Floods in New Mexico, Magnitude 

and Frequency

GEOLOGICAL SURVEY 

CIRCULAR 464
Flocxls in New Mexico, Magnitude

and Frequency

By Leon A. Wiard

Prepared in cooperation with the New Mexico State Highway Department

GEOLOGICAL SURVEY CIRCULAR 464

Washington 1962
United States Department of the Interior

STEW ART L. UDALL, SECRETARY

Geological Survey

THOMAS B. NOLAN, DIRECTOR

Free on application to the U.S. Geological Survey, Washington 25, 0. C.
CONTENTS

Page Page

Abstract _______ _____________________ 1 Flood-frequency data__- _____________ 3

Introduction __________________________ 1 Flood -frequency analysis ____________ 5

Description of the State _-_--______-__ 2 Application of curves________________ 8

Streamflow data _____________________ 3 References cited..__________________ 13

ILLUSTRATIONS

Page 

Figure 1. Map of New Mexico showing flood-frequency regions and hydrologic areas _____ 4

2. Composite frequency curves for regions A, C, D, and F______________________ 5

3. Composite frequency curves for regions B and E ___________________________ 5

4. Relation of mean annual flood to drainage area in hydrologic areas 1 3, and 12 _ 6

5. Relation of mean annual flood to drainage area in hydrologic areas 4 9________ 7

6. Relation of mean annual flood to drainage area in hydrologic areas 10,11,

and 13 _______________________________________________________________ 8

7. Relation of mean annual flood to drainage area and site altitude in hydrologic

area 14 ______________________________________________________________ 9

8. Relation of altitude at site to reduction of mean annual flood _________________ 9

9. Relation of discharge for selected flood frequencies to miles above mouth,

Canadian River main stem below Cimarron Creek ________________________ 10

10. Relation of discharge for selected flood frequencies to miles above El Paso

gaging station, Rio Grande main stem below Lobatos, Colo____--___-------- 10

11. Relation of discharge for selected flood frequencies to miles above mouth of

Rio Puerco __________________»________________________________________ 11

12. Relation of discharge for selected flood frequencies to miles above State line,

Pecos River main stem below Anton Chico gaging station __________________ 11

13. Relation of discharge for selected flood frequencies to miles below State line,

San Juan River main stem below Rosa gaging station ______________________ 12

14. Relation of discharge for selected flood frequencies to miles above State line,

Gila River main stem below Gila River near Gila gaging station ____________ 12

in
Floods in New Mexico, Magnitude and Frequency

By Leon A.Wiard

ABSTRACT

This report presents a method of determining the magnitude 

and frequency of floods that can be expected in New Mexico 

The discharge of the mean annual flood for various regions in 

the State is defined. Curves relate mean annual flood and 

drainage area. Drainage area was the only basin characteristic found to have an appreciable effect on discharge of the 

mean annual flood except in two regions where a relation with 

altitude also is defined. Composite frequency curves relate 

.discharge of the mean annual flood to the discharge of floods 

having recurrence intervals from 1.1 to 50 years. These relationships are based on records 5 or more years in length from 

gaging stations that had flow essentially unregulated.

INTRODUCTION

The location, design, construction, and insurance of structures in, over, or adjacent to 

streams require consideration of flood hazards. For most structures, except where 

probable loss of life is involved, design is 

usually based on economy. An important element of an economic evaluation is knowledge 

of the magnitude and frequency of floods to be 

expected.

This report describes methods and presents 

curves by which the magnitude and frequency 

of floods may be estimated for most sites in 

New Mexico. Extrapolation of the curves as 

presented is not justified.

The effect on flood peaks of various basin 

characteristics such as drainage area, site 

elevation, channel slope, and mean annual 

runoff, was investigated. Drainage area was 

used as a factor throughout the State. The 

other factors had no apparent effect, with the 

exception of site elevation which was found to 

be important in the Canadian and San Juan 

River basins. All streamflow records in the 

State not affected by excessive regulation or 

diversion, and of duration greater than 5 

years, were used in the analysis. In addition,

several streamflow records for Arizona, 

Colorado, and Texas were included.

