatophytes use more water than other 

vegetation in the same environment. The annual consumptive use by saltcedar (Tamarigs pentandra Pall.), 

which is almost always one of the most vigorous 

phreatophytes, may be more than 9 acre-feet per acre 

(Gatewood and others, 1950, p. 137). Most phref.tophytes have no marketable value as forage or timl ^r. 

However, many conservationists consider phreatophytes 

desirable for the maintenance of wildlife habitat.

Phreatophytes, such as saltcedar, produce a flood 

hazard by choking normal channels and reducing the 

conveyance of floodflows. (See frontispiece.) Reduction 

in conveyance causes above-normal deposition of sediment in channels and on banks, creating natural levees. 

Overbank flows do not drain back to the channel, r.nd 

the swamp that is formed creates ideal conditions for 

consumptive waste. Channel choking and ponding have 

caused problems of inflow-channel maintenance in the 

generally unused upstream end of reservoirs on siltladen streams. Elephant Butte Reservoir on the Rio 

Grande and Lake McMillan on the Pecos River in Few 

Mexico and the San Carlos Reservoir on the Gila River 

in Arizona are examples.

In arid regions, such as the Southwestern United 

States, the possibility of converting consumptive wrste 

to beneficial use has aroused wide interest. It is e?ti371-096 O - 70 - 2

Al
A2 GILA RIVER PHREATOPHYTE PROJECT, GRAHAM COUNTY, ARIZONA

mated that phreatophytes cover 2.4 million hectares 

(6 million acres) in the Southwest (Robinson, 1952, 

p. 60). Phreatophyte-control measures have been 

applied to large areas of the Rio Grande and Pecos 

River flood plains in New Mexico, and proposals have 

been made for similar measures on extensive reaches 

of the lower Colorado and Gila Rivers in Arizona. The 

methods of control have been classified by Robinson 

(1964, p. 1) as: "(1) taking the plants away from the 

water (eradication, of which there are several ways); 

(2) taking the water away from the plants (here again 

there are several ways); and (3) substituting plants of 

higher beneficial use in the project area."

OBJECTIVE

Before the present project was begun, an extensive 

study was made of available data and of the research 

projects in operation or being planned on the effects of 

phreatophyte control. The results of this study were not 

published; however, Robinson's (1964) compilation of 

phreatophyte research is similar to the findings of the 

earlier study. Information is being collected by 48 research projects sponsored by 9 Federal and 21 State 

and local agencies and individuals (Robinson, 1964). 

Most of these projects involve eradication and vegetation-control methods, vegetation studies, and the 

measurement of evapotranspiration by evapotranspirometers,- greenhouses and related experiments, and 

flood-plain evaluations. Only one of the 48 studies on 

Oottonwood Wash in Arizona (Hendricks and others, 

1960) evaluated water salvage by removal of vegetation, in this case cottonwood and willow, from a narrow 

valley.

Reduction in the evapotranspiration by applying 

phreatophyte control offers the possibility of water salvage. The hydrologic regime of the flood plain of a 

major river is a complex system of which evapotranspiration is only one part. Thus, a change in evapotranspiration changes ground-water levels, relations of 

surface water and ground water, and soil-moisture 

storage and may change the chemical quality of both 

surface and ground water, which causes many problems in hydrologic measurements. Greater precision of 

measurement can be achieved with controlled experiments, such as greenhouse or evapotranspirometer studies, than by experiments under natural conditions. 

However, the application of data from controlled experiments to natural field conditions requires a complete understanding of all environmental variables and 

their interrelation in the habitat of the phreatophytes. 

At the present time these parameters of a flood plain 

of a major river, particularly one in an arid climate, 

are not understood. Undefined scale factors may be involved in translating the results of small-area studies

to the large tracts typical of applied phreatophyte 

control.

The most obvious need in phreatophyte-control research is an evaluation of the water-salvage potential 

for a flood plain of a major river that has ?, dense 

phreatophyte cover, especially saltcedar. Such a study 

should be sufficiently intensive as to evaluate not only 

the water salvage but the hydrologic and environmental variables and any alteration of them caused by 

vegetation modification.

Objectives of the present project thus are summarized as follows: (1) to evaluate water salvage by 

phreatophyte control on a flood plain typical of areas of 

existing and proposed application, (2) to describe hydrologic and ecologic variables of the project ar°>a sufficiently for extrapolation of these data to other sites, and 

(3) to test and develop methods for evaluating hydrologic variables in a large area.

The evaluation of water salvage can be stated in 

equation form as

C^E^-Ea, (1) 

in which

Et>= evapotranspiration with phreatophytes, 

Ea =evapotranspiration with altered vegetation

cover, and 

C =the water conservation or expected reduction

in evapotranspiration.

The measurement of evapotranspiration is thus the 

primary problem of this study. The methods of making these measurements are described in the following 

sections.

PERSONNEL AND ACKNOWLEDGMENTS

The project was planned and begun under the general supervision of Thomas Maddock, Jr., and F. E. 

Clarke, former chiefs of the General Hydrology 

Branch, and G. E. Harbeck, Jr., research hydrologist. 

Since 1967 the project has been under the general supervision of R. W. Stallman, regional research coordinator. The study is under the direct supervision of R. C. 

Culler, project chief. Collection of records, analysis of 

data on surface water,, sedimentation, and chemical 

quality of water, geologic mapping, and aquifer tests 

are under the supervision of H. M. Babcock, district 

chief, Water Resources Division, in Arizona. The authors of the different sections of this report are responsible for the specific phase of the study being described.

The cooperation and assistance given by the San 

Carlos Apache Indian Tribe, C. J. Rives, superintendent of the San Carlos Agency of the Bureau of Indian 

Affairs, and M. D. Young, general engineer for the San 

Carlos Irrigation Project of the Bureau of Indian Affairs are gratefully acknowledged. Removal of phreat-
OBJECTIVES, METHODS, AND ENVIRONMENT A3

ophytes and replanting will be under the direct supervision of the Bureau of Indian Affairs.

Replacement vegetation and evapotranspiration 

along tributaries are being studied by the Department 

of Watershed Management, University of Arizona, in 

cooperation with the Bureau of Reclamation, Bureau 

of Indian Affairs, San Carlos Apache Indian Tribe, and 

U.S. Forest Service. Cooperation between -the Department of Watershed Management and the Geological 

Survey includes the joint use of instrumentation and 

exchange of data.

EVAPOTRANSPIRATION: ITS MEASUREMENT 

AND VARIABILITY

By O. E. LEPPANEN

INTRODUCTION

Hydrologic systems may extend some distance above 

and below the ground surface and may include openwater surfaces, bare-soil areas, and different kinds of 

vegetation. Water, as a liquid, flows into, out of, and 

within such systems. It also moves as vapor. When more 

vapor moves out of the system than comes in, there is a 

loss to the system, although not to the overall hydrologic 

cycle. Such losses are occasioned by evaporation from 

open water, evaporation from damp soil at or below the 

ground surface, and transpiration from plants. These 

vapor losses are categorized by the term 

evapotranspiration.

EVAPOTRANSPIRATION VARIATIONS

Evapotranspiration requires energy. This energy is 

available from various sources: direct sunlight, infrared 

radiation from clouds and the gases making up air, and 

sometimes, the heat content of the air itself. Open-water, 

bare-soil, and vegetated surfaces each respond differently to the sources of energy. Vegetation, especially, 

has a variety of responses owing to complex structural, optical, and physiological variations within and 

between species.

By far the most significant source of energy for 

vaporizing water from open-water surfaces is radiant 

heat, both direct sunlight and infrared sky radiation. 

Water bodies absorb large proportions of available 

direct solar energy because of the high optical transparence of their surfaces for this type of radiation. Sky 

radiation is of less importance, being mostly absorbed 

and then reradiated at the surface itself.

The amount of water lost from an open-water surface 

is determined mainly by the velocity and duration of 

wind over the surface and the dryness of the air relative 

to the ease with which water can be evaporated from the 

surface. More precisely, vapor loss is proportional to 

the product of wind speed times vapor deficit, the difference between the saturation vapor pressure of the water 

surface and the partial pressure of the water already in 

the air. To compute the loss from water surfaces, the 

parameter relating the loss to wind movement and varjor 

deficit must be known. For shallow water this parameter 

can be estimated, and using measurements of wind 

movement and water temperatures, losses can be evaluated. These losses will be small because such water? in 

the project area are few. Knowing this parameter and 

its seasonal variation, open-water losses can be compared with river-basin losses in the vegetated ar^as.

Losses from bare soil cannot be measured readily, nor 

can the variables that control these losses be easily isolated. Again, radiant heat is the largest energy source 

for vaporizing water, but, because of the opacity of the 

surface, much less energy is available to act upon subsurface water. Beyond the energy necessary to vaporize 

water, additional energy is necessary to overcome ca ciliary and adhesive forces in the soil.

Except after rains, there is little water-vapor los^ in 

areas of deep water table, because water is not easily 

available. Where the water table is shallow much vegetation grows, except in water courses. Evapotran^t>iration from bare soil is reduced by the shading of 

vegetation. If the soil-surface layer becomes bone-dry, 

water brought to the surface by capillarity is redurt-ed, 

because water cannot flow as a liquid but must diffuse as 

vapor through several inches of soil. High humidity 

near the surface owing to plant transpiration tend"* to 

decrease soil evaporation; however, where the wr.ter 

table is shallow factors such as large surface to sub^urface temperature differences and diurnal variation? in 

barometric pressure may result in considerable vaxx>r 

movement through porous soil. What is often called dew 

is in fact condensed vapor brought from below the 

ground surface during the night.

Dew may occur, but mostly hi areas where it would be 

but a small part of the water balance. Dew would r^ost 

likely be deposited on the upper part of tall vegetation. 

In the other areas, even on still nights, air temperatures 

are usually above the dew point temperature so that dew 

seldom occurs. Dew, even in small amounts, may b^ of 

considerable importance to the well-being of certain 

desert plants, however.

In phreatophyte areas of Southwestern United States 

it is likely that the largest losses per unit area occur 

in riparian areas dominated by saltcedar. Water use 

ranges from an estimate of 120 cm (centimeters) (4 ft) 

per year as an average for saltcedar areas in the Western States (Robinson, 1965) to measurements of 250 

cm (8^4 ft) per year for young saltcedar plants growing in two large tanks near Buckeye, Ariz. (van 

Hylckama, 1963). In 1964, water use in these tanks was
A4 GILA RIVER PHREATOPHYTE PROJECT, GRAHAM COUNTY, ARIZONA

210 cm (7 ft) from April through August (T. E. A. 

van Hylckama, written commun., 1966). Cotton areas 

in the Salt River valley would have had a consumptive 

use of 64 cm (2 ft) in the same period (Blaney and 

Griddle, 1962). At maximum potential plant density, 

water use by baccharis is about 140 cm (4i/£> ft) per 

year, use by mesquite is about 100 cm (3*4 ft), and use 

by saltcedar is about 225 cm (7% ft). These data apply 

to the flood plain of the Gila River (Gatewood and 

others, 1950).

Determination of water use in plant-covered areas 

is complicated by the differences between species as well 

as differences between plants within a species. Vegetation cannot be analyzed in the same fashion as open 

water and bare soil because it responds differently to 

changing winds, differences in constituents of the ambient air, the heat-radiation spectrum, water quality, 

water presence, daily temperature ranges, and average 

temperatures.

Most plants that use much water in summer are 

deciduous. As average temperature decreases they drop 

their leaves, and water use is negligible. The bare, rigid 

branches serve only to increase wind turbulence, and 

they allow the wind to carry away any available water 

faster. As foliage returns the wind turbulence changes. 

Wind turbulence over leaf covered vegetation does not 

increase with velocity in the same proportion as turbulence over bare soil or water. As wind velocity over 

vegetation increases, the boughs and branches bend, 

the vegetated surface becomes hydraulically smoother, 

and turbulence decreases. This is in contrast to a water 

surface where waves develop, the surface grows 

rougher, and turbulence increases.

Constituents of the air change in or near vegetated 

areas. In the heat of summer, dense thickets of saltcedar 

demand considerable water, but their water use can be 

restricted by a lessened ability of the wind to carry 

away transpired water vapor. Photosynthesis requires 

carbon dioxide, and unless the wind can supply it as 

required, plant activity may be restricted.

Leaf and branch surfaces are selective in their response to direct solar radiation (Grates, 1965). Not much 

is known about this among the many species of plants, 

but certainly they cannot be as uniformly treated as 

bare-soil and open-water surfaces.

