Salinity of Surface Water in

The Lower Colorado River

Salton Sea Area

GEOLOGICAL SURVEY PROFESSIONAL PAPER 486-E

Salinity of Surface Water in 

The Lower Colorado RiverSalton Sea Area

By BURDGE IRELAN

WATER RESOURCES OF LOWER COLORADO RIVER SALTON SEA AREA

GEOLOGICAL SURVEY PROFESSIONAL PAPER 486-E

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1971
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

Library of Congress catalog-card No. 72 610761

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

Washington, D.C. 20402 Price 50 cents (paper cover)
CONTENTS

Abstract . _.._.-_. ._...._ ..._ _-...._ ...._. ._.._... 

Introduction .._____. ..... .._..__-. - ._...-._..__..._ _.-_ ._...

General chemical characteristics of Colorado River 

water from Lees Ferry to Imperial Dam ____________

Lees Ferry .._._..__.___.______.__________

Grand Canyon ................._____________________..............._...

Hoover Dam ..........._._..- -_-._-._................-._._._._...

Lake Havasu - -_......_....-..-........ .........._............._....

Imperial Dam .--. ........_. . ...___.-_.___ _.__.__.._-_._.___ _

Mineral burden of the lower Colorado River, 1926-65 . 

Analysis of dissolved-solids loads ..._.._......... _.._. 

Analysis of ionic loads ...._ _______________________________________

Average annual ionic burden of the Colorado River

Ionic budget of the Colorado River from Lees Ferry to

Imperial Dam, 1961-65 __ ___-_ _ _ _. ___.._.

Lees Ferry . _. .........._.._....._...._________....

Paria River -___. . -.._. . ..............._...............

Little Colorado River _________________________________________________

Blue Springs ....__._................-.... ._.........._...._......_...

Unmeasured inflow from Lees Ferry to Grand 

Canyon . __________. . .-... .-._......_.................._......_...

Grand Canyon _________________________________________________________

Bright Angel Creek .__-__ __-____________________________._ ____

Page

El 

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Ionic budget of the Colorado River from Lees Ferry to

Imperial Dam, 1961-65 Continued 

Tapeats Creek .._________________.____.___-._____. . _ E26

Havasu Creek __._____________-...- _ __ -26

Virgin River ..__ .-.._..-_ --....-. ._. 26

Unmeasured inflow between Grand Canyon and

Hoover Dam .__-.....-_ .... . .-_ . _. 26

Chemical changes in Lake Mead ............-... .-.....-..... 26

Bill Williams River ......._.._......__.._....._ _......_._- 27

Chemical changes in Lakes Mohave and Havasu . 27 

Diversion to Colorado River aqueduct _________________ 27

Parker Dam to Imperial Dam _______... ... . ._ - 28

Ionic accounting of principal irrigation areas above

Imperial Dam __......... .-.- ...._. _____ ___ _._____ ____._-__. 28

General characteristics of Colorado River water below

Imperial Dam .__ .________ _ ..- _ . _ 29

Ionic budgets for the Colorado River below Imperial

Dam and Gila River .-. .. . ._- .. _......._. 34

Quality of surface water in the Salton Sea basin in

California ....-..-. ..._..._.. ._....._ .. . _____.___ 36

Summary of conclusions . ...... .-_.._-._ __ _-_ 39

References ______. ___________________ 40

ILLUSTRATIONS

Page

FIGURE 1. Map showing principal features of the lower Colorado River-Salton Sea area _. ___ __- E3

2. Graph showing annual streamflow and annual weighted-average concentration of dissolved-solids, Colorado

River at Grand Canyon, 1926-65 ..........._....... ..__........____.. ______ _______..__. _____ _._____ __________ ---- - __ 7

3. Graph showing annual weighted-average concentration of dissolved solids, sulfate, bicarbonate, and chloride, Colorado River at Grand Canyon, 1926-65 _____________ ________ _________________-____-_. _ __. ,. - 8

4. Histograms of weighted-average concentration of dissolved solids, Colorado River near Grand Canyon and

below Hoover Dam, 1935-62 ________________________________ ________________________ _____......_............__.. .... .. -... .. 9

5. Graph showing approximate relations of dissolved-solids load and concentration to flow of Colorado River

near Grand Canyon, 1926-62 ._.-_-_._._..._.._.__.._.._ _________ ____________________ ________ _____________________ _.__._.._.._._._._. 13

6. Mass diagram of cumulative dissolved-solids load for Colorado River at-Grand Canyon, 1926-65 ____________________ 14

7. Double-mass diagram of cumulative dissolved-solids load to cumulative streamflow, Colorado River at

Grand Canyon, 1926-65 ___________________________________ _______ ___ _____.. _ ___________ _. .-............. ... ..-....... 15

8. Comparative differential mass diagram for streamflow and dissolved-solids load, Colorado River at Grand

Canyon, 1926-62 _____________________________________________ __. _ ____..__......._.........................._.___........_... 16

9. Graphs showing approximate relations of annual ionic load of principal constituents to annual flow of Colorado River near Grand Canyon, 1926-62 ________ __ ____ __________________________ ____________________ 17

10. Graphs showing progressive 5-year average ionic and dissolved-solids load, Colorado River near Grand

Canyon and below Hoover Dam, 1935-65 ______________ _ _ __ _ _ __ ________________________________________ 18

11. Map showing principal features of the Wellton-Mohawk and Yuma areas ___.._._........... ...._........... _..._... 30

12. Map showing principal features of the Salton Sea area and vicinity _________________________________-_._ _ ______ 31

III
IV CONTENTS

TABLES

Page

TABLE 1. Annual weighted-average concentration of Colorado River at Lees Ferry, Ariz. ____ _ ____________________ ______._. E5

2. Annual weighted-average concentration of Colorado River at Grand Canyon, Ariz. _______ ____ _________________ _ 6

3. Summary of weighted-average concentrations of dissolved solids, Colorado River at Grand Canyon, 1926-62 9

4. Annual weighted-average concentration of Colorado River below Hoover Dam, Ariz.-Nev. __________ _ _________ 10

5. Annual weighted-average concentration of Colorado River at Lake Havasu, Ariz.-Calif. __ ____ _ _ _ _____-_. 11

6. Annual weighted-average concentration of Colorado River at Imperial Dam, Ariz.-Calif. ..___ - __________________ 12

7. Five-year summary of streamflow and ionic burden of lower Colorado River from Lees Ferry to Imperial

	Dam 1941-65 ______________-__--- -- -....._. ._ --_:___- 19

8. Forty-year summary of ionic burden of Colorado River at Grand Canyon by 5-year intervals, 1926-65 _ ___. 21

9. Averages of streamflow and ionic burden of Colorado River at Grand Canyon for different periods ________ 21

10. Comparative computations of average annual streamflow and ionic burden of Colorado River at Lees Ferry 22

11. Representative analyses of tributary inflow to lower Colorado River between Lees Ferry and Imperial Dam 23

12. Average annual streamflow and ionic burden of the Colorado River, Lees Ferry to Imperial Dam, 1961-65 24

13. Average annual water use and ionic burden in irrigated areas, Parker Dam to Imperial Dam, 1961-65 ________ 28

14. Representative analyses of surface water in Colorado River basin at and below Imperial Dam, 1966 water

	year __________________________________________________________________ _ ___ _ _____ _______ ___ 32

15. Streamflow and ionic burden of the Colorado River, Imperial Dam to south international boundary, ^966 ... 34

16. Streamflow and ionic burden of the lower Gila River, Wellton-Mohawk area to mouth, 1966 _____________ __. 35

17. Streamflow and ionic burden of inflow and outflow for combined Wellton-Mohawk and Yuma areas, 1966 ______ 36

18. Distribution of surface-water and dissolved-mineral gains and losses for combined Wellton-Mohawk and

	Yuma areas, 1966 _______________________________ ___. __________________ ________ ______ _______________________ 37

19. Selected chemical analyses of surface water in Salton Sea basin _ ______ ________ _ _____ ________________________ 38
WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

SALINITY OF SURFACE WATER IN THE 

LOWER COLORADO RIVER-SALTON SEA AREA

By BURDGE IRELAN

ABSTRACT

This report summarizes records of salinity and computations of the mineral burden of the Colorado River and tributary surface inflow from Lees Ferry to the Mexican border 

and of streams in the adjacent Salton Sea basin.

The virgin salinity regimen of the Colorado River (that 

prior to upstream irrigation) is unknown, but was probably 

similar to the regimen observed during earlier years of 

sampling. Before closure of Hoover Dam, the salinity at 

points of record on the river varied rather substantially daily, 

seasonally, and annually and also varied moderately (generally increasing) with distance downstream. Observed dissolved-solids concentrations, which ranged between 200 and 

1,800 mg/1 (milligrams per liter) consisted mainly of calcium 

bicarbonate at lower concentration levels and mixed sulfate 

and chloride salts at higher concentration levels.

The chemical-quality record for the Colorado River at Grand 

Canyon indicates that the 40-year weighted-average concentration is about 600 mg/1. The long-time average at Lees 

Ferry has been moderately less. Recent storage and diversion 

projects above Lees Ferry have apparently caused small increases in annual weighted-average mineral concentrations, 

but these increases have been less than the differences between 

10-year weighted averages.