The report was prepared in the Santa Fe 

Office of the U.S. Geological Survey under the 

direction of Wilbur L. Heckler, district engineer, Surface Water Branch, in cooperation 

with the New Mexico State Highway Department. The author was materially assisted in 

the Rio Grande basin part of the analytical 

study and in the preparation of this report by 

E. Hogue, R. Lamke, K. Medina, and Miss 

Massie Ortiz of the Santa Fe office.

The analysis for the Canadian River basin 

was made by J. L. Pattersonof the Fort Smith, 

Ark., office of the U.S. Geological Survey as 

part of a flood-frequency study of the lower 

Mississippi River basin. Credit is given to 

personnel of the Floods Section, Surface Water Branch, U.S. Geological Survey, Washington, D. C., for the analysis of the Colorado 

River basin, a part of which was utilized in 

the preparation of this report.

Results of the studies mentioned above for 

the lower Mississippi, Rio Grande, and Colorado River basins will be published in WaterSupply Papers 1681 (Part 7), 1682 (Part 8), 

and 1683 (Part 9) respectively, each of which 

will be one of a series of water-supply papers 

on the magnitude and frequency of floods in 

the conterminous United States.

Data for New Mexico streams used in the 

study were collected through investigations 

financed in whole or in part by the New Mexico 

State Highway Department, the New Mexico 

State Engineer's Office, the Interstate Streams 

Commission, the Rio Grande Compact Commission, the Pecos River Commission, the 

Costilla Compact Commission, the Pecos Valley Conservancy District, the Corps of Engineers, the Bureau of Reclamation, and various municipalities. Similar local, State, and

1
FLOODS IN NEW MEXICO, MAGNITUDE AND FREQUENCY

Federal agencies and commissions have been 

responsible for the financing of gaging stations in Arizona, Colorado, and Texas, for 

which flood data were used in this study to 

augment the New Mexico data. Credit for the 

work of these various agencies is given in the 

annual series of water-supply papers of the 

U.S. Geological Survey entitled "Surface Water Supply of the United States."

Engineers and hydro legists have made other 

studies of the magnitude-frequency relation 

of floods. One such study by M. A. Benson 

(written communication, 1962) discusses the 

factors-affecting the occurrence of floods in 

the Southwest. In Benson's study, formulas 

are presented which enable evaluation of the 

effects of nine independent variables. The 

variables included are contributing drainage 

area, main-channel slope, storage of lakes 

and ponds, rainfall intensity, length of main 

channel, average" annual number of thunderstorm days, runoff/precipitation ratio, mean 

annual precipitation, and basin elevation index.

Results obtained by methods described in 

this report and by Benson's methods may 

differ considerably for a selected site, however, average results for sites throughout 

New Mexico should be comparable.

DESCRIPTION OF THE STATE

Various physical factors of a drainage basin which affect the magnitude of floods are 

integrated by the flood peaks. The effects of 

land slope, stream length and density, altitude, latitude, and relation to mountain ranges 

and oceans are reflected in the hydrograph of 

the flood peak.

New Mexico, where elevations range from 

less than 3,000 feet to over 13,000 feet, is bisected in a north-south direction by the 

Sangre de Cristo, Manzano, San Andres, and 

Organ Mountains. This chain of mountains 

forms the eastern divide of the Rio Grande 

Valley in New Mexico. The Pecos River rises 

in the southern end of the Sangre de Cristo 

Mountains. The Canadian River has its headwaters on the eastern slopes of this same 

range, along the Colorado-New Mexico border. Ranges forming the west divide of the 

Rio Grande Valley are the San Juan and Valle

Grande, or Jemez Mountains, in the north and 

the San Mateo Mountains and Black Range in 

the south. The wide valleys of the Rio Puerco 

and Rio Salado basins separate these northern 

and southern ranges. The Sacramento Mountains are the major range in the southeastern 

part of the State. The Guadalupe Hills are an 

extension of these mountains to the southeast. 

