Hydrologic Regimen of 

Salton Sea, California

GEOLOGICAL SURVEY PROFESSIONAL PAPER 486-C

Hydrologic Regimen of 

Salton Sea, California

By ALLEN G. HELY, G. H. HUGHES, and BURDGE IRELAN

WATER RESOURCES OF LOWER COLORADO RIVER SALTON SEA AREA

GEOLOGICAL SURVEY PROFESSIONAL PAPER 486-C

A study of the variations in water 

level and water quality and their causes

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1966
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

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

Washington, D.C. 2C402 - Price 30 cents (paper cover)
CONTENTS

AbstractIntroduction. ________________

General description and history. 

Water level and volume. ______

Inflow studies______________________

Surface inflow._________________

Imperial Valley..___________

Coachella Valley.___________

Other areas_____-___--___-_

Summary of surface inflow. __

Ground-water inflow ____________

Precipitation on the water surf ace .

Evaporation studies.________________

Water-budget method, 1961-62___.

Page 

Cl Evaporation studies Continued

Energy-budget method, 1961-62___________.

Equipment and procedures.-_--------___--__.

Results of energy-budget computations ____.

Mass-transfer method, 1961-62 ________________

Comparison of results obtained by the three methods. 

Evaporation-pan data, 1948-62.__________________

Conclusions from evaporation studies...___________

Hydrologic regimen for 1908-62._____________________

Chemical regimen _______________________________

Salinity and mineral content-____________________

Chemical composition.__________________________

Temperature of the water _________________________

Future regimen.____________________________________

Schemes for regulation______________.__________.

References ______-______-__----___----__---_-__----.

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ILLUSTRATIONS

FIGURE 1. Map of Salton Sea basin__________________________________________________________

2. Contour map of the Salton Sea bed__________________________________________________

3-15. Graphs showing:

3. Relations of water level to area and volume.__________________________________

4. Monthly fluctuations of water level, surface inflow, and evaporation.. ____________

5. Comparison of three determinations of monthly evaporation.____________________

6. Comparison of monthly pan evaporation at three sites on the shore.______________

7. Monthly variations of the ratio of evaporation from Salton Sea to pan evaporation.

8. Means and extremes of monthly pan evaporation____________________________

9. Annual fluctuations of water level, surface inflow, and evaporation.______________

10. Annual fluctuations of salinity, mineral content, and volume-______-__--___----_-

11. Comparisons of chemical composition________________________________________.

12. Trends of the content of individual constituents_____.__________-_-______--__-

13. Monthly air, surface, and bottom temperatures._______________________________

14. Selected temperature profiles. _______________________________________________

15. Relation between mean annual values of water level and net evaporation________

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TABLES

TABLE 1. Monthly surface inflow from Imperial Valley, 1961-62___________________________

2. Monthly surface inflow from Coachella Valley, 1961-62.____________________

3. Monthly surface inflow from areas other than Imperial and Coachella Valleys, 1961-62.

4. Annual surface inflow to Salton Sea, 1944-62.________________________________

5. Monthly water budgets for Salton Sea, 1961-62_____________________________

6. Representative values of each term in the energy budget for Salton Sea._____________

7. Monthly evaporation from Salton Sea, determined by three methods_______________

8. Annual evaporation, 1948-62___________________________________________________

9. Annual water-budget data for Salton Sea, 1908-62__________________________

10. Chemical analyses of water from Salton Sea..____________________________________

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IV CONTENTS

SYMBOLS AND DIMENSIONS

[The numbers in parentheses refer to the equation (or figure, as indicated) where the symbol first appears]

Symbol Dimensions Description

c IST-*0-1 Specific heat of water (following 4).

e Emissivity of water, 0.970 (6).

e& ML-1 T~* Vapor pressure of the air (7).

eo ML~1 T~* Vapor pressure of saturated air at the temperature of the water surface (7).

u LT-1 Average windspeed (8).

E L3 Volume of evaporated water (1) or

L Depth of evaporated water (8). 

Ep L Pan evaporation (fig. 7). 

Et L Evaporation from Salton Sea (fig. 7). 

I g L? Volume of inflow by ground-water seepage (1). 

It IS Volume of inflow in surface channels (1). 

L 1ST-* Latent of heat of vaporization (following 4). 

M M Mineral content (9). 

N Empirical coefficient (8), 

P L3 Volume of water precipitated (1) or

L Depth of water precipitated (fig. 15) on Salton Sea.

Atmospheric pressure (3).

Incident long-wave radiation from the atmosphere (4).

Long-wave radiation reflected by the water (4).

Long-wave radiation emitted by the water (4).

Energy used by evaporation (4).

Energy conducted from the body of water as sensible heat (4).

Solar radiation reflected by the water surface (4).

Solar radiation incident to the water surface (4).

Net energy advected into the body of water (4). 

Qw MIST-* Energy advected by the evaporated water (4). 

Q# MIS T~* Increase in energy content of the body of water (4). 

R Bowen ratio (following 4), defined in equation 7. 

S Salinity, or mineral content per unit mass of water (9). 

Ta 0 Temperature of the air (7). 

7*6 0 An arbitrary base temperature (following 4). 

Te 8 Temperature at which evaporation takes place (following 4). 

TO 6 Temperature of the water surface (following 4). 

V U Volume (1). Subscripts, used with the symbol denoting an increment, indicate

the source of the increment (see equation 2).

p MLr3 Density of evaporated water (following 4). 

v MT-3e-* The Stefan-Boltzman constant for black-body radiation (6). 

A Denotes an increment of the variable following (1).

Pa

Qa

Qar

Qb.

Qe

QH

Qr

Q.

Q.

ML~1 T~

MIST-*

MIST-*

MIST-*

MIST-*

MIST-*

MIST-*

MIST-*

MIST-*
WATER RESOURCES OF LOWER COLORADO RIVER SALTON SEA AREA

HYDROLOGIG REGIMEN OF SALTON SEA, CALIFORNIA

By ALLEN G. HELY, G. H. HTJGHES, and BURDGE IRELAN

ABSTRACT

The Salton Sea is sustained almost entirely by drainage from 

irrigation districts using Colorado River water. Increasing 

quantities of drainage have maintained an upward trend in the 

water level for several decades, but this trend would be arrested 

or reversed if the quantity of water imported to the Salton Sea 

basin were appreciably reduced or if more of the imported water 

were consumed by evapotranspiration.

During 1961-62 the U.S. Geological Survey conducted a 

stream-gaging program, supplementing those of irrigation districts, to increase the reliability of the computed inflow to Salton 

Sea and of the estimated evaporation, computed by the waterbudget method. Also, meteorological data were collected and 

used to compute evaporation from the sea by the energy-budget 

and mass-transfer methods.

Annual evaporation computed by the water-budget and energybudget methods differed by less than 5 percent. Evaporation, as 

determined by these two methods, was used with data on wind 

speed and vapor-pressure difference to establish the empirical 

coefficient (#=0.00156) in the simplified mass-transfer equation, 

E=Nu(e0 Co,). The equation, therefore, does not provide an 

independent determination of total evaporation during the 2-year 

period, but it does provide an independent determination of the 

distribution of the total evaporation among the months.

The determinations of annual evaporation were also used to 

establish a coefficient (0.69) to convert average annual evaporation from three sunken pans at widely separated sites on the 

shore of Salton Sea to evaporation from the sea. Use of these 

pans is both adequate and the most practical method for the 

continuing measurement of annual evaporation, but it is not suitable for accurate determination of monthly evaporation because 

of the somewhat erratic variation of monthly pan coefficients. 

The computed evaporation for 1961-62 and the pan data for 

1948-62 indicate that normal annual evaporation from Salton 

Sea is 5.78 feet (69 in.).

The information gained from the 1961-62 investigations was 

an aid in the reconstruction of a reasonably reliable history of the 

factors that influence the water level of Salton Sea; it also 

provided a useful guide for predicting the effects of future 

changes of the inflow.

Salton Sea was formed in 1904-07 by an uncontrolled diversion 

of the Colorado River, which probably had an average salinity 

of less than 500 ppm (parts per million). However, large 

quantities of soluble minerals that had accumulated in Salton 

Sink during previous centuries were dissolved by this fresh 

water, and after 1907 the rapid reduction in volume of Salton 

Sea caused additional increases in salinity. By 1925, when the 

sea had stopped receding because of the increasing irrigation

drainage, the salinity was near 40,000 ppm, which is somewhat 

greater than that of ocean water (about 35,000 ppm). Between 

1938 and 1964 the salinity was considerably less than 40,000 ppm 

because of dilution due to an increase in the volume of water.

The stable water level of Salton Sea corresponding to any 

specific stable rate of inflow is known, provided that no works 

are constructed to regulate the sea. Increasing interest in 

recreational uses of the sea and in real-estate developments on 

its shore has, however, led to proposals of direct action for the 

control of both the water level and the salinity. Within certain 

limits and in certain circumstances, this control would be 

possible, but its feasibility also involves many factors not 

considered in this report.

INTRODUCTION

The Salton Sea was formed in 1904-07 as a result 

of an unusual sequence of events involving the diversion of Colorado River water for irrigation in Imperial Valley, Calif., and the occurrence of unexpected 

floods in the Colorado Eiver. The sea has been sustained chiefly by drainage from irrigated land, and its 

future will also depend mainly on such drainage.

As are all closed lakes, Salton Sea is saline because of 

the accumulation of minerals, chiefly salts, left by evaporation. The salinity has varied markedly, but for 

nearly three decades it has been nearly equivalent to 

that of ocean water. Although the sea is not suitable 

as a source of water for irrigation or domestic use, it 

has become an important resource for recreational uses.

For many years this "sea in the desert" was regarded 

as little more than a convenient receptacle for drainage 

and waste water, and the principal interest in the sea 

concerned encroachment of the water on arable lands 

and on some real-estate developments on the shore. 

However, its location in a famous winter-resort area 

within 150 miles of the metropolitan areas of southern 

California favors development of parks, marinas, and 

resorts on its shore. The accelerated pace of such developments in recent years has greatly increased the 

value of the sea and has also increased the need for 

reliable information on the hydrologic regimen (fluctuations of the water level and their causes and related 

changes in chemical characteristics).

Cl
02 WATER RESOURCES OF LOWER COLORADO RIVER SALTON SEA AREA

Previous investigations of the hydrologic regimen 

were severely handicapped by limitations of the methods then available for determining evaporation and, 

also, by the lack of complete inflow data. The development and testing, since 1950, of the energy-budget and 

mass-transfer methods of determining evaporation 

(U.S. Geol. Survey, 1954; Harbeck and others, 1958) 

together with the increasing concern about the trends 

of water level and salinity of the sea and about the 

availability of fresh water to supply the entire service 

area of the lower Colorado River prompted a new 

hydrologic study of the sea. This report presents results of studies of water level, inflow, evaporation, 

chemical quality, and their interrelations, based on an 

intensive investigation conducted during 1961-62 and 

on available records for previous years.

The investigations in 1961-62 were made under the 

direction of C. C. McDonald, project hydrologist, as a 

part of an appraisal of the water resources of the area 

for which the lower Colorado River is the principal 

source of water supply. Inflow and water-budget 

studies were made by Alien G. Hely; energy-budget and 

mass-transfer studies of evaporation, by G. H. Hughes; 

and studies of chemical characteristics by Burdge 

Irelan. Streamflow measurements by the U.S. Geological Survey, as a supplement to those made by the Imperial Irrigation District and the Coachella Valley 

County Water District, were directed by Walter Hofmann, district engineer, Menlo Park, Calif.

Messrs. R. F. Carter, general manager of the Imperial 

Irrigation District, and L. O. Weeks, general manager 

of the Coachella Valley County Water District, cooperated by supplying hydrologic records and other 

pertinent information. The Sandia Corporation, Albuquerque, N. Mex., granted permission to use some of 

its facilities at Salton Sea Base (Sandy Beach), and 

the North Shore Yacht Club granted permission to install a water-stage recorder on its breakwater.

GENERAL DESCRIPTION AND HISTORY

The natural drainage area of Salton Sea includes 

8,360 square miles of diverse terrain that is mostly 

in California but extends about 20 miles into Baja 

California, Mexico. Mountains on the west and northeast rims of the basin reach altitudes ranging from less 

than 3,000 feet to 11,500 feet in the San Bernardino 

Mountains. The south rim is the crest of the Colorado 

River delta, which extends from an apex near Yuma, 

Ariz., to the mountains at the west edge of the elongate 

depression that contains Salton Sea and the Gulf of 

California. About one-fifth of the basin is below or only 

slightly above mean sea (ocean) level.

The Colorado River has discharged water and sediments across its delta through many distributaries,

some of which flowed northward into the Salton Sea 

basin. For the last few centuries, however, the flow 

has generally been southward to the gulf. Consequently, the natural drainage area of Salton Sea is now topographically distinct from that of the Colorado River in 

the delta region. Early in this century, the construction 

of levees on the delta to prevent overflow to the north 

helped to complete the separation of the two drainage 

basins; later, construction of numerous flood-control 

reservoirs in the Colorado River basin ensured the 

permanence of the separation.

Figure 1 shows the principal features of the Salton 

Sea basin and its geographic relation to the head of the 

Gulf of California and to the lower Colorado River.

A contour map of the depression occupied by Salton 

Sea, adapted from a larger scale map (Littlefield, 1966), 

is shown in figure 2. Contours at and above 240 feet 

below mean sea level were derived from topographic 

maps (scale 1:24,000) based on a survey made in 1957 

by the Topographic Division of the U.S. Geological 

Survey. Contours below that level were based on 152 

soundings made in 1962 by Shawn Biehler, California 

Institute of Technology. The positions of the soundings 

were determined with the aid of radar equipment.

Most of the Salton Sea basin is extremely arid, and 

the natural runoff is insufficient to maintain a permanent water body. For a few centuries prior to 1901, 

when irrigation began in Imperial Valley, Calif, (south 

of Salton Sea), the depression now occupied by the sea 

then known as Salton Sink infrequently contained 

water as a result of unusual runoff from the bordering 

mountains or overflow from the Colorado River. 

McDougal (1914) reported that the sink contained 

water during at least 8 years of the 19th century.

The low altitude of large tracts of irrigable land within the Salton Sea basin facilitated the gravity diversion 

of Colorado River water for irrigation in Imperial Valley and, later, in Mexicali Valley, Baja California (an 

extension of Imperial Valley), and in Coachella Valley, 

Calif, (northwest of Salton Sea).

The first diversion from the Colorado River for irrigation use in the Salton Sea basin was made in 1901 

(Mendenhall, 1909). During the next few years, increasing demands for water and accumulations of sediment in the canal and at the headgate, near the California-Baja California border, caused serious water 

shortages during periods of low streamflow. During 

the summer of 1904, additional diversions were made at 

points downstream from the headgate as an emergency 

measure to relieve the shortage. No headgates were 

built at that time because of legal problems. Before 

the new channels could be properly protected, a series 

of floods eroded them so extensively, that almost the 

entire flow of the Colorado River was diverted into the
HYDROLOGIC REGIMEN OF SALTON SEA, CALIFORNIA C3

Drainage-basin boundary 

Sea level or 3000-foot contour

10

L_i

20 MILES 

_J

FIGURE 1. Salton Sea basin.
C4 WATER RESOURCES OP LOWER COLORADO RIVER SALTON SEA AREA

Stream-gaging station

4 MILES

FIGURE 2. Salton Sea bed. Adapted from Littlefleld (1966).