Water quality, particularly the amount of salt dissolved in water, affects water use by plants. Data pertaining to plants in the project area are generally lacking, but transpiration rates may change markedly with 

changing salinity. Of three sets of paired tanks containing saltcedar, those that were flushed relatively free of 

salt before the growing season used about 50 cm 

(1.6 ft) more water during the growing season than

those that were not flushed (T. E. A. van Hylckama, 

written commun., 1966). The average use of all tanks, 

located near Buckeye, Ariz., was about 150 cm (5 ft) 

during the experimental period, April through August 

1965. Thus, water use by saltcedar may depend on the 

degree to which floods and rains have leached soil salts 

or have freshened ground water.

Losses from open water and usually from soil are not 

affected greatly by water quality except under extreme 

conditions, such as local ponding, where salinity could 

increase greatly owing to evaporation until the saturation vapor pressure at the water surface would be significantly affected.

When plant roots cannot draw moisture from the soil, 

transpiration does not exist. This situation may occur 

during a general drought or during a local drought 

largely caused by the plants themselves. Small quantities of moisture may still be lost from the soil, however, 

particularly near the surface. As water available to 

plants increases from floods, rains, capillary flow, or 

from a change in ground-water level, water use increases. When there is no limitation on the water supply, plants use water freely; the use rate deponds on 

how much water is needed to keep leaf surfaces cool. 

Under severe conditions imposed by a hot desert sun, 

hot dry air, and considerable wind, the plants nay not 

be able to supply water to tiheir leaves at a rate sufficient 

to keep them cool because of physiological limitations. 

The situation becomes the same as if the roots could not 

draw moisture; the plants wilt, and water use d°>creases 

rapidly. Most hot-weather species are adapted to this 

condition and suffer no permanent damage.

For areas covered by saltcedar a definite relation between water use and depth to the water has been shown 

by van Hylckama (196S) and a similar relation for 

other species is probable. How much of the increase in 

evapotranspiration with decreasing depth to water 

table is evaporation and how much is transpiration is 

not known. T. E. A. van Hylckama (1963) state,^ on the 

basis of winter observations, that the increase is mainly 

due to evaporation from the soil in the tanks planted 

with saltcedar. Near van Hylckama's study area, however, pumping has lowered the water table constantly, 

and saltcedars that were flourishing when the study was 

begun are now dead. This is an extreme example of 

dependency on depth to water; in contrast, in the San 

Carlos Reservoir area there are 26-year-old stands of 

poorly developed but growing saltcedar who^e roots 

have not been near the water table since they were seedlings. These plants, which began growing when the 

reservoir was at its highest stage, have apparently 

become adapted to a nonphreatophytic existence.
OBJECTIVES, METHODS, AND ENVIRONMENT A5

At the other extreme is vegetation that has been inundated by water for considerable periods and dies 

because respiratory processes involving the exchange 

of carbon dioxide and oxygen gases in the roots are no 

longer possible.

EVAPOTRANSPIRATION MEASUREMENT

Three methods of measuring evapotranspiration in 

a large area of heterogeneous vegetation, bare-soil, and 

open-water surfaces are described here. They are: (1) 

the water-budget method, (2) the heat-energy budget 

method, and (3) the mass-transfer method.

The water-budget method of computing evapotranspiration requires that all flow of water as a liquid into 

and out of the hydrologic system be measured. Any 

unbalance in the budget results from the escape of 

water vapor from the system. A water budget requires 

careful measurements to avoid obscuring the evapotranspiration term with measurement errors of the 

other budget terms.

A heat-energy budget has a singular advantage; the 

evapotranspiration term is numerically multiplied by 

the amount of heat necessary to change liquid to vapor. 

This weighting factor has a value of about 585 per gram 

of water when working in the centimeter-gram-second 

system. Relatively large errors can thus be tolerated in 

the measured terms of the heat-energy budget.

The energy budget has disadvantages also. With 

present methods it can only be applied to areas with 

fairly homogeneous vegetation and soil-moisture conditions. It is an analytical approach and requires careful 

instrumentation, considerable computation, and much 

data to yield a result strictly applicable to one spot 

only. How this result, together with others from different locations, can be applied to a large area remains 

to be determined.

The mass-transfer approach, which deals with water 

after it has become vapor, has an inherent attractiveness when one realizes how much water is actually 

moved. One acre of saltcedar may transfer as much as 

40 metric tons (44 short tons) of vapor into the atmosphere in 1 day. But because the water moves in such 

diffuse form and because of the vagaries of air currents, 

theoretical and instrumental problems are formidable. 

The most comprehensive application of mass-transfer 

theory would be to monitor vapor flux at altitudes considerably above the project area where vapor flows from 

diverse sources have mixed. Unfortunately, a unified 

theory that uses economically feasible field data is not 

available at this time; however, research in this area is 

continuing.

Other methods exist for estimation of evapotranspiration that are usually grouped together and are called

empirical approaches. Some of these methods rest upon 

sound theoretical bases, and they consist fundamentally 

of devices and simplifications applied to basic theory. 

They are designed to avoid the complexities of direct 

measurement of meteorological variables. However, 

some of the methods have obscure, if any, theoretical 

bases. Because these approaches lack comprehensiveness, 

results are often unique to locations at which measurements and correlations to real evapotranspiration have 

been made. However, because of the simplicity and low 

cost of application of the empirical approaches, research 

has continued in their development with varying degrees of success. A good example is the application of 

data from U.S. Weather Bureau class A evaporation 

pans to estimate evaporation from lakes and ©vapotranspiration from vegetated areas.

SOME ASPECTS OF STATISTICAL ANALYSIS 

OF THE WATER-BUDGET METHOD

By N. O. MATAIAS 

INTRODUCTION

Phreatophyte control involves the removal of the 

phreatophytes and replacement by beneficial grasses. 

Phreatophytes, dominantly saltcedar and mesquite, are 

being replaced by grasses that will provide grazing for 

cattle. As previously stated, if ET> and Ea denote measures of evapotranspiration before and after vegetation 

change, respectively, then

is the resulting change in evapotranspiration.

Evapotranspiration is determined by means of a 

water budget defined by

(2)

where the components a?1? . . . , a?8 denote (1) surf ace inflow in the Gila River, (2) surface inflow from tributaries, (3) subsurface inflow in the alluvium of the river 

and its tributaries, (4) possible artesian inflow from 

underlying geologic formations, (5) surface outflow in 

the river, (6) subsurface outflow in the alluvium, (7) 

precipitation on the flood plain, and (8) change in moisture storage, respectively.

To evaluate equation 1, the time periods TT, and Tay before and after modification of vegetation, respectively, 

are subdivided into Ni> and Na time increments, each of 

length A£ (water-budget period), so that

(3a) 

(3b)
A6 GILA RIVER PHREATOPHYTE PROJECT, GRAHAM COUNTY, ARIZONA

For each A£, evapotranspiration is determined by the 

water budget, equation 2, which is now defined as

3=1

j=\

,Ntt

(4a)

(4b)

for before and 'after vegetation change, respectively.

The measures of evapotranspiration, Ej, and Ea , are 

defined as means of the e&'s and ett's for all or part of the 

A£'s. In the following paragraphs, a brief description is 

given of the sampling problems that must be considered 

in estimating the e's and the general statistical approach 

for evaluating C is outlined.

WATER-BUDGET PERIOD

Several factors must be considered in selecting the 

water-budget period, A£, among which the more pertinent are the redundancy in information from one period 

to the next, the magnitudes of the measurement errors 

associated with a? l5 . . . , a?8 > and the time and cost 

involved in data collection and processing. With respect 

to these factors, A£ should be sufficiently small; consequently, Nb and Na should be large in order to provide 

reliable estimates of Eb and Ea.

Some of the water-budget components such as surface 

inflow are recorded continuously; thus, they can be 

determined for any selected period A£. Others, however, 

such as the change in moisture storage, a?8 , can be determined only for a finite period, Aw, where Ai* corresponds 

to the time interval between measurements at the sampling site. In the instance of a?8 , numerous soil-moisture 

holes are distributed throughout the project area. If the 

change in soil moisture for the period, Aw, can be related 

to the continuously recorded fluctuations in the water 

table, then this soil-moisture change can be reevaluated 

to correspond to any predetermined water-budget 

period, A£.

Observations of a?i, . . . , a?8 are subject to measurement errors, the magnitudes of which vary among the 

components. Because these errors also tend to vary 

directly with the magnitudes of a?i, . . . , a?8, the errors 

vary seasonally. If the total error, sampling plus measurement, is reduced, then a more reliable evaluation of 

O Is possible. Consequently, the observations of e for 

those A^s that correspond to periods of large storms 

may be neglected. This, however, reduces the total number of observations, which in turn increases the sampling 

errors.

Sampling errors vary inversely with the total number 

of observations. If A£ is small, then N^ and Na are large; 

however, the values of e for successive A£'s would be

highly serially correlated. Serial correlation im plies a 

redundancy of information from one A£ to th^, next, 

and so the sampling errors vary inversely with NI>' <^V& 

and Na' <.Na, where N^' and Na' are functions of their 

serial correlation and represent the effective number of 

observations before and after vegetation change for 

e's independently distributed among the A£'s. The larger 

the serial correlation is, the smaller are AV and Nar 

relative to N* and Na , respectively.

Part of the serial correlation is due to the stcchastic 

nature of the e's and the remaining part is due to seasonal trends. If A£ is taken to be sufficiently large so as 

to coincide with the annual cycle, or if evapotranspiration is defined as an annual value (e summed over an 

appropriate number of A£'s), then the seasonal trends 

are absent, and the serial correlation is due to the 

stochastic nature of evapotranspiration. For small A£, 

the seasonal trends must be defined and removed from 

the values of e for each A£.

EXPERIMENTAL DESIGN AND ANALYSIS

Consider a project area divided into three subreaches which are subdivided into five sections; the 

measures of evapotranspiration for the mth section in 

the Mh subreach are denoted by Etkm and Eakm for 

before and after vegetation change, respectively, where 

k=l, 2, 3, and m=l, . . . , 5. Before the change of 

vegetation, the quantities Ebkm are to be investigated 

to determine if differences among them are significant. 

The differences, if significant, must be explained in 

terms of such factors as vegetation density, quality of 

water, and depth to ground water. Quantitative and 

qualitative measures of plant density require entailed 

mapping of the reach; quality of water and depth to 

water must be determined at a sufficient number of 

points to obtain reliable spatial estimates by m°sans of 

weighted averages of the point estimates.

Seasonal trends, if present, must be removed from 

the estimates of the different factors before tl^ estimates are related to trend-free values of evapotranspiration. Unless these trends are removed, variations 

in evapotranspiration cannot be assessed in term? of the 

explanatory factors because the total period of observation, before and after vegetation modification, may not 

be long enough to include "average" climatic conditions.

To remove seasonal trends from plant density would 

require far more detailed measurement of the vegetation than seems feasible or possible at this time. Nevertheless, despite the number of plants, there is little or 

no transpiration during the nongrowing season, and 

plant density may, therefore, be considered zero. During 

the growing season plant density may be defined as a 

single value for each subreach of the study area. These
OBJECTIVES, METHODS, AND ENVIRONMENT A7

values may then be used to evaluate variations of evapotranspiration among the subreaches.

An analysis of covariance may be used to assess 

differences among the measures of evapotranspiration 

before vegetation change, Ebkm. In the analysis, the 

dependent variable is evapotranspiration and the independent variables are such factors as quality of water 

and depth to water. Basically, the data are grouped 

according to season, subreach, and section. Seasonal 

division of the data permits investigation of evapotranspiration for the growing and nongrowing seasons. 

The sectional division of the data is not an independent 

classification of the data but is a classification nested 

in another classification, namely, the subreach.

The data may be subdivided still further by considering left bank or right bank and, because of the well 

and soil-moisture-hole alignments, the proximity of 

the data collection site to the main channel, for example, 

far intermediate, or near to the main channel. This 

latter classification is nested in the bank location, 

which in turn is nested in the section.

Usually plant density decreases with distance from 

a stream, so that a designation of this distance indirectly 

takes into account, at least partly, plant density. If 

for any of the classifications, differences among E^

km 7

prove to be insignificant at some meaningful probability 

level, then this classification in subsequent analyses 

can be regarded as replication for a better 

determination of the experimental error.

The analysis of covariance will yield a result concerning the significance of the differences among Eb

kvn

but the reliability of this result will depend on the measurement errors. If these errors are large and if the 

differences among Eb]cm when there are 110 measurement 

errors are small, the differences among the observed 

E,,km may be masked. To overcome at least partly the 

effect of measurement errors, either classification of 

season must be dropped and only the data for the nongrowing season considered or data corresponding to 

M's within the growing seasons during which large 

storms occurred must be deleted. If the former is done, 

then active effect of the phreatophytes as well as the 

effect of plant density is lost.

