Precipitation, Streamflow, 

and Major Floods at Selected 

Sites in the Gila River 

Drainage Basin above 

Coolidge Dam, Arizona

GEOLOGICAL SURVEY PROFESSIONAL PAPER 655-B

Precipitation, Streamflow, 

and Major Floods at Selected 

Sites in the Gila River 

Drainage Basin above 

Coolidge Dam, Arizona

By D. E. BURKHAM

GILA RIVER PHREATOPHYTE PROJECT

GEOLOGICAL SURVEY PROFESSIONAL PAPER 655-B

An analysis of the hydrologic variables and 

relations affecting drainage of the Gila River 

Phreatophyte Project area

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 50 cents (paper cover)
CONTENTS

Abstract- __________-__-_-_--_--__________---_-____

Introduction. ______________________________________

Purpose and scope of this report._________________

Acknowledgments ______________________________

Description of the Gila River basin above Coolidge 

Dam_ _______________________________________

Precipitation.______________________________________

Types of airmasses______________________________

Storm types___________-_---__-____--__________

Variability- ____________________________________

Streamflow. _______________________________________

Seasonal types_________________________________

Basic data.__-_-_--_-__-----_______---_--______

Frequency and variability of daily and seasonal Gila 

River flow through Safford Valley_______----___

Long-term trends. _ __--___-_-___________-___-___

Precipitation-runoff relations.____________________

Page

Bl

1

1

1

1

3

3

3

4

6

6

6

7

10

10

Streamflow Continued Fage

Water loss in Safford Valley___-___-----_-------- IM3

Major floods.______________________________________ 20

Flood of February 22, 1891___________________ 21

Flood of September-October 1895 ______-__---__-_ 21

Flood of October 1896_________________________ 21

Flood of January 1905________________________ 21

Flood of November 28, 1905_____---_-__.___--_ 24

Flood of December 3, 1906_____________________ 24

Floods of December 20, 1914, and January 30, 1915. 25

Floods of January 18-20 and 29, 1916- _ _ _ _______ 25

Flood of October 14-15, 1916_______________ 25

Flood of September 29-October 1, 1941_________ 25

Floods of December 21-24 and December 30-31,

1965. ______________________________ 26

Summary. _________________________________________ 30

References cited-__-__________-___--_-__---_-------- 32

ILLUSTRATIONS

FIGURE 1. Map showing location of precipitation gages and stream-gaging stations________--------_-_---------- B2

2. Graphs showing progressive 10-year average of seasonal precipitation ____________---_____-_-_------ 5

3. Typical hydrograph of winter flow_____________________________________------------------------ 6

4. Typical hydrograph of summer flow_____________-____-_-____- ------------------------------- 6

5-16. Graphs:

5. Duration curves of summer flow ________________-_____-_-_-------_----------------------- 8

6. Duration curves of winter flow.______________________-----___--------------_------------- 9

7. Progressive 10-year average annual flow___----------------_------------------------------- H

8. Relation of winter runoff and average winter precipitation___________-___----______-------- 12

9. Double-mass relation of measured winter runoff versus computed winter runoff __________-_---_ 12

10. Double-mass relations of measured summer runoff versus computed summer runoff.___--___--_- 14

11. Double-mass relation of measured streamflow at head of Safford Valley and that at San Carlos.. 15

12. Progressive 10-year average reduction in annual streamflow-____________-_----__-_-----_---- 16

13. Relation of annual streamflow at head of Safford Valley to that at San Carlos_____--_--------- 17

14. Double-mass relation of computed annual streamflow and measured annual streamflow-________ 18

15. Relation of summer streamflow to size of basin__------------------------------------------ 19

16. Annual floods of record in the Gila River basin_____--_-_----__--_------------------------- 22

17-21. Photographs:

17. Floods at Clifton, 1905-16______________________________._-____-__-____ 24

18. Flood of December 23, 1965, in the Safford Valley 27

19. San Francisco River flood plain at Clifton.___________-____-____--- _-- ---_ ----------- 28

20. Flood of December 21, 1965, at Clifton____-__-_________._-___ __.-___ _-- 29

21. Gila River flood plain in 1935 and flood of December 23, 1965, at Little Hollywood------------ 30

22. Hydrographs showing floodflows_____-_______-_---___-----_---_--_------------------------------- 31

23. Graph showing peak-discharge frequency curves_______________-__-______--_-_-----_--_________-- 31

m
IV CONTENTS

TABLES

Page 

TABLE 1. Precipitation data for six U.S. Weather Bureau stations in or near the Gila River basin above Coolidge Dam_ B4

2. Winter precipitation and runoff during water years 1921-30 and 1951-60.____________________________ 12

3. Mean summer streamflow at gaging stations in or near the Gila River basin, 1938-61------------------ 19

4. Estimated surface-water loss from the Gila River in the Safford Valley_______________________________ 20

5. Storm precipitation in November and December 1965 at five U.S. Weather Bureau stations in or near the

Gila River basin above Coolidge Dam______-______-___--__--__---_------_----_----------_-_-- 26
GILA RIVER PHREATOPHYTE PROJECT

PRECIPITATION, STREAMFLOW, AND MAJOR FLOODS AT SELECTED SITES 

IN THE GILA RIVER DRAINAGE BASIN ABOVE COOLIDGE DAM, ARIZONA

By D. E. BTJRKHAM

ABSTRACT

The Gila River Phreatophyte Project is a water-budget study 

to measure evapotranspiration from a 15-mile reach of the Gila 

River flood plain above Coolidge Dam in southeastern Arizona. 

Its principal purpose is to determine how much the water yield 

of the project area can be increased by replacing deep-rooted 

nonbeneficial woody plants with shallow-rooted beneficial 

grasses. Necessary to the study, and also for the application of 

the findings to other areas, is an understanding of the hydrologic 

variables and relations that affect the quantity of water draining 

toward the project area and of the environmental changes that 

would result from vegetation alteration. This report, which is 

based on available precipitation and runoff data at selected 

sites, is an analysis of those variables and relations.

The major conclusions reached in the study are that there has 

been a fluctuating decline in annual precipitation and an almost 

continual decline in annual runoff since 1920. The decrease in 

precipitation has been mainly during the winter (November 

through April) and has resulted in a lower incidence of major 

floods. For example, major floods occurred in nine winters in 

the period 1891-1916, but only one major flood (December 1965) 

occurred in the period 1917-65. No significant progressive decrease has occurred in the ratio of runoff to a given amount of 

precipitation since 1920, nor has there been a progressive increase in the streamflow losses from the Gila River in Safford 

Valley.

INTRODUCTION

PURPOSE AND SCOPE OF THIS REPORT

This report is the result of studies that were undertaken to describe the hydrologic variables pertinent to 

the Gila River Phreatophyte Project; it summarizes 

and statistically treats the precipitation and streamflow 

data from selected sites in the basin above the project 

lands. Of particular concern is the evidence for, or for a 

lack of, progressive trends in the annual surface-water 

supply to the project lands and in streamflow losses 

within Safford Valley, which is upstream from those 

lands. Also included in the report is a description of the 

major historic floods in the basin.

The main purpose of the Gila River Phreatophyte 

Project is to determine how much the water supply 

would be increased through eradication of the nonbeneficial deep-rooted native vegetation, mostly s^.ltcedar and mesquite, and its replacement with a beneficial 

short-rooted plant such as Bermuda grass (Culler, 1965, 

p. 33-38). Necessary for the determination, and also for 

the application of the findings to other areas, is an 

understanding of the environmental factors that afect 

the quantity of water draining toward the project jrrea 

and of the environmental changes that would result 

from vegetation alteration.

The native vegetation increases both the resistance to 

flow and the stability of the flood-plain boundary. 

Therefore, replacement of the native vegetation is lil-ely 

to affect changes in the rates of erosion and deposition 

and to cause changes in channel width, depth, sinuo^ty, 

gradient, and even location. Concurrently, natural flowregime modifications unrelated to vegetation replacement are likely to cause changes of the same t;rpe, 

although not necessarily in the same direction. So that 

the changes caused by one can be distinguished from 

those caused by the other, it is essential that a basis for 

identifying those resulting from natural flow-regime 

modifications be established. It is the purpose of this 

report to define, as nearly as possible, the natural flow 

regime for the period 1875-1962. The natural flowregime modifications in the channel will be established 

and described in subsequent reports.

ACKNOWLEDGMENTS

This report was prepared under the general supervision of H. M. Babcock, district chief of the Water 

Resources Division of the U.S. Geological Surve;^ in 

Arizona, and is the result of evapotranspiration studies 

for the Gila River Phreatophyte Project, of which P. C. 

Culler is the project chief.

DESCRIPTION OF THE GILA RIVER BASIN ABOVE 

COOLIDGE DAM

An area of 11,500 square miles contributes runoff to 

the 15-mile study reach of the Gila River Phreatophyte

Bl
B2 GILA RIVER PHREATOPHYTE PROJECT

110° 108° 106° 104°

Gila Rive'r ~ 

near. Clifton

Gila River at headx f 

SaffordN Valley, near Solo

'""

EXPLANATION

Gila River Phreatophyte Project 

Drainage divide

U.S. Weather Bureau precipitation gage

A

U.S. Geological Survey stream gaging station, 

except where otherwise indicated

Base from Inter-Agency Committee on Water Resources, 

Subcommittee on Hydrology Prepared under supervision 

of U.S. Weather Bureau 1960

FIGURE 1. Location of precipitation gages and stream-gaging stations.
PRECIPITATION, STREAMFLOW, FLOODS, GILA RIVER DRAINAGE BASIN, ARIZONA

Project. The drainage basin ranges in altitude from 

2,500 to 11,000 feet above mean sea level and extends 

eastward from the San Carlos Reservoir into the mountains of New Mexico (fig. 1). Topographically, it is 

typical of most of the basins in the Basin and Range 

physiographic province (Fenneman, 1931); the main 

valley along the Gila River is wide and flat and the 

mountain ranges are narrow and rugged.

Climatically, the Gila River basin is in the Sonoran 

Border zone (Thomas, 1962, p. 13). A wide range characterizes the temperature and the average annual precipitation. The temperature extremes recorded at 

Safford, which is 2,900 feet above mean sea level, are 

7° and 114°F, and at Alpine, which is 8,000 feet above 

mean sea level, the extremes are 29° and 92°F 

(Sellers, 1960). The average annual precipitation ranges 

from about 8 inches in parts of the San Simon basin to 

more than 40 inches in the mountainous areas; the 

average for the entire Gila River basin above Coolidge 

Dam is about 14 inches.

Although the mountainous areas are mostly forested 

and the flood plains support a dense cover of phreatophytes, the remainder of the basin is only sparsely vegetated. In the Gila River Phreatophyte Project area, 

saltceder (Taniarix pentandra, Pall.) is the dominant 

plant near the banks of the main channel, and mesquite 

(Prosopis jidiflora var. velutine "Woot." Sarg.) is the 

dominant plant along the flood-plain margin. Much of 

the basin is used for grazing, and many small dams have 

been built. Most of the detention and retention dams 

were constructed for sediment and erosion control.

About 108 square miles (69,000 acres) of valley land 

is under cultivation (Barr, 1954, p. 14-17), and the 

principal crops are cotton and alfalfa. Part of the water 

for irrigation is diverted from the Gila River at several 

places, and the remainder is obtained from wells. At the 

present time (1966), there are no large surface reservoirs or any water diversions into or out of the Gila 

River basin above the San Carlos Reservoir.