Since Lake Mead was formed, dissolved-solids concentrations 

in Colorado River water between Hoover and Imperial Dams 

have generally ranged between 600 and 900 mg/1, with calcium sulfate always the dominant dissolved salt. Concentrations below Hoover Dam have been higher, on the average, 

than those at Grand Canyon mainly as a result of evaporation 

from the surface of Lake Mead and solution from its bed. 

The higher concentrations, however, have been partially offset 

by precipitation of calcium carbonate in the lake. Solution of 

minerals from the bed of the lake, although still considerable, 

appears to be substantially less than during the first years 

after its formation.

The annual mineral burden of the river varies markedly, 

but average burdens for periods of 5 or more years are fairly 

stable. Although most of this burden originates above Lees 

Ferry, rather large increments originate in the discharge of 

Blue Springs, which are on the Little Colorado River a short 

distance above its mouth, and in the Virgin River. Other

Lower Basin tributaries add much smaller increments to tht 

river's mineral burden.

Low releases from Lake Powell during the first 2 years of 

impoundment caused a temporary rise in average salinity at 

Grand Canyon and contributed to later increases in the salinity 

of water in Lake Mead and in the Colorado River downstream 

from Hoover Dam.

Diversions to the California aqueduct increased substantially during 1961-65. This reduced the amount of river water 

available downstream from the diversion for dilution of 

slightly to moderately saline irrigation return flows from the 

Parker and Palo Verde Valleys and thereby caused higher 

average concentrations at Imperial Dam. Somewhat saline 

drain water from expanded irrigation in the Parker and 

Palo Verde Valleys also has contributed to the increased 

concentration at Imperial Dam.

Computations of gains and losses indicate that during recent 

years more mineral salts were removed from the Parker and 

Palo Verde Valleys in return flows than were brought into 

them in the irrigation water.

Dissolved-solids concentrations are now relatively constant 

at Imperial Dam because of upstream storage, but both the 

flow and the mineral burden of the Colorado River below the 

dam are greatly reduced by diversions to the Ail-American 

and Gila Gravity Canals. Thereafter, the salinity and mineral burden progressively increase as surface irrigation return 

flows and pumped ground water are discharged into the river.

During the last 30 years, flow of the Gila River above the 

Wellton-Mohawk area has usually been too small to affect 

materially the salinity and mineral burden of the Colorado 

River, although during the exceptional year 1966 it added 

some water of excellent quality to the irrigation supply. 

Ground water pumped to control water levels in the WelltonMohawk area and South Gila Valley has been much more 

saline than the applied irrigation water and has added substantially to the mineral burden of the lower Gila and Colorado Rivers, particularly since 1960. A salinity problem in 

Mexico caused by expanded pumping of saline ground water 

in 1961 has been brought under control by drilling new wells, 

constructing a concrete-lined conveyance channel with controlled outlets, and management of the pumping according to 

the salinity of the individual well waters and irrigation 

requirements.

El
E2 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

Colorado River water flows through the All-American 

Canal from Imperial Dam to Imperial and Coachella Valleys 

in the Salton Sea basin without material change in salinity. 

Both valleys contained areas with saline soils before they 

were irrigated, and early salinity problems developed, mainly 

because of inadequate drainage. Present drainage systems 

have been developed to the point where more dissolved minerals are removed from irrigated areas than are brought in 

by irrigation water.

The Alamo, New, and Whitewater Rivers, which drain to 

the Salton Sea, have differing water-quality characteristics. 

Some water suitable for irrigation appears to enter each 

stream as a result of present irrigation practices, and part 

of their flows possibly could be salvaged.

INTRODUCTION

The Colorado River is a major continental stream 

draining one-twelfth of the conterminous United 

States. The equitable division of its water among the 

seven basin states and Mexico has long been and 

remains difficult. The Colorado's flow is subject to 

provisions of an international treaty, interstate compacts, congressional acts, and court decrees. Today 

the river is a source of water for small cities within 

its basin, for great cities outside its basin, and for 

irrigation of large areas in and near its basin. The 

natural salinity (concentration of dissolved solids) 

of its water ranks among the highest of the great 

rivers of North America. Increasing salinity in the 

lower reaches has long been recognized as an almost 

inevitable result of increasing use of water from 

rivers flowing through arid lands. Yet, strangely, 

none of the legal documents dividing the flow of the 

Colorado River is concerned with its salinity.

The Colorado River is a mammoth transport system in which both water and dissolved-mineral salts 

continuously move downstream. The river flow is 

derived from many sources, each with individual 

chemical characteristics which blend in the river. 

The resulting changeable pattern of interrelated variations in concentration, composition, and mineral 

load l constitutes the chemical regimen of the river, 

which has been investigated for this report.

Records of streamflow had been obtained at numerous points in the Colorado River basin for many 

years before the Geological Survey began an extended systematic sampling of the variations in mineral concentrations in the river water at Grand Canyon in August, 1925. Since then the Geological Survey 

has systematically sampled the lower river at one or 

more points every year. Some of the earlier quality1 Mineral load, as used in this report, refers to the total quantity of 

dissolved-mineral salts and silica transported by the river past a particular 

point in a specified time. The term is synonymous with "salt load" as used 

in many reports, but is preferred because "salt load" sometimes refers only 

to a single salt sodium chloride.

of-water records, however, have never been summarized in the published reports of the Geological Survey. Other organizations also have sampled the river, 

some occasionally and some for extended periods.

Foreseeing the time when water in the Colorado 

River and the local ground water, which is largely 

derived from the river, together will not be sufficient 

to meet projected needs without careful management, the Geological Survey in 1960 began a comprehensive investigation of factors affecting the development and use of water in and adjacent to the 

lower Colorado River including the Salton Sea basin, 

which depends primarily on the Colorado River for 

water. This report, describing the quality of the surface water, is one of a series that constitutes an appraisal of the water resources of the lower Colorado 

River-Salton Sea area. It examines all available 

chemical-quality records of surface water in the 

study area to determine the chemical regimen of the 

river as related both to variations in ionic concentrations in the water and to mineral loads transported 

by the river.

A companion report by Hely (1969) describes the 

area considered in this report and the availability of 

its surface water, explains the division of the Colorado River drainage at compact point into Upper 

and Lower Basins, and also explains the reasons for 

making a hydrological appraisal of the area primarily served by the Colorado River water rather than 

appraising a limited part of the Colorado River basin 

by itself. Ground-water quality in the area is to be 

separately covered in several reports describing the 

occurrence and availability of ground water.

An earlier investigation by the Geological Survey 

(lorns and others, 1965) describes the water resources of the Upper Colorado River Basin in detail 

and serves as a background for the Lower Basin 

study.

Figure 1 shows the location of the area considered by this study, indicates its principal subdivision, and shows the sites of the major dams and 

principal sampling points discussed in the report.

GENERAL CHEMICAL CHARACTERISTICS OF

COLORADO RIVER WATER FROM LEES

FERRY TO IMPERIAL DAM

The salinity of Colorado River water commonly 

has been described in terms of its dissolved-solids 

concentrations, or the concentrations of dominant 

ionic constituents, stated either separately or combined as salts. A single dominant combination of 

ions, however, has rarely been adequate to define 

the river-water composition. The natural (virgin)
SALINITY OF SURFACE WATER E3

I II I I II I I I II I

Approximate boundary

/ COLORADO RIVEK INDIAN RESEK\ AT1ON 

PARKER VALLEY

FIGURE 1. Principal features of the lower Colorado River-Sal ton Sea area.

chemical regimen of the river, although not repre 

sented by chemical-quality records and therefore un 

known, was undoubtedly one of large daily and sea 

sonal variation in both salinity and composition. 

Systematic records obtained for various points on

the river since 1925 show that the chemical characteristics of the water in the lower river have varied 

both from point to point and from year to year. 

Long-term records obtained upstream from Lake 

Mead, encompassing a period that began after most
E4 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

of the Upper Basin irrigation had been developed 

and before the construction of the Glen Canyon 

Dam, represent a comparatively stable condition and 

a regimen that probably differs only slightly from 

the natural regimen. Data resulting from sampling 

below Hoover Dam and below Glen Canyon Dam 

show how the average concentrations have been increased and variations decreased as a result of man's 

control of the river.

The long-term records show that during larger 

spring floods above Lake Mead, the river water generally contains 200-350 mg/1 (milligrams per 

liter) 2 of dissolved solids, consisting mainly of calcium bicarbonate. The sulfate concentration always 

exceeds the chloride concentration. During smaller 

spring floods the floodwater usually contains 350- 

500 mg/1 of dissolved solids with sulfate concentrations about the same as bicarbonate concentrations. 

During low-flow periods, in fall and winter, the dissolved-solids concentrations have reached 1,500 mg/1 

nearly every year and occasionally have reached 

1,800 mg/1. During these periods sodium nearly always has been the principal cation, but the mixture 

of anions has been such that no single salt predominates in the dissolved solids. Short records obtained 

prior to formation of Lake Mead indicate that the 

same chemical characteristics then prevailed at 

Yuma, Ariz.