This analysis focuses attention on the question of 

whether the size of Tb, the time period before modification of vegetation, is sufficiently large, after due consideration has been given to the effect of measurement 

errors, to allow for a meaningful interpretation of the 

differences among the E^m . If Tb is found to be too 

small, then it is unlikely that the difference between 

Efi and Ea can be reliably assessed no matter how large 

Ta may be. Ta can be arbitrarily large because once 

the phreatophytes are removed and replaced by grasses,

the grasses will not be removed and replaced by 

phreatophytes except possibly by natural processes. 

However, Ta is likely to be of the same order of magnitude as T,, for practical reasons of obtaining an early 

assessment of the effect of vegetation change.

After the phreatophytes are removed, a brief transition period may have to be allowed to permit replacement vegetation to become established. An analysis of 

covariance may then be used to investigate the difference between E-^ and Ea. In addition to the various classifications of the data mentioned above, another classification before and after modification of vegetation 

is needed. Because it is unlikely that T* and Ta will be 

large, climatic conditions during Tj, and Ta may be quite 

different and, thus, the difference between E^ and Ea 

may be seriously affected. Consequently, Ei> and Ea 

must be related not only to the factors mentioned above 

but to different climatic factors as well.

SITE SELECTION

By R. G. CULLER

After careful consideration of the various methods 

of measuring evapotranspiration previously descried 

it was decided that the water-budget method woulc? be 

the most feasible. Thus, selection of a site for the phreatophyte project was based on the need for one that would 

meet the requirements of this method. Other methods 

will also be applied and tested.

The water-budget method requires that all significant movement of water in the liquid phase, either inflow or outflow, be measured with considerable accuracy ; therefore, the surface discharge characteristics of 

the river and its tributaries were considered in selecting 

a site. The geologic framework of the site was also considered as it is an important factor in controlling 

ground-water movement, chemical quality of water, 

and sediment movement.

Vegetal cover, both density and species, was of prime 

importance in the site selection. The area of phreatophyte dominance was selected to be sufficiently larg?, to 

make evapotranspiration significant in the water budget. Otherwise, the computation as a residual might be 

completely obscured by errors in hydraulic measurements. A documented history of vegetation changer on 

the site also was advantageous.

Phreatophyte control is of particular interest for 

two types of landforms the wide naturally developed 

flood plain of major streams and the sediment deposits 

in the upper reaches of reservoirs. Flood-plain topography, therefore, was a factor in site selection.

Land ownership also was considered. Access for installation and maintenance of equipment was essential. 

Owners must be amenable to uniform and consistent
A8 GILA RIVER PHREATOPHYTE PROJECT, GRAHAM COUNTY, ARIZONA

land management during the preclearing and postclearing periods.

The existence of a site that would meet all these 

requirements was unlikely. A request for recommendations was sent to several hydrologists in the U.S. Geological Survey who were familiar with the phreatophyte problem. A field reconnaissance was then made 

of recommended sites, and records describing the sites 

were studied. A reach of the Gila Eiver flood plain in 

the San Carlos Indian Reservation more nearly met 

requirements than any other site. A formal agreement 

was made on May 28,1962, between the U.S. Geological 

Survey and the San Carlos Apache Indian Tribe, with 

the approval of the Bureau of Indian Affairs, for the 

use of reservation lands for the project.

The Gila River channel improvements proposed by 

the U.S. Army Corps of Engineers between the Camelsback Reservoir site and the Salt River were authorized 

by act of Congress, Public Law 85-500, 85th Congress, 

July 3, 1958. These improvements include the application of phreatophyte control in the area of the Gila 

River Phreatophyte Project. Thus, the expensive clearing operation required to complete the hydrologic study 

had already been authorized.

The project area is a 24-kilometer (15-mile) reach 

of the Gila River flood plain extending from the highway bridge on U.S. Highway 70 near Bylas to a point 

734 kilometers (4i/£ miles) above the mouth of the San 

Carlos River (fig. 1). The reach, divided into three subreaches, extends into the upper part of the San Carlos 

Reservoir so that a large area of dense saltcedar, a 

shallow water table, and a sediment deposit typical of 

the seldom-inundated part of reservoirs in arid areas 

might be included. The upper subreach is above the 

maximum water level for which the reservoir was designed. The middle subreach is mainly above the maximum reservoir water level observed since Coolidge Dam 

was built in 1928. The lower subreach is underlain by 

sediment deposited during the period of maximum reservoir water level in 1941-42. The physical, ecologic, 

and liydrologic characteristics of the site are described 

in the following sections. The central part of the project 

area is shown in figure 2.

GEOHYDROLOGY

By E. S. DAVIDSON and W. G. WEIST, JR.

INTRODUCTION

The Gila River in the northwest end of the Safford 

basin, Arizona, lies between two mountain ranges 

and occupies a broad valley which is filled with more 

than 300 m (meters) (1,000 ft) of silt, sand, and gravel. 

Deposits are divided into basin fill and alluvium that 

underlies the flood plain and adjacent low terraces of

the Gila River and its tributaries. The basin fill forms 

the bulk of the sediment in the basin, and th<> upper 

several hundred feet has been dissected into mesas and 

benches that slope from the bordering mountains 

toward the Gila River in the central part of tH basin. 

Alluvium fills channels incised into the basin fill along 

streams between the mesas and benches. Ground water 

and surface water drain from the highlands surrounding the Safford basin to the Gila River and its associated alluvial deposits. The water thus collected in the 

lowest part of the Safford basin then moves northwestward, either as streamflow in the Gila River or as flow 

through the alluvium.

BASIN-FILL DEPOSITS

The basin fill (Davidson, 1961) is a thick, extensive 

unit of flat-lying reddish-brown to light-brown silt, 

sand, and clay; in the northwest part of the jrrea the 

fill is mostly very pale yellow to white limestor e, marl, 

and tuff (fig. 3).

Water in the basin fill is under pressure and, in wells 

along the Gila River, rises to within a few fee* of the 

land surface. Water levels in this fill are several feet 

higher than those in wells that bottom in the overlying 

alluvium of the terraces and flood plain. Wells tapping 

the basin fill obtain water from thin sand layers and 

yield only a few gallons per minute.

Water in the basin fill flows toward the lo^er terrace and flood-plain alluvium. Because of artesian pressure in the basin fill, water may also leak upward from 

this unit toward the terrace and flood-plain alluvium 

(fig. 4.).

FLOOD-PLAIN AND TERRACE ALLUVIUM

Terrace alluvium fills the trough cut by the Gila River 

into the basin fill and is exposed along low terraces on 

both sides of the valley. Flood-plain alluvium has been 

deposited in shallower troughs cut into the terrace 

alluvium by the Gila River and its tributaries (fig. 4). 

Flood-plain alluvium along the smaller tributaries is of 

very limited extent and is lumped with terrace alluvium. 

The top of the flood-plain alluvium is 5 to 8 m (15 to 

25 ft) below the top of the terrace alluvium exposed 

along the terraces, and it is 1.5 m (5 ft) above the bed 

of the Gila River. Both deposits are lithologically similar and are distinguishable chiefly by topographic 

position.

The terrace and flood-plain alluvium occupying the 

shallow troughs cut by the Gila River range from 1,200 

to 2,400 m (4,000 to 8,000 ft) wide and up to 21 m (70 ft) 

thick. Along the tributaries these deposits ran^ from 

100 to 1,200 in (300 to 4,000 ft) wide and 7 to 10 m (20 

to 30 ft) thick but locally may be more than 1C m (30
r

OBJECTIVES, METHODS, AND ENVIRONMENT A9

r

2-inch pipe for accesssoil-moisture meter

RIVER,

<g ^ AH K <

in x V x

 q

K

£

Staff v gage 

observation we! 4-inch 

LA

r3y

£ni

Storage rain gage 

Triangulation monum(

»Ux W

Z

o

PICAL CROSS SECT

P

LL.

O

_l

< 

LJ

Q

371-096 O - 70 - 3
A10 GILA RIVER PHREATOPHYTE PROJECT, GRAHAM COUNTY, ARIZONA

FIGURE 2. A view of the central part of the project area looking 

northwestward near section 17.

FIGURE 3. Exposure of basin fill in the lower part of the project

area.

ft) thick. In places, terrace alluvium is slightly more 

cemented than alluvium in the underlying flood plain. 

The bedding ranges from almost structureless horizontal thick-bedded to thickly crossbedded layers. The 

coarse material, lenticularity, and crossbedding or thick 

horizontal bedding of the terrace and flood-plain alluvium contrast markedly with the fin©/material and 

horizontal thin bedding of the basin fill.

Ground water, stored under water-table conditions, 

moves slowly downstream through the alluvium. The 

water table fluctuates in response to surface flow and 

generally is 1.5 m (5 ft) ,or less below the land surface 

near the Gila Eiver and about 12 m (40 ft) deep near 

the surface contact between the alluvium and the basin 

fill. The alluvium readily accepts water from the basin 

fill and from the river and its tributaries. Infiltration of

surface water into the alluvium is probably much 

larger and is certainly more variable in time than 

ground-water flow from the basin fill. Locally, water 

from the alluvium contributes to the flow of the Gila 

Eiver.

CLIMATE

By M. R. COXLINGS

CHARACTERISTICS

The project area generally has two distinct periods of 

precipitation a primary one during the summer and 

a secondary one during the winter. Summer rains are 

generally the product of storms in July, August, and 

September and are associated with warm moist air from 

the Gulf of Mexico (Sellers, 1960). These storms are 

triggered by the combined effect of high surface temperature and orographic uplift, which sets off strong vertical air currents for convectional overturning. Showers 

are most frequent in the late afternoon and at night, 

and the driest hours are in the early afternoon. Summer 

rains start abruptly and usually continue for less than 

half an hour.

Generally, the continental anticyclone is absent in 

the winter and cyclonic storms produce the precipitation. Winter rain and snow at higher altitudes cause 

most of the sustained winter flow of the Gila Eiver.

Partial drought is common in May and June as well 

as in October through mid-November.

Mean daily temperature ranges from about 0° to 16° C 

(32° to 60°F) in the winter and from about 18° to 38°C 

(65° to 100° F) in the summer. Mean temperature ranges 

from 8°C (46°F) in January to 31°C (87°F) in July 

(U.S. Weather Bureau, 1964). In winter, days tend to 

be cooler in the project area than in the surrounding 

area because of down slope cold-air drainage.

Average daily humidity is highest in July and August. Afternoon and night showers commonly wet the 

air and soil enough to raise the humidity considerably 

during mornings.

MEASUREMENT OF PRECIPITATION

Three types of gages are used to measure precipitation: (1) nonrecording wedge-type storage gages, (2) 

weighing-type recording gages, and (3) digital floatactuated recording gages. The nonrecording gages were 

installed at each end of the 12 cross sections shown in 

figure 1. Weighing-type recorders were installed on the 

south bank of the river at the upstream and downstream 

cross sections of each subreach (fig. 1, sections 1, 9,17, 

and 23). Digital recording gages were installed on the 

north bank of the river at these same four sections. To 

measure precipitation adequately throughout the year, 

both types of recording gages are desirable, because the
All

EXPLANATION

Terrace and flood-plain alluvium

Consists of sand and gravel and a few

Consists of silt and clay and a few thin 

layers of fine sand

Arrow shows direction of groundwater movement; size of arrow is 

proportional to amount of water

 v

FIGUBE 4. Geology and ground-water movement in the project area.

digital recorder does not record snowfall and the weighing-type recorder, which has a slow chart speed, does 

not adequately record rainfall intensities.

The fairly dense network of precipitation gages 

described above provides relatively comprehensive coverage of summer connective storms which typically 

cover only a small area at any one time.1 Most of these 

gages were placed on the terrace above the flood plain 

so as to avoid wind turbulence produced by dense 

vegetation near the river. This also provides for easy 

access to the gages during heavy rains or when the flood 

plain is inundated.

Data from the wedge-type gages are punched on 

cards in the field, aiid the cards are used directly as 

digital-computer input. Total precipitation and its time 

of occurrence, as observed at recording gages, are used 

to extrapolate the rainfall catch of the nonrecording 

gages over shorter periods of time. The Thiessen polygon method is employed to obtain an estimate of the 

mean depth of rain on each subreach during a waterbudget period.

Measurements indicate that the south side of the 

river receives more precipitation than the north side.