PRECIPITATION 

TYPES OF AIEMASSES

The climate of the Gila River basin is the result of 

five main types of airmasses. These have been identified 

by Thornthwaite, Sharpe, and Dosch (1942, p. 4) as: 

(1) cool moist Polar Pacific from the northern Pacific 

Ocean, (2) warm moist Tropical Pacific from the southern Pacific Ocean, (3) warm moist Tropical Gulf from 

the Gulf of Mexico, (4) cold dry Polar Continental 

from Canada, and (5) hot dry Tropical Continental 

from Mexico. The amount of moisture and the weather 

in general at any given time or place is influenced in

many ways by these ail-masses, but some types of movement are predominant in certain areas and seasons.

In the Gila River basin, Polar Pacific and Polar Continental airmasses account for most of the moisture in 

winter, November through April, whereas the Tropical 

Continental type predominates in the spring, May ard 

June, and the Tropical Gulf type predominates in the 

summer, July through October. Tropical Pacific airmasses move over the basin frequently and occasionally 

bring large amounts of precipitation. These airmasses 

are generated as a result of low-pressure areas between 

Hawaii and southern California, and they move eastward across the southwestern part of the United States, 

usually in late summer or early winter (Thomas, 1'9"62, 

p. 9).

Striking deviations of the weather from average conditions occur when a particular type of airmass brings 

large amounts of moisture to the basin more or less frequently than is usual. For instance, the crossing of eight 

Tropical Pacific storms over the Gila basin in early 

1941 resulted in one of the wettest winters of record; 

in late 1965 the crossing of six or more Tropical Pacific 

airmasses over the area in rapid succession also resulted 

in large amounts of precipitation.

STORM TYPES

Two distinct types of storms characterize the seasonal 

pattern of precipitation on the Gila River basin above 

Coolidge Dam. Summer storms are mainly of the local 

convective type, and storms in the rest of the year are 

generally of the convergence, or frontal, type. The tr^o 

storm types result from different circumstances or 

"populations" of synoptic regimes.

The local convective storm, most commonly called a 

thunderstorm, is characterized by rainfall of high intensity and short duration in a small area. Dorroh (1946, 

p. 5) stated: "Although rainfall may occur at many locations on a given day, there is little conformity in 

either rates or amounts that may occur at two different 

places, since very localized atmospheric conditions are 

the predominating factors involved." Because heating 

of the air near the ground is the main cause of convective action, thunderstorm occurrences decrease in ccld 

weather.

The convergence, or frontal, storm is an atmospheric 

disturbance of a general nature and commonly distributes much moisture over a large area. A convergerce 

storm may occur when airmasses of dissimilar charr^- 

teristics meet or override one another or when warm fir 

converges toward a center and is forced upward 

(Dorroh, 1946, p. 6).

Although thunderstorms occur mainly in the summer and frontal storms occur primarily in the spring
B4 GILA RIVER PHREATOPHYTE PROJECT

and winter, thunderstorm activity accompanies some 

frontal storms. When widespread low-intensity rainfall 

from frontal storms is accompanied by local highintensity rainfall from convective storms, large volumes 

of runoff may be the result.

VARIABILITY

Precipitation on the Gila River drainage basin 

above the project lands differs greatly in amount from 

place to place within any given season or year and at 

any particular location both seasonally and annually. 

Such variability is generally characteristic of the precipitation pattern in large inland areas having marked 

topographic relief and an arid climate. A large mass of 

precipitation data has been collected in the area by the 

U.S. Weather Bureau (issued annually), and it is the 

purpose of this section to summarize these data statistically and to determine whether any long-term 

trends in precipitation amounts can be identified.

Statistical analyses were made from records from the 

following Weather Bureau stations: Alpine, Bowie, and 

Clifton in Arizona and Fort Bayard, Lordsburg, and 

Reserve Ranger Station in New Mexico (fig. 1). These 

particular stations were chosen for their length of 

record and geographic location, and the amount and 

pattern of precipitation at each are assumed to be 

typical of similarly located sites within the drainage 

area above the project lands. Bowie, Clifton, and Lordsburg are in topographically low parts of the drainage 

area, and the other three are in mountainous areas.

In analyzing the frequency distribution of precipitation amounts at these six stations, the following statistics were computed for winter, spring, summer, and 

annual precipitation at each station and for the entire 

drainage area: the mean, the standard deviation, and 

the coefficient of variation. The results are presented in 

table 1.

The means for the individual stations indicate the 

amounts that would have been received seasorally and 

annually at those particular sites if the seasonal and 

annual totals for the period of record had been evenly 

distributed with time; the means for the entire drainage 

area indicate the amounts that would have been received 

seasonally and annually at any site if the seasonal and 

annual totals for the six stations had been evenly distributed areally. As means can be distorted greatly by 

extreme values, they may not be wholly typical, and 

their usefulness for predicting quantities of p^ecipitation to be expected in future periods of time is limited. 

They are useful, however, for making comparisons of 

amounts of precipitation in different seasons at the same 

site and the amounts received seasonally and annually 

at the different stations. The mean annual precipitation 

at the individual stations ranged from 9.64 to 20.48 

inches, and for all stations was 13.TT inches. Of this last 

amount, 36 percent occurred in winter, 7 percent in 

spring, and 57 percent in summer. The mean precipitation for all seasons is typically greater in the m ountains 

than in the valleys.

The standard deviation is sometimes referred to as 

the root-mean-square deviation because it is th?, square 

root of the mean of the squares of the individual deviations. It is of limited value when used in a nonnornial 

frequency distribution such as precipitation because 

the larger deviations are overemphasized in the process 

of squaring the deviations. Its value is limited further 

because, for example, a standard deviation of 1 inch of 

precipitation in a humid climate would have very little 

meaning, but in an arid region it may be highly significant. The standard deviation for the precipitation at the 

individual stations ranged from 2.02 to 2.90 inches in 

the winter, 2.06 to 3.72 inches in the summer, and 0.44 to 

0.89 inch in the spring. The standard deviation for annual precipitation at the individual stations ranged 

from 3.37 to 4.83 inches.

TABLE 1. Precipitation data for six U.S. Weather Bureau stations in or near the Gila River basin above Coolidge Dam

Station

Arizona:

Clifton.. ........

New Mexico: 

Fort Bayard. ....

Reserve Banger 

Station.. _ .

Altitude 

(feet 

above 

mean 

sea 

level)

8,000 

3,756 

3,465

6,152 

4,245

5,832

Period 

of 

record

1912-1965 

1899-1965 

1893-1965

1867-1962 

1881-1962

1917-1962

Mean (inches)

Winter

7.42 

3.82 

4.83

4.59 

3.49

5.64

4.96

uo

uCO

1.44 

.46 

.73

1.12 

.57

1.09

0.90

S

S

a &

11.61 

5.86 

7.15

9.62 

5.58

7.65

7.91

 a 

| 3

20.48 

10.14 

12.71

15.33

9.64

14.37

13.77

Standard deviation 

(inches)

Winter

2.50 

2.02 

2.90

2.68 

2.09

2.15

1

0.86 

.44

.71

.89 

.60

.79

S

CO

2.91 

2.06

2.27

3.72 

2.49

2.14

j

4.13 

3.43 

3.90

4.83 

3.49

3.37

Coefficient of variation

fe

« 

5

0.34 

.53 

.60

.58 

.59

.38

j? 

P.

CO

0.60

.98 

.96

.80 

1.05

.73

f-l 

<L>

1

0.25 

.35 

.32

.39 

.45

.28

!

0.20 

.34 

.31

.31 

.36

.23

Extremes (inches)

Winter

 AS

14.24 

10.01 

20.70

17.03 

11.19

12.22

II

3.03 

.35 

1.25

.57 

.20

2.25

Spring

c3 3

§a

3.77 

1.94 

2.60

3.74 

2.25

3.24

 a|

sa

0.10 

0 

0

0 

0

0

Summer

11§a

20.00 

11.37 

13.99

17.17 

12.77

12.20

= 1

sa

6.31 

1.44 

1.98

3.13

.99

3.63

Annual

II

33.48 

17.71 

26.71

30.64

19.78

25.56

II

sa

12.02 

3.07 

6.18

4.89 

3.96

8.54
PRECIPITATION, STREAMFLOW, FLOODS, GILA RIVER DRAINAGE BASIN, ARIZONA P5

The coefficient of variation is the ratio of the standard deviation to the mean. It is a more useful statistic 

than the standard deviation because it is a relative 

rather than an absolute statistic. The surprising fact is 

that the coefficient of variation for winter precipitation 

for all stations is larger than that for summer. This is 

probably due to the Tropical Pacific storms, which occasionally produce large amounts of precipitation in 

the Southwest, as they did in 1941. The coefficient of 

variation of winter precipitation is larger than that of 

summer precipitation, but this is true only in a temporal sense. According to McDonald (1956, p. 64), the 

spatial variability of summer precipitation is greater 

than that of winter precipitation.

McDonald (1956, p. 9) stated that the circulation 

factors governing the relative amounts of cyclonic winter precipitation in Arizona are more variable from

year to year than the large-scale factors governing the 

arrival of summer moisture and its precipitation. However, all Arizona shows a tendency to be concurrently 

either generally wet or dry in the winter but shows no 

such tendency in the summer.

Graphs of the 10-year progressive average precipitation at the six stations are shown in figure 2. These 

for summer precipitation show short periods of relatively low and relatively high precipitation but no 

long-term trends in either direction. For example, the 

10-year average summer precipitation trended downward during the decade ending in 1956 and then trended 

upward through 1962. On the other hand, winter precipitation trended generally downward from 1920 

through 1962. The reason for the downward trend in 

winter precipitation is not known, but, according to 

McDonald (1956, p. 24), the general circulation of the

RESERVE RANGER STATION, 

N. MEX.

16 

14 

12 

10 

8 

6 

4 

2 

n

\

 -

/x

.A

\ .

A.J

X-<

/ ^

Wi

rv^

/^ ^^

iter

Spring

^

Annual

V

Sum

X7

V

^s~

mer

'

^

V.

16

PRECIPITATION, INNCHES

Dl\>.^OiOOOI\>£

/

/

-^

A

/v

\-

\

Xv

v\

BOV

^-

Si

' Wir

Spr

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An

<=*Mi

mme

^^v

ter

ing

RIZ.

nual

^r

;r

 w

^*\

V A^

^

Y"

 -'

^ CLIFTON, ARIZ.

Summer

nnual

nter

y

V

FIGURE 2. Progressive 10-year average of seasonal precipitation at six stations in or near the Gila River basin. Each 10-year

average is plotted above the year that ends the decade. 

36S-750 O 70 2
B6 GILA RIVER PHREATOPHYTE PROJECT

airmasses has, in some way, been responsible for the 

fluctuating decline in winter precipitation. As the 

amount of precipitation in the spring is very small, 

trends in spring precipitation have only minor hydrologic significance.

STREAMFLOW

SEASONAL TYPES

Streamflow is classified as winter flow and as summer flow. Winter flow is the result of precipitation that 

falls from November through April, and summer flow 

is the result of precipitation that falls from July 

through October. The small amounts of precipitation in 

May and June seldom, if ever, result in any direct 

runoff.

Winter flow is mainly from frontal storms, snowmelt, 

or outflow from ground-water storage and often is a 

combination of the three. The flow rate may be fairly 

constant for several days (fig. 3). The causes of major 

winter floods are widespread heavy rainfall of long 

duration, warm weather after a large snow accumulation, or widespread rainfall on snow.

Local thunderstorms are the main source of summer 

streamflow. Individual summer thunderstorms characteristically produce high unit rates and volumes of flow 

from small watersheds, but only rarely do they produce 

high rates or volumes of flow from large watersheds. 