Because concentrations of dissolved solids generally vary with stream discharge, comparison of water quality at different sites is best made by use of 

weighted-average concentrations for a particular 

period, usually a water year in this report. These 

weighted averages approximate the concentration 

that would be obtained by analysis of a sample from 

the streamflow for the entire year if it were well 

mixed. Weighted-average concentrations are computed from the available chemical analyses and the 

streamflow records by assigning the volumes of flow 

occurring during designated time intervals to the 

chemical analyses of water samples taken during 

those flow periods and by assigning estimates of 

analyses for any unsampled periods. The weighted 

averages are the quantities obtained by adding the 

products of the concentrations and the corresponding flow volumes and dividing by the total flow for 

the period averaged.

Weighted-average concentrations have been published previously for some, but not all, of the Colo2 The original analytical data summarized in this report generally state 

concentrations in parts per million. Recently, however, the Geological Survey 

has adopted the policy of reporting concentrations as milligrams per liter 

and this report follows that system. Except for concentrations above about 

7,000 ppm, the two systems are numerically equal.

rado River sampling records. The reliability of 

weighted-average analyses representing the individual yearly flows at the specified sampling points 

depends on the number and distribution of samples analyzed, the accuracy of the individual analytical determinations, and the accuracy of the 

streamflow record. For the years of published 

weighted averages there have been numerous sampling schedules, variable completeness of the individual chemical analyses, and many different analytical 

procedures. Therefore, the published weighted averages have not been equally representative of water 

quality. Consequently, evaluating the long-term variations in Colorado River salinity and the changes 

caused by man's activities has necessarily involved 

reviewing the records of chemical analyses for completeness of sampling and representativeness of 

reported analytical values. It has also involved estimating values when none were available, recomputation of some previously computed weighted-average 

concentrations, and estimating weighted averages 

for unsampled years by using sampling records at 

other river points as guides. As a result of this reappraisal, the tables of weighted-average concentrations in this report differ in some respect from 

previously published weighted averages. The tables 

also include weighted averages of individual constituents not previously published.

Annual weighted-average concentrations for the 

five long-term sampling points most useful in evaluating water-quality variation in the lower Colorado 

River are given in tables 1-5. The tables include 

only years of actual sampling for the years prior to 

1941, but to provide a 25-year record to use in tracing mineral movement down the river they include 

estimates for all unsampled years from 1941 on.

Comparison of the ionic and dissolved-solids concentrations at different points for the same year 

shows generally increasing concentrations downstream and more variation in the annual weighted 

averages of most constituents above Lake Mead than 

below it. To understand the variation of salinity in 

the river it is therefore necessary to consider each 

sampling record in turn.

LEES FERRY

The Colorado River at Lees Ferry, which is above 

the confluence of the Paria River, contributes considerably more than 99 percent of the average surface flow at compact point, the division between the 

upper and lower Colorado River. Hence, records for 

Lees Ferry (table 1) provide accurate indices of 

streamflow and water-quality variation at compact
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E6 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

The small apparent increase in concentration for 

1965 over that for 1958-62 may be partly due to the 

combined effects of solution from the bed of Lake 

Powell and evaporation of pure water from its surface, but it is probably mainly due to errors in the 

sampling and changes in streamflow.

GRAND CANYON

A program of systematic (mostly daily) water 

sampling for chemical analysis has been in operation 

longer and with fewer unsampled periods at Grand 

Canyon than at any other point on the Colorado 

River. The Grand Canyon record (table 2) is based 

on sampling during every year except 1943, for 

which year the concentration was estimated from 

records at Lees Ferry. Because of its greater length, 

more comprehensive character, and closer proximity 

to the major areas of water use, this record provides

a better index of natural variability of lower Colorado River salinity than the shorter and less complete Lees Ferry record, which has been considered 

as the reference record in some other studies.

Comparisons between the annual concentrations 

given for Grand Canyon in table 2 with those given 

for Lees Ferry in table 1 indicate that the water at 

the lower station regularly has moderately higher 

concentrations of several constituents.

Although table 2 gives both the annual streamflows and corresponding annual weighted-average 

analyses for Colorado River water at Grand Canyon, 

the relation between streamflows and concentrations 

is not readily apparent. To make the relation clearer, 

the annual streamflows and annual weighted average of dissolved-solids concentrations are plotted as 

paired bars in figure 2. No significant change in the 

relation between annual discharge and average conTABLE 2. Annual weighted-average concentration for Colorado River at Grand Canyon, Ariz.

[Results in milligrams per liter unless otherwise indicated. (estimated) signifies concentrations determined indirectly instead of by weighting individual 

analyses]

Water 

year

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 

I960..

1961..

1962..

1963..

1964 

1965 

Total flow 

(acre-ft)