Salton Sea basin. Floodwater began to collect in the 

sea in November 1904, and the diversion was out of control for more than 2 years, until February 1907.

During the period of uncontrolled diversion, the level 

of Salton Sea rose to the extent that water covered 

more than 500 square miles (330,000 acres) and was 

more than 80 feet deep. During the next 12 years the 

water level receded 55 feet. Because of the increasing 

drainage from irrigation, the trend reversed about 1925

and was generally upward from that time until 1963. 

(A graphic history of the water level and the principal 

controlling factors is presented in the section "Hydrologic Eegimen for 1908-62" of this report.)

The chemical characteristics of the water in Salton 

Sea, discussed in the section "Chemical Regimen," underwent a continual change because of the events just 

described.
HYDROLOGIC REGIMEN OF SALTON SEA, CALIFORNIA C5

WATER LEVEL AND VOLUME

The water level and volume of Salton Sea vary 

continually in response to variations in the rates of 

inflow and evaporation (the only process by which 

water can leave this sea naturally). When inflow 

exceeds evaporation, the water level and volume 

increase, and the reverse is also true. The relation 

of the change in volume to inflow and evaporation 

for a specific period, commonly called a water budget, 

can be expressed as follows:

where

(1)

AV= change in volume, 

Is =inflow in surface channels, 

Ig=inflow as ground-water seepage, 

P precipitation on the water surface, 

E evaporation,

and all quantities are expressed in like units (acrefeet in this report).

Any term of equation 1 can be computed if all other 

terms are known, but the accuracy of the computed term 

depends on the degree of error in the terms that are 

measured or estimated. The result is not reliable if the 

probable combined error is large in relation to the computed term. Hence, the equation for Salton Sea is best 

suited to computation of the largest terms, I8 and E, 

and can provide little or no useful information regarding small terms such as Ig.

In this report the water budget is applied three ways: 

(a) to estimate evaporation from Salton Sea during 

1961-62; (b) to estimate annual surface inflow prior to 

the beginning of records in 1944; and (c) to derive the 

relation between stable mean annual inflow and the corresponding water level. The methods of evaluating 

the terms vary with the information available and are 

described in following discussions.

The change in volume of a water body is generally 

derived from a record of water level and a relation of 

water level to surface area or volume. In figure 3 the 

relations dated 1965 were based on the maps and soundings, previously described, that were used in preparing 

figure 2. The lower parts of the relations dated 1958 

in figure 3 were based on surveys that were probably 

made prior to 1905. Part of the difference between the 

two sets of curves may be a result of lack of refinement 

in the earlier surveys, and part may be a result of sedimentation on the deltas of the Alamo and New Rivers. 

Most such sedimentation probably occurred during the 

uncontrolled diversion of 1904-07. If this assumption 

is valid, the 1965 relations apply with little error since 

1907. Consequently, they were used in this report for 

all computations involving area or volume.

217-105 66 2

VOLUME, IN MILLIONS OF ACRE-FEET 

4 8 12 16

200

220

S 240

260

280 100 200 300 400

SURFACE AREA, IN THOUSANDS OF ACRES

FIGURE 3. Relations of water level to area and volume of Salton Sea. 

The relation dated 1965 was used in this report for all years after 

1907.

Monthly observations of the water level of Salton 

Sea were made on staff gages at several different sites 

from November 1904 to September 1951. A waterlevel recorder at Sandy Beach (fig. 2) has been in operation since that date. All water-level data in this report have been made comparable by reference to mean 

sea level, datum of 1929 the datum used in U.S. Geological Survey publications for records since 1951. The 

datum of 1901, which is 0.91 foot lower than that of 

1929, was used in previous publications of the data for 

years prior to 1951.

Some of the computed water levels for years prior to 

1948 may be appreciably in error because of undetermined effects of unstable gage supports, earthquakes, 

or land subsidence. Water-budget computations, however, would be affected for only a few scattered years, 

and the resulting errors are probably relatively inconsequential.

Although the records of water level at a single site 

are considered to be generally satisfactory for use in annual water budgets, more accurate records were desired 

by the authors for monthly water budgets in 1961-62. 

For short periods strong winds cause a marked lowering of the water surface at the upwind side of Salton 

Sea and a concurrent raising of the surface at the downwind side. To minimize such effects on the record of 

water levels for 1961-62, two additional recorders were
C6 WATER RESOURCES OF LOWER COLORADO RIVER SALTON SEA AREA

installed, one at Desert Beach and one at Imperial Salt 

Farm (fig. 2). All three recorders were set to read 

alike when the water surface was calm, and the average 

of the three recorded values was assumed to be the level 

of the sea. Computed changes in water level during 

1961-62 are believed to be generally within 0.01 foot of 

the actual change.

Graphic presentations of monthly and annual fluctuations of water level are herein included with discussions of "Inflow Studies" and "Hydrologic Kegimen for 

1908-62."

INFLOW STUDIES

Inflow to Salton Sea consists of discharge from 

surface channels, ground-water seepage directly to the 

sea, and precipitation on the water surface. The following discussions concern measured or estimated 

annual values since 1907, or since the beginning of 

record, and also monthly values for 1961-62. The 

monthly values illustrate typical seasonal fluctuations 

and enable the determination of monthly evaporation 

by the water-budget method.

SURFACE INFLOW

For this study the surface inflow to Salton Sea is 

classified according to its source, as follows: (a) Inflow from Imperial Valley, including drainage from 

Mexicali Valley; (b) inflow from Coachella Valley; 

and (c) inflow from other areas.

IMPERIAL VAX.LBY

During most years, more than 90 percent of the 

surface inflow to Salton Sea is from Imperial Valley. 

The relatively uniform flows of the Alamo and New 

Kivers (fig. 1) account for most of the inflow from this 

valley, but highly variable flows in more than 30 minor 

channels account for about 10 percent.

The Imperial Irrigation District has maintained 

records of total inflow from the valley since 1944. 

These records are computed each month on the basis 

of discharge measurements and gage-height records of 

the Alamo and New Kivers near their mouths (near 

Niland and Westmorland, respectively) and on the 

basis of estimates of flow in the minor channels based 

in part on records from numerous gate openings.

The large number of channels, the variability of 

flow, and other conditions have been serious deterrents 

to the collection of precise records of the total flow in 

minor channels. To appraise the accuracy of past 

records of the inflow from Imperial Valley and to 

provide a better measure of the inflow for the study 

period, the U.S. Geological Survey monitored the 

records of the Alamo and New Kivers during 1961-62 

and measured the flow in many of the minor channels.

During 1961 the minor-channel program included 

(a) operation of 1 water-stage recorder and 2 continuous-flow meters on 3 of the largest channels, (b) computation of flow from continuous gage-height records 

above 4 rated waste ways,1 and (c) weekly measurements of flow in each of 18 channels.

Monthly flow in each of the 18 channels (minorchannel program, item c) was estimated as the average 

of all measurements made during the month or within 

3 days of either end of the month. Although such 

averages for individual channels may differ markedly 

from the actual monthly flows, the differences tend to 

compensate when many averages are combined. Consequently, the sums of the computed monthly flows for 

all channels are considered to be fairly reliable.

Evidence to support this conclusion was obtained by 

comparing monthly flows in Trifolium drain 1 (near 

Westmorland) computed from a continuous gageheight record with monthly flows in the same drain 

computed from weekly measurements only. The percentage differences in computed flows for individual 

months range from about 17 to + 17, but generally 

the differences for periods of several months are insignificant.

Flow in the channels not gaged during 1961 was 

estimated to be about 10 percent of the total flow for 

the 18 channels in item c (about 0.5 percent of the 

surface inflow from Imperial Valley).

In 1962 an additional continuous-flow meter was 

installed, and the number of channels measured weekly 

(item c) was reduced from 18 to 5. Thus, the total 

number of gaged channels was reduced from 25 in 1961 

to 13 in 1962. The recorded flow in these 13 channels 

accounted for 73.5 percent of the computed total flow 

in minor channels during 1961, and the same percentage 

was assumedly applicable in 1962.

Independent computations of the discharge of the 

Alamo and New Kivers by the Geological Survey corresponded, generally within about 3.5 percent, to the 

irrigation district's records of monthly flow, and 

records of annual flow correspond within about 1 percent; consequently the irrigation district's records of 

flow in the rivers were considered by the authors to be 

satisfactory.

The Survey's estimates of the total flow in minor 

channels, however, differ markedly from the estimates 

made by the irrigation district without benefit of the 

streamflow measurements just described. Although 

these differences are large relative to the flow in minor 

channels, they are small relative to the total surface

1 Dally discharge In three of the wasteways, and dally gage heights 

at the fourth, were furnished by the Imperial Irrigation District; 

however, these records were not used in the district's estimates.
HYDROLOGIC REGIMEN OF SALTON SEA, CALIFORNIA C7

inflow from Imperial Valley. The difference for 1962 

(about 4.5 percent of the total inflow) was less than 

that for 1961 (about 6 percent of the total inflow), 

probably because the irrigation district made a change 

in the procedure used in water accounting for their 

monthly records. Table 1 summarizes inflow from 

Imperial Valley during 1961-62.

TABLE 1. Monthly surface inflow, in acre-feet, from Imperial

Valley, 1961-62 

[Records for the Alamo and New Rivers furnished by Imperial Irrigation Dist.]

January __ 

February _ 

March ______ 

April _______

July _____

August _____ 

September. 

October. _ 

November. 

December- _

Annual ___

Alamo 

River

43,280 

47,200 

64,600 

66, 920

63, 310

57,830

60, 330

58, 710 

61, 710 

65, 670 

49, 820 

36, 120

675, 500

1

New 

River

31, 840 

33, 450 

42,660 

42, 370

39, 960

35, 050

35, 090

36, 610 

39, 600 

40, 120 

30, 920 

29,310

437, 000

961

Minor 

channels

7,790 

9,910 

11,500 

11, 500

12, 000

11, 600

11, 900

13,000 

13,300 

11,700 

8,910 

7,730

131, 000

Total

82,900 

90,600 

119, 000 

121, 000

115, 000

104, 000

107, 000

108, 000 

115, 000 

117,000 

89, 600 

73,200

1, 242, 000

Alamo 

River

39,480 

36, 870 

59, 810 

68,160

61,330

59, 700

63, 620 

75, 630 

71, 070 

50, 570 

39,420

681, 300

1

New 

River

37, 290 

27, 780 

40, 560 

41, 650

39, 050

35, 750

35, 640

36,980 

41,920 

40, 940 

34,300 

43, 470

455, 300

962

Minor channels

6,430 

8,750 

15,200 

15, 100

13,500

13,500

13,700

14,800 

15, 800 

12, 400 

7,520 

7,250

144, 000

Total

83,200 

73,400 

116, 000 

125,000

114. fiflft

105, 000

109,000

115, 000 

113, 000 

124,000 

92,400 

90,100

1, 280, 000

The difference between figures for surface inflow during 1961 computed by the Imperial Irrigation District 

and those computed by the Geological Survey suggests 

a possibility of appreciable error in records for earlier 

years. The following evidence, however, indicates that 

there is no large consistent error in these earlier records. 

Annual surface inflow to the Salton Sea for 1948-60 

computed by using water budgets (described in "Hydrologic Eegimen for 1908-62" of this report) differs from 

the inflow based on available records by more than 5 percent for 4 of the 13 years, but the average values for the 

13-year period are almost identical.

Annual inflow from Imperial Valley for 1944-62 is 

listed in table 4, which summarizes the inflow from 

all areas.

COACH-ELLA VALJJBIY

Coachella Valley is drained by the Whitewater River 

and 18 minor channels. When the river was in its 

natural state, most floodwaters tended to spread over 

the desert and disappear without reaching Salton Sea. 

The lower reaches of the stream (Coachella Valley 

Stormwater Channel) have been improved, however, by 

levees constructed to confine floodflows and by dredging 

operations which provide drainage for adjacent farmlands. During 1961-62 all channel flow was relatively 

uniform because it consisted chiefly of ground-water 

seepage. Since importation of Colorado River water 

began (about 1948), drainage from irrigated lands has 

been the source of nearly all the surface inflow from 

the valley.

The Geological Survey computed records of flow in 

the Whitewater River at its mouth on the basis of 

weekly or biweekly measurements and of a continuous 

gage-height record furnished by the Coachella Valley 

County Water District. Estimates of the flow in minor 

channels, based on monthly measurements made by the 

water district, were added to measurements of the flow 

of the river to obtain estimates of the monthly inflow 

from Coachella Valley.

Comparison of these estimates with the water district's records of monthly inflow, based on current operating data, indicated that the water district's records 

were satisfactory. Differences between corresponding 

monthly flows were generally less than 10 percent, and 

differences between corresponding annual flows were 

less than 2.5 percent. Monthly inflow from Coachella 

Valley for 1961-62 is summarized in table 2.

TABLE 2. Monthly surface inflow, in acre-feet, from Coachella

Valley, 1961-62 

[Records of total inflow furnished by Coachella Valley County Water Dist.]

July.. _ __________ ___ ....

Annual ________

196

Whitewater 

River

3,160

3,150

4,420

4,640

5,380

4,300

5,120

5,270

5,370

4,520

3,900

4,160

53,390

1

Total

5,170

5,330

6,550

7,300

7,500

7,260

7,320

9,040

8,640

7,250

6,090

6,440

83,890

196

Whitewater 

River

4,690

4,920

5,740

6,140

6,560

6,100

6,350

7,060

6,950

5,760

4,530

4,790

69,590

2

Total

6,960

7,490

9,190

10, 150

10, 910

10,100

10, 730

11,600

11, 340

9,200

7,270

7,750

112, 700

The annual surface inflows from Coachella Valley 

for 1948-62 are listed in table 4. Inflow for 1948 was 

estimated because sections of the Coachella Canal contained water for one or more years prior to its completion in 1949. For previous years, inflow due to storm 

runoff is treated in this report as a part of the inflow 

from other areas.

OTHER ARKAS

No records of inflow to Salton Sea from areas other 

than Coachella and Imperial Valleys were made prior 

to 1961. During the winter of 1960-61 gaging stations 

were installed at the mouth of Salt Creek, near Mecca, 

and near the mouth of San Felipe Creek, near Westmorland (fig. 1).

The Coachella Canal crosses the lower part of the 

Salt Creek basin and several smaller drainage basins 

southeast of Salt Creek. Seepage from the canal maintains a small base flow in Salt Creek during all seasons 

and in several of the smaller streams during some 

months. Less than 5 percent of the total flow of Salt
C8 WATER RESOURCES OF LOWER COLORADO RIVER SALTON SEA AREA

Creek during 1961-62 was storm runoff; the balance 

was seepage.

San Felipe Creek drains more than a thousand square 

miles, including much mountainous area and some small 

tracts irrigated with local water supplies. During most 

winters a small base flow persists at the mouth of the 

creek. Storm runoff accounted for about 90 percent of 

the flow during 1961-62.