The crest of a flood from a thunderstorm is typically 

very sharp near the source of the surface flow but may 

become rounded or flattened downstream because of 

the regulating effects of the conveyance system. Sometimes, when the runoff from a thunderstorm enters a 

dry stretch of channel, the flood crest disappears completely because all the flow sinks into the underlying 

alluvium. The summer flow of the Gila River through 

the Gila River Phreatophyte Project area is the composite runoff that results from thunderstorms at several 

localities. A typical hydrograph shows that the flow 

varies greatly in a short period of time (fig. 4).

During the last part of September and in October, 

occasional frontal activity causes precipitation that produces widespread runoff. The combined runoff from

4000 

O 

CD Q

O O 3000

2 LU

LU QL 2000

O LU

a: Q. 

< , F, LU 1000

«£

Q

EXPLANATION -

X

Discharge measurement

APRIL, 1958 MAY, 1958

FIGURE 3. Winter flow, Gila River at Calva.

general rains and concurrent local thunderstorrrs often 

results in the major flows of the summer season.

BASIC DATA

Streamflow records from seven U.S. Geological Survey gaging stations in the Arizona part of the Gila River 

basin were used in this study. Listed in a downstream 

order, the stations are (1) Gila River near Clifton, 

(2) San Francisco River at Clifton, (3) Gila Biver at 

head of Safford Valley, near Solomon, (4) San Simon 

River near Solomon, (5) Gila River at Calva, (6) San 

Carlos River near Peridot, and (7) Gila River at San 

Carlos(fig.l).

The drainage area of 4,010 square miles above the 

gage on the Gila River near Clifton is about 50 percent 

mountainous terrain. The 43-year (1911-17 and 1927- 

64) surface-water yield was 32.9 acre-feet per square 

mile per year (U.S. Geological Survey). At the present 

time (1966), surface water is diverted for the irrigation 

of about 14,300 acres above the station.

The drainage area of 2,766 square miles above the 

gage on the San Francisco River at Clifton is mostly 

mountainous. The 40-year (1913-15,1916-17, and 1927- 

64) surface-water yield for the period of record was 47.1 

acre-feet per square mile per year. Most of the, major 

floods of the Gila River at San Carlos originate in the 

mountains near Clifton. At the present time (1966), 

surface water is diverted for mining, municipal use, 

and the irrigation of about 2,700 acres above the station.

The flow at the Gila River at head of Safford Valley 

gaging station is essentially the sum of the flows past 

the San Francisco River at Clifton and the Gila River 

near Clifton gaging stations. Discharge from Eagle 

Creek and other small tributaries contributes to the flow. 

Eagle Creek and the other small tributaries have drainage basins that total about 1,120 square miles.

4000

cc.

a! 3000

2000

1000

500 I I 1 I I I_____LJ_____I_____I I I I I

AUGUST 18, 1957

FIGURE 4. Summer flow, Gila River at Calva.
PRECIPITATION, STREAMFLOW, FLOODS, GILA RIVER DRAINAGE BASIN, ARIZONA B7

The drainage area of the 2,192-square-mile San Simon 

basin is mostly nonmountainous terrain. The surface 

flow from the San Simon basin is partly regulated by 

conservation reservoirs. The 30-year (1931-32,1935-64) 

surface-water yield was 5 acre-feet per square mile per 

year (U.S. Geological Survey). At the present time 

(1966), about 13,800 acres of the basin is under irrigation. Most of the water for irrigation is obtained from 

wells.

The gaging station on the Gila River at Calva is in 

the Gila River Phreatophyte Project area; the basin 

above the station is described in the "Introduction." The 

35-year (1929-64) surface-water yield was 15.2 acrefeet per square mile per year (U.S. Geological Survey).

The drainage area of the 1,027-square-mile basin upstream from the gage on the San Carlos River near 

Peridot is mostly mountainous. The 35-year (1929-64) 

surface-water yield was 31.4 acre-feet per square mile 

per year. At the present time (1966), about 600 acres is 

under irrigation above the station.

The data for the Gila River at San Carlos were recorded at the station "Gila River at" or "near" San 

Carlos prior to the completion of Coolidge Dam in 1927; 

subsequent to 1927 the record is the composite data from 

two stations, Gila River near Calva and San Carlos 

River near Peridot. Ungaged tributaries having a composite area of 389 square miles exist between the two 

systems of gaging stations. In this report, the sum of 

the seasonal or annual flow in the Gila River at Calva 

plus the seasonal or annual flow in the San Carlos River 

near Peridot are assumed to be equivalent to the seasonal 

or annual flow in the Gila River at San Carlos. In describing the sum of flows in the two rivers, the phrase 

"flow in the Gila River at San Carlos" is used unless 

otherwise noted.

FREQUENCY AND VARIABILITY OP DAILY AND 

SEASONAL GILA RIVER PLOW THROUGH SAFFORD 

VALLEY

The following discussion is based on data from two 

gaging stations Gila River at head of Safford Valley 

and Gila River at Calva. The record at Calva was used 

because an analysis of the frequency of occurrence of 

seasonal flow was available from a study of errors in 

streamflow data (Burkham and Dawdy, 1970). The 

data for the Gila River at head of Safford Valley were 

used because the station has the longest continuous 

record of any station in the Gila River basin. The "head 

of Safford Valley" gage is about 55 miles upstream from 

the Gila River Phreatophyte Project. The variability 

and range in flows at the two stations are typical of 

mainstem flows.

The average summer flow for 1914-64 past the head of

Safford Valley gage was about 97,300 acre-feet, or 32 

percent of the annual average discharge. The extremes 

in summer flow were about 15,700 acre-feet in 1956 r,nd 

345,000 acre-feet in 1916; the standard deviation was 

71,300 acre-feet, and the coefficient of variation was 

0.71. The lowest average summer discharge for 10 years 

(1943-53) was about 44,800 acre-feet, and the highest 

(1914-24) was 164,000 acre-feet.

The characteristics of summer flow are summarized 

by flow-duration curves (fig. 5), which show the frequency distribution of the average daily flow past the 

"head of Safford Valley" gage and the "at Calva" gage 

for 1930-40 and 1951-61. The two periods represent 

wet and dry periods, respectively. The steep slopes 

of the duration curves, which denote a large variability 

in flow past, the Calva gage, are characteristic of the 

ephemeral streams of the Southwest. The median flow 

flow that, is equaled or exceeded about 50 percent of the 

time past the Calva gage was 45 cfs (cubic feet per 

second) for 1930-40 but only 5 cfs for 1951-61. The 

median flow at the head of Safford Valley was 175 cfs 

and 95 cfs for the wet and dry periods, respectively. 

The flow that was equaled or exceeded about 10 percent 

of the time had about the same frequency of occurrence 

during the two periods.

The average winter flow at the head of Safford Valley 

gage for 1914-64 was about 210,000 acre-feet, or 68 percent of the average annual discharge. The least winter 

flow was about 19,600 acre-feet in 1959, and the greatest 

was about 1,180,000 acre-feet in 1916; the standard deviation was 220,000 acre-feet, and the coefficient of variation was 1.04. The highest average winter discharge 

for 10 years (1914-24) was about 377,000 acre-feet, and 

the lowest (1949-59) was about 105,000 acre-feet 

about a 270 percent difference in 10-year averages.

The characteristics of winter flow are summarized by 

flow-duration curves (fig. 6), which show the frequency 

distribution of the average daily flow past the head of 

Safford Valley gage and the Calva gage for 1930-40 and 

1951-61. The median flow past the Calva gage was 120 

cfs for 1930-40 and 25 cfs for 1951-61; at the head of 

Safford Valley the median flow was 120 cfs and 80 cfs 

for the same time periods.

The average annual flow for 1914-64 past the Had 

of Safford Valley gage was about 316,000 acre-feet. 

The low of 49,100 acre-feet (1956) is about 15.6 percent 

of average, and the high of about 1,600,000 acre-feet 

(1915) is about 510 percent of average. The average 

flow was exceeded only four times in the 22-year period 

1942-64 and six times in the 31-year period 1938-64. 

The standard deviation of the annual flow for the 50- 

year period 1914-64 is 250,000 acre-feet, and the coefficient of variation is 0.79. The wide range in annual flow
B8 GILA RIVER PHREATOPHYTE PROJECT

10,000

1000

100

10

1.0

EXPLANATION

Summer flow, 1930-40, 

Gila River at Calva

Summer flow, 1951-61, 

Gila River at Calva

Summer flow, 1930-40, 

Gila River at head of Safford Valley

Summer flow, 1951-61, 

Gila River at head of Safford Valley

PERCENTAGE OF TIME FLOW IS EQUALED OR EXCEEDED

FIGURE 5. Duration curves of summer flow, Gila River at head of SafEord Valley, near Solomon, Ariz., and

Gila River at Calva, Ariz.
PRECIPITATION, STREAMFLOW, FLOODS, GILA RIVER DRAINAGE BASIN, ARIZONA B9

10,000

1000

100

10

1.0

I I I I I I I 1 I I I

EXPLANATION

Winter flow, 1930-40, 

Gila River at Calva

Winter flow, 1951-61, 

Gila River at Calva

Winter flow, 1930-40, 

Gila River at head of Safford Valley

Winter flow, 1951-61, 

Gila River at head of Safford Valley

I I I I I I I 1

I-H CM do *t ir> 10 i-v oo en en en 

PERCENTAGE OF TIME FLOW IS EQUALED OR EXCEEDED

FIGURE 6. Duration curves of winter flow, Gila River at head of Safford Valley, near Solomon, Ariz., and

Gila River at Oalva, Ariz.
BIO GILA RIVER PHREATOPHYTE PROJECT

and the high coefficient of variation are considered normal for the station during this period.

The coefficients of variation of runoff are higher than 

the coefficients of variation of precipitation because runoff represents the rather small difference between the 

highly variable precipitation and a somewhat independent and highly variable evapotranspiration. Significantly, the coefficients of variation for both precipitation 

and runoff in winter are greater than those for precipitation and runoff in summer. Moreover, the range 

between high and low average flows is greater for winter 

than for summer. Thus, although thunderstorms produce short-duration small-volume flashfloods in an 

erratic fashion, the probability of the average seasonal 

flow occurring in any given year is greater in the summer than in the winter.

LONG-TERM TRENDS

A fluctuating decline in runoff for 1920-62 (fig. 7) 

has paralleled the general downward trend in winter 

precipitation. In order to illustrate the trend satisfactorily, the period of record for the Gila River at San 

Carlos was extended by using estimates of flow made 

by the U.S. Army Corps of Engineers (written 

commun., 1945) and Olmstead (1919, p. 19). The 

1945 estimates of the Corps of Engineers are based on 

measured discharge at upstream points and (or) precipitation-runoff relations. The discharge data used in 

the relations are for different upstream sites and different time periods. No streamflow data are available for 

any upstream sites prior to 1905, and only a few continuous discharge records are available prior to 1915.

The Corps of Engineers (written commun., 1945) 

made a comparison of gaged flows for 1914-40 at the 

Coolidge damsite with computed flows for the same 

period from their runoff-rainfall relations. The mean 

of the computed summer discharge was 10.4 percent less 

than the mean of measured flow, and the mean of the 

estimated winter discharge was 1.2 percent less. The 

maximum difference between the gaged annual flow and 

the estimated annual flow for a single season was 192 

percent of the measured flow.

The discharge estimates made by Olmstead (1919) 

are lower than those made later by the Corps of Engineers (written commun., 1945). Although the basis of 

Olmstead's (1919) estimate is unknown, it is significant 

that both estimates indicate greater flow prior to 1920 

than since.

PRECIPITATION-RUNOFF RELATIONS

Studies were made to determine if the decline in 

annual runoff since 1920 was caused by a reduction in

the ratio of runoff to precipitation. So that large changes 

in long-term trends could be identified, double-mass 

techniques and simple statistical methods were a oplied. 