Although of relatively low altitude these hills 

are an important contributing cause of floods 

in the lower part of the Pecos Valley. In the 

southwestern corner of the State, the Mogollon 

and Tularosa Mountains join to form an important mountain system. The Chuska Mountains are farther to the north, on the ArizonaNew Mexico border.

Leopold (1944) and Dorroh (1946) describe 

in detail the air masses producing precipitation in New Mexico and the effects of the 

ranges and basins upon distribution of precipitation. Of particular interest is the fact 

that highest intensities for a particular storm 

are usually to be found at or near the base of 

mountain slopes as exemplified by the Alamogordo storm of August 17, 1959. A maximum of more than 3 inches of precipitation 

was recorded in about 2^ hours close to the 

base of the Sacramento Mountains east of 

Alamogordo. Only half an inch was recorded 

at a site less than 1^ miles from the storm 

center.

Extensive lava flows are an important geologic feature affecting floodflows. Precipitation of cloudburst intensity on an area of lava 

flows may cause little or no flood runoff. 

These areas also absorb floodflows discharged 

onto or adjacent to them from a surrounding 

area. Thus, the absorptive characteristic of 

lava beds tends to reduce the effective drainage area of a stream in regard to floods.

Streams in New Mexico fall into two distinct categories the perennial streams with 

year-around flow, and the ephemeral streams 

which carry flow only during periods of precipitation or snowmelt. The majority of the 

streams are of the latter type and have two 

characteristics which are important in flood 

studies: (a) they carry infrequent flows of 

short duration but of high maximum discharge 

in relation to total flood volume; and (b) channel losses are significant, with a high rate of 

loss .within a few miles.
FLOOD -FREQUENCY DATA

STREAMFLOW DATA

Streamflow records 5 or more years in 

length from 102 continuous-record gaging 

stations and crest-stage gages in New Mexico, not appreciably affected by regulation or 

diversion, were used in the analysis. In that 

part of the analysis made in the Santa Fe office, 1 additional gaging-station record in 

Arizona, 3 in Texas, and 16 in Colorado were 

also used. If drainage areas for stations on 

the same stream are within 25 percent of 

each other, the longer record was used.

FLOOD-FREQUENCY DATA

Gaging-station records are random samples of streamflow, whether daily, monthly, 

annual, or instantaneous peaks are being considered. It follows that a frequency curve 

based on records from several stream-gaging 

stations in a region reflects the variable 

characteristics of the region more adequately 

than do the individual station frequency 

curves. However, flood-frequency curves for 

the individual sites are necessary as a preliminary step in deriving the regional curves.

A common base period is used in making a 

regional flood-frequency analysis so that all 

records will be comparable. In the analysis 

made in the Santa Fe office, the period 1938 

59 was used. Although slightly different periods were used for the Colorado and the Canadian River basins, the difference should 

have little effect on results. To provide a 

basis for extension beyond the base period, 

peak discharges outside the base period were 

used where such peaks exceeded those within 

the base period.

Flood-frequency relations were not defined 

for the area between the Rio Grande and the 

San Andres Mountains, and for that to the 

east of the Pecos River south of the 34th 

parallel (shown crosshatched on figure 1) 

because of inadequate base data.

Flood data for use in a flood-frequency 

analysis may be compiled into one of two 

series, either annual or partial-duration. An

annual flood is defined as the maximum instantaneous discharge occurring during a 

given annual period, usually the water year 

October 1 through September 30. The annual 

flood series, based on these annual maximums, has the disadvantage that when several high floods occur in the same water year, 

some floods higher than many annual floods 

are disregarded. The partial-duration series overcomes this objection because it 

contains all peaks above a selected base discharge, which is usually selected so that in 

general 3 or 4 peaks per year will exceed the 

base. The floods in the partial-duration series, however, may not be entirely independent events; it is possible that one flood will 

set the stage for another.