Table 3 indicates the monthly flows in Salt and San 

Felipe Creeks and the estimated flows from ungaged 

areas. Ungaged inflow from the northeast, mostly 

seepage from the Coachella Canal, was estimated to be 

about the same as flow in Salt Creek, which includes 

seepage from about half of the reach of canal that is 

near the shore. Ungaged inflow from the southwest 

was estimated to be twice the estimated storm runoff 

in San Felipe Creek (total runoff less base flow not 

given in table 3). The latter estimate was based on 

the assumptions that virtually all measured storm runoff originated near the gaging station and that the 

storms also caused runoff from the more mountainous 

area northwest of San Felipe Creek. These estimated 

quantities of ungaged inflow are very small in comparison to total inflow to Salton Sea; therefore, errors are 

relatively unimportant.

TABLE 3. Monthly surface inflow, in acre-feet, from areas other 

than Imperial and Coachella Valleys, 1961-62

February ______

July.. ______

September. ___

November _____

December _____

Annual ____

Salt

Creek

1470

391

393

226

176

129

108

186

215

298

354

528

3,470

19

San

Felipe

Creek

23

23

13

0

0

0

0

944

0

0

0

123

1,130

61

Ungaged

470

390

390

230

180

130

110

2,100

220

300

350

760

5,630

Total

960

800

800

460

360

260

220

3,230

440

600

700

1,410

10,200

Salt

Creek

474

430

449

392

344

266

184

198

309

377

441

554

4,420

19

San

Felipe

Creek

336

15

11

1

0

0

0

0

0

0

0

11

374

62

Ungaged

1,110

430

4Kfl

^on

340

270

ISO

200

310

380

440

560

5,060

Total

1,920

880

910

780

680

KAn

360

400

620

760

880

1,120

9,850

1 Partly estimated.

Surface inflow from areas other than the principal 

irrigated valleys is very small during most years but 

is appreciable during periods of maximum storm intensity. For example, a field reconnaissance in 1951 indicated that considerable storm runoff had occurred in 

several tributaries during July or August of that year. 

Also, during the period September 1-11,1939, the level 

of Salton Sea rose 0.8 foot, which corresponds to an 

increase in volume of about 150,000 acre-feet. An unknown amount of this increase was caused by rainfall 

on the water surface, but the major part was probably 

caused by storm runoff. The official records of rainfall

during the period include 6.33 inches at Brawley and 

2.03 inches at Indio. An unofficial observation of 11 

inches in 6 hours near Coachella was reported by the 

Coachella Valley County Water District (Gatewood, 

1945).

For the years prior to 1961 the surface inflow from 

areas other than the principal irrigated tracts (including Coachella Valley prior to 1948) was assumed to be 

about the same as that for 1961-62, which was about 

10,000 acre-feet each year, because there is no basis for 

reliable estimates for individual years. Seepage from 

the Coachella Canal which was a major component of 

the inflow from these areas in 1961-62, was not a factor 

prior to 1948. Nevertheless, this assumption is reasonable because Coachella Valley was included with "other 

areas" prior to 1948, and also because precipitation was 

above normal for several years prior to 1948. Precipitation during the period prior to 1948 was about two 

or more times the normal amount in 7 years, but since 

1948 it has exceeded the normal amount only once, and 

then only slightly.

SUMMARY OF SURFACE INFLOW

Most of the surface inflow to Salton Sea during 1961- 

62 was determined at conventional stream-gaging stations or continuous-flow meters, a much smaller part 

was estimated on the basis of periodic measurements, 

and a very small part was not measured. The percentages of the inflow in each category are summarized as 

follows:

1961

Gaging stations 91.6 

Periodic measurements_____ 7.5 

Ungaged__ _ .9

The errors in computed annual inflow for 1961-62 

are probably less than 5 percent, Errors in other annual 

values and in monthly values for 1961-62 probably are 

generally less than 10 percent.

The monthly surface inflows to Salton Sea for 1961- 

62, itemized in tables 1-3, are summarized with other 

items of the water budget in the discussion of evaporation. The annual flows for 1944-62, described by areas 

in the preceding sections, are summarized in table 4.

GROUND-WATER INFLOW

Salton Sea and the surrounding area are underlain 

by thick deposits of alluvium, which are rather impermeable except in Coachella Valley and locally at the 

mouth of San Felipe Creek. The relative impermeability in Imperial Valley is indicated by the extremely low 

yields of wells near the sea and by data from a line of 

auger holes that extends across the valley just south of 

the sea. The greater permeability of the alluvium in 

Coachella Valley is demonstrated by the yields of many 

artesian and water-table wells.

91.4 

5.5 

3.1
HYDROLOGIC KEGIMEN OF SALTON SEA, CALIFORNIA C9

TABLE 4. Annual surface inflow to Salton Sea, in thousands 

of acre-feet, 1944-62

Total inflow for each year from 1944 to 1960 is the sum of flows from Coachella and 

Imperial Valleys plus an estimated 10,000 acre-feet of inflow from other areas. 

Records for Imperial Valley for 1944-60 were furnished by Imperial Irrigation 

Dist. Records for Coachella Valley were furnished by Coachella Valley County 

Water Dist., except the one for 1948, which was estimated]

Year

1944 _ ...........................

1945. . -

1946.- ...................... ...

1947- 

1948 

1949 _ 

1950. ____ _ ... .. _ -. ...

1951-- __ ...

1952 _ . 

19(53. 

1954. . 

IQ5B.. ............................

19BK.. ............................

1957- ----- __ -- __ -. _ ------

1958- - 

1959- _____ _ _ . _ -. ...

I960-. .... ... ... ... ....... -

1961. .

1962. .-. 

Imperial 

Valley

1,090

1,070

1,120

1,070

1,050

1,130

1,140

1,210

1,300

1,380

1,300

1,120

1,170

1,080

1,080

1,140

1,180

1,242

1,280

Coachella 

Valley

20

36

65

108

86

63

72

85

71

53

56

57

70

84

113

Total

1,100

1,080

1,130

1,080

1,180

1,180

1,220

1,330

1,400

1,450

1,380

1,220

1, 250

1,140

1,150

1,210

1,260

1,340

1,400

The total ground-water inflow to Salton Sea was estimated to be about 50,000 acre-feet per year. The California Department of Water Eesources (1964, p. 133- 

137) estimated the annual ground-water inflow from 

Coachella Valley to be about 30,000 acre-feet (including 

the discharge of uncontrolled flowing wells), on the 

basis of hydrologic investigations conducted during 

1960-61. On the basis of geologic and hydrologic studies 

made during 1961-64, J. H. Eobison of the U.S. Geological Survey (oral commun., 1964) estimated that the 

annual inflow through the alluvium bordering San Felipe Creek was about 10,000 acre-feet and that inflow 

through the alluvium of Imperial Valley was less than 

2,000 acre-feet.

Seepage from the Coachella Canal is a source of recharge for aquifers northeast of Salton Sea, but most 

of the water lost from the canal appears to be discharged 

by evapotranspiration and surface inflow rather than 

by ground-water inflow. The average annual loss from 

the canal in the reach bordering the sea is about 26,000 

acre-feet, of which about 8,000 acre-feet enters the sea 

from surface channels. Evaporation from the canal, 

evapotranspiration from wet areas (chiefly stream channels covered with dense vegetation), and increasing 

ground-water storage could reasonably account for the 

rest.

Although both seasonal and long-term variations in 

ground-water inflow may occur, the magnitude and nature of the fluctuations are not sufficiently well known 

to justify estimates for individual months and years. 

Consequently, the rate of ground-water inflow was assumed to be constant.

PRECIPITATION ON THE WATER SURFACE

The best available index of precipitation on the water 

surface for 1948-62 is the average computed from three 

rain gages on the shore. These gages are located at 

Sandy Beach, Devils Hole, and Imperial Salt Farm 

(fig. 2) and are part of the set of three evaporation 

stations subsequently described in this report.

For the period 1908-47, Weather Bureau records of 

precipitation at Brawley, Imperial, Indio, and Mecca 

(fig. 1) provide an index of precipitation on the water 

surface. Records for all four stations were available 

for 23 of the 40 years, and records for three stations 

were available for all but one of the remaining years. 

Because precipitation at Indio generally is slightly 

higher than at the other three stations and is included 

in all multiple-station averages, these averages were 

multiplied by 0.95 to derive the estimated depth of precipitation on the Salton Sea. The conversion factor, 

0.95, is the ratio of the average for Brawley and Mecca 

(the stations nearest the sea) to the four-station average 

for 23 years.

The average annual depth of precipitation on Salton 

Sea for 1931-60 (corresponding to the current Weather 

Bur. normal) is 0.21 foot (2.5 in.), and the average for 

1908-62 is 0.22 foot. Quantities of precipitation on the 

water surface (average depth, in feet, times the surface 

area, in acres) 'are summarized with other water-budget 

data in later sections.

The amount of precipitation during most years was 

so small that any errors involved have relatively little 

effect on computations in this report, but the precipitation during exceptional storm periods may have differed significantly from the quantities corresponding 

to precipitation at the index stations.

EVAPORATION STUDIES

As all known methods of determining evaporation 

from Salton Sea involve considerable error, relatively 

independent determinations by the water-budget and 

energy-budget methods were made for the period 

1961-62. These results were then combined with masstransfer data and evaporation-pan data in an effort to 

determine the most practical means of continuing measurements of evaporation and estimating evaporation 

for previous years.

WATER-BUDGET METHOD, 1961-62

The best known method of determining evaporation 

from a water body is the solution of the water-budget 

equation. (The measurement of evaporation from 

pans is a small-scale application of the method.)
CIO WATER RESOURCES OF LOWER COLORADO RIVER SALTON SEA AREA

For many applications of the water budget, use of 

equation 1, wherein the change of volume, AF, is determined as previously described, is adequate. The 

effects of bank storage and thermal expansion of water, 

however, must sometimes be considered in order to 

obtain the most reliable estimates of evaporation.

Bank storage. The term "bank storage" applies to 

the quantity of ground water that drains into a water 

body as a direct result of a recession of the water level. 

Conversely, the term applies to the quantity that flows 

from the water body into the banks or that is prevented 

from draining from the Banks into the water body as 

a direct result of a rise in the water level. Such storage 

is fully effective only during long-term changes of water 

level because of the slow movement of the ground water.

Rough estimates of the effect of bank storage at 

Salton Sea (based on length of shoreline and estimates 

of ground-water gradients and soil porosity) indicate 

that is was negligible for monthly changes in water 

level during 1961-62 and was probably less than 5 

percent of the change in volume, indicated by the 

1965 relation hi figure 3, during the rapid recession 

of 1908-20. Therefore, no adjustments for the effects 

of bank storage were included in computations for 

this report.

Thermal expansion. Changes in the volume within 

a water body may be caused by thermal expansion 

or contraction of the water as well as by a net gain 

or loss of water. The effects of expansion and contraction are generally negligible for budget periods of 

one or more years but are often significant for periods 

of a month or less when the water is rapidly warming 

or cooling.

To account for the effects of thermal expansion and 

contraction, the following relation was used in monthly 

water budgets for Salton Sea:

AFW =AF-AF,, (2) 

where

AyM =the net gain or loss of water,

AF = the total change in volume indicated by

the change in water level, and 

AVt = the change in volume resulting from thermal 

expansion (AFt is negative when the volume of water is contracting).

The method of computing the thermal expansion 

term is described in the Lake Hefner report (U.S. Geol. 

Survey, 1954) and is illustrated by the following computation for the month of June 1961. Interpolation 

between average temperatures determined by thermal 

surveys of Salton Sea (described in the discussion of 

the energy budget) indicated that the water temperature was about 23°C at the beginning of the month and

about 29 °C at the end. If the relative volume of 

water at 4°C (the temperature for maximum density) 

is assigned the value of 1.00000, then the volume at 23 °C 

is 1.00244, and at 29°C, 1.00405 (Hodgman and others, 

1957, tables of relative density and volume of water). 

The ratio of the volume of a given mass of water at the 

end of the month to the volume of the same mass at the 

beginning is 1.00405/1.00244=1.00161. The approximate change in volume due to thermal expansion is 

equal to (1.00161 1) multiplied by the average volume 

of the sea for that month (5,590,000 acre-ft), which is 

9,000 acre-feet.

For some types of gage installation, thermal expansion of the structure must be considered in the determination of the changes in water level and in total volume. 

The basic reference gage for Salton Sea, however, consisted of 3.3-foot-long enameled-steel sections attached 

to a wooden pile in shallow water, and the effects of 

expansion and contraction of the gage were considered 

to be negligible.

Computed evaporation. Monthly and annual evaporation is computed from the water level and inflow 

data, previously described, by solving equation 1 for 

E and using the equivalent of AFW (as defined by equation 2) for AF as follows:

E=Is +Ig+P AF+AF*. (3)

Each term of the budget (except ground-water inflow, 

which has been treated as a constant) is listed in table 5.

The accuracy of the computed evaporation is affected 

by errors in all other terms of equation 3. The resulting error is probably less than 7 percent for annual 

values and less than 12 percent for most monthly values, 

but errors of 20 percent or more may affect values for 

some months. The smallest computed monthly values 

are generally affected by the largest percentage errors.

The principal source of error in computed evaporation is the error in surface inflow records, which is 

generally less than 5 percent for annual flows and less 

than 10 percent for monthly flows. An error of 50 

percent in the estimated ground-water inflow would 

correspond to an error of less than 2 percent of annual 

evaporation or of 10 percent of evaporation for some 

winter months. The amount of precipitation is so 

small that errors are inconsequential.

An error of 0.01 foot in water level corresponds to a 

change in volume of about 2,200 acre-feet that is, 

about 7 percent of the smallest monthly evaporation. 

Although the correction for thermal expansion is insignificant relative to the total volume of Salton Sea, it 

is as much as 7 percent of the monthly evaporation and 

is greater than the change in volume indicated by water 

levels for some months.
HYDROLOGIC REGIMEN OF SALTON SEA, CALIFORNIA Cll

TABLE 5. Monthly water budgets, in acre-feet, for Salton Sea, 1961-62

Ground-water inflow (J,) estimated as 50,000 acre-feet per year, or 4,170 acre-feet per month. Evaporation shown here is computed from the water budget, and is compared

with other determinations in table 7]

February _____ .. ....

March _______ .....

April.....................

July..- .............. .

November _ ... .._....

1961

Surface inflow 

(W

89,000 

96,700 

126,000 

129, 000 

123,000 

112,000 

115,000 

120,000 

124, 000 

125, 000 

96,400 

81,000

1, 337, 000

Precipitation 

(P)

4,500 

0 

0 

0 

0 

0 

0 

15,700 

2,200 

0 

0 

11,200

33, 600

Change in 

volume (A V)

+67, 000 

+44, 800 

+51, 700 

+20, 300 

-29, 300 

-4,500 

-29, 200 

-38, 100 

-44, 700 

-15,600 

+13, 400 

+51, 400

+87. 200

Thermal expansion (A Vt)

+1,100 

+1, 200 

+3,000 

+3,100 

+2,300 

+9,000 

+5, 100 

-3,400 

-6,000 

-7,900 

-4, 500 

-1,800

+1,100

Evaporation 

(E)

31,700 

57,300 

81,500 

116, 000 

159,000 

130,000 

153. 000 

175, 000 

169, 000 

137, 000 

82,700 

43,200

1, 335, 000

1962

Surface inflow a.)