The data from the six precipitation stations p.nd the 

discharge data from the Gila River at head of Safford 

Valley were used in the double-mass relations.

Ordinarily, if a series of wet years is followed by a 

series of dry years (or vice versa), a significant change 

will be indicated in the long-term relation of runoff to 

precipitation. However, because the runoff-precipitation 

relation generally is curvilinear, direct comparisons of 

runoff to precipitation in a double-mass relatior can be 

misleading. In order to eliminate the effects of the curvilinear relation, the method of Oltman and Traoy 

(1951, p. 20-21) was used in this study of seasonal runoff to seasonal precipitation. Summarized briefly, the 

method is: (1) prepare a curve showing the average relation between seasonal streamflow and the corresponding average seasonal precipitation, and (2) study the 

consistency of the synthetic or computed runoff from 

the curve and the measured runoff by use of the doublemass relation.

The relation of winter runoff at Gila River at head 

of Safford Valley to the average winter precipitation 

at the six stations for 1916-62 is shown in figure 8. The 

line through the plotted points yields the relation: winter runoff=0.013 (measured winter precipitation) 2- 1. 

The index of correlation is 0.96, determined graphically, and the standard error of estimate is 0.10 log 

unit. The double-mass relation of computed rmoff to 

measured runoff is shown in figure 9; no change or 

trend toward reduced winter runoff for the same precipitation for 1920-62 is apparent.

In order to place some confidence limits on the reality 

of no apparent change in the relation of runoff to precipitation, two simple statistical tests the ^ariance 

ratio or F test and the two-sided Student's t test 

were applied to the streamflow data obtained at the 

head of Safford Valley. The streamflow data for two 

10-year periods (1920-30 and 1950-60) in which the 

precipitation means and deviations from the means were 

about the same (table 2) were used in the tests. The null 

hypothesis is that the two samples are from the same 

population.

The two-sided Student's t test shows that thn runoff 

means for the two periods are not significantly different 

at the 5-percent or 1-percent levels. The variance ratio 

test was applied to check the homogeneity of the variances, and the difference between the variances was not 

significant at the 5-percent level.

The results of the tests indicate that any cl ange or 

trend, if one occurred, toward reduced winte" runoff 

for 1920-62 for the same amount of precipitatior was too
PRECIPITATION, STREAMFLOW, FLOODS, GILA RIVER DRAINAGE BASIN, ARIZONA 111

EXPLANATION

Streamflow estimated

Streamflow partly estimated

Streamflow gaged

I I I I I I II I I I I I I I I II I I I I

Estimate by U.S. Army Corps cf

Engineers (written commun., 1945)

Estimate by Olmstead (1919)

1915 1925 1935 1945

GILA RIVER AT HEAD OF SAFFORD VALLEY

1955 1965

800

600

400

200

1895 1905 1915 1925 1935 

GILA RIVER AT SAN CARLOS

1945 1955 1965

FIGURE 7.- Progressive 10-year average annual flow, Gila River at head of Safford Valley, near Solomon, Ariz., and Gila Ri^er 

at San Carlos, Ariz. Prior to completion of Coolidge Dam in 1927, the Gila River flow at San Carlos was measured at one 

station "Gila River at San Carlos." Subsequent to 1927, the record is the composite from two stations, Gila River near Calva and 

San Carlos River near Peridot. Each 10-year average is plotted above the year that ends the decade.
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WINTER RUNOFF, IN INCHES

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PRECIPITATION, STREAMFLOW, FLOODS, GILA RIVER DRAINAGE BASIN, ARIZONA P13

small to be identified by the methods used. A more detailed approach than that used in this study would be 

necessary in order to demonstrate that a small change 

occurred.

The double-mass relation of computed summer runoff to measured summer runoff is shown in figure 10. 

The computed summer runoff of figure 10 is from the 

relation: computed summer runoff=0.00052 (measured 

summer precipitation) 2 - 8. Several changes or trends, as 

defined in the double-mass relation of runoff to precipitation, are indicated. The correlation between summer 

precipitation and summer runoff is poor the index of 

correlation is 0.73, and the standard error of estimate 

is 0.30 log unit and the changes or trends in figure 10 

may not be real. Instead, they may be due to poor definition of the true relation between runoff and precipitation. After 1935, however, the changes apparently correspond in time to changes in the relation of runoff to 

precipitation observed in a similar analysis made for 

the Cornfield Wash area in northwestern New Mexico 

about 70 miles west of Santa Fe (Burkham, 1966). 

Changes in the runoff-precipitation ratio in the Cornfield Wash area were attributed to changes in intensity 

of summer precipitation. An unusually large number of 

frontal storms having low-intensity precipitation, which 

occasionally move through the Southwest during September and October, may have caused the decrease in 

the ratio of runoff to precipitation.

In summary, this study suggests that no continuous 

decline in the ratio of runoff to precipitation for 1916- 

62 occurred in the Gila River basin above the head of 

Safford Valley. Relatively short periods having a reduced ratio of runoff to precipitation have occurred in 

the summer, which may be due to a change or shift in 

the predominance of a storm pattern for example, a 

change from thunderstorms, which have typically high 

rates of precipitation, to frontal storms, which have 

typically low rates of precipitation.

Although no changes or trends in the ratio of runoff 

to precipitation are indicated, some may have occurred. 

A more detailed approach than that used in this study 

would be necessary to identify them.

WATER LOSS IN SAFFORD VALLEY

The decrease in streamflow at San Carlos since 1920 

may be due to an increase in the use of surface water 

for irrigation in the Gila River basin. Comparative 

analyses of the amounts of surface water lost annually 

in the Safford Valley have been made to determine if 

progressively larger amounts of water were consumptively used during the period 1920-64. The native vegetation and cultivated crops and the farming methods 

used in Safford Valley are somewhat similar to those of

368-750 0 70 3

upstream valleys; therefore, the streamflow losses in 

Safford Valley should be indicative of the streamf ow 

losses in upstream valleys. In the Safford Valley, 

streamflow losses are due to direct evaporation from the 

water surface and seepage into the alluvium underlying 

the valley. Water diverted for irrigation is lost by direct 

evaporation, seepage, or is returned to the river as surface flow.

Water from the Gila River has been used for irrigation in the Safford Valley since about 1865; by 1£20, 

about 32,500 acres was under cultivation (Cushman p,nd 

Halpenny, 1955), but there has been relatively Ihtle 

change in irrigated acreage in the last 45 years. The irrigable area is limited by natural conditions, and the 

area irrigated with surface water is limited effectively 

by the Gila River decree of 1935 (Thomas and others, 

1963, p. 29). The small amount of added acreage has 

been mainly along the flood plain, where the native 

vegetation has been replaced by cultivated crops. Although the amount of irrigated acreage has not increased appreciably, increased use of the cultivated l*\nd 

in the last 45 years may require more surface water for 

irrigation.

The amount of surface-water depletion in the Safford 

Valley in any year depends on several factors timeliness of rainstorms during irrigation seasons, type of 

crops grown, and the depth to ground water, ^he 

changes in the use of ground water by flood-plain vegetation may cause changes in the amount of surfrcewater loss.

Apparently no depletion difference between Gila 

River flow at head of Safford Valley and at San Carles 

in streamflow occurred in the Gila River in the Safford 

Valley through about 1920. This would mean that the input from different sources such as tributary streams, 

ground-water discharge into the river channel, and 

precipitation on the river surface equaled or exceeded 

the losses. With the exception of 1941, however, a trend 

toward slightly greater annual depletion occurred from 

1920 through 1964 (fig. 11).

Average trends with time in surface-water depletion 

within the Safford Valley were analyzed using the difference between surface-water inflow to the valley and 

surface-water outflow. Figure 12 indicates that the 10- 

year progressive average annual reduction in streamf ow 

ranged from about 10,000 to 60,000 acre-feet in the Gila 

River within the Safford Valley.

In the Safford Valley, the studies of trends in depletion of surface flow indicate that the years of least depletion correspond to the wet periods of record, and, inversely, that the years of greatest depletion correspond 

to the years of least flow. This implies either more use of 

surface water during dry years, or a curvilinear effect
B14

ii

GILA RIVER PHREATOPHYTE PROJECT

10

 5rI 4 

O

z

O 

Z 3

D 

CC

I960,

1955

1950

1945

-1940

CUMULATIVE 

01234

MEASURED SUMMER RUNOFF, IN INCHES

(AFTER BURKHAM.1966, fig. 20)

34567 

CUMULATIVE MEASURED SUMMER RUNOFF, IN INCHES

10

FIGURE 10. Double-mass relations of measured summer runoff versus computed summer runoff, Gila River at head of Safford 

Valley, near Solomon, Ariz., and Rio Puerco at Rio Puerco, N. Mex. Computed summer runoff of Gila River at head of Safford 

Valley 0.00052 (measured summer precipitation) 2- 8 ; computed summer runoff of Rio Puerco at Rio Puerco=0.0038 

(measured summer precipitation).2
CUMULATIVE ANNUAL STREAMFLOW, IN MILLIONS OF ACRE-FEET, GILA RIVER AT HEAD OF SAFFO

> (Jl

< u^
B16 GILA RIVER PHREATOPHYTE PROJECT

60,000

10,000

1920 1930 1940 1950 1960 1970

FIGUEE 12. Progressive 10-year average reduction in annual streamflow, Gila River at head of Safford Valley, near Solomon, 

Ariz., and Gila River at San Oarlos, Ariz. Bach 10-year average is plotted at the year that ends the decade.

from the precipitation-runoff relation of water yields 

from tributaries, or, perhaps, both. Tributary inflow 

generally adds appreciable amounts of water to the Gila 

River during wet years and almost none during dry 

years. The relation of surface-water loss, by seepage and 

evaporation, to rate of surface flow in the Gila River is 

probably curvilinear.

An attempt was made to eliminate possible curvilinear 

effects of the relation of streamflow losses to the rate of 

river flow by using the method previously described in 

the section "Precipitation-runoff relations." The average relation between annual streamflow at head of Safford Valley and that at San Carlos (fig. 13) is given 

by the equation: streamflow at San Carlos=0.037 

(measured flow at head of Safford Valley) 1-24 . Figure 

14 is a double-mass comparison of the computed annual 

streamflow and the measured annual streamflow for 

Gila River at San Carlos. As streamflow records were 

not available for Gila River at San Carlos for 1928-29, 

the flow of 1930 was added to that of 1927 in order to 

complete the graph. The double-mass comparison of 

annual computed streamflow with gaged streamflow 

for Gila River at San Carlos indicates a fairly consistent 

relation since 1914.

Independent studies of the curvilinear effects for 

summer and winter flows were made for the gaging stations at head of Safford Valley and at San Carlos. The 

results of the studies indicate no continuous inconsistency in the relation of streamflow at the head of Safford 

Valley to that at San Carlos.

In order to place some confidence in the reality of no 

apparent change in the relation of inflow to outflow, a 

two-sided Student's t test and an F, or variance ratio, 

test were applied, respectively, to the means ard variances of the annual depletion, or difference between the 

flows of the Gila River where it enters and where it 

leaves the Safford Valley. The streamflow data for periods 1920-30 and 1950-60, which were used for the confidence test of no apparent change in the runoff-precipitation relation, also were used in these tests. The 

mean precipitation was about the same for the two 

periods. The null hypothesis was made that the two 

samples were from the same population. The means of 

the annual difference between the Gila River inflow to 

and outflow from Safford Valley were about 51,200 and 

51,000 acre-feet, respectively, for 1920-30 and 1950-60. 

The streamflow means for the two periods were not significantly different at the 1 percent level, as shown 

by the two-sided Student's t test, and the difference between the variances was not significant at the 5-percent 

level, as shown by the variance ratio test.