There is a basic difference between the two 

series. The annual series enables -one to 

predict the average interval of recurrence of 

a given event, as an annual maximum. The 

recurrence interval defined by the partialduration series is the average interval between events of a given size regardless of 

their relationship tp a given time period. 

For the larger floods, the recurrence interval is very nearly equal for both series. The 

following table by Langbein (1949) shows the 

relation between recurrence intervals by the 

two series:

Recurrence intervals in years 

Annual flood Partial-duration

series

1.16.......

1.58......

2.00.......

2.54.......

5.52.......

10.5........

20.5.........

50.5.........

100.5.........

0.5

1.0

1.45

2.00

5.0

10.0

20.0

50.0

100.0

It should be stressed that a recurrence interval of, say, 50 years does not mean that 

the given event will recur every 50 years. It 

is quite possible for two 50-year floods to 

occur within a short period of time, or many 

more than 50 years may elapse before the 

occurrence of one 50-year flood.
FLOODS IN NEW MEXICO. MAGNITUDE AND FREQUENCY

Flood-frequency regional boundary Regional and areal boundaries coincident

Hydrologic areal boundary

0

Flood-frequency relations undefined

50

I

50

i

100 MILES

_I

Figure 1. Map of New Mexico showing flood-frequency regions and hydrologic areas.
FLOODS IN NEW MEXICO,

FLOOD-FREQUENCY ANALYSIS

Procedures followed in drawing the curves 

presented are explained by Dalrymple (1960). 

Certain items are briefly discussed so that 

one can properly use and interpret the charts.

MAGNITUDE AND FREQUENCY D

Regions were established in which records 

for all gaging stations show similar floodfrequency characteristics, the criterion being 

the ratio of the 10-year to the mean annual, 

or 2.33-year, peak discharge. An average 

value of this ratio was obtained for a group

1.0!

cr

1.5 2 5 10 20 30 40 50 100 

RECURRENCE INTERVAL, IN YEARS

Figure 2. Composite frequency curves for regions A, C, D, and F.

2 5 10 20 

RECURRENCE INTERVAL, IN YEARS

Figure 3. Composite frequency curves for regions B and E.

100
ROODS IN NEW MEXICO, MAGNITUDE AND FREQUENCY

1 \J}\J^J ^/

5000

o 

z 

o 

o

UJ "> 2000 

tr 

u 

c_

H 1000

Ltl 

UJ

g 50°

13 

O

5

g 200 

o

e

-J 100

^ 

ID 

Z

< 50

z 

<

LU

5

20 

in

'

>

/

/

/

f

s

/

s

_^ s^ s^

/

/

S

/

/ 

^*^/

s

/

/

/

/

3/*

/

r

/

/

>

/

s*

s

/

/

s

/

s

s

/

s

/

s

*

f

/

s

<s

s

/

/

/

/

.s s

^

/

Note; Adjust 

area 12 

factor,

A

/

^

s

^

s

/

/

_.* ^^

/

^

2

A

/

s

/

s

/

/

,

^

/

/

curve values for hydrolo 

by use of flood reductio 

fig.8 |

12

gic 

n

2 5 10 20 50 100 200 500 

DRAINAGE AREA, IN SQUARE MILES

Figure 4. Relation of mean annual flood to drainage area in hydrologic areas 1-3, and 12.