__ 14,420,000

__ 17,260,000

__ 15,630,000

__ 19,430,000

__ 13,420,000

__ 6,721,000

__ 15,970,000

-..10,010,000

__ 4,656,000

-..10,220,000

__ 12,320,000

__ 12,410,000

__ 15,630,000

__ 9,618,000

__ 7,435,000

__ 16,940,000

_ .17,260,000

.-.11,430,000

 .13,530,000

-..11,870,000

. _ 9,089,000

 .13,740,000

_ .13,870,000

__ 14,370,000

__ 11,080,000

.... 9,839,000

....18,160,000

__ 8,879,000

__ 6,229,000

.... 7,580,000

__ 8,860,000

-..17,500,000

 14,550,000

_ . 6,935,000

. _ 9,584,000

.... 7,050,000

. __ 15,250,000

.... 2,742,000

... . 2,727,000

 .-10,980,000

discharge (cfs) Mean 

19,920 

23,840 

21 , 530 

26,840 

18,540

9,283 

21,990 

13,820 

6,431 

14,110

16,970 

17,140 

21,590 

13 , 290 

10,240

23,400 

23 , 840 

15,790 

18,630 

16,400

12,550 

18,970 

19,100 

19,840 

15,300

13,590 

25,020 

12,260 

8,604 

10,470

12,210 

24,170 

20,100 

9,579 

13,200

9,739 

21,060 

3,788 

3,756 

15,170

Dissolved solids

6

en

03

& 

in

19 

17 

17 

18 

16

13 

13 

13 

15 

14

16 

12 

14 

17 

15

15 

13 

 18 

13 

15

14 

12 

14 

15 

14

14 

15 

15 

14 

16

15 

16 

18 

 16 

 16

 15 

 18 

 15 

 14 

 12

I

a

y

1 

O

66

77 

66 

74 

81

93 

73 

82 

105

74

83 

83

76 

85 

92

79 

69 80 

77 

80

93 

82 

81 

84 

91

87 

84 

95 

105 

99

82 

75 

85 

98 

84

108 

77 

114 

115 

83

-3 

&

a

 a 

a

1

s

21 

22 

22 

23 

26

34 

21 

26 

39 

22

23 

25 

22 

28 

31

22 

23 27 

24 

26

29 

25 

23 

24

28

29 

23 

31 

34 

30

25 

19 

22 

29 

21

29 

20 

38 

35 

24

'oS

5,

a

1en

75 

77 

65 

73 

85

131 

74 

93 

159

81

79 

85 

73 

96 

115

76 

69 85 

73 

82

97 

76 

73

75 

84

90 

66 

101 

132 

111

85 

60 

74 

116 

86

115 

68 

171 

170 

92

*

a %

1cw

5.7 

5.5 

4.3 

6.2 

5.0

4.7 

4.1 

4.9 

6.1 

3.9

6.0 

6.1 

4.6 

5.3 

4.6

5.1 

5.3 

 4.0 

4.6

7.2

7.0 

6.0 

4.1 

4.1

5.8

 6.0 

5.3 

6.8 

6.3 

6.2

5.1 

4.5 

4.7 

 7.0 6.1

 6.0 

 5.0 

 8.5 

 7.0 

 5.0

B 

3

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g

io

5

159 

162 

162 

164 

184

201 

176 

181 

206

177

186 

193 

189 

198 

200

193 

160 

«202 

204 

207

235 

211 

212 

220 

235

219 

233 

243 

231 

228

201 

184 

199 

207 

192

195 

195 

234 

219 

175

Hardness 

as CaCOs

Sum

6 

s $03 

CO

201 

235 

187 

229 

252

325 

202 

249 

392 

204

228 

238 

199 

254 

296

214 

212 

 232 

200 

220

248 

217 

195 

201 

231

241 

184 

262 

335 

281

215 

168 

210 

 303

 227

 323 

 181 

 396 

 399 

251

§

!XI

O

56 

53 

48 

48 

62

107 

54 

74 

136 

69

61 

64 

53

77 

95

53 

50

 67 

56 

65

81 

58 

59 

57 

70

76 

48 

86 

111 

93

78 

49 

60 

 97 

 70

 102 54 

 153 

 149 

76

g 

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«.3 

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 4

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3 &

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. 2.4

2.4 

. 2.5

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3.3 

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5.1 

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1.9 

1.9 

2.7 

2.5

1.6 

2.2 

 4.0 

3.1 

2.1

2.1 

1.7 

1.8 

2.6 

1.9

2.2 

2.9

2.7 

4.2 

4.5

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2.9 

2.8 

 4.5 

 1.9

 4.5 

 2.5 

 6.3 

 5.5 

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523 

569 

491 

555 

622

813 

531 

635 

960 

559

591 

610 

538 

662 

750

561 

523 

 620 

552 

601

688 

583 

556 

572 

642

673 

558 

719 

856 

753

600 

486 

576 

779 

624

814 

531 

1,050 

1,030 

652

35

 &S £* $

rS Ct*

s

525 

570 

493 

556 

622

815 

532 

636 

960 

560

591 

612 

538 

664 

751

562 

524 

 619 

553 

601

689 

584 

557 

573

644

655 

543 

722 

858 

755

609 

486 

576 

 775 

 60S

 792 

 522 

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 1000 

632

t-n= S*7 

a i>

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0.71

.77 

.67 

.75 

.85

1.11 

.72 

.86 

1.31 

.76

.80 

.83 

.73 

.90 

1.02

.76 

.71

 .84 

.75 

.82

.94 

.79 

.76

.78 

.87

.92 

.76 

.98 

1.16 

1,02

.82 

.66 

.78 

1.05

.85

1.11 

.72 

1.43 

1.40 

.89

a

y

ft3S 

0

251 

282 

255 

279 

309

372 

268 

312 

422 

275

302 

310 

280 

327 

357

288 

266 

 310 

290 

306

351 

308 

296 

308 

342

336 

304 

364 

402 

370

308 

265 

302 

364 

296

388 

272 

440 

431 

306

1

|

1 

fc

121 

150 

122 

144 

158

208 

124 

163 

254 

130

149 

152 

125 

164 

193

130 

136 

 135 

124 

137

158 

134 

123 

128 

150

156 

113

166 

212 

184

143 

114 

140 

194 

138

228 

112 

248 

252 

162

Specific conductance 

(micromhos 

25°C) at 

 800 

 869 

 752 

 848 

 948

 1,240 

 811 

 970 

 1,460 

 854

 901 

 933 

 814 

 1,010 

 1 , 130

856 

799 

 946 

861 

919

 1,040 

882 

862 

880 

996

987 

831 

1,100 

1,300 

1,140

927 

746 

877 

1,170 

930

1,190 

803 

1,570 

1,540 

987
SALINITY OF SURFACE WATER E7

24.0

20.0

16.0

12.0

8.0

4.0

n r.

Streamflow 

Concentration

1000 0

800

600

400

200

WATER YEAR

FIGURE 2. Annual streamflow and annual weighted-average concentration of dissolved solids, Colorado River at Grand Canyon, 1926-65.

centration is suggested by the figure, except the 

temporary one caused by closure of Glen Canyon 

Dam in 1963. The figure clearly shows that the years 

with the greatest streamflow have had among the 

lowest dissolved-solids concentrations and that years 

of approximately equal streamflow have had only 

moderate variations in average concentrations. Thus, 

so far as can be determined from the parallel plotting, the Colorado River had a nearly stable chemical regimen during the years 1926-62. The great 

change in regimen caused by closure of Glen Canyon Dam in 1963 seems to have been limited to 2 

years, as the relation between salinity and streamflow for 1965 is within the range that might have 

been expected for the volume of flow.

Comparison of the annual analyses in table 2 

shows that all the major ions contribute to the variation in dissolved solids at Grand Canyon. Most of 

the salinity changes, however, result from changes 

in the concentrations of the anions, so the general 

nature of the chemical regimen of the river can be 

determined by considering only the major anions. 

Thus, the line connecting yearly dissolved-solids concentrations in figure 3 is roughly parallel to lines 

formed from yearly weighted-average concentrations 

of sulfate, bicarbonate, and chloride; this indicates 

fairly consistent inter-ionic relationships. Figure 3 

shows that the annual chloride concentration at 

Grand Canyon has always been much less than the

annual bicarbonate and sulfate concentrations, that 

in most years the sulfate concentration has exceeded 

the bicarbonate concentration, but that for those 

years with low dissolved-solids concentrations the 

sulfate was nearly equal to or less than the bicarbonate.

Most of the annual bicarbonate concentrations at 

Grand Canyon prior to 1943 were lower and changed 

less from year to year than the later ones. A possible 

explanation for this apparent change in regimen is 

that during the first years of sampling long delays 

occurred between sample collection and analysis. 

Consequently, there may have been considerable calcium carbonate precipitation in the more concentrated samples prior to chemical analysis that would 

have resulted in low values for the yearly bicarbonate concentrations. If during the early years the 

individually determined bicarbonate concentrations 

averaged 20-30 mg/1 lower than the true values a 

reduction which appears possible from a study of 

figure 3 and of the original data the long-time dissolved-solids concentration reported as 598 mg/1 in 

table 6 may be 10-15 mg/1 less than the true value.

Records of water quality obtained at Grand Canyon after the formation of Lake Powell in 1963 are of 

too short duration to determine the probable future 

effect of this lake on downstream river-water quality. Chemical analyses of samples obtained through 

1965, however, suggest that some solution of calcium
E8 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

1200

1000 

800 

600 

400 

200 ^-

WATER YEAR 

FIGURE 3. Annual weighted-average concentration of dissolved solids, sulfate, bicarbonate, and chloride, Colorado River at Grand Canyon, 1926-65.

sulfate and sodium chloride from the lakebed has 

occurred and that there may have been some precipitation of calcium carbonate in the lake.

As annual river flows are known to have a small 

degree of dependence on immediately preceding annual flows with either high or low flow years tending 

to come together, it is possible that there is a similar 

sequential dependence of annual weighted-average 

concentrations. Study of the record for Colorado 

River at Grand Canyon, however, suggests that any 

such dependence is small and that annual concentrations are mostly related to annual discharge. Treating the annual concentrations as entirely random is 

helpful in a statistical summary of their variation 

(table 3). As most of the flow at Grand Canyon is 

now regulated by Lake Powell, future fluctuations in 

annual dissolved-solids concentrations will no doubt 

be less than those during 1926-62. Nevertheless, table 3 is of interest because it provides a summary of 

actual variations during a period of nearly stable 

irrigation development in the tributary area. The 

table shows that annual concentrations differ markedly but that averages for periods of 10 or more 

years usually differ only slightly.

In table 3, concentrations are given in tons per 

acre foot as well as milligrams per liter because irrigators in the lower Colorado River service area generally are familiar with dissolved-solids concentrations so expressed. Load data, described later, are 

also given either in tons or tons-equivalent because 

such expressions have been customary in reports 

about the Colorado River.

HOOVER DAM

The record of annual weighted-average concentrations for Colorado River below Hoover Dam (table
SALINITY OF SURFACE WATER E9

TABLE 3. Summary of weighted-average concentrations of dissolved solids, Colorado River at Grand Canyon, during selected

periods prior to closure of Glen Canyon Dam

Period and type of weighted average

Weighted average for selected years during 1926-62 : 

Year of median streamflow (1936). -_-.__._._________-._____ _____ _.___

Year of median weighted average (1956)____ ______________________ _____

Year of maximum streamflow (1929) ___ ___ __ _________________________

Year of minimum weighted average (1957)__._ ______________________ ___

Mean of annual weighted averages __ ___________________________________

Weighted averages for selected periods during 1926-62: 

Total period. ___ ._._ _____ _____ _ __ ___________ ____ __ ___ ___

Period of inflow to Lake Meade, 1936-62 _ ._-_____ _ _. __ _.. ---------

1936_45

1946-55-----.- ----_-_------_---___----------.----------.._-----_--- -._

1953-62-.-.-. -.--. ._._-.____-...-.---.-_---.-__-_-----_----__. _---.

1956-62- -------_--_------__-------------__-_--_---------_-__---------

Weighted-average concentration

(acre-ft) Milligrams 

per liter

12,320,000 

8,860,000 

19,430,000 

4,656,000 

17,500,000 

12,130,000

12,130,000 

11,543,000 

11,890,000 

12,780,000 

12,840,000 

11,280,000 

10,240,000 

11,390,000

591 

609 

556 

960 

486 

629

598 

607 

602 

584 

586 

629 

630 

590

Tons per 

acre-foot

0.804 

.828 

.756 

1.31 

.661 

.855

.814 

.826 

.819 

.794 

.797 

.856 

.857 

.803

4) includes years when samples were collected at 

Willow Beach, 10 miles downstream, immediately 

prior to and during the early part of the filling of 

Lake Mead. It also includes several years when analyses of samples obtained at various depths between 

the intake towers of Lake Mead were used as measures of the quality of the water in the river.

Lake Mead is comparable to a huge mixing bowl 

into which pour the widely variable flows of the Colorado River, the much smaller Virgin River flows, 

several small spring-fed streams, and the infrequent 

flows from several generally dry channels. The lake 

alters the chemical regimen of the river below the 

lake as well as the streamflow regimen. Thus, it has 

virtually eliminated the natural daily and seasonal 

variations of concentration and has much reduced 

the annual variation. It has brought about changes 

in the water resulting from precipitation of calcium 

carbonate and silica and by solution of gypsum and 

possibly common salt from its bed. Also, evaporation 

of pure water from the lake has constantly increased 

the salinity of released water.