As indicated previously (p. B13), the difference 

in the amount of surface flow entering and leaT7ing the 

Safford Valley by the Gila River does not represent 

the total loss of surface flow within the valley; direct 

precipitation on the water surface and tributary inflow
PRECIPITATION, STREAMFLOW, FLOODS, GILA RIVER DRAINAGE BASIN, ARIZONA

add to the river flow. A simple budget can be used to 

evaluate the total loss of surface water within the 

Safford Valley. As applied to the valley, the budget 

stated in equation form is:

or

in which

QIO+Qir+P= Qoa+E± QIS 

E±QIS=Q,a+QiT+P-QoG

QJG inflow of the Gila Eiver,

Q,IT = inflow of tributaries to the valley,

P = precipitation on all water surfaces within

the valley,

QOG outflow of the Gila Eiver, 

E = direct evaporation from all water surfaces

within the valley, and

QIS net interchange between surface and subsurface water.

The long-term average loss of surface flow, E ± Qi&, 

is evaluated for 1938-61 because more information on 

tributary flow was available in that period than in any

other period of comparable length. The Gila Eiver 

inflow to the Safford Valley is that gaged at the head 

of Safford Valley, and the Gila River outflow is that 

gaged at Calva. The precipitation that falls on the 

water surface is a small item in the budget and is estimated to be 350 acre-feet annually for 1938-61. The 

inflow from 2,192 square miles of the total 3,584 

square miles drained by tributaries to Safford Valley 

is measured at the gaging station on San Simon Eiver 

near Solomon.

An estimate of the ungaged flow from the remaining 

1,392 square miles drained by tributaries was made by 

using the simple relation of measured flow to the size 

of the contributing area at 16 gaging stations within 

or near the Gila Eiver basin above Coolidge Dam (table 

3 and fig. 15). As the ungaged inflow to the Safford 

Valley probably occurs mainly in the summer, the f ow 

during that season is used in the correlation of runoff 

to size of contributing basin. The index of correlation 

for the relation is 0.89 (determined graphically), and 

the standard error of estimate is 0.37 log unit.

2,000,000

1,000,000

100,000

30,000

EXPLANATION

 58 

Streamflow for 1958 water year

10,000 100,000 

STREAMFLOW, IN ACRE-FEET, GILA RIVER AT SAN CARLOS

1,000,000 2,000,000

FIGURE 13. Relation of annual streamflow at Gila River at head of Safford Valley, near Solomon, Ariz., and at Gila River at San

Oarlos, Ariz., 1915-64.
B18

14

13

12

fc 11

GILA RIVER PHREATOPHYTE PROJECT

10

CO

z 

o 

li 9

1960-

1950.

1930

1915

3456789 10 11 

CUMULATIVE COMPUTED ANNUAL STREAMFLOW, IN MILLIONS OF ACRE-FEET

12 13 14

FIGUBE 14. Double-mass relation of computed annual streamflow and measured annual streamflow, Gila River at San Oarlos. 

Ariz. Streamflow records not available for 1928-29. Computed streamflow=0.037 (measured flow at head of Saflford Valley) 1+24.
PRECIPITATION, STREAMFLOW, FLOODS, GILA RIVER DRAINAGE BASIN, ARIZONA B19

100,000 I I I I I II I

10,000

,11

3* +6

LU 1000 

cc

,12

EXPLANATION

 12

Baging-station number 

referred to in table 3

100

10 I III i | I I I I I I I 111 I I I I I I I

0.1 10 100 

DRAINAGE AREA, IN SQUARE MILES

1000 10,000

FIGURE 15. Relation of sammer streamflow to size of basin for watersheds in southeastern Arizona, 1938-61. 

TABLE 3. Mean summer streamflow at gaging stations in or near the Gila River basin, 1938-61

Plot No.

(see 

fig. 15)

Gaging station

Location

Lat (N.) Long (W.) Section, township, and range

Land-surface

altitude 

- (feet above 

mean sea 

level)

Drainage

area

(sq mi)

Mean

summer

streamfl.w

(acre-f,)

1 Gila River below Blue Creek, near Virden, 

N. Mex.

2 Gila River near Clifton, Ariz................

3 San Francisco River near Glen wood, N. 

Mex.

4 San Francisco River at Clifton, Ariz._______

5 Gila River at head of Safford Valley, near 

Solomon, Ariz.

6 San Simon River near Solomon, Ariz_

7 San Carlos River near Peridot, Ariz_.__..

8 San Pedro River at Charleston, Ariz _______

9 Santa Cruz River near Nogales, Ariz..-- _..

10 Sonoita Creek near Patagonia, Ariz...._....

11 Santa Cruz River at Tucson, Ariz_..____ ___

12 Sabino Creek near Tucson, Ariz_ ________

13 Rillito Creek near Tucson, Ariz_ ____________

14 ARS WI near Safford, Ariz_.._..___._.___._.

15 ARS WTI near Safford, Ariz.................

16 ARS WIV near Safford, Ariz........_.__.___

32°38'55';

32°57'50' 1 

33°15'05"

33°02'50" 

32°52'10"

32°48'06"

33°19'20"

31°37'40"

31°20'40"

31°30'00"

32°13'15"

32°19'00"

32°17'40"

32°50'

32°50'

32°40'

108°50'45"

109°18'15" 

108°52'40"

109°17'50" 

109°30'40"

109°38'19"

110°26'50"

110°10'30"

110°51'05"

110°49'00"

110°58'50"

110°48'35"

110°59'05"

109°30'

110°00'

109°40'

. 18, T. 19 S., R. 19W..

. 30, T. 58., R. 30 E.. 

. 23, T. 12 S., R. 20 W.

. 31, T. 48., R. 30 E. 

.31, T. 68., R.28E_.

. 25, T. 7 S., R. 26 E._____._.

. 30, T. 1 S., R. 19 E. (unsurveyed). 

sec. 11, T. 21 S., R. 21 E........

NWH sec. 18, T. 24 S., R. 15 E. (unsurveyed) . 

sec. 21, T. 22 S., R. 15 E__..._.__ 

c. 14, T. 14 S., R. 13 E_____ _

sec. 9, T. 13 S., R. 15 E..........

M sec. 14, T. 13 S., R. 13 E.....____

T. 7 S., R. 28 E.. ___________________________

T. 78., R. 28 E._..._._._._._._.__._________

T. 9 S., R. 27 E.._.._________-.-_-_____-___.

3,875

3,339

4,552

3,431

3,065

2,960

2,583

3,954

3,702

3,818

2,323

2,720

2,284

3,100

3,100

3,100

3,203

4,010

1,653

2,766

7,896

2,192

1,027

1,219

533

209

2,222

35.5

918

.81

1.07

1.13

31, 739

32,184 

11, 78

27, £ 22 

68,250

10, P30

32,124 

10,2?7 

3, 1"" 

13,. 27 

1,526 

3,647 

16.2 

21.3 

14.7
B20 GILA RIVER PHREATOPHYTE PROJECT

The results of the budget study for 1938-61 (table 

4) indicate that the total annual input to Safford Valley was about 257,000 acre-feet and that the average 

annual outflow at Calva was about 145,000 acre-feet. 

Therefore, the average annual loss of surface water 

within the valley was about 112,000 acre-feet, or about 

2,040 acre-feet per mile per year for the 55-mile length 

of the valley.

The mean annual losses for 5-year periods beginning 

in 1938 also were computed (table 4). They increased 

from about 85,600 acre-feet for 1938-43 to about 124,000 

acre-feet for 1958-63; the difference of 38,400 acre-feet 

was 34 percent of the average annual loss for 1938-61. 

If losses are computed on an annual instead of a 5-year 

basis, the range expressed in percent of the average for 

1938-61 is even greater.

An average annual water loss of about, 1,360 acre-feet 

per mile occurred in a 5.7-mile-long reach, from near 

Bylas gaging station to the at. Calva gaging station (fig. 

1), of the Gila River Phreatophyte Project for 1963-65; 

in 1963,2,110 acre-feet per mile; in 1964,1,270 acre-feet 

per mile; and in 1965, 680 acre-feet per mile. The loss 

is the difference between the sum of the Gila River 

flow plus tributary flow minus outflow from the Gila 

River.

The streamflow-depletion studies within the Safford 

Valley do not indicate any major increase in the annual 

quantity of surface water retained within the Safford 

Valley for 1920-62, although the year-to-year variation 

is relatively large. The curvilinear relation of precipitation to runoff from tributaries and (or) the curvilinear relation of streamflow rates to losses resulted in an 

apparent increase in the amount of surface water used 

in the valley during the years of low surface flow. When 

the streamflow data are adjusted for the effects of the 

curvilinear relations, the inconsistency in the doublemass relation of inflow to outflow is not apparent.

In summary, because surface flow in the Gila River is 

depleted by evaporation and seepage, it can be assumed 

that the net effects of factors that control evaporation

and seepage have not changed in magnitude enough that 

the change in surface-water use, if any, could be identified by the methods used in this report. A. more elaborate 

study of the factors that control evaporation and seepage will be necessary to identify small changes, if any, 

since 1920 in the rate of surface water used or lost in 

the Safford Valley.

MAJOR FLOODS

Catastrophic floods exert tremendous forces on objects in their paths. Often, these forces are of such magnitude that the debris and vegetation on the flood plain 

are flushed downstream, and the stream channel is 

altered extensively. All the recorded major flood^1 on the 

Gila River occurred in the period late September 

through February (fig. 16). The principal causes were 

(1) widespread heavy rainfall of long duration, (2) 

warm weather after a large snow accumulation, or (3) 

widespread rainfall on snow. The following hirtory of 

flooding provides a background for channel-change 

studies underway as part of the Gila River F^reatophyte Project.

Authoritative information on Gila River floods prior 

to 1905 is scarce. Although there are historical references to floods in 1833,1862,1869,1880,1884,18£9,1891, 

1895, and 1896, the discharge of none of thes3 floods 

was measured. Most reports on the earlier major floods 

are newspaper accounts, and the magnitudes of the 

floods and extent of flood damage differ with the reporter. According to Davis (in Lippincott, 1900, p. 35), 

the flood of 1891 near Florence (75 miles downstream 

from Coolidge Dam) probably was the greatest in 25 

or 30 years, and, according to Smith and Heckler (1955, 

p. 61), the flood of 1905 at the same site exceeded that 

of 1891. Thus, the relative magnitudes of the floods 

from 1861 through 1905 are approximated for the site 

near Florence. In this report the description of major 

floods begins with that in 1891, the first- for which any 

quantitative data are available.

TABLE 4. Estimated surface-water loss from the Gila River in the Safford Valley 

[Values are annual means, in acre-feet, for specified periods]

Period

1938-61......

1928-33... ____.....

1933-38..__. .......

1938-43... ..........

1943-48............

1948-53.. ..__.......

1953-58. ............

1958-63. .........