1000 2000

of stations in a given area, assumed to be 

homogeneous. The mean annual discharge at 

the individual stations was multiplied by this 

average and the recurrence interval noted 

from the station frequency curve. This recurrence interval was plotted versus the effective length of record on a specially designed test graph. The effective length of 

record was defined as the number of years 

of actual record plus one-half the number of 

years of record computed by correlative 

methods. The test graph was constructed on 

a 95 percent confidence level to indicate 

homogeneity 19 times out of 20. If the points 

tested are distributed normally on the test 

graph the region is considered to be homogeneous. It may be that the original area 

can be enlarged. In that case, a new average

of the ratios of the 10-year to mean annual 

flood is recomputed and the process repeated.

Available records define six floodfrequency regions in New Mexico. These regions are shown on the map (fig. 1). Regional 

or composite frequency curves, derived from 

the median values of ratios of the 1.1-year, 

10-year, 25-year, and 50-year floods to the 

mean annual flood for the individual stations, 

are shown in figures 2 and 3.

The composite frequency curves show ratios of floods of various magnitudes to the 

mean annual flood. It is therefore necessary 

to define the mean annual flood in terms of 

some easily measured or determined basin
FLOOD-FREQUENCY ANALYSIS

Q

Z

8 5000

OC 

UJ

a- 2000

LJ 

LJ

u. 1000 

o 

m

3 50°

Z

0 200 

O

o

U- 100

i 50

Z

< 20

LJ

10

)

s*

,, 

7

.*'*

s* -

\ 0

-

~:

'. 

2 0.5

Q ^x X"'

^X"

. ''

X^_^

Xx^

x**

X

X

X*

X

x

x

^

x

x

%

X

x

/

^ '

 ,'

^'

x^

^ ^

_^r ^x*^^

s^

-X .^*

_^^ x^^

Jr ^^*^

f ^^^

X

s* ,x^

x~^

/

^X

x^

^^^

x^

r

x

X 

X*

,x

x;

x

x

X

/

X

X

X

X

x

X

X-

^^

^

s

x"

x^

x^

^

x^

^x^ ^j^^

_y

^x

/r

'^x^

^

x^

x "

, x^

X

x^

^

^^

x

x^

^^

X

X

^

X*

X

>

X1

X

X

^d

X

,0

^

x 

X

X

X

X

'

^

6

 *

! 

£

^1

X

r-l

X" «? ,

^^x^.^

« ""^

x

K

-7-

^

12 5 10 20 50 100 200 500 1000 2000

DRAINAGE AREA, IN SQUARE MILES

Figure 5. Relation of mean annual flood to drainage area in hydrologic areas <M3.

characteristic. The characteristic or parameter most easily measured, and fortunately the most effective, is drainage area.

The separate hydrologic areas were determined by trial. Curves of relationship 

between mean annual flood and drainage area 

were established for individual areas, 14 in 

number, each containing streams of similar 

flood-producing characteristics. These 

curves are shown in figures 4 7. Likenumbered areas to which they apply are outlined on figure 1.

Altitude, as well as drainage area, is an 

effective parameter in areas 10 14, the Canadian and San Juan River basins. An adjustment curve for use with the curves for 

areas 10 13 (figs. 4 and 6) is shown in figure 

8. This curve gives the relation between 

the ratio of adjusted mean annual flood, 

Q2 33, and computed mean annual flood,

Qc 2 33. and site altitude. Curves of relation between mean annual flood, drainage 

area, and site altitude, for use in area 14 

are shown in figure 7.

Although gaging stations on the Rio Grande, 

Rio San Jose, Rio Puerco, and the Canadian, 

Pecos, Gila, and San Juan Rivers have been 

used in the analysis, use of the area curves 

should be limited to the headwaters of these 

streams. Curves of relation between peak 

discharge for selected frequencies and mileage upstream from a given point are shown 

in figures 9 14. These curves are to be 

used rather than the curves of relation between mean annual flood, drainage area, and 

site elevation for the part of each mainstem 

stream indicated in figures 9 14^ Generally, 

hydrologic effects on a large stream have 

become so integrated that it is sometimes 

better to consider such streams on the basis 

of their individual flood-frequency characteristics.