1 "Convective-type storms, [in the Southwest] therefore, do not 

ordinarily produce rain of a general nature nor is there influence of particular note when consideration of peak discharges from larger watersheds is concerned. They are of utmost importance, however, in the 

production of maximum runoff from watersheds of ten square miles 

or less or from portions of large watersheds." (Dorroh, 1946).

Although long-term records are not available, the orographic effect produced by the high mountains south 

of the river seems to be reflected in the catches of the 

nonrecording gages at the end of each section.

SURFACE WATER

By D. E. BUKKHAM

PURPOSE AND SCOPE

Surface-water aspects of the project consist of measurement of streamflow for water-budget studies and 

evaluation of changes in low-flow and floodflow channels of the Gila River. Measurement of streamflow is 

important because: (1) during many periods streamflow is the largest item in the water budget, (2) streamflow is the major source of ground-water recharge, and 

because of hydraulic interconnections, streamflow influences the movement of ground water, and (3) streamflow data are more accurate than some other data and 

can be used to test evaluations of other factors.

Evaluation of changes in the low-flow and floodplain channels, as affected by vegetation alteration, is 

not a main objective of the study, but attempts will be 

made to document these changes. Natural river channels 

or streamflow conveyance systems are formed, altered, 

and maintained through the interrelation of the forces 

involved in the flow of water, movement of debris, 'and 

stresses in the mobile boundary of the channel (Leopold
A12 GILA RIVER PHREATOPHYTE PROJECT, GRAHAM COUNTY, ARIZONA

and others, 1964, p. 169). Gravity provides the force by 

which water and debris are moved, and resistance to flow 

is provided by the boundary. The forces and stresses involved are related to the character and composition of 

the debris carried by the water and to the materials 

in the boundary. Vegetation on the boundary adds to 

the resistance to flow and to the stability of the boundary. Changes in erosion, deposition, and resistance to 

flow, therefore, may be expected when the vegetation is 

altered. Removal of saltcedar and substitution of grasses 

may cause the river channel to change frequently in 

size, shape, and location. In addition, changes may occur in the channel pattern and sinuosity. It is possible, 

of course, for changes in stream channels to take place 

simultaneously with changes in the regimen of flow and 

with the removal of vegetation, so that changes attributable to vegetation modification would be difficult to 

detect.

PHYSICAL DESCRIPTION OF THE GILA RIVER 

DRAINAGE AREA

The Gila River drainage area is divided, for discussion, into (1) the Gila River above the study reach, (2) 

tributaries adjacent to the study reach, and (3) the Gila 

River through the study reach.

GILA RIVER DRAINAGE AREA ABOVE 

THE STUDY REACH

The drainage area of the Gila River above the study 

reach is about 29,800 sq km (square kilometers) (11,500 

sq mi) and extends eastward into the mountains of 

New Mexico. The altitude of the basin ranges from 760 

to 3,350 m (2,500 to 11,000 ft) above mean sea level. 

Topographically, the basin is typical of those in the 

Basin and Range physiographic province (Fenneman, 

1931) and is a comparatively flat, wide, sediment-filled 

valley between narrow rugged mountain ranges.

Native grasses and shrubs in the valleys and lower 

levels of the basin are generally sparse, but much of the 

mountain area is forested. The valley's flood plain has 

a dense cover of phreatophytes, consisting primarily of 

saltcedar (Tamariw pentandra) and mesquite (Prosopis). Much of the basin is used for grazing. Currently 

(March 1965), there are many small detention and retention reservoirs associated with range conservation 

and grazing on the Gila watershed.

About 27,900 hectares (69,000 acres) of valley land 

above the study reach is under cultivation (U.S. Geological Survey, 1961, p. 416), and the usual crops are cotton 

and alfalfa. Irrigation water is obtained from the Gila 

River at several diversion points and from groundwater storage. At the present time (March 1965), there 

are no large manmade reservoirs in the Gila River basin 

above Calva, Ariz.

TRIBUTARIES ADJACENT TO THE STUDY REACH

The area tributary to the study reach, 717 sq km (277 

sq mi), is drained by many ephemeral washes. The tributary basins are long and narrow, ranging in size from 

less than 0.3 to 101 sq km (0.1 to 39 sq mi), and 

drain the Gila Mountains on the north and Mount Turnbull on the south. The altitude of the basins ranges from 

760 to 2,700 m (2,500 to 9,000 ft). Extremely steep 

slopes and sparse vegetation induce rapid runoff.

GILA RIVER THROUGH THE STUDY REACH

The flood plain through subreaches 1 and 2 numbered in downstream order is about 900 to 1,200 m 

(3,000 to 4,000 ft) wide. During low and medium flows 

the main channel is 24 to 30 m (80 to 100 ft) wide, has a 

slope of about 0.001 meter per meter (0.003 ft per foot), 

and consists primarily of pools and riffles. The bottom 

of the pools usually consists of easily erodible sand during low flows, while the riffles are formed from fairly 

stable gravel bars. The banks of the main channel and 

the flood plain are stabilized by saltcedar and mesquite.

The main channel and flood plain of subreach 3 

are different from those of subreaches 1 and 2 presumably because of the influence of San Carlos Reservoir. Sediment deposited in the reservoir during the 

period of maximum storage, 1941-42, and subsequent 

sediment deposition from flows in the San Carlos and 

Gila Rivers have appreciably decreased the slope of the 

main channel and flood plain. The vigorous growth of 

saltcedar has gradually encroached on the channel and, 

together with the reduced slopes, has decreased the flow 

capacity of the channels. Over-bank flow of sedimentladen floodwater has resulted in the formation of natural levees by deposition when the velocity of the water 

is reduced on entering the saltcedar thicket. The deposition of sediment has aggraded the channel and its 

levees until they are the highest part of the flood plain 

(fig. 5). Floatable debris mainly logs carried by the 

floodflows has been deposited in the channel owing to 

the screening effect of the saltcedar, and the end result 

is a plugged channel; additional sediment was then 

deposited in the log jam (fig. 6).

The development of natural levees and the decrease in 

channel slope have been gradual; however, the process 

of channel plugging and filling progressed upstream at 

a rapid pace once log jamming started. Aerial photographs taken in 1935, 1947, and 1962 indicate no log 

jamming and no significant change in channel location 

from 1935 to 1062. A log jam on the Gila River 2.4 

kilometers (iy2 miles) above the mouth of the San 

Carlos River was first observed in January 1963. This
OBJECTIVES, METHODS, AND ENVIRONMENT A13

FIGTJEE 5. Lower part of the project area during high water 

and the natural levees formed as a result of the saltcedar 

reducing the velocity of the water.

FIGTJRE 6. Log jam and sediment accumulation below section

23.

jam probably occurred during the floodflows of September 27 to 30, 1962. Since January 1963, the upstream 

progress of the channel plugging has been observed and 

has been documented by photographs. During the summer flows of 1963 and 1964, the jam progressed upstream 4.8 and 8.8 kilometers (3 and 5.5 miles) from the 

mouth of the San Carlos River, respectively. At the 

present time (March 1965), the upstream end of the log 

jam is within 90 m (300 ft) of section 23.

Channel plugging by log jams has increased the area 

and duration of ponding behind the natural levees; reservoir inflow may have been decreased as a result of 

higher evapotranspiration rates from these ponds and 

swampy areas.

STREAMFLOW CHARACTERISTICS

GILA RIVER

Flow in the Gila Eiver, which constitutes a large part 

of the water in the water-budget study, conies from two 

seasonal types of precipitation. Flow from summer precipitation extends from July through October, and flow 

from winter precipitation extends from November 

through June.

Summer streamflow results mainly from small thunderstorms, but occasional frontal activity brings precipitation that produces widespread runoff in late September and throughout most of October. Streamflow caused 

by summer precipitation generally varies considerably 

within a short period of time. Periods of no flow occur 

during most summers. Sediment concentration is generally high during summer flow. Average summer flow 

from 1930 through 1961 was 5.15 cu m per sec (cubic 

meters per second) [182 cfs (cubic feet per second)], 

ranged from 0 to 790 cu m per sec (27,900 cfs), and 

was 26 percent of the average annual amount.

Flow from November through June is mainly from 

frontal storms, snowmelt, or ground-water storage and 

may be fairly constant for long periods. Flow, if any, is 

generally small in May and June.

The average November through June flow from 1930 

through 1961 was 7.16 cu m per sec (253 cfs), ranged 

from 0 to 609 cu m per sec (21,500 cfs), and was 74 percent of the average annual amount.

Major flows of record have occurred during the winter as a result of large amounts of widespread rainfall, 

a warming trend during a time of large snow accumulation, or extensive rainfall on snow. Maximum known 

discharge of the Gila Eiver in the study reach was more 

than 2,800 cu m per sec (100,000 cfs) in 1916. From 1916 

to the present (March 1965), the largest flood was 790 

cu m per sec (27,900 cfs) in 1941.

TRIBUTARIES

Flow in tributaries to the study reach generally occurs in summer as a result of thunderstorms and is 

characterized by high peak rates and small volumes. 

Only a small amount of tributary flow reaches the Gila 

River as surface runoff. Some infiltrates to the tributary 

alluvium, the Gila River terrace alluvium, and to the 

Gila River flood plain. Some is ponded behind natural 

levees of the Gila River and is depleted by infiltration 

and evaporation. Because of infrequent occurrence and 

small volume, runoff from tributaries is an important 

factor in only a small number of budget periods. If a 

water-budget study is to be useful during the rare occasions when tributary surface flow is large relative to 

water from other sources, flow records must be accurate.
A14 GILA RIVER PHREATOPHYTE PROJECT, GRAHAM COUNTY, ARIZONA

DATA-COLLECTION PROGRAM

Data necessary to evaluate factors in the water-budget 

study include: (1) continuous records of surface flow 

to and from each subreach, (2) discharge measurements 

at about 6-week intervals at each cross section to evaluate the interchange of surface- and ground-water flows, 

and (3) stage readings, usually at about 3-week intervals, at each cross section.

GILA RIVER SURFACE FLOW

Gaging stations on the Gila River in the study area 

are maintained at the end points of each subreach and 

are referred to as: (1) near Bylas, (2) at Calva, (3) 

near Calva, and (4) above Coolidge Dam. Each gaging 

station is equipped with a 15-minute digital stage recorder and a continuous analog stage recorder, both of 

which are activated by the same float. The continuous 

record of stage is desired in addition to the punched 

record during measurements of needle-peak-type flows. 

The continuous graph also is useful in defining shifts 

in the stage-discharge relation.

A brief description of each gaging station follows.

GILA RIVER NEAR BYLAS, ARIZ.

The gage is on the downstream side of the bridge on 

U.S. Highway 70 (fig. 1). Flow past the stilling well 

is somewhat turbulent, but its effect on the stage-discharge relation is not excessive.

High-water measurements were made from the bridge 

through the spring of 1964. However, because of large 

approach angles, turbulence, excessive scour around the 

piers, and uneven velocity distribution, the bridge site 

was not ideal for measurements of high flow. A cableway 

that spans the main channel was installed 43 m (140 

ft) downstream in the summer of 1964. Flows in excess 

of the capacity of the main channel, about 110 cu m per 

sec (4,000 cfs), still must be measured from the bridge. 

Low flows are measured at wadable sections near the 

gage.

The control section for flows ranging from 1.4 to 110 

cu m per sec (50 to 4,000 cfs) is an old road crossing 

46 m (150 ft) downstream from the gaging station. The 

section of gravel, small rocks, and sandbanks overgrown 

by saltcedar is fairly stable. The low-water control is 

the shifting sand bars that form upstream from the old 

road crossing.

GILA RIVER AT CALVA, ARIZ.

A gaging station has been in operation at this site 

since October 1929. The station was originally equipped 

with a continuous analog stage recorder, and the stilling 

well was attached to the downstream side of the railroad 

bridge that spans the Gila River flood plain. Many factors including trash accumulation, shifting of the lowflow channel, and channel changes associated with 

bridge maintenance made the location undesirable. A 

new station was established in December 1962, 162 m 

(530 ft) below the bridge. The new station, originally 

a bubble-gage type but currently a stilling-well type, 

is on the left bank of the river.

Before 1962, all high-water measurements were made 

from the railroad bridge. Because of large approach 

angles, turbulence, excessive scour around piers, and uneven velocity distribution, the bridge site was not ideal 

for high-water measurements. In December 1962 a 

cableway spanning the main channel was constructed 

122 m (400 ft) downstream from the bridge. Flows 

in excess of the capacity of the main channel, about 110 

cu m per sec (4,000 cfs), still must be measured from 

the bridge. Measurements of low flow are made at wadable sections at several places near the gage.