Q/o= surface inflow, 

Oila River

335,800

244,040

352,300

144 Rfin

234 128

214 966

263,402

Q/r= tributary inflow

San Simon 

River

11,240

10,672 

8,018 

7,802 

18,774 

7,868

Ungaged 

tributaries

14,390 

i 49, 500 

127,000 

16,500 

11,300 

14,000 

14,600 

10,000

on water surface

350 

315

274 

262 

206 

158 

242 

250

Total input

257, 100 

385,615 

271, 314 

379, 734 

164,084 

256,088 

248,582 

281, 520

Qoo= surf ace 

outflow, Gila 

River at Calva

145,043 

272,825 

176,780 

294,144 

75,450 

145, 902 

137,234 

157,478

E+ Qis =evaporation+net 

interchange between surface 

and subsurface water = 

Qio+QiT+P-Qoo

112,057 

112, 790 

94,534 

85,590 

88,634 

110,186 

111,348 

124,042

i Includes estimates of flow in the San Simon River.
PRECIPITATION, STREAMFLOW, FLOODS, GILA RIVER DRAINAGE BASIN, ARIZONA B21

FLOOD OF FEBRUARY 22, 1891

The flood of February 22, 1891, probably was the 

result of widespread rainfall on snow. No gaging stations were in operation at the time, but the magnitude 

of the flood can be estimated from information furnished 

by A. T. Colton, "a competent engineer" (Lippincott, 

1900, p. 36), for a site about 15 miles upstream from 

Florence. Da vis (in Lippincott, 1900, p. 34-35) described the 1891 flood thusly:

The best evidence thus far obtained regarding past freshets on 

this river was kindly furnished by Mr. Albert T. Colton. The 

greatest rise so far recorded on the Gila River occurred on the 

22d of February, 1891. Considerable evidence was obtained 

that no such flood has occurred since a date many years before 

the advent of the white man. Irrigating ditches supposed to be 

extremely old were overflowed and destroyed. Lands were overflowed that had retained no evidence of any previous inundation.

On June 12, 1892, about sixteen months after this flood, 

Mr. Colton found marks of high water on both banks of the river 

far above any of the ordinary freshets, which he attributed to 

the great flood. This point was about 3*4 miles below the head 

of the Florence canal, or approximately 6 miles below the Buttes. 

With his level he took a cross section of the river at this point 

and measured the slope of the channel. The cross section he 

obtained was 6,600 square feet. The slope measured was 10.56 

feet per mile. The channel was sandy and free of brush or large 

boulders or other obstructions for a distance of 300 feet above 

and 300 feet below the cross section. This information, meager 

as it is, is the best we have upon which to estimate the discharge 

of the river at that time.

The difficulty in obtaining correct results of this discharge 

lies in the uncertainty of the retarding effect of the channel upon 

the flow of the water. This retarding effect in a rough river bed 

is very great. Assuming this quantity as small as it could possibly be, a computation of the discharge was made, using Kutter's 

formula. The factor of roughness designated in the formula as 

"n" was taken as 0.025. Not that this was considered the correct 

factor, as it is almost certainly too small, but by assuming the 

smallest possible value of "n" we obtain the largest discharge, 

and it is the largest discharge that should be provided for in 

the construction of a spillway. It is thought, therefore, that 

this computation will give conservative results, and that a 

spillway based upon the discharge obtained would be safe. The 

result obtained was 102,566 cubic feet per second.

Although Colton's indirect discharge measurement 

would not meet present-day requirements for a good 

indirect measurement, it certainly is of the right order 

of magnitude. The "conservative" results based on the 

n of 0.025 may not be conservative at all, as recent 

studies have shown that the n for a sand channel may be 

as low as 0.010. Furthermore, the use of the channel 

slope instead of the energy gradient for determining 

discharge may not have introduced a great error; some 

researchers (Dawdy, 1961, p. 4) of the hydraulics of 

sand-channel streams have assumed the energy-gradient 

slope to be equal to the channel slope. The most undesirable part of Colton's estimate is that he used only 

one cross section in his measurement.

How closely the estimate of 102,566 cfs for the 

Florence site approximates the peak discharge past rpstream points is not known. Olmstead (1919, p. 64- 5) 

presented evidence that the peak discharge of the Gila 

Eiver below its confluence with the San Francisco River 

was substantially greater. He stated that the peak discharge of the San Francisco at Clifton, although not 

measured, was the second highest of record and that the 

first and third largest flows recorded at that site pror 

to 1919 were 143,450 cfs and 107,870 cfs, respectively. 

Moreover, according to Patterson and Somers (19-3, 

p. 394), the flow of the Gila River a short distance upstream from the confluence may have exceeded 28,000 

cfs.

FLOOD OF SEPTEMBER-OCTOBER 1895

The flood during the week of September 27 to Oc*ober 4, 1895, was the restilt of 4 days of continual rain 

and caused considerable damage near Safford and 

Solomon. According to the Graham County Guardian 

(Oct. 3, 1895), the Gila River was nearly half a irile 

wide. A large part of Solomon was flooded by the £an 

Simon River, but, although flooding was severe at 

Safford and Solomon, it probably was not of a magnitude to cause widespread damage. The precipitation 

data available, although meager, do not indicate widespread flooding.

FLOOD OF OCTOBER 1896

Another locally destructive flood similar to that of 

October 1895 occurred near Safford and Solomon during the week of October 9-16,1896. It was a result of 3 

days of continual rain (Graham County Guardian, 

Oct. 18,1896), and Solomon again was flooded by water 

from the San Simon River.

FLOOD OF JANUARY 19O5

The flood of January 10-11, 1905, caused extensive 

damage because it was the first major flood after a rr^atively long period of economic development on the flood 

plain. It was the direct result of two general rains. The 

first, early in December 1904, was continuous for 4 days 

at Solomon. It undoubtedly left the watershed in a 

thoroughly wetted condition and also left a cover of 

snow in the higher parts of the basin. The second rain 

was in January 1905. It lasted for 2 days and produced 

more than 3 inches of precipitation at Safford (Graham 

County Guardian, Jan. 13, 1905). Flooding of the 

San Francisco River not only caused severe damage but 

cost the lives of three persons at Clifton; flooding of 

the Gila resulted in severe damage at Dimcan, Solomon, 

and Safford. The damage along the entire reach of the 

Gila River in Arizona probably exceeded $1,000,000 

(Graham County Guardian, Jan. 21,1905).
PEAK DISCHARGE, IN THOUSANDS OF CUBIC FEET PER SECOND

PEAK DISCHARGE, IN THOUSANDS OF CUB

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Aug. 6 

Aug. 3 

Feb. 21 

Aug. 22 

Aug. 21 

Aug. 10 

Dec. 28 

Sept. 4 

Apr. 6 

Feb. 17 

Aug. 28

July 29 

Aug. 11 

Feb. 12 

Sept. 9 

Aug. 28 

July 31 

Sept. 11 

Feb. 9 

Mar. 5 

Aug. 7 

Oct. 9 

Jan. 2 

Oct. 1 

Sept. 28 

Sept. 27 

Aug. 3 

Oct. 10 

Aug. 24 

Aug. 7 

Jan. 15 

July 30 

Aug. 4 

Jan. 20 

July 30 

Mar. 25 

Aug. 4 

Oct. 5 

Sept. 1 

Mar. 26 

Aug. 26 

Jan. 14 

Aug. 23 

Sept. 29 

Oct. 20 

Sept. 26 

Aug. 14 

Dec. 24

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Sept. 12 

July 15 

Sept. 23 

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Feb. 10 

July 23 

Aug. 26 

Sept. 1 

Feb. 17 

Feb. 8 

Mar. 4 

Apr. 6 

Sept. 6 

Dec. 31 

Dec. 11 

Mar. 5 

Sept. 26 

Aug. 22 

Sept. 5 

Aug. 23 

June 1 

Jan. 13 

July 27 

Aug. 29 

Jan. 19 

Aug. 18 

Aug. 7 

July 23 

Oct. 4 

July 26 

Sept. 12 

Aug. 28 

Jan. 12 

Sept. 10 

Sept. 26 

Oct. 18 

July 31 

Aug. 2 

Dec. 22

Ja
PEAK DISCHARGE, IN

THOUSANDS OF 

CUBIC FEET PER SECOND

PEAK DISCHARGE, IN THOUSANDS OF 

CUBIC FEET PER SECOND

PEAK DISCHARGE, IN THOUSANDS OF 

CUBIC FEET PER SECOND

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July 25 

Mar. 11 

Sept. 22 

Aug. 6 

Dec. 20 

Jan. 18 

Oct. 15

July 

July 

Aug. 

Sept 

July 

Sept 

Aug 

Aug Aug 

Feb. 

Aug 

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Oct. Sepl 

Aug Sep 

Aug 

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Jan 

July 

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Feb. 17 

Feb. 7 Mar. 4 

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Mar. 14

Dec. 12 Sept. 26 

Sept. 27 Aug. 9 

July 27 

Aug. 8 Aug. 2 

Jan. 9 

July 21 

Aug. 29 

Jan. 13 

Aug. 27 

Mar. 23 

Aug. 6 Jan. 29 

July 26 

Mar. 22 

Aug. 18 

Dec. 26 

July 22 

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PEAK DISCHARGE, IN

THOUSANDS OF CUBIC

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July 16 

Aug. 

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Sept. 10 

Aug. 21 

July 12 

Aug. 14 Sept. 5 

Aug. 17 

Sept. 11 Aug. 15 

Sept. 25 

Aug. 10 

Aug. 30 

June 18 

Aug. 6 

Aug. 8 

Sept. 18 

Aug. 2 

Aug. 17 

July 7 

Sept. 12 

July 30 

Oct. 4 

Aug. 30 Aug. 16 Aug. 23 

Sept. 9 

Aug. 22 

Sept. 26 

Aug. 26 

July 14 

Aug. 29 

Sept. 15

w
B24 GILA RIVER PHREATOPHYTE PROJECT

In addition to the flood in January, there were high 

flows in February, March, and April (Olmstead, 1919, 

p. 19). The gaging station on the Gila Kiver at San 

Carlos, which was washed away in January and was reestablished in February, was washed away again in 

March.

FLOOD OF NOVEMBER 28, 1905

Three different weather disturbances during November 1905 and the previous exceptionally high winter 

and spring precipitation resulted in a flood on the 28th 

of that month (Graham County Guardian, December 1, 

1905). The precipitation of the previous spring and 

winter had left the soil in much of the basin nearly 

saturated. The first of the disturbances in November 

was a spell of low-intensity precipitation, most of which 

was absorbed by the soil. Then a storm from November 21-23 provided additional soil moisture and a 

moderately heavy snow cover. Another storm, November 25-28, resulted in heavy rain that evidently melted 

much of the snow. Because the soil was already

saturated, this rain and the snowmelt resulted in a high 

rate of overland runoff.

Overflow from the San Francisco River flooded part 

of Clifton (fig. 17). Although damage along the Gila 

River was considerable, it was less than in the preceding 

spring because the floods earlier in the year had widened 

and deepened the river channel and thus facilitated the 

discharge of later floodwater. The estimated peak discharge of the Gila River at San Carlos was 150,000 

cfs (Smith and Heckler, 1955, p. 61) and near Florence 

was 190,000 cfs (Corps of Engineers, 1914, p. 84).

FLOOD OF DECEMBER 3, 1906

Factors contributing to the flood of December 3,1906, 

were soil moisture carried over from the previous year, 

additional soil moisture resulting from two moderate 

storms during the preceding month, and runoff from 

precipitation that began on December 1. According 

to the Corps of Engineers (written commun., 1945), 

two different storms were the immediate cause of the

A C

B D

FIGURE 17. Floods at Olifton, 1905-16. A, Railroad station after flood of November 28, 1905. B, Flood of December 3, 1906; looking 

downstream toward railroad bridge. C, Flood of January 19, 1916; looking downstream toward railroad bridge. D, Houses and 

debris lodged against railroad bridge after flood of December 3,1916. Photographs furnished by Risdon Studios, Clifton.
PRECIPITATION, STREAMFLOW, FLOODS, GILA RIVER DRAINAGE BASIN, ARIZONA B25

flood-producing runoff. The first, which moved in from 

the Pacific Ocean, left snow on the mountains, and the 

second, which moved in from Mexico, resulted in warm 

rain. Although the precipitation was widespread, 

severe flooding was confined to the upper part of the 

basin.