92,100 

81,800 

126, 000 

136, 000 

126,000 

116,000 

120, 000 

127, 000 

145,000 

134, 000 

101, 000 

99,000

1, 404, 000

Precipitation 0°)

9,000 

2,300 

0 

0 

0 

0 

0 

0 

2,300 

0 

0 

9,000

22,600

Change in 

volume (A V)

+62, 900 

+38, 300 

+61, 000 

+47, 600 

-38, 500 

0 

-36, 200 

-33, 800 

-4.500 

+4,500 

+6,800 

+54, 200

+162,300

Thermal expansion (A Vt)

-700 

+700 

+3,100 

+4,500 

+1,300 

+6,400 

+5,700 

+700 

-4,000 

-7,400 

-5,600 

-2,800

+1,900

Evaporation

(E)

41,700 

50,700 

72,300 

97,100 

170, 000 

127,000 

166,000 

166,000 

152,000 

126,000 

92,800 

55,200

1, 317, 000

The figures for surface inflow and evaporation given 

in table 5 illustrate typical seasonal fluctuations.of these 

quantities. In figure 4 these figures are graphically 

shown in relation to corresponding fluctuations of 

water level.

The evaporation determined by the water-budget 

method is compared with other evaporation data in a 

later section.

ENERGY-BUDGET METHOD, 1961-62

The energy budget is an accounting for all heat 

energy reaching, stored in, and leaving a water body, 

the objective being to determine the amount of energy 

utilized in the evaporation process and, hence, the 

quantity of water evaporated. The results are only 

slightly dependent on the water budget because the

energy content of the inflowing water is relatively 

small. Evaporation determined by the energy-budget 

method, consequently provides a means for verifying 

that determined by the water-budget method (which 

has obvious deficiences).

The energy-budget method, its underlying theory, 

and the required instrumentation are described in considerable detail in a report of studies at Lake Hefner, 

Okla. (U.S. Geol. Survey, 1954), where the first field 

tests were made, and in a report on studies at Lake 

Mead, Arizona-Nevada (Harbeck and others, 1958). 

The method has also been used on several other lakes, 

although few investigations have provided as good 

opportunities as the one on Salton Sea for comparison 

of results obtained by different methods and for a 

critical evaluation of the different methods. The basic

233

234 -

235 -

1961 1962

FIGURE 4. Monthly fluctuations of water level, surface inflow, and evaporation, 1961-62. (Water level at the end of each month and

evaporation determined by water-budget method.)
C12 WATER RESOURCES OF LOWER COLORADO RIVER SALTON SEA AREA

data and an evaluation of methods are given in a separate technical report (Hughes 1966). The following 

discussion summarizes results and indicates the general 

nature of the method as applied to Salton Sea during 

the period January 9, 1961-January 8, 1963.

The energy budget for a body of water can be expressed as follows:

Q,- Qr+ Qa~ Qar- Qbs + QV ~Q#= Qe+ Q»+ QW) (4)

where

Qs = solar radiation incident to the water surface,

Qr= solar radiation reflected by the water surface,

Qa= incident long-wave radiation from the atmosphere,

Qar long-wave radiation reflected by the water 

surface,

(2&s=long-wave radiation emitted by the body of 

water,

(2»=net energy advected into the body of water,

Q£= increase in energy content of the body of water,

Qe= energy used by evaporation,

Qh= energy conducted from the body of water as 

sensible heat, and

Qw= energy advected by the evaporated water. 

This equation does not include minor terms, such as 

conduction of energy through the bottom of the water 

body, heating due to chemical and biological processes, 

and transformation of kinetic into thermal energy. 

The terms on the left side of equation 4 are either 

measured directly or computed from theoretical or 

empirical relations. Their algebraic sum represents the 

total energy available for evaporation processes and 

conduction to the atmosphere. As of 1961-62 direct 

determination of the terms on the right side was not 

practical, but the distribution of the available energy 

among them was determined by the use of the Bowen 

ratio (discussed in a following paragraph headed "The 

Bowen Ratio") and the fact that the mass of water 

involved in Qe and Q,w is the same. To convert equation 4 to a usable form, the following equivalents are 

substituted for the three terms on the right:

Qh=RQe f ' and Qu= pcE(Te - T6) , 

where

p density of evaporated water, 

E volume of evaporated water, 

L= latent heat of vaporization, 

jR=the Bowen ratio, 

c= specific heat of water,

Te= temperature at which evaporation takes place 

(usually taken as water-surface temperature, TQ), and

temperature (arbitrarily selected as 0° 

C; when Te and Tb are defined as above,

Thus, E is expressed in terms of measurable or known 

quantities as follows:

l~ P[L(l+R)+cT0]

If quantities are expressed in terms of unit area and 

unit time, E is the volume per unit area (depth) of 

evaporated water.

The instruments and methods used to obtain each 

quantity in equation 5 are described in the following 

paragraphs. Instruments at Sandy Beach (fig. 2) were 

used for all measurements of radiation and air temperature, and the values measured there were assumed to 

be applicable to the entire sea.

EQUIPMENT AND PROCEDTIREIS

Incident solar radiation. Incident solar radiation 

(Qs) was measured by an Eppley pyrheliometer connected to a potentiometer recorder. Measurements were 

recorded at 3-minute intervals. Mean hourly values 

were obtained from the recorder chart and added to 

determine total radiation for 1 day. During periods 

of broken cloud cover, when radiation was extremely 

variable, values for periods shorter than 1 hour were 

computed.

Re-fleeted solar radiation. The amount of solar radiation reflected from the water surface (Qr) was computed as the product of hourly values of the measured 

incident solar radiation and corresponding values of 

the reflectivity (ratio of reflected radiation to incident 

radiation) .

Anderson (1954, p. 78-88) showed that reflectivity is 

primarily a function of sun altitude but that it is also 

affected by the extent and height of cloud cover, and he 

presented empirical equations relating these factors. 

The sky over Salton Sea during this study was clear 

most of the time, particularly during the summer 

months, when evaporation was high. As relatively 

little information on the extent and height of cloud 

cover was available, clear-sky conditions were assumed 

for 'all computations of reflectivity. An analysis of the 

probable effects of this assumption indicated that the 

resulting error in computed evaporation might be as 

much as 5 percent for some winter months but is negligible for annual values.

Incident long-wave radiation. A total hemispherical radiometer, calibrated by the manufacturer, was 

used to measure total incident radiation. At night all 

incident radiation is long- wave radiation from the atmosphere (Qa)- To obtain incident long- wave radiation during daylight hours, the solar radiation was subtracted from the total.

The radiometer output was recorded on the strip-
HYDROLOGIC REGIMEN OP SALTON SEA, CALIFORNIA CIS

chart potentiometer at 3-mimite intervals. Mean 

hourly values were corrected for variations due to 

change in temperature of the radiometer surface in 

accordance with the Stefan-Boltzman law (discussed in 

this section under the paragraph heading "Long-wave 

Radiation Emitted by the Water").

Reflected long-wave radiation. Reflected long-wave 

radiation (Qar) was computed as 0.030 times the measured incident long-wave radiation. This computation 

was based on a study made in connection with the Lake 

Hefner investigation (Anderson 1954, p. 96-98), which 

indicated that the reflectivity for long-wave radiation 

from the atmosphere varies only slightly from 0.030 

regardless of the water temperature or salinity.

Long-wave radiation emitted by the water. Thermal 

radiation emitted by any body depends on the emissivity and temperature of the surface. Under conditions 

governing the exchange of radiant energy between the 

atmosphere and the Salton Sea, the emissivity of the 

water surface may be considered to be the complement 

of its reflectivity (Anderson 1954, p. 96). As the reflectivity is 0.030 (preceding section), the emissivity is 

computed to be 0.970.

Thermal surveys, subsequently described in this 

report, indicate that the average temperature of the 

entire water surface for a period of several days is 

closely approximated by the average of the water temperatures recorded continuously at the two buoys indicated in figure 2. Daily values of long-wave radiation 

emitted by the water were computed by use of these 

temperatures in the equation expressing the StefanBoltzman law:

&8=e<r(T0+273) 4, (6) 

where,

e=the emissivity (0.970),

o-=the Stefan-Boltzman constant for black-body 

radiation

(1.171X10-7 cal cm~2 deg~4 day-1), 

T0== water-surf ace temperature in °C.

Advected energy. The advected-energy term (Qv ) 

for Salton Sea represents the energy content (relative 

to that at an arbitrary base of 0°C) of the inflowing 

water from all sources and was computed as the product 

of the volume, density, specific heat, and temperature 

of the inflow. The volume of the inflow was discussed 

in the section "Water-Budget Method, 1961-62"; the 

density and specific heat are nearly the same as those 

of pure water 1.00 g per cu cm and 1.00 cal per g per 

°C, respectively. Frequent or continuous temperature 

measurements of all components of the inflow would be 

impractical. However, the daily average water temperature for shallow streams generally differs only

217-105 66 3

slightly from the daily average 'air temperature. Moreover, the flow of the Alamo and New Rivers is about 

three-fourths of the total inflow to the sea. Hence, a 

relation between water temperatures periodically measured near the mouths of the two rivers and daily air temperatures from a continuous record at Sandy Beach provided a suitable basis for estimating with little error the 

average temperature of all inflow.

Energy content. Determination of the increase in 

energy content (Q&) during any given period of time 

requires a determination of the energy content of the 

water (above that at the arbitrary base of 0°C) at the 

beginning and at the end of that period. The energy 

content at any time depends on the volume, density, 

specific heat, and temperature of the water. The basis 

for determining the volume of water in Salton Sea is 

described in the section "Water Level and Contents." 

The density was determined to be 1.023 g per cu cm. 

The specific heat of ocean water, 0.94 cal per g per °C, 

was used because the salinity of Salton Sea at the time 

of this investigation was approximately the same as that 

of ocean water. The temperature of the water, however, 

varies with both depth and areal location. Consequently, computation of the energy content required 

many temperature observations.

The necessary temperature data were obtained from 

thermal surveys of the Salton Sea made at about 14-day 

intervals. Each thermal survey consisted of a series 

of temperature measurements at each of 35 stations 

spaced so as to provide representative sampling of the 

sea on an areal basis. Station locations were generally 

determined only approximately by observation of the 

two buoys (fig. 2) and of the landm'arks on shore. The 

measurements were made at selected depths below the 

surface so that each was made at the center of a uniformly thick layer of water. Because the widest variations in temperature generally occur near the surface, 

temperature measurements were made within layers 2 

feet thick above a depth of 10 feet and 4 feet thick below that depth. Assumedly, the average temperature 

of the water in each layer was the average of the temperatures measured in that layer.

The energy content of each layer (above the arbitrary 

base temperature) was computed as the product of the 

average temperature, density, specific heat, and volume; 

and the total energy content at the time of any thermal 

survey was the sum of the values computed for all layers. The change in energy storage was determined only 

for the periods between thermal surveys, and equation 

5 was applied only to such periods.

The Bowen ratio. When a temperature difference 

exists between the air and the water surface, energy is 

transferred by convective and conductive processes that 

cannot be readily measured. The ratio of energy so
C14 WATER RESOURCES OF LOWER COLORADO RIVER SALTON SEA AREA

transferred to that used by evaporation was expressed 

byBowen (1926) asfoUows:

P 0.6lCZV-ra)Pa

_£J, - ;;

where (7) (e0 -ea) 1,000 

T0 = water-surface temperature in °C, 

Ta air temperature in °C, 

e0 vapor pressure, in millibars, of saturated air at

the temperature of the water surface, 

ea=vapor pressure, in millibars, of the air at a selected point,

Pa atmospheric pressure, in millibars. 

The water-surface temperature, Tg, was that measured at the two buoys and used to obtain the long-wave 

radiation emitted by the water. The saturation vapor 

pressure of air, e0 , corresponding to values of T0 , was 

taken from standard vapor-pressure tables for a sodiumchloride solution of concentration approximately equal 

to the salinity of Salton Sea.

The temperature, T^ and vapor pressure, e0, of the 

air were obtained from wet-bulb and dry-bulb temperatures at a level about 8 m above the average water level 

of Salton Sea, recorded at 16-minute intervals at Sandy 

Beach.

RESULTS OF ENERGY-BUDGET COMPUTATIONS

The basic computations of evaporation were made for 

intervals between thermal surveys (budget periods) as 

explained in the discussion of energy content. Values 

of each term in the energy budget (eq 4) for selected 

budget periods and for one period of a few days more 

than 1 year are shown in table 6 to illustrate the relative magnitudes and seasonal variations of the terms.

TABLE 6. Representative values, in calories per square centimeter 

per day, of each term in the energy budget for Salton Sea

Period

Jan, 15-29, 1962.. __ ....

Apr. 2-16, 1962. _ .......

July 16-30, 1962..........

Nov. 5-20, 1962... _ ..

Jan. 2, 1962-Jan. 8, 

1963.. - 

Q.

275

fi71

591

303

4R4

Qr

27

39

3R

30

35

Q.

591

772

953

fi48

736

Qor

18

?3

29

19

m

Q».

754

853

970

869

868

Q.

6

15

17

9

12

Qtf

-2

+216

+102

-210

+3

Q.

7?

?56

4?8

2?3

283

Q*

+l

-38

-29

+20

-11

<? 

2

9

23

9

12

To obtain monthly evaporation from that computed 

for budget periods, it was necessary to prorate the evaporation for those periods that include parts of 2 months. 

This was done on the basis of mass-transfer data (described in the next section), because these data reflect 

the variations in the rate of evaporation within the 

budget period.. Evaporation for the first 9 days of 

January 1961 (prior to the beginning of energy-budget 

measurements) was assumed to be equal to that determined by the mass-transfer method.

Monthly evaporation determined by the energy-budget method is shown in table 7 with other determinations 

for convenient comparison.

MASS-TRANSFER METHOD, 1961-62

In contrast with the energy-budget and water-budget 

concepts, in which either the energy used by evaporation or the volume of water evaporated is considered as 

one item in a complete budget for the water body, the 

mass-transfer concept involves only the process by 

which the water vapor is transferred from the water 

body to the atmosphere. The application of masstransfer theory to field determination of evaporation is 

described in previous reports on the energy-budget 

method (U.S. Geol. Survey, 1954; Harbeck and others, 

1958), and the basic data and evaluation of the method 

for Salton Sea are presented in the report by Hughes 

(1966). The general nature of the method and a summary of results are presented herein.

A simplified mass-transfer equation, developed during the Lake Hefner studies, relates evaporation from 

a water surface to the product of the windspeed multiplied by the humidity gradient of the air. A single 

empirical coefficient represents the combined effect of 

other properties of the atmosphere and of the water body 

that may influence the interchange of water vapor between the water surface and the atmosphere. The magnitude of the coefficient is influenced by the size and 

shape of the water body and by exposure of its surface 

to wind (Harbeck, 1962); hence, a determination of the 

coefficient is required for each site. Once the coefficient 

is established, however, the mass-transfer equation provides a convenient means of computing evaporation for 

any period for which base data are available.