Histograms of the annual weighted-average concentration of dissolved solids for 1935-62 (fig. 4) 

illustrate the increased concentrations and reduced 

annual variation of Colorado River water below 

Hoover Dam as compared with that near Grand 

Canyon.

The records show that the concentrations of Colorado River water below Hoover Dam are still responsive to changes in flow, although the response has 

been muted by Lake Mead. During wetter periods of 

a few years, more water has flowed into Lake Mead 

than could be stored, so more has been released than 

actually needed by users downstream. During such

12

Near Grand Canyon

14

=3 12 Below Hoover Dam 

0 

ANNUAL WEIGHTED-AVERAGE CONCENTRATION, 

IN MILLIGRAMS PER LITER

FIGURE 4. Histograms of dissolved-solids concentration near Grand Canyon 

and below Hoover Dam, 1935-62.
E10 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

TABLE 4. Annual weighted-average concentration for Colorado River below Hoover Dam, Ariz.-Nev.

[Results in milligrams per liter unless otherwise indicated. (estimated) signifies concentrations determined indirectly instead of by weighting individual

analyses]

Dissolved solids

Water 

year

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...

1963 

1964 ...

1965 ...

Total flow 

(acre-ft)

_ 5,556,000

_ 6,282,000

_ 5,826,000

_ 6,168,000

_ 8,473,000

... 7,694,000

 11,730,000

_ 17,880,000

_ 12,500,000

_ 14,450,000

 12,940,000

_ 11,290,000

_ 10,660,000

 12,750,000

_ 13,200,000

_ 12,940,000

_ 9,981,000

 14,370,000

--.12,780,000

_ 10,690,000

... 9,276,000

 . 7,818,000

 8,088,000

...12, 270, 000

... 9,757,000

... 9,251,000

_ 8,661,000

_ 8,304,000

... 8,810,000

_ 8,234,000

 7,917,000

1 

I

1

7,674

8,653 

8,048 

8,519 

11,700 

10,600

16,200 

24,690 

17,260 

19,910 

17,870

15,600 

14,730 

17,570 

18,230 

17,870

13,790 

19,800 

17,650 

14,760 

12,810

10,770 

11,170 

16,940 

13,480 

12,740

11,960 

11,470 

12,170 

11,340 

10,940

^

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% 

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13

13 

10 

11 

13 

13

11 

12 

13 

12 

 12

 10 

 12 

 11 

 11 

 11

13 

 13 

 13 

 13 

 13

 13 

 12 

11 

11 

11

10 

12 

10 

10 

10

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82

78 

102 

103 

102 

110

110 

103 

95 

92 93

 89 

 90

 88 

 85 

 84

84 

83 

83 

88 

102

104 

96 

87 

84 

88

92 

101 

98 

93 

101

-S 

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29

24 

25 

25 

26 

28

28 

27 

26 

28 30

 30 

 29 

 27 

 25 

 26

28 

27 

23 

25 

27

32 

31 

24 

24 

25

27 

26 

24 

27 

29

* g

g, Q

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108 5.8

85 5.7 

93 5.4 

90 5.7 

93 6.1 

98 5.2

98 6.4 

98 

89 

90 5.9 

95

90 

96 

89

84 

81

90 

 90 «4.5 

82 «4.2 

90 «5.0 

106 «5.0

117 «5.3 

110 «5.3 

86 4.2 

81 4.0 

87 3.9

92 4.6 

98 4.3 

96 4.3 

97 4.3 

115 5.4

W

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152 

157 

153 

158 

159

153 

156 

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159 

 166

 162 

 161 

 157 

 156 

 158

167 

 160 

 162 

 164 

 167

170 

171 

158 

158 

158

160 

162 

160 

154 

156

Hardness 

as C CDs

Sum J

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102

268

242 

314 

314 

321 

348

355 

329 

303 

299 302

 288 

 294 

 281 

 263 257

267 

 273 

 253 

 274 

 320

 350 

 320 

269 

261 

 270

288 

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290 

292 

335

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 94

 103 

 98 

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3.0 

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 1.8 

 1.8 

 1.8 1.9

2.0 

 2.1 

 2.0 

 2.1 

 2.2

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 2.2 

2.9 

3.2 2.5

3.5 

3.5 

2.7 

1.2 

1.6

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693

596 

703 

696 

712 

761

766 

719 

673 

679 

 696

 664 

 688 

 649 

 615 

 606

663 

652

632 

677 

778

837

791 

661 

622 

656

694 

725 

700 

703 

814

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694

599 

704 

696 

716 

762

767 

722 

673 

677 

 695

 662 

 680 

 646 

 615 

 606

639 

 645 

 604 

 652 

 753

 813 

 760 

634 

614 

 639

680 

727 

691 

691 

782

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0.94

.81 

.96 

.95 

.97 

1.03

1.04 

.98 

.92 

.92 

.95

.90 

.92 

.88 

.84 

.82

.90 

.89 

.86 

.92 

1.06

1.14 

1.08 

.90 

.8.5 

.89

.94 

.99 

.95 

.96 

1.11

a 

a!

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324

293 

358 

360 

362 

390

390

367 

344 

344 356

 346 

 344 

 330 

 315 

 316

324 

318 

302 

322 

366

391 

367 

316 

308 

322

340 

359 

343 

328 

371

'§

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185

168 

229 

234 

232 

259

264 

239 

214 

214 

 220

 212 

 212 

 202 

 187 

 187

188 

187 

168 

188 

228

252 

227 

186 

178 

193

210 

226 

212 

202 

243

s-g 

§§P 

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{&*

02

 1,070

 907 

 1,060 

 1,040 

 1,070 

1,140

1,140 

1,080 

1,010 

1,030 

 1,060

 1,030 

 1,040 

 985 

 939 

 927

977 

974 

938 

1,010 

1,150

1,230 

1,170 

985 

944 

983

1,040 

1,090 

1,050 

1,030 

1,210

periods the concentrations have generally decreased 

from year to year. During some dry periods inflow 

concentrations have been relatively high, and the 

outflow has been more nearly restricted to downstream water needs; so outflow has exceeded inflow 

for 2 or 3 consecutive years. The salinity of released 

water has always risen during such periods.

Because the changes in chemical characteristics 

of water released from Lake Mead have been of public concern, a brief statement of explanation is in 

order. Lake Mead began to form in 1935; during the 

years 1936-41 its contents increased every year except 1940, the maximum levels yet attained were 

reached in 1941. In 1936, the chemical character 

of water released from Lake Mead was similar to 

the weighted-average flow of the Colorado River at 

Grand Canyon, but was rarelv like it thereafter. Solution from the newly flooded bottom of Lake Mead 

was probably greater during the years of the rising 

lake level than at any time since. As a result of bed 

solution and the more concentrated inflows of 1939 

and 1940, the weighted-average concentrations of

dissolved solids and sulfate below Hoover Dam 

trended upward from 1936 to a maximum in 1940.

During the years 1942-52 the flow at Grand Canvon averaged 13,430,000 acre-feet, and only 1946 

and 1951 had flows of less than 10 million acre-feet. 

As a result of this long period of comparatively high 

streamflow, the concentration of dissolved solids, 

sulfate, and chloride generally declined, reached the 

lowest on record in 1950, rose slightly in 1951, and 

again declined to almost the previous lows in 1953.

The years 1953 to 56, inclusive, had the four lowest consecutive annual flows ever recorded at Grand 

Canyon and correspondingly high concentrations. 

Consequently during this 4-year period the concentrations of dissolved solids, sulfate, and chloride below Hoover Dam rose each year, with the highest 

annual averages yet experienced occurring in 1956. 

Rather high inflow to Lake Mead occurred in 1957-58, 

and in 1959 the concentrations of the water released 

from Lake Mead were nearly as low as the minimums of 1953. Three successive years of below-
SALINITY OF SURFACE WATER Ell

average inflow during 1959-61 then resulted in 

increased concentrations below Hoover Dam each 

following year. High inflow to Lake Mead in 1963 

was followed by reduced salinity below Hoover Dam 

in both 1963 and 1964.

The regulated low flows at Grand Canyon in 1963 

and 1964, each of which was less than two-thirds 

the unregulated minimum of 1934, were followed 

in 1965 by markedly higher concentrations below 

Hoover Dam, with the chloride concentrations reaching an all-time maximum.

This pattern of low inflow at Grand Canyon being 

followed by rising concentration levels below Hoover 

Dam, together with the demonstrated effects of Lake 

Mead on water quality below Hoover Dam, suggest 

what will happen as Lake Powell rises to higher operating levels. Lake Powell will decrease the variability of concentrations downstream and may cause a 

slight increase in average concentrations. The resulting more uniform concentrations in the inflow 

to Lake Mead will further reduce the variability of 

the concentrations below Hoover Dam, possibly by 

half.

LAKE HAVASU

Lakes Mohave and Havasu have only minor effects 

on the quality of Colorado River water because of

their relatively small storage capacity is equal to 

only a few months of river flow. The inflow between 

Hoover and Parker Dams is generally so small that 

its effect on the quality of river water is also negligible.