The channel control of sand and gravel is unstable. 

There is a fairly stable gravel bar in the channel 60 m 

(200 ft) below the present gaging station that may act 

as a partial control during flows near bankfull stage. 

Vegetation along the banks also affects the stage-discharge relation at flows near bankfull stage or higher.

GILA RIVER NEAR CALVA, ARIZ.

This station was started in January 1963 when a 

bubble gage was installed on the right bank of the river 

37 m (120 ft) upstream from an old highway bridge 

near the mouth of Salt Creek (fig. 1). The wood shelter 

burned in June 1963, and all the instruments and about 

3 weeks of stage record were destroyed. Another bubble 

gage was installed in August 1963. The bubble gage was 

abandoned in October 1963, and a stilling-well-type 

gage was installed. The stilling well of the new gage is 

attached to a concrete pier of the bridge on the right 

bank of the main channel 37 m (120 ft) downstream 

from the bubble-gage site.

A measuring cableway that spans the main channel 

was installed about halfway between the site of the 

bubble gage and the stilling-well-type gage. No attempt 

will be made to measure flows in excess of the capacity 

of the main channel, about 85 cu m per sec (3,000 cfs). 

Because of the wide flood plain and poor measuring 

conditions low-flow measurements are made at various 

wadable sections in the channel near the gage.

GILA RIVER ABOVE COOLIDGE DAMa ARIZ.

Accurate measurement of streamflow at the downstream end of subreach 3 has been extremely difficult 

because of channel plugging by debris. In 1962 a 

bubble gage was installed on the right bank of the 

main channel about 4 kilometers (2*4 miles) upstream 

from the mouth of the San Carlos River. At that time
OBJECTIVES, METHODS, AND ENVIRONMENT A15

the main channel was 30 m (100 ft) wide and had a 

bankfull capacity of about 57 cu m per sec (2,000 cfs). 

Only 4 months of streamflow record was obtained 

and this was largely faulty because of malfunctions 

associated with the bubble gage before the channel 

became filled with debris and the flood plain became 

a lake.

In February 1964 a new gaging station was established about 3 kilometers (2 miles) upstream with a 

stilling-well-type gage. The sand-bed channel at this 

site has a conveyance capacity of about 43 cu m per 

sec (1,500 cfs) at bankfull stage. A cable way spanning the main channel was constructed in May 1964.

Because of channel plugging, only small flows currently can move down the main channel the remaining streamflow spills onto the flood plain. As a result, 

only records of median and low flow are being 

obtained.

When the project was started in 1962, bubble gages 

manometers using gas to transmit river stage by 

pressure were installed at the "at Calva," "near 

Calva," and "above Coolidge Dam" sites, but they 

were soon discontinued owing to instrument malfunctions and incorrect registering of gage heights. The poor 

record generally occurred during stage recessions and 

apparently resulted from plugged orifices caused by the 

movement and deposition of sand and clay over them.

Discharge measurements, which are necessary to 

establish the stage-discharge relation at each gaging 

site, are made using established techniques. Because the 

channels are composed of sand and gravel, they are 

subject to some shifting at all flows, although shifting 

is not excessive. Some factors contributing to changes 

in the stage-discharge relation are scouring and filling 

in the controlling reach of the river, sediment in transport, and seasonal vegetation changes. Most shifting in 

ratings are probably associated with the movement of 

sediment.

To insure necessary accuracy of flow records, frequency of discharge measurements is geared to the 

movement of sediment. Sediment transport is high in 

the summer during the continual variation of flow rates 

and therefore requires that discharge measurements be 

made about three times weekly. Measurements during 

the more constant winter flows are made about once 

a week.

TRIBUTARY SURFACE FLOW

The tributary surface flow generally contributes 

water to the reach for only a small part of the time 

and is assumed to be a small part of the total waterbudget for most periods. Therefore, accurate records 

of flow for each tributary will not be required. Difficulties in accurately measuring high rates of discharge 

from tributaries will require that water budgets which 

include large storms from tributaries be omitted from 

the study.

In order to estimate surface flow from tributaries, 

62 gaging stations 16 with continuous stage recorders 

and 46 with crest-stage gages were installed. The 

tributaries on which the 16 recording gaging stations 

have been established were selected on the basis of 

basin size, physiographic characteristics, and orientation along the study reach.

Because runoff increases with the size of a basin, 10 of 

the 16 recording gages were established in the 10 largest 

basins. About 54 percent of the total tributary area is 

included in these basins. The remaining six recording 

gage sites were selected on the basis of physiographic 

characteristics and orientation. About 396 sq km (163 

sq mi) or 59 percent of the total tributary area is included in these 16 basins.

The 16 recording gaging stations were established at 

highway or railroad structures (fig. 1). The control sections at the gaging stations range from stable concretebox culverts to unstable sand. Owing to the extremely 

steep channel slopes, the velocity of the flow past the 

gaging sites is almost always supercritical.

The 46 crest-stage gages (fig. 1) are maintained on 

tributaries having drainage basins ranging in size from 

0.2 to 21 sq km (0.1 to 8 sq mi). These gages are located 

at bridges or culverts wherever possible. The control 

sections are similar to those at the recording gages.

Discharge records are obtained for tributaries equipped with the continuous recorders by using established 

techniques. Current-meter measurements are made 

whenever possible; otherwise, data necessary for indirect measurements are obtained.

Discharge estimates at crest-stage gages are obtained 

by the use of a peak-discharge versus storm-volume relation. This relation is established using data from calibrated stations equipped with the continuous recorders. 

The peak discharge is obtained from ratings defined by 

established techniques.

CHANGES IN THE STREAMFLOW 

CONVEYANCE SYSTEM

Changes in the streamflow conveyance system as a result of vegetation alteration may be slow or rapid. Evaluations of changes will be made by comparing the conveyance systems of treated (cleared) and untreated 

(hereafter called the control reach) replicated reaches 

subjected :to the same flows. Analysis of pretreatment 

history of surface flow, channel configuration, and floodplain vegetation for replicated reaches will be made.
A16 GILA RIVER PHREATOPHYTE PROJECT, GRAHAM COUNTY, ARIZONA

The analysis will be duplicated after treatment to evaluate changes that can be credited to vegetation alteration. The treated reach is the same as that used in the 

water-budget study; the control reach, which has not 

been selected, will be upstream.

The data-collection program in the treated reach consists of (1) repetitive surveys of 15 cross sections of the 

stream channel and flood plain, (2) repetitive aerial 

photographs of the stream channel and flood plain, (3) 

contour mapping of the flood plain and channel, and 

(4) mapping flood-plain inundation after overbank 

flows, Changes in resistance to flow associated with 

vegetation alteration should be reflected in the stagedischarge relation of overbank flow. Data associated 

with flood-plain inundation will be correlated with the 

stage-discharge relation in evaluating changes in resistance to flow.

The cross sections were surveyed and permanent horizontal and vertical controls were established in 1964. 

The vertical control was referenced to mean sea level 

datum by second-order leveling and the horizontal control was tied to the Arizona Zone East Grid System by 

third-order triangulation. Monuments were placed at 

the end of each section and 15.2 m (50 ft) landward 

from the bank of the main channel. The sections will be 

resurveyed at regular intervals.

The present density of phreatophytes precludes precise mapping by photogrammetric methods. After the 

phreatophytes have been removed, maps at a scale of 

1:7,200 and contour intervals of 2 ft (0.6 m) will 

be prepared from aerial photographs.

Three topographic maps are available. One, which 

has 5-ft (1.5-m) contours and a scale of 1:12,000, was 

prepared in 1914 15 by the Soil Conservation Service 

from planetable surveys. Another, which has 5-ft 

(1.5-m) contours and a scale of 1:7,200, was prepared by the Corps of Engineers from aerial photographs taken in 1946. The map by the Corps of Engineers covers the project reach except for 1 mile (1.6 

kilometers) at the upstream end. In 1960 the Geological 

Survey prepared 7%-minute quadrangle maps of the 

area with 40-ft (12.2-m) contour intervals at a scale 

of 1:24,000.

Aerial photographs taken in 1935, 1942, 1947, 1954, 

and 1964 are available. Additional aerial photographs 

will be taken as the project progresses.

After the control reach is selected, permanent cross 

sections will be established, and frequent surveys will be 

made to document changes in altitude and channel shape 

and size. Aerial photographs will be used to document 

changes in channel configuration.

GROUND WATER

By R. M. MYKICK

INTRODUCTION

The only significant aquifers are the two previously 

described geologic units the basin fill and the terrace 

and flood-plain alluvium. Basin fill underlies the alluvium and forms adjacent valley slopes. Available 

data indicate that water in the basin fill is under artesian pressure and in places it contributes water to the 

alluvium. The alluvium rests on the basin fill and underlies the channel, flood plain, and terraces of the Gila 

River and constitutes the major aquifer in the area. 

The permeability of the alluvium is high but variable. 

Water storage changes seasonally in the alluvium.

Movement of ground water is influenced by consumptive use by phreatophytes. During the growing season a 

tract of this vegetation creates an area of lowered water 

table similar to that of a field of closely spaced lightly 

pumped wells. The movement of ground water is further 

complicated by gravitational movement of water 

through the alluvium and recharge from the flow of the 

Gila River, which, in the project area, loses water to 

the alluvium during most of the year.

Storage coefficients and transmissivity of the alluvium were estimated by means of an aquifer test. The 

slope of the water table downstream and at right angles 

to the valley is computed from water levels measured in 

wells. This information will be used to calculate values 

of subsurface inflow and outflow both downstream 

and across the valley, when the thickness of the aquifer 

at the ends and sides of the three subreaches is known. 

An estimate of consumptive use at each well can be computed by the phreatophyte-well method (White, 1932). 

To improve the estimate of storage coefficient at an 

individual well, changes in storage as measured at soilmoisture observation wells adjacent to each water well 

will be used.

The depth to water is measured monthly at several 

stock wells in and near the project area. These wells 

extend into the basin fill and are perforated below the 

contact with the alluvium. Measurement of changes in 

artesian head in these wells will give an indication of 

changes in rate of inflow from the basin fill.

Flow from the basin fill to the alluvium has been estimated by two different methods as 0.3 to 0.7 meter 

per square meter (1 to 2 ft per square foot) of area of 

contact per year. Rates of inflow are expected to differ 

appreciably during the year; therefore, installation of 

additional wells is planned to measure artesian head 

throughout the year.
OBJECTIVES, METHODS, AND ENVIRONMENT A17

OBSERVATION-WELL NETWORK

A network of observation wells was established to 

measure inflow into and outflow from the project area 

and to define movement of the ground water. Lines of 

wells were drilled at about 1.6 kilometer (1 mile) intervals (fig. 1) across the valley. Each line other than 

section 1 at the upstream end of the project crosses the 

main channel at about a right angle; section 1 is parallel 

to the highway embankment. Each section consists 

of three wells on each side of the river. (See detail 

of typical cross section, fig. 1). Two wells are near the 

river channel. Location of the other four wells in each 

section was determined by considering vegetation type 

and density and topography.

Drilling of wells in the upper subreach was started 

in the fall of 1962 and was completed in July 1963. 

Wells in the middle subreach were completed in December 1963, and those in the lower subreach were completed in June 1964. In the summer of 1964, the water 

table declined far below any previously measured water 

level, and it was necessary to deepen some of the wells.

All wells were cased with 11.4-cm (41^-in.) lightweight steel tubing into which a 10.8-cm (4^4-in.) 

plastic liner was inserted. The wells were not perforated 

but were left open at the bottom. Where necessary, pipes 

were encased in concrete at the ground surface to eliminate pipe movement and to prevent surface runoff from 

raising water levels.

Digital recorders, which punch the water level in code 

on paper tape at 30-minute intervals, were installed on 

all observation wells on the cross sections (fig. 7). The 

size of the wells limited the diameter of the recorder's 

float to 8.9 cm (3y2 in.) A 5.1-cm (2-in.) steel pipe 

2.4 m (8 ft) long was used as a counterweight tube to 

permit water-table fluctuations of 2.4 m (8 ft) without 

adjusting the float cable. The counterweight tube was 

plugged in areas where the water table would possibly 

rise above the bottom of the tube. The possibility of 

flooding required installation of a submergence cover 

to protect the recorders.

WATER-LEVEL RECORDS

The water-level recorders are inspected at least once 

every 3 weeks, and the charts are removed every 12 

weeks (one cross section each week). If a time error 

on the chart or a minor recorder malfunction has occurred the chart is moved ahead at the time of inspection. Additional recorders are available to replace 

equipment that requires major repair or adjustments.