The empirical mass-transfer equation is:

E=Nu(e0 -ea), (8) 

where

E evaporation, in inches per day, 

JV=an empirical coefficient, 

u=aver age windspeed, in miles per hour, at a

selected height above the water surface, 

eQ vapor pressure, in millibars, of saturated air 

at the temperature of the water surface, and 

ea=vapor pressure of the air, in millibars, at a

selected height above the water. 

At Salton Sea, the windspeed was measured at a 

height 2 m above the water surface by anemometers 

mounted on two buoys located as shown in figure 2. 

The average of the windspeeds measured at the two 

buoys was assumed to be the average for the entire 

water surface. Since anemometer readings of cumulative movement, in miles, were obtained only when 

thermal surveys were made, average windspeed at the 

buoys could be computed only for the previously 

described energy-budget periods.

To obtain windspeed data for partial energy-budget 

periods, for computation of monthly evaporation, the
HYDROLOGIC REGIMEN OF SALTON SEA, CALIFORNIA C15

wind movement at the two buoys for the entire period 

was assumed to be distributed between the two partial 

periods in the same proportion as the wind movement 

continuously measured at Sandy Beach.

The methods by which values of e0 and ea were 

obtained have been described in the discussion of the 

Bowen ratio (p. C13-C14). The vapor pressure difference, e0 ea, was computed from average values of each 

for the energy-budget periods or partial periods; consequently, the adequacy of the values obtained is comparable to that of the values of windspeed.

Using the total evaporation during the study period 

(Jan. 9, 1961-Jan. 8, 1963), determined by the waterbudget and energy-budget methods, with the corresponding value of the product of windspeed and vaporpressure difference, the coefficient, N, was determined 

to be 0.00156. It should be noted that this coefficient 

value is valid only for the Salton Sea and only when 

base data are obtained at virtually the same points as 

those used during the study.

Because of the manner in which the coefficient was 

determined, the total evaporation for the 2-year period 

computed by the mass-transfer equation depends on results of the other two methods. Distribution of the 

evaporation within the period, however, is entirely independent of the water budget, and it is nearly independent of the energy budget because a factor of major 

importance in one method is of minor importance in the 

other.

COMPARISON OF RESULTS OBTAINED BY THE THREE 

METHODS

Monthly evaporation determined by each of the three 

previously described methods and reduced to a common 

unit (inches of depth) is listed in table 7 and plotted in 

figure 5.

TABLE 7. Monthly evaporation from Satton Sea, in inches, 

determined by three methods

February. __

April..........

July.... . 

September. . . _

November. ... 

December. ....

Annual.

Water 

budget

1.70

3.07 

4.35

6.18

8.47

6.93

8.17

9.36

9.08 

7.36

4.45 

. 2.32

71.4

19

Energy budget

1.28

2.63 

4.73

6.98

9.60

9.09

9.18

10.09

9.55 

6.74

3.62 

1.53

75.0

61

Mass 

transfer

1.77

3.14

5.26

6.69

9.34

7.85

7.55

8.61

8.78 

7.15

3.82 

2.22

72.2

Average 

evaporation

1.58

2.95

4.78

6.62

9.14

7.96

8.30

9.35

9.14 

7.08

3.96 

2.02

72.9

Water 

budget

2.23

2.70 

3.84

5.14

9.00

6.73

8.81

8.83

8.10

6.77

4.94 

2.93

70.0

19

Energy budget

1.73

2.24 

3.96

6.77

9.67

8.50

10.07

10.02

7.56 

6.16

3.21 

1.07

71.3

62

Mass 

transfer

2.59

2.55 

4.10

6.11

8.86

7.22

8.12

9.29

7.56 

7.42

4.67 

2.64

71.1

Average 

evaporation

2.18

2.50 

3.97

6.01

9.18

7.48

9.00

9.38

7.74

a 76

4.27

2.22

70.7

The approximately independent values of aggregate 

evaporation from Salton Sea during the 2-year period, 

determined by the water-budget and energy-budget

methods, differ by about 3 percent. The maximum 

difference between annual values determined by the 

three methods for a particular year is about 5 percent. 

Monthly values, however, differ by substantially larger 

percentages.

The comparisons in table 7 and figure 5, as well as 

several other comparisons of evaporation and basic 

data (Hughes 1966), show that the differences between 

monthly evaporation computed by water-budget and 

mass-transfer methods are as much as 21 percent of 

computed evaporation, but the distribution of these 

differences tends to be random rather than seasonal. 

Monthly evaporation determined by the energy-budget 

method differs, however, from that determined by 

either of the other methods or their means by substantial 

amounts that vary in a distinctly seasonal pattern; 

energy-budget values are too high in spring and summer and too low in fall and winter.

EVAPORATION-PAN DATA, 1948-62

Evaporation from pans of various types is a useful 

index of evaporation from Salton Sea if the relation 

between the respective rates of evaporation is known. 

Because of the wide differences between the physical 

characteristics of pans and of the sea, however, the 

relation was unknown until evaporation from the sea 

was determined by some method that does not depend 

on data on pan evaporation.

Several attempts to determine evaporation from 

Salton Sea by using evaporation-pan data have been 

made, but only one set of pans that has been maintained 

continuously since 1948 is discussed herein.

Three evaporation stations Sandy Beach, Devils 

Hole, and Imperial Salt Farm (fig. 2) were established in 1947 by the U.S. Soil Conservation Service; 

operation of these stations was taken over by the Imperial Irrigation District in 1951. Each station 

includes a recording rain gage, an anemometer with a 

cumulative wind-movement indicator, and a 2-foot 

sunken and screened evaporation pan.

Monthly evaporation during 1961-62 from each of 

the three pans is shown in figure 6. The large differences in rates of evaporation at the three sites are 

consistent with corresponding differences in the measured windspeed. Hence, they may be due mainly to 

the local differences which affect pan exposure rather 

than to their location in relation to Salton Sea and the 

direction of prevailing winds. Comparison of evaporation at the three sites suggests that a single pan record 

would not be a reliable index of evaporation from the 

sea. Because the three stations appear to be well 

located to sample the meteorological environment of 

the sea, however, the average evaporation from the 

three pans is probably a reliable index.
C16 WATER RESOURCES OF LOWER COLORADO RIVER SALTON SEA AREA

10

J FMAMJ JASONDJ FMAMJ JASOND 

1961 1962

FIGURE 5. Comparison of three determinations of monthly evaporation from Salton Sea.

Imperial 

Salt Farm

r I

J FMAMJ JASONDJ FMAMJ JASOND

1961 1962 

FIGURE 6. Comparison of monthly evaporation from sunken screened pans at three sites on the shore of Salton Sea.
HYDROLOGIC REGIMEN OF SALTON SEA, CALIFORNIA C17

The ratio of evaporation from Salton Sea (Es, average from table 7) to the corresponding evaporation 

from pans (Ev , average for three pans) for each month 

during 1961-62 is shown in figure 7. The plotted ratios 

vary from month to month and also for corresponding 

months of the 2 years. Comparison of the monthly 

evaporation computed by three methods indicated the 

probability of seasonal bias in the energy-budget evaporation ; accordingly, values of the ratio based 011 evaporation computed by the other two methods were 

plotted (not shown), but the resulting variations were 

no less erratic than those shown. The available data 

are sufficient to indicate only the general nature of the 

seasonal changes in the ratio.

Most of the variation of the ratio, E8/E^ is caused 

by factors that vary seasonally. Disposition of the 

energy that reaches a water body is strongly influenced 

by the water temperature and its relation to the temperatures of the air and the surrounding earth. As the 

temperature of a large water body responds to changes 

in air temperature much more slowly than that of a 

small one, the respective rates of evaporation respond 

similarly to changes in air temperature. Appreciable 

differences between ratios for corresponding months of 

different years are to be expected because the seasonal 

fluctuations of temperature and other meteorological 

variables are not identical from year to year.

The ratio for annual values varies much less than 

that for monthly values because of the cyclical nature 

of the fluctuations just discussed. Although some variations are to be expected, they are undoubtedly small 

enough to be within the limits of accuracy of definition 

of the ratio.

The ratio E8/EV for 1961 is 0.694, and that for 1962

i.o

0.8

0.6

0.4

1962,

1961 \

\

M M O N D

FIGURE 7. Monthly variations of the ratio (Es/Ef) of evaporation 

from Salton Sea to pan evaporation (average for three sunken 

pans).

is 0.685. The average of these two ratios, 0.69, is considered by the authors to be a good estimate of the 

normal value of the annual coefficient for the three 

sunken pans. This coefficient should not be confused 

with the coefficient of 0.70 commonly applied to U.S. 

Weather Bureau Class A evaporation-pan data. The 

similarity is purely coincidental.

The 15-year record of evaporation from the three 

sunken pans is summarized in figure 8 and in table 8. 

Table 8 lists the annual evaporation from each pan, the 

averages for all three pans, and the evaporation from 

Salton Sea computed as 0.69 multiplied by the three-pan 

average (except for 1961-62). Figure 8 indicates the

TABLE 8. Annual evaporation, in feet, from sunken pans at 

three stations and from Salton Sea, 1948-62

[Records of pan evaporation furnished by Imperial Irrigation Dist. Evaporation 

from Salton Sea for 1948-60 is average pan evaporation multiplied by 0.69. Average 

value from table 7 given for 1961-62]

Sandy

Year Beach

1948....... . _ ..... 10.13

1949 ....... __ .. ... 9.54

1950..... 9.37

1951..... 10.24

1952...... .......... 9.62

1953.. ................. 10.67

1954................... 9.39

1955..... 11.21

1956..... ........... 11.29

1957..-. . - 9.76

1958 ..-.----. __ .... 10.09

1959.... ____ .... 10.20

I960..... . 10.37

1961...... ______ - 10.44

1962 10. 35

A

(ft

LU

I

o

VAPORATION, IN 

o

LLl

MONTHLY 01

0

.verage, 1948-62. 10. 18

1 1 1 I 1

_

1 {]

Devils Imperial

Hole Salt Farm

8.27

8.01

7.60

7.81

7.41

7.89

7.18

7.40

7.56

7.25

7.11

7.41

7.48

7.85

7.52

7.58

1 1 1

[ttj

7.89

7.50

7.38

7.52

7.24

7.33

6.78

6.91

7.35

6.91

7.02

7.46

7.62

7.98

7.94

7.39

1

4

Pan

average

8.76

8.35

8.12

8.52

8.09

8.63

7.78

8.51

8.73

7.97

8.07

8.36

8.49

8.76

8.60

8.38

1 ! 1

1

1

SaUon Se

6.C

5.7

5.6

5.8

5.£

5.S

5.3

5.8

6.0

5.5

5.5

5.7

5.8

6.0

5.8

5.7

1

_

-

T EXPLANATION ' 1

1 1 Maximum 1 ~~ 

_ 1 Mean __ 

1 Minimum

1 1 1 1 1 1 1 1 1

JFMAMJ JAS

FIGURE 8. Means and extremes of monthly

1 1 1

O N

pan evaporation,

1

D

1948-62

(average for three sunken pans on the shore of Salton Sea).
CIS WATER RESOURCES OF LOWER COLORADO RIVER SALTON SEA AREA

seasonal pattern of the average values and the range of 

values for each month.

CONCLUSIONS FROM EVAPORATION STUDIES

Determinations of the annual evaporation from 

Salton Sea for 1961-62 by the water-budget and energybudget methods closely correspond. The average of 

these two determinations was used to establish the empirical coefficient (^=0.00156) in the mass-transfer 

equation, and to establish an annual coefficient of 0.69 

for use with the average evaporation from three sunken 

pans. These coefficients are applicable only when the 

mass-transfer data and evaporation-pan data are obtained in the same manner as they were obtained during 

the study.

Agreement of monthly evaporation values computed 

by different methods is less satisfactory than for annual 

values, and energy-budget data appear to be affected by 

seasonal bias. Monthly pan coefficients vary somewhat 

erratically from month to month, and for corresponding 

months in different years; consequently, observed pan 

evaporation without additional water-temperature and 

meteorological data is suitable for only rough estimates 

of monthly evaporation.

The principal need for evaporation data on Salton 

Sea is for annual rather than monthly values, and these 

may be obtained most readily by means of the three 

sunken evaporation pans. Consequently, no data for 

either energy-budget or mass-transfer computations 

have been gathered since 1962. If future inflows are 

determined with sufficient accuracy, the water budget 

may be used to verify the evaporation determined from 

pan data.

The average annual evaporation from Salton Sea for 

1948-62 was 5.78 feet (69 in.), and this is considered to 

be a good estimate of the normal annual evaporation. 

This estimate closely corresponds to those of some previous investigators. For example, LaRue (1916, p. 142) 

estimated the average annual evaporation to be 5.8 feet, 

and Blaney (1955) concluded that the average was about 

6.0 feet.

The average annual evaporation from Salton Sea determined herein is markedly lower than that from Lake 

Mead, which is the nearest large body of water in a 

desert environment and is about 200 miles northeast of 

the sea. The average annual evaporation from Lake 

Mead for 1948-62 was about 86 inches 2 17 inches more 

than the evaporation from the sea during the same 

period.

2 The average for 1952-62 was 85.9 inches, from records published 

in annual reports on the surface-water supply of the United States. 

The average was not appreciably altered by inclusion of evaporation for 

the water years 1948-51, which was computed by Kohler, Nordenson, 

and Fox (1958, table 25), who used evaporation-pan and meteorological 

data and adjusted for advected energy.

Part of this difference in average annual evaporation 

may be due to errors in computed evaporation, but most 

of it can be accounted for by the effects caused by certain 

characteristics of the two water bodies and their environments, including the salinity, the volumes and temperatures of inflow and outflow, 'and the mean distance 

traveled by the wind over the water.

Salinity depresses the evaporation from Salton Sea 

relative to that from fresh water by about 2 percent 

(Harbeck, 1955). Thus, salinity accounts for only 1.4 

inches of the 17-inch difference.

The volume and temperature of water entering Salton Sea are nearly the same as the volume and temperature of the water evaporated; hence, they have little 

effect on the average rate of evaporation. Although the 

long-term average volumes of water entering and leaving Lake Mead are nearly the same and the water evaporated may be at about the same temperature as that 

of the inflow, most water leaving the lake (as streamflow below Hoover Dam) has a much lower average 

temperature. Kohler, ISTordenson, and Fox (1958, p. 

57, table 25) calculated that the resulting gain of energy 

caused an increase of about 5.5 inches in the annual 

evaporation from Lake Mead during 1941-53.

As air moves across a water surface, evaporated moisture tends to increase the humidity of the air and 

thereby decrease the rate of evaporation. Consequently, the rate of evaporation tends to decrease with 

distance from the windward shore, and average rates 

for different water bodies tend to vary inversely with 

the mean over-water distance traveled by the prevailing 

winds. However, lake-evaporation data available at 

the time of the Lake Hefner studies, although admittedly not conclusive, indicated that for lakes of approximately circular shape with diameters ranging from 12 

feet to about 4 miles the diameter had no appreciable 

influence on the rate of evaporation (Kohler, 1954, p. 

148).

Later, the evaporation data for Lake Mead tended to 

confirm the conclusion that the rate of evaporation is 

independent of the size of the water body. If the mean 

over-water distance rather than surface area is considered to be the measure of size, however, Lake Mead 

is not much larger than the largest lakes represented 

by the original data, because Lake Mead is composed 

of several basins nearly surrounded by desert and connected by narrow water-filled canyons.