The first major diversion of water from the lower 

Colorado River is the water pumped into the Colorado 

River aqueduct of the Metropolitan Water District of 

Southern California from Lake Havasu. Hill (1965) 

published a table of the 20-year (1941-60) ionic burden, in tons, of the Colorado River at Lake Havasu 

based on analytical records of the Metropolitan Water District. For this report Hill's data were recomputed to give weighted averages representative of 

inflow to Lake Havasu (table 5), and the period of 

record was extended through 1965 by using analyses 

of the Geological Survey and the U.S. Public Health 

Service. The yearly weighted-average concentrations 

for Lake Havasu computed from Hill's table agree 

very well with those for the same years at Hoover 

Dam, except that Lake Havasu water generally has 

somewhat less calcium and bicarbonate than the 

Hoover Dam releases. This difference suggests continued precipitation of calcium carbonate in Lakes 

Mohave and Havasu.

TABLE 5. Annual weighted-average concentration for Colorado River at Lake Havasu, Ariz.-Calif.

[Results in milligrams per liter unless otherwise indicated. All silica concentrations are estimated]

Dissolved solids

Hardness 

as CaCOs

Sum

Water year

1941 _____ ..

1942 _____ .

1943..........

1944,. ____ .

1945-------.

1946 .......

1947 .......

1948----....

1949 ______ .

1950... ...

1951---.....

1952..-..- .

1953 ______ .

1954.---...

1955--..-.--.

1956.. ..

1957.. . .

1958 ______ ,

19.59 ____

I960..--.....

1961. __ . _ .

1962.. ____ .

1963... _ ....

1964 ______ .

1965 --.-..

Total now 

(acre-ft)

. 11,825,000

. 17,468,000

U fiQI fW)

. 13,898,000

. 12,447,000

. 10,962,000

. 10,416,000

. 12,581,000

. 12,917,000

. 12,224,000

. 8,656.000

. 13,872,000

. 12,786,000

. 9,815,000

. 9,333,000

. 7,375,000

. 7,412,000

. 11,738,000

. 9,458,000

. 8,808,000

. 8,320,000

. 7,939,000

. 8,450,000

. 7,903,000

. 7.625.000

Silica (SiO2>

11

12

1 °.

11

11

11

12

12

12

12

13

1 °.

13

14

14

14

12

IQ

TO

13

19

12

11

12

11

Calcium (Ca

1 AQ

102

94

90

86

86

86

85

Q9

77

Q1

7Q

75

QO

oo

Qfi

Qfi

QQ

80

an

96

104

QQ

«Q

104

Magnesium I

9Q

Oft

OQ

27

OQ

9ft

28

27

25

25

26

eyn

24

29

31

34

33

OQ

26

07

27

25

97

30

"3- S

5 8 

5 'I

3 a

CO PH

101QQ

95

Q/t

95

Q7

Qfi

QO

QQ

oe

QO

92

as

Q°.

i ns.

121

117

QO

DO

fiQ

96 4.6

1ft9 A, °.

inn A. °.

Qft 4. °,

120 5.9

Bicarbonate

159 I<;Q

1 CQ

158

158

159

158

155

i w

i <;i

153

150

1 Afi

153

152

152

152

150

140

i err

159

157

1 f\{\

155

5 50,

I

1

02

Q("O

Q9Q

QAC

OQQ

OO*T

97Q

9ft/t

9^9

270

97n

247

278

316

352

343

286

9fi c*

269

299

325

302

290

348

Chloride (Cl)

7Q

*7Q

7<;

75

76

 7Q

*TQ

76

72

66

75

7Q

fi/t

76

92

106

103

QO

fiQ

75

opr

91

90

90

113

Milligrams liter per 

7«;a

726

688

669

662

666

fifid

648

618

KQ1

633

627

577

648

724

798

779

664

fin<;

621

7f)9

748

712

685

811

Tons per acre-ft

1 HQ

QQ

Q4

Q1

90

Q1

an

.88

84

80

.86

oc

.78

.88

.98

1.09

1.06

on

.82

.84

.95

1.02

.97

.93

1.10

Calcium, 

magnesiun

OQQ

Q7H

^*;n

336

330

330

330

323

308 ">QK

309

304

286

324

347

379

375

334

306

306

OKfi

373

349

334

383

Noncarbonat

OEQ

OOQ

220

206

9nn

199

200

196

183

171

184

167

198

222

254

250

212

192

192

222

244

220

210

256
E12 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

The table of weighted averages for Colorado River 

at Lake Havasu also represents very nearly the concentrations of water diverted for irrigation in the 

Colorado River Indian Reservation (Parker Valley, 

Ariz.) and in the Palo Verde Valley, Calif.

IMPERIAL DAM

At Imperial Dam the Colorado River water is 

divided into three parts: the major part is diverted 

to the All-American Canal, a lesser amount to the 

Gila Gravity Main Canal, and the remainder is released down the river channel. Samples are collected 

at regular intervals from the Yuma Main Canal, 

which receives water from the All-American Canal. 

The analyses of these samples, published in annual 

water-supply papers of the U. S. Geological Survey 

"Quality of Surface Waters of the United States" 

as Yuma Main Canal, thus represent the quality of 

the water at Imperial Dam. This water is used for 

irrigation and municipal supply in most areas below the dam and in much of the Salton Sea basin. 

The record in table 6 for Colorado River at Imperial 

Dam also includes some years during which the 

sampling was directly from the Colorado River at 

Yuma and some estimated averages.

Comparison of the data in table 5 with those in 

table 6 shows that concentrations of dissolved solids 

and most of the major ionic constituents at Imperial 

Dam are greater than those at Lake Havasu and 

that the differences have been increasing. The increases are caused mainly by irrigation drainage 

returned to the river in the Colorado River Indian 

Reservation (Parker Valley) and the Palo Verde 

Valley, where there have been rather large increases 

of irrigated acreage in the past 25 years. Diversion 

through the Colorado River aqueduct to southern 

California, however, has increased during the same 

period from nearly insignificant amounts to about 

one-seventh of the water released at Hoover Dam. 

This increase has resulted in less water being available to dilute the saline irrigation return flows from 

Parker and Palo Verde Valleys and thereby has 

raised the salinity of water at Imperial Dam.

MINERAL BURDEN OF THE LOWER 

COLORADO RIVER, 1926-65

The mineral burden, or dissolved load, of the 

Colorado River at any point is the total quantity 

(weight) of dissolved minerals in the water flowing

TABLE 6. Annual weighted-average concentration for Colorado River at Imperial Dam, Ariz.-Calif.

[Results in milligrams per liter unless otherwise indicated. « (estimated) signifies concentrations determined indirectly instead of by weighting individual

analyses]

Dissolved solids Hardness 

as CaCOa

Water 

year

Total flow 

(acre-ft)

Sum

U

J2 Sr 5*

ndu hos 

)

1941 ......

1942......

1943... .

1944, _ ...

1946----..

1947.. __ .

1948___---

1949--.---

1950 ......

1951. --..

1952......

1953.. -.

1954-.----

1955--.---

1956......

1957---.-.

1958------

1959------

1960. __ ..

1961..-.-.

1962...... 

1963---,.-

1964_-.--.

1965------

11,060,000

16,980,000

10,820,000

13,240,000

11,800,000

10,160,000

9', 714, 000

11,730,000

12,270,000

11,500,000

7 , 760 , 000

13,040,000

11,970,000

8,950,000

8,398,000

6,323,000

6,279,000

10,707,000

8,246,000

7,338,000

6,527,000

6,220,000 

6,012,000

6 , 076 , 000

5,766,000

30) %

15,270

23,460

14,950

18,230

16,300

14,040

13,420

10,160

16,940

15,890

10,730

17,970

16,540

12,360

11,600

8,710

8,673

14,790

11,390

10,110

9,016

8,591 

9,133

8,370

7,964

_0

55

'12

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14

11

11

13

12

13

13

13

14

14

14

16

16

15

13

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16 

15

16

16

£ "3 

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"110

«103

96

92

91

87

92

89

88

84

86

85

83

86

95

106

110

93

91

93

98

99 

100

95

104

SP %

'28

'27

26

28

29

30

31

28

28

27

28

29

29

28

33

34

34

27

25

26

27

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27

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31

 3

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"107

98

99

98

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89

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121

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130

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112

126

133 

129

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150

a 

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158

165

163

160

165

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172

169

170

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164

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164 

167

165

168

£

CO

'363

"336

312

306

300

295

310

292

281

265

281

283

273

287

333

375

364

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320

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a GO

«i , 200

 1,120

1,050

1,070

1,070

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1,100

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985

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1,070

1,200

1,340

1,340

1,140

1,080

1,130

1,220

1,260 

1,240

1,240

1,380
SALINITY OF SURFACE WATER E13

in the river past that point in a definite time interval. Loads of specific periods are computed from the 

weighted-average concentrations found by chemical 

analyses and the volumes of streamflow in the same 

periods and are usually stated in tons per day or 

tons per year. In the unregulated part of the river, 

high concentrations and smaller loads generally occur during periods of low streamflow and low concentrations and larger loads occur during periods of 

high streamflow. Thus, prior to construction of Glen 

Canyon Dam, the seasonal loads above Lees Ferry 

changed less than the flows or concentrations. Below 

Hoover Dam, where streamflow is almost completely 

regulated, concentrations now change rather slowly 

and almost independently of river volume, whereas 

loads change very nearly in proportion to streamflow.