When recorder tapes are received from the field, they 

are edited and forwarded to the Automatic Data Processing Unit, Washington, D.C., for translation to a 

computer format and storage on magnetic tape. A

FIGURE 7. Water-level observation well, showing installation 

of digital recorder.

printout of hourly stage and daily maximum, minimum, 

and mean stage is made. Changes in the water table 

seldom are more than 0.9 cm (0.03 ft) during half an 

hour; therefore, all days having a change in stage greater than 0.9 cm (0.03 ft) in half an hour are flagged. 

These flagged readings may indicate a poor record or 

a marked change in ground-water levels near the river 

due to a rapid change in river stage.

Data printout sheets are reviewed for poor record 

resulting from malfunction of the recorder or a sticking float. At the end of each water year the magnetic 

tape is updated. Where feasible, missing and poor 

records are estimated on the basis of records from surrounding wells. In the future, updating can be quarterly, if required.

SOIL-MOISTURE OBSERVATIONS

By R. M. MYRICK

Changes in moisture storage in the unsaturated zone 

are important in evaluating evapotranspiration. A network of soil-moisture observation wells similar to that 

of water-level observation wells previously described 

was established to measure moisture in storage at the 

beginning and end of each budget period. Normally, 

the change in ground-water storage is determined from 

the specific yield and the change in water-table altitudes. But specific yield, by definition, applies to gravity 

drainage; therefore, total reduction in storage resulting 

from withdrawal by phreatophytes cannot be deter-
A18 GILA RIVER PHREATOPHYTE PROJECT, GRAHAM COUNTY, ARIZONA

mined from observations of changes in the water-table 

altitude.

To obtain accurate measurements of storage, the soil 

surrounding the observation wells should be disturbed 

as little as possible; therefore, the wells were drilled 

with a hydraulic rotary vacuum drill (fig. 8) having a 

bit slightly smaller than the inside diameter of the 

casing. The wells were drilled by extending the drill 

bit 1.27 cm (i/2 in.) below the casing and lowering the 

casing by hydraulic pressure as the hole was deepened. 

As drilling progressed, 1.83-m (6-ft) lengths of casing, 

4.45 cm (1.75 in.) in diameter, were brazed together 

until the casing extended 0.61 m (2 ft) or more below 

the lowest expected water table. The casing consists of 

aluminum pipe having walls 0.32 cm (% in.) thick so 

as to prevent deformation; aluminum casing was used 

to minimize its deterioration from highly saline soils 

and water. After installation, the bottoms were sealed 

with rubber stoppers (U.S. Department of Agriculture, 

1962, p. 116-117), and the casings were bailed dry.

Neutron-scattering soil-moisture meters are used to 

measure moisture content. Each meter consists of a 

probe that contains a source of fast neutrons and a slowFIGUEE 8. Hydraulic rotary vacuum drill used to install soilmoisure wells.

neutron counter attached by a cable to a sealer that 

records the counts. This method of measuring soil moisture is based on the facts that hydrogen atoms slow fast 

neutrons more than other elements common in soil and 

that most hydrogen in soil occurs as moisture. The more 

moisture present (the greater the number of hydrogen 

atoms), the greater the number of fast neutrons that 

are reduced to slow neutrons and the higher the count.

Accurate positioning of the probe in an observation 

well is important. Near the water table, large changes 

in moisture are recorded within small changes in depth. 

A standard reference for positioning the meter, which 

also serves as a receptacle for the shield of the soilmoisture probe, was made by attaching a steel pipe, 

0.30 m (1 ft) long and 5.08 cm (2 in.) in diameter, to 

the top of the casing; the bottom of this pipe was placed 

level with the land surface (fig. 9). A steel tape is attached to the probe and cable so that the probe may be 

positioned at precisely the same depths each time measurements are taken.

Readings (counts) of 1-minute duration are recorded 

at the 0.15-m (V2-ft) depth and at 0.30-m (1-ft) intervals from 0.30 m (1 ft) below the land surface to the 

bottom of the hole.

A field calibration was made to check the factory calibration of the meter count versus percentage moisture for each probe. Three 0.76-cu m (1-cu yd) tanks 

were filled several times with different soils having moisFIGTJEE 9. Typical observation site, showing observation well 

with digital recorder and soil-moisture well with neutronmoisture meter in place.
OBJECTIVES, METHODS, AND ENVIRONMENT A19

ture contents ranging from air dry to 20 percent. The 

probes also were calibrated when the soils were saturated. A calibration curve was then developed for each 

probe from the tank data.

Two probes were then calibrated against the probe 

containing the strongest source to reduce small errors 

introduced when interchanging measuring equipment at 

an observation well. This calibration was done by making observations at 15 different depths in each of 10 

wells with each of the three probes. The 10 well sites 

were selected with an equal distribution of data over the 

entire range of moisture in storage and to represent 

several types of soil. Rating curves for the two probes 

with weaker sources were developed using the percentage moisture as measured by the probe with the strongest source. The difference between the curves developed 

by this method and the best-fit curves constructed from 

the first calibration, although small, would introduce an 

error in the soil-moisture data when equipment was 

interchanged.

Soil-moisture measurements are made in one subreach each week. Soil-moisture data and other pertinent 

information are punched on 40-colmnn cards in the field. 

A computer program converts the field data to percentage moisture by volume, using the calibration developed 

for each of the probes. A printout is obtained of the 

percentage moisture, change in moisture content since 

the last observation, and other pertinent data that have 

been entered on the cards. The percentage moisture for 

each depth is punched automatically on a second set of 

cards to be used in the analysis of soil-moisture data.

The zone of aeration, in which pores are normally 

occupied partly by water and partly by air, extends 

from the water table, or the top of the zone of saturation, 

to the land surface. The zone of aeration from the land 

surface downward may be divided into the belt of soil 

water, the intermediate belt, and the capillary fringe 

(Meinzer, 1942, p. 393-394). Normally the belt of soil 

water is not saturated, but it is recharged by precipitation and, in places, occasionally by floodwater. The intermediate belt extends from the lower limit of the belt 

of soil water to the upper limit of the capillary fringe, 

and it is recharged by downward-moving water. The 

capillary fringe extends upward from the water table 

to the maximum height of capillary rise or to the belt of 

soil water if the water table is only a few feet below land 

surface.

Data from each soil-moisture observation well are 

separated according to each of the three belts of the 

zone of aeration, and changes in storage during a budget 

period are calculated for each belt. Changes in storage 

related to precipitation, and occasionally to flooding, 'are 

restricted mainly to the belt of soil water. Changes in

storage in the intermediate belt, penetrated only by the 

deeper wells on the terraces, are only minor over long 

periods of time. Major changes in storage are restricted 

to the capillary fringe and are controlled by vegetrl 

cover, depth to water, and fluctuations of the water table. 

Change in storage during a budget period in each belt 

in each subreach are computed by the Thiessen polygon 

method. The bottom of the soil-water belt was set arbitrarily at 1.37 m (4.5 ft) below land surface because 

little or no change in storage has been observed between 

this depth and the capillary fringe in the wells on th°- 

terraces. The intermediate belt extends from this depth 

to the maximum recorded capillary rise. The capillary 

fringe extends from the water table to the intermediaie 

belt or to the soil-water belt in wells on the flood plain 

where the intermediate belt is not present. Further 

analyses will require a more exact method of determiring the extent of these belts in individual wells.

VEGETATION

By B. M. TURNER

CHARACTERISTICS

Phreatophytes grow along streams and on flooi 

plains and stream terraces where favorable moisture 

balance enables these plants to attain a height and density far greater than that of adjacent upland communities. The most common phreatophytes include mesquite 

(Prosopis julifiora var. velutine (Woot.) Sarg.), willow 

(Salix sp.), cottonwood (Populus fremontn Wats.), 

seepwillow (Baccharis glutin-osa Pers.), saltcedar (Tamarix pentandra Pall.), and seep weed (Suaeda torreyana S. Wats.). Campbell and Dick-Peddie (1964) 

described phreatophytes along the Rio Grande in New 

Mexico, where many of these same plants grow.

The vegetation of the uplands (basin fill and older 

terraces), in contrast to that of the valley bottom, forms 

uniform low open stands. The most abundant plants 

here are creosote bush (Lm^rea tridentata (Sesse & Mo^. 

ex DC.) Coville), white thorn (Acacia constricta 

Benth.), catclaw (Acacia greggii A. Gray), and 

mesquite.

There is a strong mosaic pattern to the vegetation of 

the terraces and, particularly, the basin fill in the part 

of the Gila River valley included in this study. Soils of 

strikingly different chemical and physical characteristics are exposed. The plant life has responded to tl ?. 

variety of habitats and has assumed a patchwork design, 

often with sharp boundaries between adjacent patches.

Several distinct phreatophyte communities occupy 

some of the lowlands. About 1,420 hectares (3,500 acres) 

are dominated by mesquite, 1,900 hectares (4,700 acres) 

by saltcedar, and 63 hectares (155 acres) by seepweed; 

about 24 hectares (59 acres) are barren.
A20 GILA RIVER PHREATOPHTTE PROJECT, GRAHAM COUNTY, ARIZONA

The mesquite community is above the flood plain on 

fairly stable land surfaces. Mesquite forests often extend to the top of recent vertical cuts where an abrupt 

transition occurs to the flood-plain vegetation below. 

The outer edge of the mesquite-dominated areas usually 

abuts the base of bluffs bordering the Gila River valley. 

Mesquite also grows up tributary washes. Along the 

floors of these washes, the phreatic zone gradually 

merges with upland xerophytic communities, and 

mesquite plants decrease in size along the gradient of 

diminishing water availability.

Other woody perennials growing with mesquite are 

catclaw, white thorn, grey thorn ( Condaliopsis lycioides 

(A. Gray) Suesseng.), and four-wing saltbush (Atriplex canescens (Pursh) Nutt.). The total coverage of 

these plants seldom exceeds that of the mesquite with 

which they grow.

The trees of the low mesquite forest may be 4% to 6 

in (15 to 20 ft) high. The trees lose their leaves in late 

fall and produce new ones in April or May. At the onset 

of the summer rainy season, the trees produce a second 

crop of leaves, which increases the total transpiring 

surface. The second flush of leaf growth is apparently 

in response to precipitation and the renewed supply of 

available moisture in the upper soil horizons.

Saltcedar covers more than 50 percent of the area and 

generally grows in areas of overbank flooding, although 

it occupies some arid uplands that have previously been 

subjected to flooding. Where saltcedar is most dense, it 

is usually unaccompanied by other woody perennial 

plants, but seepwillow may grow widely scattered 

among taller saltcedars or as a narrow fringe along the 

open channel margin.

Saltcedars form nearly impenetrable thickets 4% to 

6m (15 to 20 ft) high where growth is most dense. In 

other places the stands are open, probably because of 

poor synchronization between flooding and seed production, frequent burning, and a deep water table.

The densest and tallest, saltcedar grows near the river 

channel. The transition zone is abrupt between areas 

occupied by saltcedar and by adjacent vegetation. The 

sharply defined boundaries probably result from two 

characteristics of the seeds of this plant. First, because 

each saltcedar plant produces large quantities of seeds, 

many are deposited simultaneously. Second, germination and establishment depends on flooding. Level flood 

plains, uniformly flooded and densely peppered with 

seeds of saltcedar, later support heavy stands of this 

aggressive plant; adjacent areas that have not been 

flooded do not.

Saltcedar stands are thinnest at the lower end of the 

project area on old terraces that were colonized by the 

plant after San Carlos Lake reached its highest stage

(1941-42). Preflood vegetation, mainly creosote bush, 

was killed by submergence, and saltcedar replaced it as 

the lake water receded. At the present time (1965), the 

saltcedars are short (about 1 to 2 m (3 to 6 ft)) and 

widely spaced, and each is a cluster of small steins, 

most of which are dead. A few new sprouts are produced 

annually, but most die later through drouth pruning. 

Where the water table is deep, these stunted plants 

probably depend wholly on rainfall for moisture and 

are, therefore, xerophytes and not phreatophytes. Once 

established, the plant is capable of growing under a wide 

range of moisture conditions.

The saltcedar is leafless during the winter; branchlets and scale leaves first appear in March or April. 

It is in full leaf by June or July and remains in leaf 

until late fall, when the branchlets, which bear the scale 

leaves, are shed.

Seepweed grows in dense stands toward the outer 

edges of the flood plain occupied by saltcecfar. Until 

recently, most seepweed was in the upper subreach, but 

because of cultivation only small areas of this vegetation 

remain.