When evaporation data for Salton Sea are included 

with the previous data, the range of mean over-water 

distances (effective diameters) is extending to about 20 

miles and considerable influence of effective diameter 

on the evaporation rate is indicated.

Although a precise accounting of the proportions of 

the 17-inch difference between evaporation rates at Lake
HYDROLOGIC REGIMEN OF SALTON SEA, CALIFORNIA C19

Mead and Salton Sea attributable to each cause is not 

possible, the authors believe that the factors previously 

discussed considered with other factors, such as effects 

of surrounding terrain on the turbulence of the air over 

the water bodies, satisfactorily account for the difference and that no large error in either rate is involved. 

The U.S. Weather Bureau evaporation map of the 

United States (Kohler and others, 1959, pi. 2; Meyers, 

1962, pi. 3; Hely and Peck, 1964, pi. 6) is based on scant 

data for the Salton Sea area and is highly generalized; 

it indicates 82 inches of annual evaporation at the site 

of Salton Sea. Although the possibility of an appreciable difference between the indicated map rate and the 

actual rate of evaporation at a specific locality must 

be recognized, the map rates may be approximately 

correct for evaporation from small bodies of fresh 

water. Because of its large effective diameter, the 

Salton Sea probably modifies the overlying air sufficiently to account for most of the 13-inch difference between the map rate and the rate derived herein for 

the sea. About 1.4 inches of the difference is accounted 

for by salinity, as prevously noted in the comparison 

of rates for Salton Sea and Lake Mead.

HYDROLOGIC REGIMEN FOR 1908-62

By combining information gained from the investigations conducted during 1961-62 with other hydrologic records, all terms of the annual water budgets 

for Salton Sea since 1908 could be determined with 

sufficient accuracy to indicate trends of surface inflow 

and evaporation. The annual values of all terms are 

listed in table 9.

The available records of water level are generally 

adequate for determination of the annual change in 

volume; precipitation records provided a suitable basis 

for computing the quantity of rainfall on the water surface; and ground-water inflow was estimated to be 

50,000 acre-feet per year.

Annual amounts of evaporation from Salton Sea during 1948-62 are adequately defined by the annual rates 

in table 8 and the corresponding values of surface area. 

None of these annual rates differ from the average by as 

much as 10 percent, and only two differ by as much as 5 

percent. Similarly, the annual evaporation from Lake 

Mead, Arizona-Nevada, differed from the average rate 

by more than 5 percent in only 2 of the 11 years, 1952- 

62. Consequently, the average annual evaporation rate 

for the Salton Sea (5.78 ft per yr) is considered to be 

satisfactory for computation of approximate amounts 

of evaporation prior to 1948.

Suitable records of the major part of the surface 

inflow are available only since 1944 (table 4), but because approximate values of all other terms of the 

water budget are known, surface inflow for earlier years

can be computed by equation 1. The values computed 

in this manner are adequate for determination of trends 

or averages for several years, but they are not regarded 

as reliable estimates for individual years. Computed 

annual inflow is affected by the use of the average rather 

than actual annual rate of evaporation, as well as the 

usual errors in other budget terms.

Annual water-budget equations for 1944-62 based on 

data from table 9 do not balance because none of the 

terms for those years were derived from the equations. 

Surface inflow determined by the water budget differs 

from that shown by as much as 11 percent, but the averages for the 19-year period differ by little more than one 

percent.

Figure 9 shows the average annual evaporation and

TABLE 9. Annual water-budget data, in thousands of acre-feet, for 

Salton Sea, 1908-62

[ Ground-water inflow (10) was estimated to be 50,000 acre-feet per year. Evaporation 

prior to 1948 was computed by using average annual rate (table 8); surface inflow 

prior to 1944 was computed by the water-budget method and is only a rough 

approximation]

Surface Precipita- Change in 

inflow tion volume Evaporation 

Year (I,) (P) (AF) (E)

1908.

1909. 

1910-

1911.

1912.

1913.

1914.

1915.

1916.

1917.

1918.

1919.

1920.

1921.

1922.

1923. 

1924- 

1925. 

1926-

1927.

1928.

1929.

1930.

1931. 

1932-

1933.

1934. 

1935-

1936.

1937.

1938-

1939.

1940.

1941.

1942.

1943.

1944.

1945.

1946.

1947.

1948.

1949.

1950.

1951-

1952-

1953.

1954.

1955.

1956-

1957-

1958.

1959-

1960- 

1961. 

1962-

160

370

190

300

330

300

410

110

220

500

250

440

610

700

740

920

670

910

1,060

1,000

930

1,130

1,080

930

940

850

390

750

940

1,180

1,090

1,290

890

1,200

950

1,020

1,100

1,080

1,130

1,080

1,080

1,180

1,220

1,330

1,400

1,450

1,380

1,220

1,250

1,140

1,150

1,210

1,260

1,340

1,400

74

93

23

44

63

33

70

76

67

26

29

32

68

69

20

29

9

38

81

81

7

17

31

67

63

18

5

51

40

15

48

127

64

102

32

77

51

57

25

19

27

29

4

30

45

1

24

18

2

33

40

33

36

34

23

-1, 520

 1,220

-1,400

-1,180

-1,080

-1,080

-869

-1,100

-917

-568

-725

-437

-208

-94

-92

+108

-169

+122

+285

+180

+17

+219

+156

+18

+35

-105

-536

-81

+97

+297

+206

+446

-55

+278

-56

+56

+38

+85

-18

0

-58

+105

+117

+228

+316

+197

+219

+99

-18

+16

-3

+53

+113

+87

+162

1,800

1,730

1,660

1,570

1,520

1,460

1,400

1,340

1,250

1,140

1,050

960

940

910

900

890

900

880

910

950

970

980

1,010

1,030

1,020

1,020

980

930

930

950

1,020

1,060

1,070

1,090

1,090

1,100

1,100

1,100

1,110

1,150

1,110

1,090

1,160

1,140

1,260

1,170

1,290

1,330

1,210

1,230

1,280

1,310

1,360

1,330
C20 WATER RESOURCES OF LOWER COLORADO RIVER SALTON SEA AREA

surface inflow, as listed in table 9, and the corresponding annual changes in the water level. The water-level 

graph is based on several observations during each year 

prior to 1908 and on the observed or recorded level for 

December 31 of each succeeding year, and normal seasonal fluctuations (fig. 4) are thereby eliminated from 

figure 9.

The tendency for the water surface to rise when inflow exceeds evaporation and to fall when the inflow 

is less than evaporation is evident if an approximate 

allowance is made for the additional inflow that occurs 

as ground-water seepage and precipitation on the water 

surface (table 9). The unusually low inflow during 

1934 was a result of low flow in the Colorado River, 

which was not controlled by Hoover Dam until 1935.

CHEMICAL REGIMEN

The role of Salton Sea in the economy of southern 

California depends on the chemical characteristics of the 

water, as well as the water levels and other factors previously discussed. Suitability of the water for fish

and for recreational uses is controlled to a large degree 

by its salinity (concentration of dissolved solids), 

which is subject to wide fluctuations but which has a 

tendency to increase with time. Commercial freshwater fishing was carried on for a few years after formation of the sea (1904-07) but ceased when the increase in salinity prevented fish from propagating. 

More recently, salt-water fish were introduced into Salton Sea, and sport fishing has become popular.

Ancient shorelines visible in parts of the Salton Sea 

basin indicate that water stood for long periods at about 

the level of the divide between Salton Sea and the Gulf 

of California. The latest existence of such a lake, 

known as Lake Cahuilla, may have been as recent as a 

few centuries ago. Evaporation of the tremendous volume of water from Lake Cahuilla, and from an unknown number of smaller lakes that followed it, left 

large deposits of soluble minerals on the surface in Salton Sink when it was dry. Some of the mineral residues may have been blown away, and some were probably buried under sediments, but some remained on the

200

240

280

_LJ_ I I I

.

2.0 O

1.5

1.0

0.5

FIGURE 9. Annual fluctuations of water level (datum of 1929), surface inflow, and evaporation.
HYDROLOGIC REGIMEN OF SALTON SEA, CALIFORNIA C21

surface and were redissolved when water again collected in the sink. Because of the presence of these 

soluble minerals, Salton Sea has been saline since its 

formation (1904-07), even though it was formed by a 

flood of fresh water from the Colorado Eiver.

Common salt (NaCl) was extracted from surficial 

deposits in Salton Sink prior to the flooding of 1904-07; 

evaporative saltworks on the shore of the Salton Sea 

were operated from 1936 to 1945 and were then flooded 

by the rising water. As the water becomes more saline 

it becomes more attractive for salt recovery; consequently, the salt industry may again become a major 

factor in the economic exploitation of the sea.

Chemical analyses of Salton Sea water have been 

made at irregular intervals since 1907. Analyses were 

made at least annually during 1907-16 and 1945-47, and 

at least twice a year during 1948-64, but only one reasonably reliable chemical analysis and one determination of 

dissolved solids by evaporation were found for the intervening period 1917-44. The analyses are summarized 

in table 10.

The data listed in table 10 were derived by several 

analysts using different analytical procedures; hence, 

these data probably differ in reliability. The analytical values originally reported were made as consistent 

as possible by rounding to the same number of significant figures, by replacing a few inconsistent sodium 

and potassium values by calculated values, and by calculating the salinity as the sum of concentrations of the 

ionic constituents using only half the bicarbonate. For 

1929, however, salinity determined by evaporation of 

a sample is listed. The calculated sum represents 

more than 99 percent of the dissolved solids including 

minor undetermined constituents and is therefore 

nearly synonymous with the total content of dissolved 

minerals.

All early analyses and some recent ones were of single 

samples of water collected some distance from the shore. 

Other data represent the averages of several samples 

or represent the analyses of composite samples. Since 

1944 the Imperial Irrigation District has collected samples, in sets of five, from widely separated points on 

Salton Sea and has had each sample analyzed. However, comparison of concentrations of constituents and 

their changes indicated that one sample in each of several sets may have been unduly influenced by fresh 

water from the Alamo Eiver or the New Eiver. Consequently, the average results of only four of the analyses in each set were listed in table 10. Most of the 

recent Geological Survey analyses were of composite 

samples collected from about 35 points.

The temperature data gathered for the evaporation 

studies previously described indicate that the Salton Sea 

is generally well mixed. A study by Arnal (1961) of the

areal variations in chlorinity (concentration of chloride and other halides) supports this conclusion. Consequently, the single samples should have been fairly 

representative of the entire sea, provided that they were 

collected sufficiently distant from the mouths of tributaries particularly the Alamo and New Eivers.

SALINITY AND MINERAL CONTENT

Changes of salinity in a body of water that has no 

surface outflow are most effectively described in conjunction with changes of volume of water and of mineral content 3 because the salinity at a particular time 

depends on both the amount of water and the quantity 

of dissolved minerals. The annual values of volume 

of water (table 9) and those of mineral content and 

salinity of Salton Sea, derived from analyses in table 10, 

are shown together in figure 10.

The volume of Salton Sea at any time is derived as 

explained in the discussion of the water budget. Salinity at the time of sampling is determined by chemical 

analysis of a water sample. The sample is assumed to 

be representative of the entire sea. Mineral content is 

computed from salinity and volume in accordance with 

the following relation:

1/=0.00136F/S', (9) 

where

M=mineral content, in tons, 

V=volume of water, in acre-feet, 

S=salinity, in parts per million.

The last two columns of table 10 show the volume 

and mineral content at the time each sample was taken. 

These computed values of mineral content are the principal basis for the mineral-content graph in figure 10. 

A useful guide to the shape of the 1916-45 graph, 

which is mostly unsupported by chemical data, was 

obtained by plotting a cumulative graph (not shown) 

of the inflow during that period (table 9).

Average annual values of salinity computed from 

the corresponding values of volume and mineral content 

were then used to define the salinity graph in figure 10.

At the time of the first chemical analysis, June 3, 

1907, the mineral content of Salton Sea was approximately 77 million tons, of which only a small part could 

have been contained in the Colorado Eiver water that 

formed the sea. The weighted-average concentration 

of dissolved solids in the Colorado River water was 

probably less than the 513 ppm (parts per million) 

determined for Colorado River at Yuma, Ariz., during 

October 1927-September 1928 (Howard, 1955). If

8 Mineral content is the total quantity of dissolved minerals in the 

water body. It is synonymous with the term "salt content," as used in 

many reports, but "salt content" is also used sometimes in reference to 

the content of a specific salt, such as sodium chloride.
C22 WATER RESOURCES OF LOWER COLORADO RIVER SALTON SEA AREA

TABLE 10. Chemical analyses of water from Salton Sea 

[Concentrations in parts per million]

JuneS, 1907.. ________ ...

Nov. 12, 1907 __________ _

Feb. 28, 1908. ...... _ .........

May 25, 1908 

Junes, 1909... - ___ _ 

May 22, 1910 

JuneS, 1911--.--- ____ . . .

June 10, 1912... ... . .

June 18, 1913... .... _ .. ...

June 12, 1914... ___ ... _. .

June 8, 1915. .. __ . . ....

June 10, 1916...- .. -. _ 

June 10, 1923... --. _ . _ ...

Mar. 21, 1929. ____ __ . __

Dec. 22, 1945. _ 

Dec. 20, 1946... . __ ___ ...

Dec. 17, 1947-- 

Sept. 20, 1948. 

Dec. 15, 1948.. __ __ . __

Sept. 19, 1949, - -- .. . __ -

Dec. 15, 1949.. .- . __ - _ -

Sept. 20, 1950.---- ___ ... ._..

Dec. 20, 1950... 

May 19, 1951 

Sept. 25, 1951. 

June 4, 1952... ____ - ____ -

Nov. 19, 1952 ___ ,. __ ...

May 18, 1953-. __ .. _ _.

Nov. 23, 1953... .........

May 24, 1954... ....... ..........

Nov. 15, 1954... ............

June 13, 1955 ____ - ____ ...

Nov. 21, 1955 ____ ....

May 21, 1956. - ____ - ___ ...

Dec. 10, 1956 . 

May 27. 1957- .. . 

Nov. 25, 1957 

May 12, 1958-.. _ ...

Nov. 10, 1958- 

May 25, 1959- __ _ -

Nov. 9, 1959_ ____ . .- .......

May 27, I960, __ - _ ... ....

Nov. 11, I960... ....... ...

Apr. 4, 1961... .............

May 22, 1961--. ________ -

Sept. 22, 1961. .................

Nov. 20, 1961.-. .....

Jan. 29, 1962 _ - .......

Mar. 19, 1962-... .........

May 21, 1962.-... __ ...... ...

Sopt. 10, 1962. ____ __ ....

Nov. 12, 1962.-. ..

May8, 1963-. ......

Oct. 10, 1963 ..

Nov. 4, 1963-. ..

May 18, 3964 _ ... ... ..... ... ..

May 28, 1964-- .............

Agency l

CI.. .

USGSUSGS- -

CI. - .... 

CI-. 

CI.. ... ..... ...

CI-. ...

CI.. ..... 

CI. - - 

CI-. .... 

CI ...... .... 