The peak discharge of the San Francisco River at 

Clifton was estimated by Olmstead (1919, p. 64) to 

have been 143,540 cfs, and it may have been the largest 

known flood at that location. Contributing to that peak 

was water that rushed down Chase Creek when a dam 

at Morenci failed. Several houses in Clifton were 

washed away, and soil was removed from many acres of 

farmland in that vicinity (fig. 17). The peak discharge 

probably decreased downstream, but no estimates of the 

flow at downstream points have been published.

FLOODS OF DECEMBER 20, 1914, AND JANUARY 30,

1915

After 8 years without a significant flood, the Gila 

River overflowed twice within a period of 6 weeks. The 

first of these floods occurred on December 20,1914, and 

was caused by a storm that originated over the Pacific 

Ocean; moderate amounts of rain fell on a large area, 

and high-intensity rains fell locally (Corps of Engineers, written commun., 1945). The second, on January 30, 1915, probably was the result of rapidly 

melting snow.

The peak flow during the December flood was 50,000 

cfs at the head of Safford Valley and 42,000 cfs downstream at San Carlos. The January flood had a peak 

flow of 48,000 cfs at the head of Safford Valley.

FLOODS OF JANUARY 18-2O AND 29, 1916

A combination of climatological events set the stage 

for the floods that occurred January 18-20 and 29, 

1916. The first of these was a heavy snowfall on most 

of the basin in early December 1915. The snow at the 

lower altitudes soon melted, but a thick snow cover 

remained on the mountains when light rains fell on 

January 10-12. Evidently most of the rain was added 

to the moisture content of the snow, as runoff from the 

additional precipitation was negligible. Two storms, 

both originating over the Pacific Ocean, were the immediate causes of the two floods. The first, January 15- 

21, began with a warm rain that was followed by snow, 

and it was the warm rain, together with the earlier

snow it melted, that caused the flooding on January 20. 

The second storm, January 25-30, was less severe and 

consisted mostly of warm rain that melted much of the 

remaining snow cover. The flood of January 29 resulted 

from the combined rain and snowmelt.

The earlier flood was the greater. The San Francisco 

River had a peak discharge of 90,000 cfs at Clifton (fig. 

17), and the Gila River had peaks of 100,000 cfs and 

130,000 cfs at the head of Safford Valley and at San 

Carlos, respectively. On January 29 the peak discharge 

of the Gila River at the head of Safford Valley was a 

measured 28,000 cfs and at San Carlos was estimated 

by Smith and Heckler (1955, p. 61) to have been 30,000 

cfs. These floods may have been the most costly up to 

that time, owing to greater economic development of the 

flood plain. They were especially destructive in the lower 

Gila River basin.

FLOOD OF OCTOBER 14-15, 1916

The flood of October 14-15,1916, was the direct result 

of rainfall from a storm that originated in the Gulf of 

Mexico. The storm passed over the Gila River basin on 

October 8-15 (Corps of Engineers, written commun., 

1945) and produced an average of 5.10 inches of precipitation in the San Francisco drainage basin above Clifton. According to Olmstead (1919, p. 64), the storm 

caused the highest flows known to that time in the upper 

San Francisco River and Tularosa River.

The storm caused the San Francisco River to have an 

estimated peak flow of 107,870 cfs at Clifton (Olmstead, 

1919, p. 64) and the Gila River to have recorded peak 

flows of 19,500 cfs near Clifton, 67,900 cfs at the head 

of Safford Valley, and 74,000 cfs at San Carlos. The 

large reduction in peak flow as the flood moved from 

Clifton to San Carlos indicates that the volume of the 

flood was relatively small.

FLOOD OF SEPTEMBER 29-OCTOBER 1, 1941

The only significant flood occurring in the period 

1917-64 was that on the Gila River in late September 

1941. During the preceding several months, precipitation was much more abundant than usual so the moisture 

content of the soil was high. Then a storm originating 

in the Gulf of Mexico resulted in heavy rain on the upper 

part of the area drained by the Gila River above its 

confluence with the San Francisco River. Considerable 

damage was done to farmland in the Virden and Duncan Valleys. At Virden, the bridge over the Gila was
B26 GILA RIVER PHREATOPHYTE PROJECT

washed out, and at Duncan the business and residential 

sections and the approaches to the bridge over the Gila 

were inundated.

Downstream, at the gaging station at the Gila River 

near Clifton, the peak discharge was 28,200 cfs on September 29 and, according to Patterson and Somers (1966, 

p. 394), may have been the highest at that site since 

1891. Farther downstream, at the head of Safford Valley 

and at San Carlos, the peak discharges were 31,900 cfs 

on September 31 and 27,900 cfs on October 1, respectively both less than one-third the peak discharge of 

the recorded maximum flood at those sites. The peak 

discharge of the San Francisco River at Clifton during 

this flood was only 7,300 cfs.

FLOODS OF DECEMBER 21-24 AND DECEMBER 30-31,

1965

A succession of storms beginning in late November 

1965 contributed to the flooding that occurred December 21-24 and December 29-31 of the same year. (See 

table 5.) Those of November 22-27, December 8-12, and 

December 13-18 thoroughly soaked the lowland soils 

and left a large accumulation of snow on the mountains. 

Then on December 21-23 warm rain fell at altitudes of 

as much as 9,000 feet and caused rapid melting of part 

of the snow cover; the resulting runoff caused the earlier 

of the two December floods. Within a week another 

warm rain caused additional melting of the snow and 

more flooding. All the precipitation associated with 

these two floods was the result of Tropical storms that 

originated over the Pacific Ocean and moved eastward 

across Arizona. Warm rain at such high altitudes and 

so abundant a moisture supply were highly unusual for 

the time of year.

TABLE 5. Storm precipitation in November and December 1965 

at five U.S. Weather Bureau stations in or near the Gila River 

basin above Coolidge Dam

Station

Precipitation (inches)

Nov. Dec. Dec. Dec. Dec. Total 

22-27 8-12 13-18 21-24 29-31

Arizona: 

Alpine ______------._

Clifton... ............

New Mexico: 

Fort Bayard. _._.. 

Lordsburg __..__. 

Reserve Ranger Station.

Avg_______ ......

1.55 

.90

0.11

3.00

1.93

1.50

0.93

2.15

1.39 

.35

5.91

7.90

.56 1.87 .16 .90 .24 3.73

.20 1.40 1.65 .70 .44 4.39

.69 2.64 1.50 .95 .97 6.75

0.78 1.80 1.35 1.13 0.68 5.74

Flood-plain developments since the flood of October 

1916 contributed to the high cost and nature of the flood

damage. Most of the fertile flood plain, stripped of 

natural vegetation, had been transformed into irrigated 

cropland through construction of diversion dams, 

canals, and headgates and by building dikes to protect 

the cropland from floods. Meanwhile, the river channel 

and the part of the flood plain not developed for irrigation had become congested with a heavy growth of 

saltcedar. Not only was the size of the main river channel reduced, but the resistance to flow of water on the 

flood plain was increased greatly. The reduction in size 

of channel and the increased resistance to flow of water 

resulted in a relatively low conveyance capacity for the 

river. Thus, when the floodwave moved downstream, 

the conveyance capacity of the channel and bordering 

undeveloped flood plain was soon exceeded, the dikes 

broke, and water flowed onto the cultivated fields (fig. 

18). As most of the fields had raised borders, they filled 

until the border either broke or was overtopped at some 

point, and then the temporarily stored water spilled 

onto the adjoining lower lying field. Several fields were 

left with large channels through them, and many of the 

irrigation canals were breached. During the recession of 

the first flood, and also during the second flood, the rate 

of discharge in some of the fields was greater than in 

the adjoining river channel. Most of the roads on the 

flood plain were under water, and several were breached. 

The approaches to the bridges over the Gila River at 

Solomon, Safford, and Pima were overtopped and closed 

to traffic for several hours (fig. 18).

The estimated damage to farm real estate in Greenlee 

County was $465,000 (Greenlee County Agriculture 

Disaster Committee, written commun., January 14, 

1966), and in Graham County it was $1,260,000 (Joint 

Graham County and Cities Civil Defense, written commun., January 14, 1966).

The flood damage in cities and small communities in 

the Gila River basin was relatively small. In the north 

part of Clifton a few homes were flooded, but in the 

south part the water did not overtop the walls that had 

been constructed to protect that part of town from 

flooding (figs. 19 and 20). Damage to public property 

in Clifton sewage systems, roads, and parks was 

estimated at $25,000 (Tony Rodrigues, mayor of Clifton, 

written commun., January 28, 1966).

In Safford, the estimated flood damage was $25,000 

(Joint Graham County and Cities Civil Defense, written commun., January 14, 1966). The damage was 

mostly to roads, sewers, and water systems.
PRECIPITATION, STREAMFLOW, FLOODS, GILA RIVER DRAINAGE BASIN, ARIZONA B27

A C

B D

FIGURE 18. Flood of December 23, 1965, in the Safford Valley. A, Looking south toward approach to the bridge on the Gila River; 

Safford is in the background. B, Looking south and downstream toward the Pima Bridge. C, Looking downstream near Pima. 

D, Looking south and downstream across the recently cleared (1965) flood plain in the Gila River Phreatophyte Project area; 

U.S. Highway 70 isi in the foreground, and the foothills of Mount Turnbull are in the background. Photographs furnished by 

the U.S. Bureau of Land Management, Safford.
B28 GILA RIVER PHREATOPHYTE PROJECT

c

B D

FIGURE 19. San Francisco River flood plain at Olifton. A, Looking upstream toward railroad bridge over the San Francisco River ; 

shows the flood plain prior to 1900. B, Looking downstream toward the railroad bridge; shows the flood plain prior to 1900. 

C, Looking upstream toward railroad bridge, April 27, 1966. D, Looking downstream toward railroad bridge, April 27, 1966, 

Photographsi furnished by Mr. Charley Brown and Mr. Clarence McBride, Safford.
PRECIPITATION, STREAMFLOW, FLOODS, GILA RIVER DRAINAGE BASIN, ARIZONA B29

i

B

FIGURE 20. Flood of December 21, 1965, at Clifton. A, Looking 

downstream and across San Francisco River toward railroad 

bridge. B, Looking upstream toward railroad bridge; the flood 

dikes were not overtopped in this reach of the river. Photographs furnished by Risdon Studios, Clifton.

Many dwellings in Little Hollywood, a community 

of about 500 farm workers, were flooded as a result of 

high flows in the Gila River (fig. 21). Although the 

community is on the flood plain near the confluence of 

the Gila and San Simon Eivers, the dwellings did not 

wash away. Fortunately, the San Simon River carried 

only a small rate of flow.

The magnitude of damage to rural areas and small 

communities along the headwaters in the mountains is 

unknown, but severe damage occurred on several farms 

and ranches owing to flooding of Bonita and Eagle 

Creeks and the Blue and San Francisco Rivers. High 

flows in the San Carlos River flooded several homes in 

the town of San Carlos.

During the flood of December 21-24, the Gila River 

at head of Safford Valley peaked three different times 

twice on the 23rd and once on the 24th (fig. 22). The 

first of the three peaks was the greatest, although it 

preceded the single peak (30,000 cfs) on the San Francisco River at Clifton by 11 hours and the peak on the 

Gila River near Clifton by 33 hours. Apparently, about 

15,000 cfs of the 43,000 cfs peak discharge at the head 

of Safford Valley was due to tributary inflow to the 

Gila River below the gaging stations at and near Clifton, as the hydrographs in figure 22 indicate that no 

more than about 18,000 cfs could have been runoff from 

above those two upstream stations. The second peak 

(36,000 cfs) was due, in part, to the floodwave on the 

San Francisco River, which had crested about 3i/£ hours 

earlier at Clifton, and the third peak (14,000 cfs) was 

due to the floodwave on the Gila River, which had 

crested a little less than 4 hours earlier at the gaging 

station near Clifton.