Seepweed, a herbaceous perennial with narrow fleshy 

leaves, often grows on saline soil with other halophytes, 

such as pickleweed (Allenrolfea occidentalis (S. Wats.) 

Kuntze). Each plant forms a compact globose clump 1 

to 11/4 m (3 to 4 ft) high. They usually form dense 

stands that change from dark green during tha- summer4 

to brown in winter, when all but the main stems die.

PLAN OF STUDY

The volume of transpiring vegetation has to be 

known to evaluate effects of phreatophyte removal, but, 

because the size of the project area is large, only a 

generalized method of determining the volume can be 

used. The method used is the volume-density method described by Gate wood and others (1950). Data for expressing volume density are derived from three measurements : total area occupied by vegetation, |: ercentage 

of the area actually covered by plant croons, and 

height of plants.

The area occupied by plants can be determined 

readily from aerial photographs. For this purpose black 

and white prints at a scale of about 1:14,000 were used. 

Tentative boundaries of vegetation types (patches with 

uniform appearance) were first drawn on the photographs. All areas were then checked in the field, and 

new boundaries were drawn or old ones were, removed 

where the field check revealed errors (HcHon and 

others, 1964). Dominant plants of each area were then 

listed in order of abundance.

With boundaries established, percentage coverage 

may be determined from the photographs, using a dissecting binocular microscope one ocular of which is
OBJECTIVES, METHODS, AND ENVIRONMENT A21

fitted with a square reticle divided into 100 squares, 

each 1 square millimeter in area. Each square was 

considered to be a plot projected onto the photograph. 

The magnification of the microscope was set on X10 

so that a 1 millimeter square of the reticle circumscribed a 1 cm square on the aerial photograph, and 

the image within the square was enlarged 10 times. 

Each plot thus established is roughly equivalent to 2 

hectares (5 acres) on the ground. Total coverage was 

estimated by sampling one-eighth of the total area.

Coverage of plant crowns in each of the sample plots 

was estimated according to a procedure described by 

Daubenmire (1959), using six broad classes of coverage 

during the plot-by-plot microscopic examination yet 

ultimately arriving at a numerical value for percentage 

coverage.

Average plant height is usually estimated during the 

field reconnaissance. Broad classes of plant height are 

commonly used where great precision is not warranted. 

Thus, for saltcedar, the following three classes were 

used: shorter than 2 m (6 ft), 2 ito 4 m (6 to 13 ft), and 

taller than 4 m (13 ft). The value of 4 m (13 ft) was 

accepted from Gatewood and others (1950) as the maximum foliage depth attained by saltcedar crowns in 

closed canopies. Thus, all saltcedar 4 m (13 ft) or taller 

was assigned a vertical density 2 of 100 percent. Vegetation types falling in the 2- to 4-m (6.5- to 13.0-ft) 

class were assigned a vertical density of 75 percent 

(midway between the upper and lower limits of the 

class); for plants shorter than 2m (6.5 ft) a vertical 

density of 25 percent was used. Vertical density of 

mesqtiite and seepweed is not known and will require 

special study.

PHREATOPHYTE REMOVAL

Clearing vegetation rapidly and completely from the 

reach is a problem of great importance. Parker and 

Martin (1952) have reviewed methods for mesquite 

eradication. Eobinson (1964) described all recent saltcedar-eradication research in eight Western States. The 

most promising methods for eliminating saltcedar and 

mesquite are mechanical clearing and spraying with 

herbicides. Although it is costly and slow, mechanical 

clearing probably can be used except where flooding or 

high water table make the use of heavy equipment 

in feasible.

Herbicides, such as Silvex (2-, 4-, 5-TP), have 

proven effective against saltcedar, but plant kill usually 

is less than 100 percent on flood plains (Kobinson, 1964, 

p. 9). Silvex was applied in mid-May 1964 by helicopter 

at the rate of 4.5 kilograms per hectare (4 pounds per 

acre) on a 16-hectare (40-acre) plot 1.6 kilometers

2 See Gatewood and others (1950, p. 25) for definitions of vertical 

density, aerial density, and volume density.

(1 mile) downstream from section 23. The Silvex killed 

only about 20 percent of the saltcedar, except in lowlying areas where floodwaters rose a few months after 

herbicide application and submerged the root crowns'. 

Here the herbicide was nearly 100 percent effective, 

which encourages its use in lowland areas.

The final selection of a clearing method will depend 

upon criteria such as cost (including preparation of the 

soil for revegetation) and speed (rapid clearing is 

desirable).

REVEGETATION

Removal of phreatophytes from the banks or flood 

plain of a river ordinarily is not practical, regardles? 

of the water used by the plants. Cleared areas will no*, 

remain clear for long because, inevitably, seeds and 

fruits are carried to such favorable habitats, and nev^ 

plants shortly take root. The phreatophytes must be 

replaced by less objectionable vegetation if removal i<* 

to be practical. Replacement vegetation should transpire 

less than the phreatophytes and should supply a valuable product.

Revegetation is being studied by the Watershed 

Management Department of the University of Arizona. 

Two cleared and fenced areas are being used to screen 

seven grass species for use under irrigation and dryland 

conditions. The grasses are being judged by the following criteria: rate of seedling emergence after sowing, 

rate of establishment, forage yields with and without 

irrigation, and ability to withstand reinfestation 07 

phreatophytes. Screening also includes transpiration 

studies.

QUALITY OF WATER 

By R. L. LANET

CHARACTERISTICS

Water quality may be considered in terms of four 

major hydrologic environments: the Gila River; its 

tributaries; alluvium along the river; and the basin-fill 

deposits on which the alluvium lies. Water from each 

environment has identifiable characteristics.

Dissolved-solids content of Gila River water varies 

inversely with discharge less than 500 mg/1 (milligrams per liter) at high flow to more than 4,000 mg/1 at 

low flow. The chemical composition of the river water 

also varies with discharges sodium bicarbonate type at 

high flow and sodium chloride type at low flow. Flow? 

usually are highest in July, August, and September. 

During most of the year, sodium and chloride are tli3 

principal ions.

Major tributary flow, which is a result of localized 

high-intensity rainfall, is a sodium-calcium bicarbonate 

type and contains less than 400 mg/1 dissolved solids.
A22 GILA RIVER PHREATOPHYTE PROJECT, GRAHAM COUNTY, ARIZONA

Water from 56 observation wells that tap the alluvium 

was analyzed. Dissolved-solids content ranges from 

about 1,000 to 20,000 mg/1. Sodium, chloride, and sulf ate are the principal constituents.

Water from 10 wells tapping the basin-fill was analyzed. Dissolved-solids content ranged from 214 to 847 

mg/1 and averaged 411 mg/1. Generally, the water is a 

calcium-sodium bicarbonate type.

PLAN OF STUDY

Water-quality investigations began in June 1964. The 

object was to determine the chemical quality of the 

water and any changes caused by phreatophyte eradication. The study involves: (1) conductivity monitoring 

and periodic sampling of water in the Gila River, (2) 

determination of areal distribution of dissolved solids in 

the water in the alluvium four times a year, and (3) determination of the chemical composition of soil water.

DATA ANALYSIS

Maps that show areal distribution of dissolved solids 

in the water in the alluvium have been prepared based 

on conductivity of water from more than 70 wells. 

These maps will be included in a later report. Conductivity measurements are taken in March, June, September, and December. Dissolved solids are obtained by 

multiplying the conductivity in micromhos by a factor 

that is appropriate for the water tested. This factor was 

previously determined by dividing the analytically determined dissolved solids by conductivity of 56 water 

samples from the alluvium and taking the arithmetic 

mean. The dissolved solids values are grouped into six 

zones of dissolved solids and each zone is assigned a 

number from 1 through 6. The project area has been 

divided by a grid into segments of about 23 acres each. 

A tabulation is then made of the dissolved-solids zone 

for each segment. These data are processed by a computer and compared to other parameters obtained on 

the same grid, such as depth to water and foliage density, height, and species. In addition, a tabulation is 

made of frequency of occurrence of the dissolved-solids 

zones. These data will be used to slhow changes in water 

quality caused by phreatophyte eradication. In an attempt to verify this change, a frequency distribution, 

arithmetic mean, and median is being determined for 

the conductivity data for each sampling period.

Interpretation of data collected thus far indicates that 

the amount, location, frequency, and duration of floodflow are major controls on ground-water quality in the 

Gila River flood plain, and these controls may obscure 

any possible effects of changes in amounts of 

phreatophytes.

Preliminary data regarding chemical composition of 

soil water in the alluvium indicate considerable vertical

and lateral variation in dissolved-solids content. This 

may have a profound effect on the quality of ground 

water, if soil water of high dissolved-solids content contributes to ground-water recharge during a period of 

rising water table. Prolonged flooding by the. Gila River 

apparently flushes the salts from the soil. When the 

flood waters have receded, dissolved-solids content of 

the soil water gradually increases. Soil-wr.ter studies 

may aid in determining the relation between recharge, 

evapotranspiration, and water quality.

SOIL-MOISTURE-ENERGY FACTORS IFFLUENCING EVAPOTRANSPIRATION IN RIPARIAN 

VEGETATION

By R. F. MILLEB and I. S. McQuEEN

Soil-moisture-energy relations under and adjacent to 

selected riparian vegetation in the Gila and San Carlos 

Rivers, are also being studied. These studies are designed to evaluate probable effects of tree removal on 

flood-plain soil moisture. The principal question is: Will 

increased solar energy reaching soil surface^ after tree 

removal cause increased evaporation that will offset 

reduced transpiration ?

Changes in energy gradients that may result from 

increases in solar energy reaching the soil surface after 

tree removal are inferred from differences measured 

under and adjacent to selected trees. Soil-moisture stress 

and soil-temperature gradients are the principal parameters measured at each site. These are supplemented 

by laboratory measurements of chemical and physical 

properties of soil obtained near measuring rites.

Differences in characteristics of use of sc;l moisture 

by saltcedar, cotton wood, willow, mesquite, and adjacent bare ground are being studied. Comparisons of 

soil-moisture stress and temperature gradients are used 

to evaluate differences in forces that move moisture 

either as liquid or vapor (Miller and otKrs, 1961). 

Differences in soluble sodium percentage ard total soluble cations with depth in each soil profile are used to 

define recurring patterns and modes of moisture migration (Miller and Ratzlaff, 1961; 1965).

Experimental devices, designed to monitor changes in 

total soil-moisture stress and soil temperature, are installed under and adjacent to a selected clump of Tamarisk trees. These devices use electrical resistance-type 

vapor pressure sensors to measure soil-moisture stress 

and thermistors to measure soil temperatures. The stress 

sensors are enclosed in individual chambers designed 

to expose them to the soil air but to preclude direct 

contact with soil or soil solutions.3 Periodic sampling

8 The effectiveness of these devices was impaired by prolonged flooding 

of the sites and the devices were destroyed during dredging operations 

in the river channel (McQueen and Miller, 1966).
OBJECTIVES, METHODS, AND ENVIRONMENT A23

yields detailed information on stress gradients. The 

filter-paper method is used for measuring moisture stress 

described by McQueen and Miller (1966) and by Miller 

and others (1961). Specially treated filter paper, which 

acts as a gravimetric moisture-stress sensor is inserted 

into cans containing soil samples. The samples are stored 

in the laboratory at constant temperature to permit 

equilibration of moisture between paper and soil. The 

moisture content of both the sample and the paper is 

then determined gravimetrically. The total stress is 

read from the calibration curve which shows the relation between water content and stress for the filter 

paper.

Some study sites have been relocated since the project 

began, but objectives and methods have not. The saltcedar site on the Gila River has been inundated but 

is still giving useful data under high water-table conditions. The cotton wood, willow, and mesquite sites on 

the San Carlos River have yielded satisfactory field 

data. Laboratory analyses of these soil samples are 

presently (1965) being made.

THE ENERGY BUDGET FOR 

EVAPOTRANSPIRATION MEASUREMENT

By O. E. LiEPPANEN

The heat-energy budget method of measuring evapotranspiration is being applied at locations within the 

project area. The purpose is to estimate evapotranspiration typical of these locations by a method independent 

of the water budget and to compare the water loss in 

each reach as computed by the two methods.

The energy budget is a general method of determining 

evaporation and transpiration. If application to the 

Gila River Phreatophyte Project area proves successful 

it could be applied confidently to similar areas. Furthermore, testing of massrtransfer methods and fly-over 

remote sensing techniques will be facilitated by using 

the energy budget observations as a control.