CI.- ... .

CI.. ....

Cal.- ... 

IID. ..... .

IID. ...... .....

IID. ......

IID ..... ...

IID. ....

IID ...

IID _

IID , 

IID .

IID , 

IID .......

IID ...

IID 

IID ... 

IID .. ,

IID. ....... 

IID..... 

IID. ... .

IID. .... 

IID. . _

IID. .

IID. ...........

IID. ......

IID. ...... 

IID. 

IID. ........

IID. .... 

IID 

IID. ......

USQS..... 

IID. . 

USQS ..... 

IID. ......

USQS..... .

USQS.... ........ .

IID. .... ......

USQS..... .....

IID ........

USQS..... ....

USQS .- . 

IID. ...... ....

IID. ..........

USQS..... 

Calcium 

(Ca)

100

107

142

119

127

137

156

173

198

222

253

299

684

766

831

742

780

869

Q1Q

Q7n

909

782

850

836

818

812

808

964

912

872

742

721

708

756

738

774

759

762

803

840

807

813

821

813

850

01 -I

889

831

796

cm

802

77 e

792

820

Qf»e

776

Magnesium 

(Mg)

64

fift

77

76

on

QS

117

136

190

oofi

272

659

880

921

996

1,020

QCQ

1,120

963

990

ono

939

899

OQ1

070

822

936

889

QOQ

905

QI n

939

951

886

QQO

877

Qen

QOQ

Qfi7

1,020

991

one

QOQ

QC7

985

1,010

QOO

Qfid

Qfift

1,010

QOQ

Sodium 

and potassium 

(Na+K)

1,140

1 260

i 9ftn

1,370

1,620

1,900

2,280

2,710

3,220

3,810

4,430

5,330

12,500

11,100

11,000

11,100

19 inn

11, 300

n oon

11, 200

11, 700

11, 200

10,800

12, 100

10, 600

10,200

10 000

9

QQri

9,940

9,620

10,000

9

QQA

10,200

9

QOfl

10,200

10,100

10.300

10,100

W cnn

10,400 in 4.m

9,830

10,100

10,100

10,100

10 000

9,910

10,100

10, 100

10,100

9

eQfi

9 74ft

9 380

9* 700

9

e4.fl

Bicarbonate 

(HCOs)

134

165

182

156

149

129

117

246

229

223

242

232

169

207

207

210

198

213

206

217

202

221

204

209

213

192

212

212

226

215

208

204

204

200

200

200

189

179

208

204

191

199

182

197

174

188

183

174

196

177

192

167

178

198

180

Sulfate 

(SOj)

476

559

562

567

659

764

917

1,070

1,250

1,480

1,740

2,080

5,380

6,780

6,900

6,990

7,490

7,150

7,580

7,160

7,350

7,120

6,950

7,210

6,820

7,120

6,780

6,690

6,500

6,560

6,520

6,810

6,830

7,160

7,050

7,300

7,170

7,330

7,100

7,360

7,130

7,290

7,060

7,230

7,260

7,260

7,250

7,140

7,280

7,320

7,260

6,980

7,210

5,900

7,410

7,010

Chloride 

(CI)

1,700

1,830

1,920

2,040

2,410

2,810

3,390

3,950

4,740

5,600

6,510

7,880

18,300

16,000

15, 900

16,000

17,400

16,500

17,200

16, 400

17,100

16,200

15,800

17, 600

14,900

15,200

14,600

14, 700

14, 400

14,300

13,900

14,200

14,100

14,300

14,100

14,300

14,300

14,500

14,300

15,200

14,600

14,800

14,000

14,400

14,600

14,400

14,200

14,100

14,300 14 4rm

14,400

13,600

13,800

14,400

13,900

13,500

Salinity 

(calculated) 2

3,550

3,910

4,070

4,250

4,980

5,770

6,920

8,160

9,680

11,400

13,300

16,000

37,600

33,200

35,600

35,700

35,900

38,900

36,900

38,700

36,800

38,200

36,400

35,500

38,800

34, 000

34,800

33,400

33, 400

32, 600

32,600

31,800

32,700

32,600

33,400

32,900

33,600

33,400

33,900

33,300

35,200

33,900

34,400

32,700

33,600

34,000

33,700

33,300

33,000

33,500

33,700

33,700

32,000

32,600

31,600

33,000

31,800

Volume of 

water 

(millions of 

acre-ft)

16

15

15

14

13

12

10

9.3

8.2

7.2

6.3

5.3

2.5

3.1

4.05

4.05

4.01

3.94

3.97

4.02

4.08

4.11

4.20

4.40

4.34

4.72

4.67

4.94

4.92

5.24

fi. 16

5.30

5.24

5.42

5.26

5.40

5.23

5.45

5.23

5.40

5.26

5.48

5.40

5.60

5.60

5.48

5.47

5.58

5.67

5.72

5.63

5.65

5.92

5.92

6.97

6.15

6.13

Mineral 

content 

(millions of 

tons)

77

80

83

81

88

94

94

100

110

110

110

120

130

140

196

197

196

208

199

211

204

214

208

212

229

218

221

224

223

232

228

229

233

240

239

241

239

247

241

245

252

253

253

249

256

253

251

253

255

261

258

259

258

262

257

276

265

1 Agencies responsible for publication or file data: CI, Carnegie Institution of Washington; Cal, state of California; IID, Imperial Irrigation District; USQS, U.S. Qeo- 

"urvey. Data were obtained from the following publications or files:

Years Symbol Source

1907-16 CI.. . . Sykes(1937).

1907-08 . USQS Van Winkle and Eaton (1910).

1923. --____ CI..._______.. Carnegie Institution of Washington (1924).

1929 Cal. Coleman (1929).

1945-64 ___ IID-___._._.. Files of the Imperial Irrigation District.

1961-64 USQS -_ Files of the U.S. Geological Survey.

2 Calculated as the sum of constituents shown using half the bicarbonate concentration, except that for 1929, which was determined by evaporation.
HYDROLOGIC REGIMEN OF SALTON SEA, CALIFORNIA C23

16

14

12

10

250

200 -

- 'd. 150

Z 100 -

FIGCEB 10. Annual fluctuations of salinity, mineral content, and volume of Salton Sea, 1907-63.

this is true, the quantity of minerals contributed to 

Salton Sea by the Colorado River between November 

1904 and June 1907 was less than one-seventh of the 

mineral content on June 3, 1907. The floodwater may 

have dissolved additional minerals as it came from 

Yuma to Salton Sea, but most of the balance of the 

mineral content on that date must have been dissolved 

from the bed of the sea.

The solution of minerals from the bed apparently 

continued for several years. By 1914 the mineral content had increased to about 110 million tons, although 

the relatively small inflow from 1907 to 1914 (fig. 9)

could have contributed only minor quantities of minerals. The rate of increase in mineral content slowed 

gradually as the quantity of soluble minerals on the 

bed decreased and probably ceased or became negligible 

within a few years after 1914.

The annual increments of mineral content tended to 

increase gradually after 1920 because of the increasing 

inflow and the development of drainage systems for 

irrigated tracts. However, since 1945 the annual increments apparently have varied only slightly from the 

1945-63 average increment of about 4 million tons.

Annual increments of mineral content may differ
C24 WATER RESOURCES OF LOWER COLORADO RIVER SALTON SEA AREA

slightly from the corresponding annual loads of minerals in the inflow because of attrition resulting from 

chemical reactions and precipitation of salts, biological 

activities, and wind and wave action. Precipitation 

of slightly soluble salts is an important cause of change 

in the chemical composition of the water, but since 1907 

the combined effect on salinity of all attrition processes 

in Salton Sea has been small. The effect of precipitation will increase in importance as salinity increases. 

Computation of the approximate amount of minerals in 

the inflow for 1961-62, based on numerous analyses of 

samples from the principal tributaries, indicated that 

the annual loads of minerals were approximately the 

same as the annual increments of mineral content; however, the computations were not precise enough to define 

the amount of attrition.

The salinity graph (fig. 10) shows a rapid rise in 

mineral concentration from about 3,600 ppm in 1907 to 

about 40,000 ppm in 1925, caused chiefly by the solution 

of minerals from the bed of Salton Sea and the rapid 

decline in volume of the sea. Salinity doubled about 

every 4 years during its steepest rate of rise. It reached 

a second, 'and higher, peak of about 43,000 ppm in 1936, 

as a result of a decline in volume of the sea caused by a 

shortage of irrigation water in 1931-35. A subsequent 

increase in volume counteracted the continuing increase 

in mineral content and caused salinity to decline to about 

34,000 ppm in 1942. Salinity fluctuated within a relatively narrow range of between 32,000 and 37,000 ppm 

during 1942-63.

CHEMICAL COMPOSITION

Chemical composition of water in Salton Sea changes 

with time, not only because of changes in volume and 

mineral content but also because the proportions of the 

various constituents in the inflow differ from those in 

the sea, and because the least soluble minerals that can 

form by combination of the available ions precipitate 

from the solution when concentrations are above certain 

levels. Although precipitation of minerals has been 

relatively minor compared to the total mineral content, 

it will probably increase markedly as concentrations 

increase.

Bar graphs showing the concentrations, in chemical 

equivalents, of dissolved solids in Salton Sea on selected dates are shown in figure 11. Similar graphs for 

Colorado Eiver water, inflow to Salton Sea, and typical 

ocean water are included for comparison.

Most inflow to Salton Sea consists of Colorado Eiver 

water, which is modified by evapotranspiration in the 

irrigated areas, by deposition of some constituents in the 

soils, and by solution of minerals from the soils (leaching). The first bar shown in figure 11 represents the

unaltered Colorado Eiver water. Although available 

records are not adequate to enable precise determination 

of the average chemical quality of the inflow, the second bar may be fairly representative of this average. 

It is based on typical water samples of the New and 

Alamo Eivers, collected at different times during 1962 

when streamflow was near average.

Comparisons of the concentrations and proportions 

of constituents in the inflow to the sea with those for 

Colorado Eiver water indicate a large increase in the 

concentration of all ions except bicarbonate (HCO3 ). 

Apparently carbonate was deposited in the soils or removed by biological activity. Concentration by evapotranspiration can account for only part of the increase 

in sodium plus potassium (Na + K) and chloride (Cl). 

Large amounts of these constituents have probably been 

leached from soils irrigated with Colorado Eiver water.

The quantity of minerals leached from soils undoubtedly varies from year to year but cannot be accurately determined from available records. If the area 

involved does not increase, a long-term downward trend 

in the quantities of leached minerals reaching the sea 

can be expected.

The chemical composition of water in Salton Sea 

prior to 1923 was governed mainly by the solution of 

minerals from the bed. A comparison of the graphs 

of composition for the early years with those for later 

years shows the gradual change in proportions of constituents resulting from the additions of minerals in 

the inflowing water.

Graphs of the cumulative content of the individual 

constituents (similar to the mineral-content graph in 

figure 10) are more useful than the graphs in figure 11 

for predicting future chemical characteristics. Accordingly, cumulative-content graphs are shown in figure 12.

At any particular time the chemical composition of 

Salton Sea water depends on its earlier composition, the 

relative accretions of the various ionic constituents since 

that earlier time, and the individual solubilities of the 

various possible ionic combinations.

Sodium and chloride have been the dominant dissolved constituents in Salton Sea and will undoubtedly 

remain so indefinitely because of the high solubilities 

of sodium and chloride minerals which could form by 

ionic combination. Sulfate (SO4 ) has been the next 

most abundant ion. During most of the life of the sea 

its content ratio of sulf ate to chloride has increased and 

is still increasing.

Concentrations of calcium (Ca) and sulf ate are apparently at or near levels which will cause combination 

to form a gypsum (CaSO4 -2H2O) precipitate. In an 

effort to determine whether the water was saturated 

with gypsum in 1965 a portion of a sample of the water 

was analyzed; another portion was agitated overnight
HYDROLOGIC REGIMEN OF SALTON SEA, CALIFORNIA 

700

C25

EXPLANATION

Na + K

Mg

Ca

Cl

so*

HCO,

Dated bars are 

for Salton Sea

70

60

50

40

30

. - 20

10

June 3, 

1907

Alamo 

and 

New

Rivers

Colorado 

River

600

d 500

5 

o:

400

300

200

100

Dec. 22, 

1945 Ocean

May 28, 

1964

B

FIGURE 11. Comparisons of chemical composition, in equivalents. A, Weighted average for the Colorado River at Imperial Dam during 

1962; weighted average of typical analyses for the Alamo and New Rivers, which contributed about three fourths of the inflow 

to Salton Sea; and Salton Sea on June 3, 1907. B, Salton Sea, on selected dates, and typical ocean water.

with some powdered gypsum, then filtered and analyzed. The results of the experiment indicated that the 

water was near saturation with gypsum, as only slight 

increases of calcium and sulfate (probably within the 

range of analytical errors) were obtained. Whether 

or not the calcium and sulfate concentrations are now 

partly controlled by the precipitation of gypsum, they 

no doubt will be in the future increasingly so, as the 

salinity increases. This control may result in a nearly 

constant sulfate concentration after the sea has become 

saturated with gypsum.

Calcium, magnesium (Mg), and bicarbonate (HCO3 ) 

have been relatively minor constituents. Since the

formation of Salton Sea, the concentration of bicarbonate has, to a small degree, fluctuated about an apparently quasi-stable level. Although calcium and bicarbonate can exist together in low concentrations, higher 

concentrations cause the formation of calcium carbonate 

(CaCO3 ), which is nearly insoluble. Although magnesium carbonate (MgCO3 ) may be precipitated under 

some conditions, it is much more soluble than calcium 

carbonate. Gypsum may precipitate if concentrations 

of its ions are only moderately high. Magnesium sulfate 

(MgSO4 ), in contrast, is highly soluble. These solubility 

relationships have resulted in nearly stable bicarbonate 

concentration and slowly rising calcium concentration,
026 WATER RESOURCES OF LOWER COLORADO RIVER SALTON SEA AREA

120

100

80

V)

z.

9 60

40

O 20

hz

LJ

Ck

Na+Kv

SO,

10

HCO, as CO,

FIGURE 12. Trends of the content of individual constituents in Salton Sea. Magnesium (Mg) is shown in both parts of the diagram to help

indicate the relation between the parts.
HYDROLOGIC REGIMEN OF SALTON SEA, CALIFORNIA C27

which may be at or near peak level, and in continual 

increases in magnesium concentration. The magnesium concentration will probably increase to several 

times that of the calcium concentration, as in ocean 

water.

TEMPERATURE OF THE WATER

Water temperatures exert great influence on aquatic 

life and on most uses of the Salton Sea. Although no 

long-term records of water temperature are available, 

the data gathered for the evaporation studies exemplify 

the variations to be expected.

Figure 13 shows the variations during 1961-62 of 

the monthly air temperature at Sandy Beach, the 

monthly temperature of the water surface as measured 

at the two buoys (fig. 2), and the monthly temperatures 

of water at the bottom of the sea. The bottom temperatures were determined by averaging all measurements observed in the bottom layer for each thermal 

survey; monthly temperatures were estimated from a 

graph of the individual determinations.

Although the period of record is much too short for 

a significant determination of mean monthly water 

temperatures, the relations between seasonal patterns 

of water temperature and of air temperature should 

enable estimation of water temperatures within a few 

degrees if the air temperature is known.