The peak discharge of 39,000 cfs, corresponding to 

the first peak at the head of Safford Valley, in the Gila 

River at Calva occurred in the early afternoon of December 24. The second peak, which occurred at the head 

of Safford Valley, was not noticeable at Calva. The third 

peak was barely noticeable at Calva on December 26 .

The peaks of the year-end flood were much lower 

than those of the flood a week earlier. The San Fran-
B30 GILA RIVER PHREATOPHYTE PROJECT

B

FIGURE 21. Gila River flood plain in 1935 and flood of December 

23, 1965, at Little Hollywood. A, Aerial photograph of the Gila 

River flood plain taken in 1935; the intersection of the Gila 

River, which flows west, and the San Simon River, which flows 

north, is in the upper right quarter; the site where Little 

Hollywood is now located is in the upper left quarter. B, Flood 

of December 23, 1965, at Little Hollywood and the flood plain. 

Photographs furnished by Rogers Studios, Safford.

cisco River at Clifton peaked at about 17,000 cfs twice 

within 12 hours, but the Gila River peaked only once 

at the gaging stations near Clifton, at the head of Safford Valley, and at Calva. The earlier of the two floodwaves on the San Francisco River was the cause of the 

single peak at the head of Safford Valley; apparently, 

the later floodwave on the San Francisco merely caused 

a slowing of the recession from the single peak on the 

Gila River at the head of Safford Valley.

According to Patterson and Somers (1966, p. 1-57), 

the peak flows for December 22-24 at the gages in the 

San Francisco River at Clifton, Gila River at head of 

Safford Valley, and the Gila River at Calva have return 

intervals of about 12, 16, and 17 years, respectively 

(fig. 23). The return interval for the smaller floods at 

the same stations on December 30-31, 1965, and January 1,1966, was about 6 years.

SUMMARY

In the Gila River basin, precipitation is the result 

of five types of airmasses: (1) cool moist Polar Pacific 

from the northern Pacific Ocean, (2) warm moist 

Tropical Pacific from the southern Pacific Ocean, (3) 

warm moist Tropical Gulf from the Gulf of Mexico, (4) 

cold dry Polar Continental from Canada, and (5) hot 

dry Tropical Continental from Mexico. In the winter 

the weather usually is the result of types 1 and 4, but 

occasionally type 2 brings large amounts of precipitation. Type 5 is predominant in the spring. In the summer the weather usually is the result of type 3, although 

type 2 may bring large amounts of precipitation in late 

September and October. A change in the predominance 

of an airmass may shift the weather from an average 

condition. At times the shift is striking, as in 1941 and 

1965, when more than a normal number of Tropical 

Pacific storms brought large amounts of precipitation 

into the basin and caused large amounts of runoff. The 

major floods in 1905 through 1916 presumably are the 

result of shifts in the predominance of the Tropical 

Pacific airmasses.
PRECIPITATION, STREAMFLOW, FLOODS, GILA RIVER DRAINAGE BASIN, ARIZONA P31

Z 

g 45,000

Ld

^ 40,000 

ce

Ld

°- 35,000

1-

uj 30,000 

u.

2 25,000

CD

D

O 20,000 

Z 

- 15,000

Ld 

O 

K 10,000

0 5000

Q o

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1

-4

f

/

P

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21 22

1

^ 

\ 

\ /\

-

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V

I

V

\

23

\

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26 27 28 29 30 31

EXPLANATION 

Gila River near Clifton 

San Francisco River at Cliftc 

Gila River at head of Safforc 

Valley, near Solomon 

Gila River at Calva 

Discharge measurements

/\|

k~"-- |

M...L...

 

.^ii".r

^^

^=^= ^r

1 -M -^

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,T7Tt7;,77

L 2 3 4

DECEMBER 1965 JANUARY 1966

FIGURE 22. Floodflows, December 21,1965, to January 4,1966.

100,000

90,000

80,000

70,000

LJ 60000

£L

LU

LU

u_

y 50,000

CD

D 

O

LU 40,000

O

OL

o

Q 30,000

20,000

10,000

EXPLANATION

San Francisco River at Clifton

Gila River at head of Safford Valley

l.Ol 1.5 3 4 56789 10 

RECURRENCE INTERVAL, IN YEARS

20 30 40 50 100 200

FIGURE 23. Peak-discharge frequency curves for San Francisco River at Clifton, Gila River at head of SafEord Valley, and Gila

River at Calva. Curves adapted from Patterson and Somers (1966).
B32 GILA RIVER PHREATOPHYTE PROJECT

Since 1920, there has been almost continual decrease 

in the amount of precipitation in the Gila River basin. 

The decrease has been mainly in winter precipitation, 

and there has been a parallel decline in winter streamflow. A lower incidence of major floods also has been 

noted. For example, major floods occurred in nine winters during period 1891-1916, but only one major flood 

(December 1965) occurred in the period 1917-65. The 

December 1965 flood in Safford Valley had a peak discharge of 43,000 cfs, which had a return interval of 

about 12 years. The change or decrease in precipitation 

and runoff is associated with a shift in the predominance of the airmasses that control the climate of 

the Gila River basin.

In the Gila River basin the summer precipitation is 

mainly from local convective thunderstorms, which 

produce rainfall of high intensity and short duration 

over small areas. The long-term average of summer precipitation at six sites was 7.91 inches, or 57 percent of 

the average annual precipitation. The means ranged 

from 5.58 inches in the lower altitudes to 11.61 inches in 

the mountains, and the coefficients of temporal variation 

ranged from 0.25 to 0.45.

Winter precipitation is mainly from convergence, or 

frontal, storms that distribute moisture over large areas. 

Owing to the infrequent occurrence of large amounts of 

precipitation from Tropical Pacific storms, the temporal variability of winter precipitation is larger than 

that of summer precipitation. The long-term average of 

winter precipitation at six sites was 4.96 inches, or 36 

percent of the average annual precipitation. The means 

ranged from 3.49 to 7.42 inches, and the coefficients of 

temporal variation ranged from 0.34 to 0.60.

The average summer flow (1914-64) past the Gila 

River at head of Safford Valley gaging station was 

about 97,300 acre-feet, or 32 percent of the average annual flow. The standard deviation was about 71,300 

acre-feet, and the coefficient of variation was 0.71. The 

summer flow ranged from 15,700 acre-feet in 1956 to 

345,000 acre-feet in 1916. The highest consecutive 10- 

year average was 164,000 acre-feet per year from 1914 

through 1924, and the lowest consecutive 10-year average was 44,800 acre-feet per year from 1943 through 

1953. There has been no long-term trend toward reduced 

summer streamflow.

The average winter flow (1914-64) of the Gila River 

at head of Safford Valley gaging station was about 

210,000 acre-feet, or 68 percent of the average annual 

flow. The standard deviation was 220,000 acre-feet, and 

the coefficient of variation was 1.04. The winter flow 

ranged from 19,600 acre-feet in 1959 to about 1,180,000 

acre-feet in 1916. The highest consecutive 10-year average was 377,000 acre-feet per year from 1914 through

1924, and the lowest consecutive 10-year average was 

105,000 acre-feet per year from 1949 through 1959 

about a 270 percent difference in 10-year averages. Except for the relatively short period 1936-42, tl <^re was 

a fluctuating decline in winter streamflow from 1920 

through 1962.

Preliminary studies of the relation of runoff to precipitation during the period 1916-64 show no continual 

decrease in the ratio of the former to the latter. Therefore, the decrease in streamflow after 1920 was mainly 

due to the decrease in winter precipitation. Studies of 

the depletion of flow in the Gila River withir the 55- 

mile length of the Safford Valley since 1920 indicate no 

long-term trend toward greater flow losses. A Ithough 

some small changes in trend may have occurred, they 

could be detected only by making detailed studies. A 

budget of inflow versus outflow for 1938-61 indicates 

that the average annual surface-water loss in Safford 

Valley was 112,000 acre-feet, a loss of 2,040 acre-feet 

per mile per year.

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Agr. Expt. Sta. Bull. 252,18 p.

Burkham, D. E., 1966, Hydrology of Cornfield Wash area and 

effects of land-treatment practices, Sandoval County, New 

Mexico, 1951-60: U.S. Geol. Survey Water-Supply Paper 

1831, 87 p.

Burkham, D. E., and Dawdy, D. R., 1970, Error analysis of 

streamflow data for an alluvial stream: U.S. Geol. Survey 

Prof. Paper 655-C. (In press.)

Culler, R. C., 1965, The Gila River Phreatophyte Project: Arizona State Land Dept. Ninth Annual Watershed Symposium 

Proc., p. 33-38.

Gushman, R. L., and Halpenny, L. C., 1955, Effect cf. western 

drought on the water resources of Safford Valley, Arizona, 

1940-52: Am. Geophys. Union Trans., v. 36, no. 1, p. 87-94.

Bawdy, D. R., 1961, Depth-discharge relations o* alluvial 

streams discontinuous rating curves: U.S. Geol. Survey 

Water-Supply Paper 1498-C, 16 p.

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., 534 p.

Graham County Guardian, 1895, 1896, 1905: Safford, Ariz., 

issued weekly.

Lippincott, J. B., 1900, Storage of water on Gila River, Arizona: 

U.S. Geol. Survey Water-Supply Paper 33, 98 p.

McDonald, J. E., 1956, Variability of precipitation in an arid 

region a survey of characteristics for Arizona.: Arizona 

Univ. Inst. Atmospheric Physics Tech. Kept. 1, 88 p.

Olmstead, F. H., 1919, Gila River flood control a report on 

flood control of the Gila River in Graham County, Arizona : 

U.S. 65th Cong., 3d sess., Senate Doc. 436, 94 p.

Oltman, R. E., and Tracy, H. J., 1951, Trends in cliirate and in 

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Geol. Survey Circ. J)8, 113 p.
PRECIPITATION, STREAMFLOW, FLOODS, GILA RIVER DRAINAGE BASIN, ARIZONA B33

Patterson, J. L., and Somers, W. P., 1966, Magnitude and frequency of floods in the United States Part 9, Colorado 

River basin: U.S. Geol. Survey Water-Supply Paper 1683, 

475 p.

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

Press, 60 p.

Smith, Winchell, and Heckler, W. L., 1955, Compilation of flood 

data in Arizona, 1862-1953: U.S. Geol. Survey open-file 

report, 113 p.

Thomas, H. E., 1962, The meteorologie phenomenon of drought in 

the Southwest: U.S. Geol. Survey Prof. Paper 372-A, 43 p.

Thomas, H. E., and others, 1963, Effects of drought in the 

Colorado River basin: U.S. Geol. Survey Prof. Paper 372- 

F, 51 p.

Thornthwaite, C. W., Sharpe, C. F. S., and Dosch, E. F., 1942, 

Climate and accelerated erosion in the arid and semiarid 

Southwest, with special reference to the Polacca Wa<?h 

drainage basin, Arizona: U.S. Dept. Agriculture Bull. 808, 

134 p.

U.S. Army Corps of Engineers, 1914, San Garlos Irrigation Project, Arizona: U.S. 63d Gong., 2d sess., H. Doc. 791, 168 p.

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

States Part 9, Colorado River basin: U.S. Geol. Survey 

water-supply papers (published annually through I960; 

published periodically, 1961 to present).

U.S. Weather Bureau, issued annually, Climatological data, 

Arizona: U.S. Dept Commerce.

 U.S. GOVERNMENT PRINTING OFFICE: 1970 O 368-750