Although load computations have no immediate 

importance to water users, they are important in 

salinity appraisals because they show downstream 

movement of dissolved minerals and indicate chemical changes in the river and in the storage reservoirs.

Load analysis is a technique of investigating the 

chemical regimen of a river by comparing mineral 

loads carried at different points or during different 

times. In the remainder of this report, load analysis 

of the Colorado River is the principal investigative 

technique. Load analysis is used to investigate the 

chemical regimen first by considering the loads of 

all the dissolved solids and then by considering the 

dissolved-solids load as made up of individual ionic 

loads undergoing chemically related changes.

ANALYSIS OF DISSOLVED-SOLIDS LOADS

Plotting annual dissolved-solids loads near Grand 

Canyon against annual river discharges for the period 1926-62 (fig. 5) results in a scatter diagram 

unlike that produced by plotting the annual concentrations against annual discharges (fig. 5). The relation between the annual loads and the annual 

discharges can be represented approximately by a 

straight line for the range defined by data. As the 

load for a year of no flow would be zero, however, 

the relation logically includes a curving segment for 

very low annual flows. In contrast to the load-flow 

curve, which rises with increasing annual flow, the 

concentration-flow curve declines with increasing 

annual flows. The latter curve changes in slope at a 

decreasing rate as flow increases, and this change 

indicates that at very high discharges the mineral 

concentrations are mostly related to the solubility 

of products of rock weathering and are less controlled by the fairly constant quantities of soluble 

salts entering the river in ground-water flow.

The scatter of the points in figure 5 shows that 

the relation between the annual dissolved-solids 

loads at Grand Canyon and the annual discharges 

is somewhat variable. A question arises as to whether there have been any real changes in the chemical 

regimen during the period of record. Although the 

question cannot be positively answered, several different methods of plotting dissolved-solids loads 

against time or stream discharges give indications 

of a small change in .regimen with the dissolvedsolids load in proportion to discharge somewhat 

greater after the middle 1950's.

A mass diagram of cumulative dissolved-solids 

loads for Colorado River at Grand Canyon for 

1926-62 shows six time-trends indicated by letter 

arrows in figure 6; the trends are predominantly 

related to wet or dry periods lasting for several 

years but may also be influenced by upstream developments. The trends shown for the 1960's resulted 

from the filling of Lake Powell and other upstream 

reservoirs. Although the diagram indicates trends 

lasting a few years have characterized the chemical

15

10 h

5 10 15 

ANNUAL FLOW, IN MILLIONS OF ACRE-FEET

20

FIGURE 5. Approximate relations of dissolved-solids load and concentration 

to flow of Colorado River near Grand Canyon, Ariz., 1926-62.
E14 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

400

300 

200 

100

WATER YEAR 

FIGURE 6. Mass diagram of cumulative dissolved-solids load, Colorado River at Grand Canyon, 1926-65.

regimen of the Colorado River, the amount of 

changes indicated are quite small and do not suggest 

any major change during the period of record.

A double-mass diagram, produced by plotting 

cumulative dissolved-solids loads against cumulative 

annual river discharges at Grand Canyon (fig. 7), 

shows a nearly linear slope of about 0.8 prior to 

1952, indicating a very stable load-flow regimen. 

After 1952, the plotted points increasingly diverge 

from the line with 0.8 slope. Such a change in slope

suggests a change in the relation between the two 

variables cumulatively plotted. The departures after 

1952 from the previous line of relation, however, 

are small and in the same direction and are attributed to the expansion of storage of the headwater 

areas of the river in Colorado and transmountain 

diversion of water from them. These regimen 

changes began about 1950 and increased irregularly 

thereafter.

To ascertain whether the changing relation indi-
SALINITY OF SURFACE WATER E15

400

100 200 300 

CUMULATIVE STREAMFLOW, IN MILLIONS OF ACRE-FEET

400 500

FIGURE 7. Double-mass diagram of cumulative dissolved solids load to streamflow, Colorado River at Grand Canyon, 1926-65.

cated by figure 7 is mainly related to factors causing 

variation in annual streamflow, parallel differential 

mass diagrams for the Colorado River at Grand 

Canyon relating the cumulative departures of annual discharge and annual dissolved-solids loads to 

their means for the period were plotted together 

(fig. 8). The joint plotting suggests that any climatic variation affecting streamflow also affects dissolved-solids loads but to somewhat lesser degree.

ANALYSIS OF IONIC LOADS

One of the most informative methods of appraising the chemical regimen of the Colorado River is

analysis of ionic-load variations. The annual loads 

of the several ions constituting the bulk of the mineral burden of the river vary individually, so the 

portion of the dissolved-solids burden represented 

by each ion changes from year to year. Approximate 

relations of annual constituent loads to discharge 

near Grand Canyon are indicated by lines on scatter 

diagrams in figure 9. The scatter of the points on 

the three cation and the chloride diagrams are 

rather well defined. The much greater scatter for 

sulfate and bicarbonate results from the variability 

of sources of inflow because some Upper Basin tributaries contribute large sulfate loads compared
E16 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

WATER YEAR 

FIGURE 8. Comparative differential mass diagrams for streamflow and dissolved-solids load, Colorado River at Grand Canyon, 1926-62.

with their bicarbonate loads and others yield much 

less sulfate in relation to bicarbonate.

Five-year progressive averages of ionic loads near 

Grand Canyon, compared with those below Hoover 

Dam in figure 10, emphasize the time-associated 

changes in the chemical character of water in the 

river resulting from storage in Lake Mead. The 

decreasing differences between the 5-year averages 

at the two points indicate that solution of gypsum 

(calcium sulfate) and common salt (sodium chloride) was much greater during the early years of 

reservoir storage than it has been recently. The new 

holdover storage of water in Lake Powell (which 

began in 1963) substantially reduced both the flow 

and the ionic loads downstream, so the last three 

5-year progressive averages are lower than those for 

5-year loads before storage in Lake Powell began.

Accumulated ionic loads have also been used by 

several authors to show chemical changes in water 

moving down the river. Howard (1960) compared 

tonnages of major ionic constituents at Grand Canyon with those below Hoover Dam to estimate chemical precipitation in Lake Mead and solution from 

its bed. More recently Hill (1965) and Bliss (1965) 

compared ionic loads expressed in tons-equivalent 

at Lees Ferry and at Lake Havasu for intervals of 

20 years or more and used the comparisons to estimate the future average salinity of Colorado River 

water at Lake Havasu. Loads in tons-equivalent are 

computed by dividing the individual ionic loads in 

tons by their respective chemical-equivalent weights. 

This method of stating loads has the advantage that 

equivalency simplifies computations and makes chemical change readily detectable.
SALINITY OF SURFACE WATER E17

4 -

- 3

Q 

< 

O

o

1 -

10

0

SO.

15 20 0 5 10 15

ANNUAL FLOW. IN MILLIONS OF ACRE-FEET

FIGURE 9. Approximate relations of annual ionic load of principal constituents to annual flow of Colorado River near Grand Canyon, Ariz., 1926-62.

20

Comparison of individual ionic loads at widely 

separated sampling points for single years is not 

very informative because the time required for water to flow down the river and the modifying effect 

of the large holdover reservoirs obscure some chemical effects. Better understanding of the pattern of 

salt accretion and movement in the lower Colorado 

River is obtained by comparisons of flow and load 

totals for successive periods of a few years each. 

To facilitate such comparisons, cumulative totals of 

streamflow and ionic loads for successive 5-year 

periods are given on table 7 for the five lower Colorado River sites with long-time chemical-quality 

records. Also shown are computed gains or losses of 

ionic loads during the specified periods caused by 

increments to streamflow, changes in reservoir storage, or diversions out of the Colorado River basin.

Several changes in river-basin development need 

to be considered in making comparisons between 

the 5-year periods. For example, during the 25-year

period of 1941-65, diversion to the Colorado River 

aqueduct increased from nearly zero to approximately full capacity of the aqueduct. Lake Mohave 

filled in the middle of the period. Storage in Lake 

Powell began early in 1963 and increased nearly 

every month thereafter. Also, combined irrigated 

acreage in the Parker, Palo Verde, and Cibola Valleys approximately tripled, so consumptive use of 

water by irrigation may have tripled. Differences 

between gains or losses for identical items in table 7 

are related to all those developments.