Average-temperature profiles were computed from 

the 35 profiles obtained during each thermal survey. 

Selected profiles (fig. 14) determined during 1961 illustrate a variety of shapes that occur during an annual 

cycle of warming and cooling.

Early morning temperatures of the water surface at 

the two buoys (fig. 2) indicate that the sharp bend to 

the right near the top of many profiles was caused by 

warming of the surface during the day of the thermal 

survey. When air temperature is higher than water 

temperature during long periods of calm, pronounced 

thermal stratification tends to occur, as illustrated by 

the profiles for April 4 and July 10. In contrast with 

this tendency for stratification, water in the sea is mixed 

to various depths by wind and by convection currents 

during periods when air temperatures are lower than 

water temperatures.

FUTURE REGIMEN

Man's influence on the hydrologic regimen of Salton 

Sea has been almost entirely through the effects of 

irrigation. Because of the rapidly increasing use of 

the sea for recreation, however, proposals for controlling both water level and salinity by works in or 

near the sea are being considered.

If no works are constructed to accomplish direct 

control of Salton Sea or that add significant amounts

100

I 90

z

UJ

tr 

I 

<

u.

ul 80

UJ tr 

a

UJ

a

70

60

50

Water surface

I I I I I I I

JFMAMJJASONDJFMAMJ JASOND

35

30

25

20

ic 10

10

u

1961 1962 

FIGURE 13. Monthly temperatures of water at the surface and at the bottom of Salton Sea and of air at Sandy Beach. 1961-62-
C28 WATEB RESOURCES OF LOWER COLORADO RIVER SALTON SEA AREA

50 60

TEMPERATURE, IN DEGREES FAHRENHEIT 

70 80 90

0 -

10 -

20

30

40

ti

LU 

U.

Z 10

X

Q. 

LU

Q 20

30

40

10 15 20 25

TEMPERATURE, IN DEGREES CENTIGRADE

FIGURE 14. Selected 1961 temperature profiles of Salton Sea.

30 35

of minerals, the future hydrologic regimen will depend 

mainly on the amount of water imported to the Salton 

Sea basin and on how efficiently the water is used. The 

trends of annual inflow and water level (fig. 9) should 

not be expected to continue when there is no surplus 

water in the Colorado River, because those trends were 

established when a surplus for all actual uses existed. 

Although some future events may tend to increase inflow, the competition for available water and the high 

cost of new supplies will probably tend to reduce inflow. 

Increased inflow might result from installation of 

drains in Mexicali Valley, where continued successful 

irrigation will probably be dependent on the provision 

for drainage by either drains or wells, or an increase 

in inflow might result from the conversion from irrigation to municipal and industrial uses, which generally consume a relatively small part of the total water 

withdrawn.

An average annual seepage loss of more than onethird of a million acre-feet from the Coachella Canal 

and the part of the All American Canal that is within 

the Salton Sea basin could possibly be reduced sharply 

by use of canal linings or sealants. The net effect of 

such seepage reduction on inflow to Salton Sea cannot 

be evaluated or predicted with confidence because the 

effect would depend on the disposition of the salvaged 

water and, also, because the amount of seepage that now 

reaches the sea is unknown. Eeduction of seepage 

probably would not markedly reduce inflow unless it 

were to be accompanied by a reduction in the amount 

of water imported to the Salton Sea basin.

A significant reduction in inflow to Salton Sea might 

be caused by reduction of operational losses (unused 

water discharged to Salton Sea) and, also, by reuse of 

drainage water. A curtailment of imports, enforced
HYDROLOGIC REGIMEN OF SALTON SEA, CALIFORNIA C29

during 1964, resulted in the significant reduction of 

operational losses and of inflow to the sea.

If the annual inflow to Salton Sea from both surface 

and underground sources were to stabilize, the water 

level would also tend to stabilize after it had risen (or 

fallen) to the level at which mean annual values of gain 

and loss are equal. The water level would then continue 

to fluctuate within a range of a few feet in response to 

seasonal changes in evaporation and inflow (fig. 4) and 

the effects of occasional storms, but it would have no 

upward or downward trend. For this condition the 

long-term water budget (eq 1) reduces to

I.+I,=E-P, (10)

because the change in volume (AF) is zero. Evaporation (E) and precipitation (P) are placed together on 

the right side of equation 10 because both are atmospheric phenomena and the quantities of water involved 

vary with the surface area. Thus instead of treating 

precipitation as an increment of the inflow, it is subtracted from the evaporation to obtain the net loss to the 

atmosphere, commonly called net evaporation.

The normal annual net evaporation per unit of surface area is 5.57 feet, computed from the previously determined values of evaporation (5.78 ft) and precipitation (0.21 ft). The corresponding mean annual volumes 

of net evaporation equal this rate multipled by the surface area, which varies with water level (fig. 3). Although the relation between water level and net evaporation is merely a replica of the relation in figure 3, it is 

shown in figure 15 with a different horizontal scale for 

the convenience of readers who wish to estimate the 

probable stable water level corresponding to assumed 

future inflows. The two dashed lines indicate the position of the relation if the actual evaporation per unit 

area is either 5 percent more or 5 percent less than the 

value derived in this report.

When conditions of long-term stability are being considered, inflow may be substituted for net evaporation 

(eq 10) in figure 15.

To illustrate the application of figure 15, assume that 

the annual surface inflow during some future period 

will vary only slightly from 1,350,000 acre-feet. Then 

the sum of surface- and ground-water inflow will be 

1,400,000 acre-feet, and the water level will stabilize at 

about 224 feet below mean sea level. Similarly, if the 

surface- and ground-water inflow should be 800,000 

acre-feet, the stable water level would be about 254 feet 

below mean sea level.

Increasing salinity of Salton Sea may cause a gradual 

decrease in the average rate of evaporation. Although 

Harbeck (1955) stated that "It is impossible to define 

a simple relationship between salinity and the decrease

in evaporation," his data indicated that evaporation of 

ocean water (salinity, about 35,000 ppm) is about 2 percent less than that from fresh water in the same environment. The corresponding reduction would be about 3 

percent for a salinity of 60,000 ppm, and about 6-7 percent for a salinity of 100,000 ppm. Evaporation from 

a sample of brine from Great Salt Lake (salinity, 

251,000 ppm) was about 20 percent less than that from 

fresh water.

Figure 15 is based on an evaporation rate that was 

applicable when the salinity was near 34,000 ppm and, 

consequently, will not be applicable when the salinity is 

increased to several times that amount, unless the relation line is adjusted accordingly. The effect of moderate changes in salinity, however, may be less than the 

effect of errors involved in the definition of the relationship.

The graph of total mineral content of Salton Sea (fig. 

10) indicates a rather stable rate of increase for 1945-63 

of about 4 million tons per year, which can probably be 

projected for a few years with relatively little error. 

Any decrease in the quantity of inflow resulting from 

an increase in the efficiency of water use will probably 

be at least partly offset by an increase in salinity of the 

inflow.

Future events, however, may cause changes in the 

average annual increment of mineral content. A proposed development to produce electric power from 

steam supplied by a geothermal well field near Niland, 

Calif., would contribute significant amounts of brine

200

Mean annual evaporation, in feet 

5.78-Derived in this report 

5.49-lf actual evaporation is 5 

percent less than that derived in this report 

6.07-lf actual evaporation is 5 

percent greater than that derived in this report

MEAN ANNUAL NET EVAPORATION (E-P), 

IN MILLIONS OF ACRE-FEET

FIGURE 15. Relation between mean annual values of water level and 

net evaporation, and between water level and inflow (of both surface 

water and ground water) when inflow and net evaporation are in 

equilibrium.
C30 WATER RESOURCES OF LOWER COLORADO RIVER SALTON SEA AREA

to the sea, unless other means of waste disposal are 

provided. Construction of an extensive drainage system in Mexicali Valley whereby effluent would be discharged to the Alamo and New Rivers would tend to 

increase the inflow of minerals to the sea. Precipitation 

of gypsum (as described in the section "Chemical Composition") or a gradual decrease in the amount of sodium 

chloride leached from soils however, may reduce the 

average increment. The annual increment of calcium 

content during 1945-63 (about 140,000 tons) is sufficient 

for removal of about 480,000 tons of calcium sulfate in 

the form of gypsum if concentrations become high 

enough.

Estimates of the future salinity of the unregulated 

Salton Sea involve estimates or assumptions of the corresponding values of both mineral content and volume 

of water (eq 9). The following examples are based on 

the values used in previous examples of stable water 

levels, where applicable, and are illustrative only.

Assume that the annual inflow stabilizes at 1,400,000 

acre-feet before 1980 and that the average annual increment of mineral content for the 17-year period 1964-80 

will be 4,500,000 tons. The mineral content in 1980 

would then be about 340 million tons, the volume (corresponding to the stable water level of 224 ft below 

mean sea level), about 8 million acre-feet (fig. 3), and 

the salinity, about 31,000 ppm.

Similarly, assuming 800,000 acre-feet for the stable 

inflow and 3,600,000 tons for the average annual increment of mineral content, the corresponding stable water 

level would then be 254 feet below mean sea level, and 

the volume, about 2 million acre-feet; the mineral content and salinity in 1980 would be calculated as 320 

million tons and 120,000 ppm, respectively.

SCHEMES FOR REGULATION

A progressive increase in the salinity of Salton Sea 

would inevitably cause gradual deterioration of its 

value for recreation. Moreover, any large changes in 

water level, particularly when associated with large 

lateral changes in shorelines, would hinder the utilization of the sea and operation of marinas and other shore 

installations. Because of these menaces to the rapidly 

increasing recreational uses of the sea, agencies and 

consultants of the State of California began an investigation in 1964 of the feasibility of limiting the salinity 

and of regulating the water level.

In the following discussion of hydrologic and chemical aspects of regulation, the amount of drainage from 

irrigated tracts will assumedly be determined by the 

available water supply and irrigation economics, not by 

requirements for regulation of the sea. Also assumed 

is the fact that evaporation suppression by use of chemical films will not be practical on large windswept water

bodies, although such suppression has been achieved 

experimentally on small water bodies.

The most practical procedures for control of salinity 

and water level of Salton Sea include (a) removal of 

water and minerals by pumping, and (b) the use of 

dikes to limit the surface area and reduce the quantity 

of water evaporated.

A long-term increase in salinity of Salton Sea can be 

avoided only by removing minerals at a rate sufficient 

to compensate for the inflowing minerals and the effects 

of any changes in volume of the sea. Hence, removal 

of water is an essential part of any plan for long-term 

control of the sea. The removal of water to control 

salinity would be compatible with its removal for control of water level if inflow were relatively high, but it 

would aggravate the problem of controlling water level 

if inflow were relatively low. If inflow were insufficient 

to maintain the desired water level in the entire sea, 

a system of dikes could be constructed so that net evaporation from the surface of the principal regulated 

basin would be in equilibrium with the net inflow (total 

inflow less water removed by pumping).

Limiting values of salinity and water level for use 

in designing and operating regulating works would depend on the values considered to be desirable or tolerable and on the costs of maintaining various values. 

Although no specific standards for such values have been 

set (1965), some of the hydrologic problems involved 

in regulating Salton Sea are hereby illustrated by use 

of assumed values, as in preceding examples.

1. Assume that inflow stabilizes at the relatively high 

annual value of 1,400,000 acre-feet, that the average 

annual addition to the mineral content of the sea 

after 1963 is 4,500,000 tons, and that the average annual salinity is to be limited to 40,000 ppm. With 

no regulation, the corresponding stable water level 

and volume would be 224 feet below mean sea level 

(fig. 15) and 8 million acre-feet (fig. 3), respectively. 

At the specified salinity, the mineral content would 

be about 430 million tons (eq 9) that is about 170 

million tons more than the mineral content in 1963. 

This quantity of minerals would accumulate in 38 

years after 1963, and the salinity would reach 40,000 

ppm by about the year 2001. Prevention of later increases in mineral content and salinity, however, 

would require the annual removal of 83,000 acre-feet 

of water with a salinity of 40,000 ppm. Hence, the 

final stable water level would be about 230 feet below mean sea level (corresponding to an average net 

inflow of 1,320,000 acre-ft). Prevention of a large 

rise and later decline of water level would accordingly require regulation by pumping several years 

earlier.
HYDROLOGIC REGIMEN OF SALTON SEA, CALIFORNIA C31

2. Assume that the values of inflow and addition of 

minerals are the same as those in example 1 but that 

the regulated water level is at 234 feet below mean 

sea level. At that level the annual net evaporation 

from Salton Sea would be 1,250,000 acre-feet, and the 

removal of an additional 150,000 acre-feet would be 

required for regulation. The annual removal of this 

quantity of water at a salinity of 25,000 ppm would 

be sufficient to prevent an increase of mineral content. 

Thus, the salinity of the sea would gradually approach 25,000 ppm as a limit.

3. Assume that inflow stabilizes at the relatively low 

annual value of 800,000 acre-feet, that the average 

annual addition of minerals is 3,600,000 tons, and 

that the limiting average annual salinity is to be 

40,000 ppm (as in example 1). Kemoval of a quantity of minerals equal to the annual additions would 

require removal of 66,000 acre-feet of water per year 

at the specified salinity. Subtracting this from the 

assumed inflow leaves 734,000 acre-feet per year to be 

dissipated as net evaporation, which requires a surface area of about 130,000 acres (less than 60 percent 

of the natural surface area of the sea in 1962). For 

any actual system of dikes that would provide such a 

small area for the principal regulated basin, an appreciable part of the inflow would probably enter 

auxiliary basins rather than the principal basin, and 

appropriate adjustments of the computations would 

be required.

The ultimate disposal of minerals or brine is an important part of any scheme for regulating Salton Sea. 

Water could be evaporated from separate basins or from 

diked-off parts of the sea. Saline residues left at altitudes above the surface of Salton Sea, however, might 

involve a serious danger of contaminating usableground-water supplies. Moreover, because of the great 

quantities of minerals involved, long-term operation of 

any regulating works would require removal of minerals 

from auxiliary evaporating basins.

Disposal of concentrated brine by pipeline to the Gulf 

of California or to Laguna Salada (fig. 1), a dry salt 

playa that is slightly below mean sea (ocean) level, 

would avoid most of the danger of contamination but 

would require an international agreement.

Because of similar brine-disposal problems, the feasibility of regulating Salton Sea and feasibility of commercial development of power from the geothermal 

well field near Niland may be interrelated. Wells 

drilled in this area and tested in 1962 yielded steam and 

concentrated brine. Except for disposal of the brine, 

the feasibility of developing power from the steam has 

been demonstrated. Actual development, however, 

may depend on a satisfactory plan for brine disposal

that would accommodate brines from both the well field 

and Salton Sea.

The average rate of evaporation from Salton Sea 

derived in this report would apply with little error to 

a relatively large regulated water body but would not 

apply to auxiliary basins because evaporation from 

brines is as much as 20 percent less than that from fresh 

water. Also, the evaporation from small basins would 

be affected by their location with respect to the principal 

water body and the direction of prevailing winds.

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C32 WATER RESOURCES OF LOWER COLORADO RIVER SALTON SEA AREA

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O