The theory of the energy-budget method has been 

presented by several authors. A good general description 

of the physical variables which need to be considered 

has been given by Tanner (1960). The measurement of 

these variables in the project area is discussed in the 

following section.

The sun is the source of most of the radiant energy 

used in transpiration from plants and evaporation from 

the soil. Considerable solar energy is also reflected by 

plants and bare surfaces, particularly water surfaces. 

The amount of reflected radiant energy becomes significant when the sun is low in the sky. These surfaces 

become warmer by mid-day and reradiate more heat to 

the atmosphere as infrared radiation. Clouds and gases 

in the air, such as water vapor and carbon dioxide, also

contribute significant amounts of heat to the surface and 

also receive heat from surface radiation.

Instruments called net radiometers measure the new 

flow of radiant energy through a horizontal plane located above the ground surface. These instruments integrate energy flows having wavelengths from the ultraviolet to the far infrared.

At night, transpiration usually decreases and the 

amount of heat stored in the vegetation bulk is small. 

Evaporation from soil may not change radically from 

day to night because the heat stored during the day 

becomes available to the damp soil at night. Water 

bodies store solar energy readily as evidenced by the 

gradual warming of lakes and rivers throughout the 

summer months. Most of this energy becomes available 

for evaporation from the water surface, sometimes at 

a later date or even many months later.

Heat flow into and out of soil can be evaluated in two 

ways. In the first method, heat stored at the end of a 

period is compared with that stored at the beginning. 

Thus, an integration of the heat flows is known if the 

heat capacity of the mass can be computed. The other 

way of determining heat flow is by direct measurement 

of the rate of flow using heat-flow plates and then integrating these measurements over a time period. The 

instruments used in this method are similar to the net 

radiometer that measures net radiant-energy flows. The 

time-rate of flow also may be approximated by temperature measurements made at several depths, which, when 

heat capacity and heat conductivity are known, allow 

computation by the classical methods of Newton and 

Fourier. Heat stored in water masses is generally determined by the change-in-storage method mentioned 

above, that is, by comparing average temperatures and 

water volumes at the beginning and end of a time period.

The vegetation, ground, and water surfaces constitute 

a system that exchanges heat with passing air. During 

the day large amounts of sensible heat are removed from 

the surfaces; this heat results in increased air temperature. Just before and after sunset, some heat may be 

withdrawn from the ambient air and utilized for evapotranspiration; this heat loss causes a noticeable cooling 

of air near isolated stands of vegetation. The measurement of these advected heat flows is, at present, one of the 

less accurate parts of the energy budget. Using recent 

data from the Buckeye Project, Ariz., for saltcedar 

growing in tanks (T. E. A. van Hylckama, written 

commun., 1966), it may be possible to modify the present 

methods of evaluation and improve the measurement 

of the advected heat flows. Because water use can be 

measured for periods as short as two hours, various 

micrometeorological theories may be tested for application over longer periods.
A24 GILA RIVER PHREATOPHYTE PROJECT, GRAHAM COUNTY, ARIZONA

The energy-budget method of measuring evapotranspiration has been tested by several groups of scientists, 

principally in areas covered by agricultural crops. The 

control methods applied to measure actual water use 

by the crops have been of varying accuracy, but most 

tests imply that the energy budget will give results 

accurate to ±20 percent when used on vegetated areas 

similar to those over which tests have been made. In a 

field test over alfalfa, for example, measurements from 

the energy budget and water budget differed by about 

20 percent (Leppanen and Harbeck, 1960). From an 

analysis of unpublished computations by T. E. A. van 

Hylckama from the Buckeye Project, it was decided 

that the energy-budget method could be used over other 

vegetation, particularly tall bushy plant cover such as 

saltcedar. Measured water use in the tanks on the Buckeye Project and the use predicted from the energy 

budget agreed within 18 percent. The energy budget has 

only been used at single, reasonably homogeneous sites.

If it were not for the necessary micrometeorological 

measurements of temperature and water-vapor content 

above tihe surface, simultaneous measurements at many 

sites would not be difficult. Plans are to operate energybudget stations at three different sites for several 

months in order to sample various types of vegetation 

(fig. 10). Both average evapotranspiration during the 

operating period at each site and fluctuations of evapotranspiration within these periods will be related to 

measurements of hemispherical radiation, air temperature, and vapor pressure at a fixed station at Ooolidge 

Dam. This fixed station also is used to determine evaporation from San Carlos Lake by energy-budget 

methods.

Considerable data are involved in energy-budget experiments. Transducers and recording instruments for 

the energy-budget studies allow automatic data processing. Paper tape suitable for electronic data processing 

is punched at the field site so that time lag between field 

observations and a usable evapotranspiration estimate 

will be minimal.

SUMMARY

By B. C. CTJLIJSR

Quantitative evaluation of water conservation by 

phreatophyte control requires that changes in evapotranspiration be measured or estimated. Because components of a hydrologic system are interrelated, a 

change in evapotranspiration, for example, can be expected to alter other parts of the system, such as the 

altitude of the water table. The measurement of evapotranspiration from a flood plain of a major river, before 

and after the application of phreatophyte control, was 

selected as the primary method of evaluating water

FIGURE 10. Energy-budget station in operation at section 19.

conservation by phreatophyte control. A water budget 

is being computed in which evapotranspiration is the 

difference between the water inflow and outflow to a 

reach, adjusted for changes in storage. The energybudget method is being used to measure evapotranspiration from small areas on the flood plain. The results will 

give an independent evaluation of evapotranspiration. 

The project area consists of a 24-kilometer (15-mile) 

reach along the Gila Eiver west of Bylas on the San 

Carlos Apache Indian Eeservation. It includes all of 

the flood plain and extends on to the lower terraces 

along the river. Three contiguous reaches along the flood 

plain are being used for this study. Each reach is about 

8 kilometers (5 miles) long and contains about 800 

hectares (2,000 acres) of phreatophytes. The flood plain 

is densely covered by phreatophytes, mainly saltcedar. 

The terraces are covered by less dense growths of saltcedar and by mesquite. The entire area is underlain by 

basin-fill deposits, which are fine grained and yield 

small amounts of water. Coarse-grained alluvium overlies the basin fill throughout most of the study reach. 

The alluvium forms the principal aquifer, and the 

phreatopliyites obtain most of their water from it.
OBJECTIVES, METHODS, AND ENVIRONMENT A25

The water budget will provide a measure of the 

quantity of water vaporized from water, soil, and 

vegetal surfaces during periods as short as 3 weeks. The 

quantity will be related to type of vegetation, meteorologic conditions, depth to water, and chemical quality 

of the ground water. Only the vegetal surfaces will be 

intentionally changed by phreatophyte control. Preclearing evaluation includes 1963-67, and postclearing 

evaluation will continue through 1972.

Four gaging stations have been installed along the 

Gila Eiver, and 62 stations have been installed on tributaries. Water-level fluctuations are recorded in 72 observation wells spaced in lines of 6 wells, each extending 

across the valley. An access tube for a neutron soilmoisture meter is located adjacent to each observation 

well. Precipitation is measured in rain gages installed 

at both ends of each line of wells.

Many previously developed techniques are being used 

in this study. Innovations are being made in the application of techniques and in methods of computation.

REFERENCES CITED

Blaney, H. F., and Griddle, W. D., 1962, Determining consumptive use and irrigation water requirements: U.S. Dept. 

Agriculture Tech. Bull. 1275, 59 p.

Campbell, O. J., and Dick-Peddle, W. A., 1964, Comparison of 

phreatophyte communities on the Rio Grande in New 

Mexico : Ecology, v. 45, p. 492-502.

Daubenmire, Rexford, 1959, A canopy-coverage method of vegetational analysis: Northwest Sci., v. 33, p. 43-64.

Davidson, E. S., 1961, Facies distribution and hydrology of interniontane basin fill, Safford basin, Arizona, in Short 

papers in the geologic and hydrologic sciences: U.S. Geol. 

Survey Prof. Paper 424-C, p. 151-153.

Dorroh, J. H., Jr., 1946, Certain hydrologic and climatic characteristics of the Southwest: Albuquerque, New Mexico 

Univ. Press, 64 p.

Fenneman, N. M., 1931, Physiography of Western United States: 

New York, McGraw-Hill Book Co., Inc., 534 p.

Gates, D. M., 1965, Heat transfer in plants: Sci. Am., v. 213, 

no. 6, p. 76-84.

Gatewood, J. S., Robinson, T. W., Colby, B. R., Hem, J. D., and 

Halpenny, L. C., 1950, Use of water by bottom-land vegetation in lower Safford Valley, Arizona: U.S. Geol. Survey 

Water-Supply Paper 1103, 210 p.

Hendricks, E. L., Kam, William, and Bowie, J. E., 1960, Progress report on vise of water by riparian vegetation, Cottonwood Wash, Arizona : U.S. Geol. Survey Circular 434, 11 p.

Horton, J. S., Robinson, T. W., and McDonald, H. R., 1964, 

Guide for surveying phreatophyte vegetation: U.S. Dept. 

Agriculture Handb. 266, 37 p.

Leopold, L. B., Wolman, M. G., and Miller, J. P., 1964, Fluvial 

processes in geomorphology: San Francisco, W. H. Freeman and Co., 522 p.

Leppanen, O. E., and Harbeck, G. E., 1960, A test of the energybalance method of measuring evapotranspiration: Internat. 

Assoc. Sci. Hydrology Pub. 53, p. 428-437.

McQueen, I. S., and Miller, R. F., 1966, Calibration and evaluation of a wide-range method for measuring moisture stress 

in field soil samples: UNESCO, Symposium on water in the 

unsaturated zone, Wageningen, Netherlands, June 1966.

Meinzer, O. E., ed., 1942, Hydrology: New York, Dover Publications, Inc., 712 p.

Miller, R. F., Branson, F. A., McQueen, I. S., and Culler, R. C., 

1961, Soil moisture under juniper and pinyon compared 

with moisture under grassland in Arizona, in Short papers 

in the geologic and hydrologic sciences: U.S. Geol. Survey 

Prof. Paper 424-B, p. 233-235.

Miller, R. F., and Ratzlaff, K. W., 1961, Water movement and 

ion distribution in soils, in Short papers in the geologic and 

hydrologic sciences: U.S. Geol. Survey Prof. Paper 424-B, 

p. 45-46.

 1965, Chemistry of soil profile indicates recurring patterns and modes of moisture migration: Soil Sci. Soc. 

America Proc., v. 29, no. 3, p. 263-266.

Parker, K. W., and Martin, S. C.. 1952, The mesquite problem 

on southern Arizona ranges: U.S. Dept. Agriculture Circ. 

908, 70 p.

Robinson, T. W., 1952, Phreatophytes and their relation to water 

in Western United States: Am. Geophys. Union Trans., v. 

33, no. 1, p. 57-61.

 1958, Phreatophytes: U.S. Geol. Survey Water-Supply 

Paper 1423, 84 p.

 1964, Phreatophyte research in the Western States, 

March 1959 to July 1964: U.S. Geol. Survey Circ. 495, 31 p. 

1965, Introduction, spread, and areal extent of saltcedar

(Tamarix) in the Western States: U.S. Geol. Survey Prof. 

Paper 491-A, 12 p.

Sellers, W. D., ed., 1960, Arizona climate: Arizona Univ. Press, 

60 p.

Tanner, C. B., 1960, Energy balance approach to evapotranspiration from crops: Soil Sci. Soc. America Proc., v. 24, 

p. 1-9.

U.S. Department of Agriculture, 1962, Field manual for research 

in agricultural hydrology: U.S. Dept. Agriculture Handb. 

224, 215 p.

U.S. Geological Survey, 1961, Surface water supply of the United 

States, 1960, Part 9, Colorado River basin: U.S. Geol. Survey Water-Supply Paper 1713, 520 p.

[U.S.] Weather Bureau, 1964, Dicennial census of United States 

climate Climatic summary of the United States Supplement for 1951 through 1960, Arizona: U.S. Dept. Commerce, 

Climatography of the United States 86-2, 95 p.

van Hylckama, T. E. A., 1963, Growth, development, and water 

use by saltcedar (Tamarix pentandra) under different con* 

ditions of weather and access to water: Internat Assoc. 

Sci. Hydrology, Pub. 62, p. 75-86.

White, W. N., 1932, A method of estimating ground-water supplies based on discharge by plants and evaporation, from 

soil results of investigations in Escalante Valley, Utah: 

U.S. Geol. Survey Water-Supply Paper 659-A, 105 p.

U.S. GOVERNMENT PRINTING OFFICE : 1970 O - 371-096