In preparing figures 9 14, every effort 

was made to eliminate the effects of storage 

and flood-control reservoirs, thereby placing the frequencies on a natural basis, as 

far as possible. The effects of manmade 

changes should be considered in using results obtained from the curves presented.
FLOODS IN NEW MEXICO, MAGNITUDE AND FREQUENCY

0 50,000

O 

O 

UJ

Q, 20,000

UJ 

CL

uJ 10,000

UJ 

LL

- 5000 

CO

O

z

0- 2000

O 

O 

_J

^ 1000

ID 

§ 500 

<

z 

<

2 200 

inn

>'

,--

 - ,

, ^^

X

^

r

x

X

^

X

^

X

/*

' 

.X

x ^

xx

jr

/

/

_J

/

x

x

^

s

^

/

s

/

'

t

f

/

s

'

*

t

./

y""^

s^

v^ ^

' S^

.s

t

Note;

^

X

/

jf s^

X

X

/J

/£

x

X

'

"^

X

s

s'

Adjust curve values by use of 

flood reduction factor, fig. 8

'10

10 20 50 100 200 500 1000 2000 5000 10,000 20,000 

DRAINAGE AREA, IN SQUARE MILES

Figure 6. Relation of mean annual flood to drainage area in hydrologic areas 10, 11, and 13.

Flood records for the area below Elephant 

Butte and Caballo Reservoirs provide a good 

example of the effects of manmade changes^ 

An analysis of flood records below Caballo 

Reservoir shows that normal operation of the 

reservoir would provide 50-year flood discharges not in excess of 3,200 cfs, on the 

basis of 21 years of record. However, in one 

of these years of record, 1942, when Elephant 

Butte and Caballo Reservoirs spilled, a maximum daily mean discharge of 7,650 cfs occurred. Therefore, to define the natural peak 

discharges of the lower Rio Grande in New 

Mexico, discharges for the period of record 

at San Marcial and data from International 

Boundary Commission Report no. 6 for their 

El Paso gage were used.

APPLICATION OF CURVES

Two general sets of curves are presented 

for use in obtaining the magnitude of floods

of given recurrence intervals at any specific 

site. These are the composite frequency 

curves and the curves of relation between 

mean annual flood and drainage area, with 

altitude involved as a parameter in one case. 

Both the mean annual flood versus drainage 

area curves and the composite frequency 

curves were drawn to limits warranted by 

the base data. Extension of any curve shown 

is not recommended,because values thus obtained may be considerably in error. When 

flood magnitudes are to be determined at 

sites on the main stems of certain large 

streams, a third set of curves is presented 

(figs. 9 14). To use the curves the following 

steps should be followed:

1. Determine if the selected site is in the 

reach of r main-stem stream shown in 

figures 9 14. If so, determine the peak 

discharge directly from the appropriate 

one of the curves in figures 9 14. If not, 

proceed as follows:
APPLICATION OF CURVES

20,000

o 

o

UJ

a:

UJ

a.

10,000

I- 5000

UJ 

UJ

o

o

2000

a" 1000

o

o

^ 500

200

UJ

' &

inn \\J\J _ . ' _____ . __ __ - ._ ~

50 - 

10 20 50 100 200 500 1000 2000 5000 

DRAINAGE AREA, IN SQUARE MILES

10,000 20,000

u_ 

o

o

UJ

H

c/>

Z>~3

QUJ 

<0 

OL

5

OO

^

<Q 

Q=_J

co< <s1o

2° £ K

^o ^ 

oo:

p ? 0 S z> ^

Q«2 

UJQ

o:

a 

o 

o

 b

o bo

p b>

o *

o ro

Figure 7. Relation of mean annual flood to drainage area and site altitude in hydrologic area 14.

2. From available maps, preferably quadrangle maps published by the U.S. Geological 

Survey, determine the drainage 

above the selected site.

Note; This curve applicable only in

hydrologic areas 10-13

area

2 4 6 8 10 

ALTITUDE OF SITE IN THOUSANDS 

OF FEET

3. From figure 1, determine the region and 

hydrologic area in which the site is 

located.

4. Deter mine, from figures 4 7 the mean annual flood corresponding to the drainage 

area above the site, using the curve for 

the area within which the site is located. 

Apply adjustment coefficients for site 

elevation through use of the curve in 

figure 8 for areas 10 13. The mean annual flood for sites in area 14 can be obtained from figure 7.

5. Determine the ratio of peak discharge to 

mean annual flood for the selected flood 

frequency for the region in which the 

site is located, using curves of figures 2 

or 3.

Figure 8.- -Relation of altitude at site to reduction of mean 

annual flood.
10 FLOODS IN NEW MEXICO, MAGNITUDE AND FREQUENCY

300

500 600 700 800 

DISTANCE, IN MILES,ABOVE MOUTH

900

Figure 9. Relation of discharge for selected flood frequencies to miles above mouth, Canadian River main stem below Cimarron Creek.

100 200 300 400 500 

DISTANCE, IN MILES, AfeOVE EL PASO GAGING STATION

600

Figure 10. Relation of discharge for selected flood frequencies to miles above El Paso gaging station, Rio Grande main stem below Lobatos,

Colo.
APPLICATION OF CURVES 11

Rio Puerco below mouth of 

Rio San Jose

0 20 40 60 80 100 

DISTANCE, IN MILES, ABOVE MOUTH OF RIO PUERCO, NEAR BERNARDO, N. MEX.

Figure 11. Relation of discharge for selected flood frequencies to miles above mouth of Rio Puerco, Rio San Jose and Rio Puerco main

stem below mouth of Rio San Jose.

200

a

z 

o

uj

CO

a:

ui

UJ

u. 

o

CD

ID 

o

u. 

o

CO

o

z

CO

o

I

UJ

o

01

<

I 

o

CO

100

0 100 200 300 400 

DISTANCE, IN MILES, ABOVE NEW MEXICO-TEXAS STATE LINE

500

Figure 12. Relation of discharge for selected flood frequencies to miles above State line, Pecos River main stem below Anton Chico

gaging station.
12 FLOODS IN NEW MEXICO, MAGNITUDE AND FREQUENCY

100

0 25 50 75 100 125 150 175 200 225 

DISTANCE, IN MILES, BELOW NEW MEXICO-COLORADO STATE LINE

Figure 13. Relation of discharge for selected flood frequencies to miles below State line, San Juan River main stem below Rosa gaging station.

0 10 20 30 40 50 60 

DISTANCE, IN MILES, ABOVE ARIZONA-NEW MEXICO STATE LINE

70

Figure 14. Relation of discharge for selected flood frequencies to miles below State line, Gila River main stem below Gila River near

Gila gaging station.
REFERENCES CITED 13

6. Multiply the mean annual flood obtained in 

step 4 by the ratio determined in step 5 

to determine the peak discharge.

7. A complete frequency curve for ajsiie may 

be constructed by repeating steps 5 and 

6 for several selected frequencies and 

drawing a smooth curve through the plotted points.

REFERENCES CITED

Dalrymple, Tate, 1960, Flood-frequency analysis: U.S. Geological Survey Water-Supply 

Paper 1543-A, p. 1-80.

Dorroh, J. H., Jr., 1946, Certain hydrologic 

and climatic characteristics of the Southwest: University of New Mexico Publications in Engineering.

Langbein, W. B., 1949, Annual floods and the 

partial-duration flood series: Am. Geophys. 

Union Trans., v. 30, p. 879-881.

Leopold, Luna B., 1944, Characteristics of 

heavy rainfall in New Mexico and Arizona: 

Trans. Am. Soc. Civil Engrs., v. 109, p. 

837-866.

INT.DUP.,D.C.62-l'«26T