When the 5-year tables are compared, certain 

loads are found to be more or less proportional to 

flows, whereas other loads show little relation to 

flows. Chloride loads above Lake Mead, in particular, appear to be mostly unrelated to flow. For example, the maximum chloride load at Lees Ferry for 

any of the four periods prior to closure of Glen 

Canyon Dam was only about 10 percent more than 

the minimum chloride load even though the maxi-
E18 WATER RESOURCES OP LOWER COLORADO RIVER-SALTON SEA AREA

2 0

1 6 -

1.2

y 04

I I I I I I I I I I

60 -

5.5 -

5.0 -

45 ^

4.0 h

3 5

3.0

2.5

! I I

S04

1.6

1 2

0.8

04 L2.0

14.0

130

12.0

11.0

100

90

80

7.0

6.0

- ' 5.0 u

Dissolved solids

J__L

EXPLANATION

Near Grand Canyon 

Below Hoover Dam

I I I I I I I I I

O"i O> O*> O>

o> < co LO r^ o> 

co ^ -^ *fr ^ ^t i i i i t i i i Lnr^a^^comr^a^

(V)POCY)<vt^J-<vt ^^J"

O> <T* O*> <T* <T* 0s* O** <T*

no m r^ a> ^ co m

WATER YEARS

FIGURE 10. Progressive 5-year average ionic and dissolved-solids load, Colorado River near Grand Canyon and below Hoover Dam, 1935-65.
SALINITY OF SURFACE WATER E19

TABLE 7. Five-year summary of streamflow and ionic burden of lower Colorado River from Lees Ferry to Imperial Dam

[Ionic gains (+) and losses ( ) in thousands of tons-equivalent; streamflow and storage change in thousands of acre-feet]

Measuring point or increment

Total 

streamflow or 

storage 

change

Cations

Ca Mg Na + K

Total 

cations 

or 

anions HCOs

Anions

S04 Cl + NOa

1941-45

1. 

2. 

3. 

4. 

5. 

6. 

7. 

8.

9. 

10. 

11. 

12. 

13.

Lees Ferry. -_-----_._-----_____________

Lees Ferry to Grand Canyon, ____________

Grand Canyon to Hoover Dam____ _..__._

Hoover Dam release..... -______.__.____

Storage change in Lake Havasu. _ _______

Hoover Dam to Colorado River 

aqueduct intake. _-____---__-_._-___-.

Flow ac Colorado River aqueduct intake... 

Diversion to Colorado River aqueduct- ____

Parker Dam release _____________________

Parker Dam to Imperial Dam. ___________

Inflow to Imperial Dam _______ ____...__

69,000 

+2,030 

71,030 

-1,054 

-476 

69,500 -165

-2,006 

67,329 

-221 

67,108 

-3,208 

63,900

303.5 

+65.1 

368.6 

+67.7 

+28.4 

464.7 

-.5

-25.6 

438.6 

-1.4 

437.2 

-10.5 

426.7

177

+ 14 

191 

+28 

-4 

215

-3

211

210 

-14 

196

.1 

.2 

.3

.8 

.5 

.6 

.6

.6 

.4

.7 

.7 

.1 

.6

278 

+54 

333 

+35 

+21 

390

-5 

385 

-1

384 

+3 

388

.8 

.8 

.6 

.8 

.5 

.9 

.4

.2

.3 

.2 

.1 

.9 

.0

759.4 

+ 134.1 

893.5 

+ 132.3 

+45.4 

1,071.2 

-1.5

-34.4 

1,035.3 

-3.3 

1,032.0

-20.7 

1,011.3

232.9 

+69.3 

302.2 

-49.3 

-3.6 

249.3 

-.7

-10.9

237.7 

-.8 

236.9 

-9.8 

227.1

410.3 

+21.2 

431.5 

+ 149.3 

+43.5 

624.5 

-.5

-24.4 

599.6 

-1.9 

597.7 

-10.5 

587.2

116.2 

+43.6 

159.8 

+32.1 

+5.5 

197.4 

-.3

+ .9 

198.0 

-.6 

197.4 

-.4 

197.0

1946-50

1. 

2.

3. 

4. 

5. 

6.

7. 

8.

9. 

10. 

11. 

12. 

13.

Lees Ferry_ -_---.._--___--_____________

Lees Ferry to Grand Canyon...... _______

Grand Canyon --_.___-__--_____________

Grand Canyon to Hoover Dam_-_-_--____

Storage change in Lake Mead.... . .....

Hoover Dam release. _ _-__.--__ _______

Hoover Dam to Colorado River

Flow at Colorado River aqueduct intake. ._

Parker Dam release. _. ... _____________

Inflow to Imperial Dam___._______.....

61,262 

+887 

62,149 

-2,474 

+ 1,165 

60,840 

-375

-1,365 

59,100 

-690 

58,410 

-3,036 

55,374

299.7 

+60.3 

360.0 

-18.6 

+ 18.2 

359.6 

-1.8

-23.9 

333.9 

-4.2 

329.7 

_ 2

329 .'5

168 

+8 

176 

+3 

+6 

185

-9 

175

-2 

172 

+4 

177

.1 

.1 

.5 

.0 

.3 

.8 

.1

.7 

.0 

.1 

.9 

.3 

.2

243 

+59 

303 

+ 

+ 11 

315 

_ i

+6

320 

_ 2

316

+3 

320

.6 

.9 

.5 

.3 

.3 

.1 

.7

.9 

.3 

.8 

.5 

.6 

.1

711.4 

+ 128.6 

840.0 

-15.3 

+35.8 

860.5 

-4.6

+26.7 

829.2 

-10.1 

819.1

+7.7 

826.8

233.5 

+ 73.2 

306.7 

-91.2 

+2.8 

218.3 

-1.4

-12.8 

204.1 

-2.4 

201.7 

+ .9 

202.6

369.9 

+9.1 

379.0 

+67.5 

+27.5 

474.0 

-2.2

-14.2 

457.6 

-5.7 

451.9 

-.9 

451.7

108.0 

+46.3 

154.3 

+8.4 

+5.5 

168.2 

-1.0

+ .3 

167.5 

-2.0 

165.5 

+ 7.0 

172.5

1951-55

1. 

2. 

3. 

4. 

5. 

6. 

7.

8.

9. 

10. 

11. 

12. 

13.

Lees Ferry.. ______'________________ . _

Lees Ferry to Grand Canyon _____ .

Grand Canyon _____________ _ _

Grand Canyon to Hoover Dam....... _ _

Hoover Dam release. ._- . -------- ...

Storage changes in Lakes Mohave 

and Havasu. _--_-_. ________________

Hoover Dam to Colorado River

Flow at Colorado River aqueduct intake. __ 

Diversion to Colorado River aqueduct. __ _

Parker Dam to Imperial Dam._-_-- ...

49,955

+ 732 

50,687 

-1,238 

+7,648 

57,097

-832

-1,803 

54,462 

-1,320 

53,142 

-3,018 

50,124

279.2 

+34.7 

313.9 

+5.4 

+ 19.0 

338.3

-8.0

-33.2 

297.1 

-7.3

289.8 

+3.9 

293.7

147 

+ 10 

158 

-15

+22 

165

o

+2 

165 

-4 

161 

+2 

163

.3 

.9 

.2 

.6 

.9 

.5

.7

.7 

.5 

.2 

.3 

.5 

.8

232

+52 

284 

+22 

+8 

315

-7

-8 

299

__ -7

291

+22 

314

.1 

.7 

.8 

.6 

.1 

.5

.8

.4 

.3 

.5

.8 

.3 

.1

658.6 

+98.3 

756.9 

+ 12.4 

+50.0 

819.3

-18.5

-38.9 

761.9 

-19.0 

742.9

+28.7 

771.6

217.8 

+43.7 

261.5 

-75.0 

+24.8 

211.3

-3.4

-25.1 

182.8 

-4.5 

178.3 

+ 12.3 

190.6

339.0

+7.8 

346.8 

+ 75.4 

+22.3 

444.5

-10.6

-11.1 

422.8 

-10.5 

412.3 

-1.2 

411.1

101.8 

+46.8 

148.6 

+ 12.0 

+2.9 

163.5

-4.5

-2.7 

156.3 

-4.0 

152.3

+ 17.6 

169.9

1956-60

1. 

2. 

3. 

4.

5.

6.

7.

8.

9. 

10. 

11. 

12. 

13.

Lees Ferry to Grand Canyon. ___________

Storage change in Lake Mead __._---___._

Storage changes in Lakes Mohave 

and Havasu _ __._.___ ....... _______

Hoover Dam to Colorado River

Flow at Colorado River aqueduct intake. __ 

Diversion to Colorado River aqueduct. __ _

Parker Dam release.- .... _ ..__

Inflow to Imperial Dam .__.._. _..______

56,204 

+ 1,225 

57,429 

-2,397

+7,848 

47,184

-178

-2,215 

44,791 

-3,107 

41,684 

-2,791 

38,893

314.6 

+8.1 

322.7 

-.1 

-30.6 

292.0

+ 1.3

-27.7 

265.6 

-18.3 

247.3 

+9.6 

256.9

136 

+6 

142 

+ 13, 

-14 

141,

+2 

144, 

-10. 

134 

-10, 

124,

.0 

.5 

.5 

.0 

.0 

.5

.5

.9 

.9 

.0 

.9 

.4 

.5

223.7

+53.9 

277.6 

+ 18.4 

-24.7 

271.3

+ 1.4

-11.2 

261.5 

-18.1 

243.9 

+37.0 

280.4

674.3 

+68.5 

742.3 

+31.3 

-69.3 

704.8

+3.2

-36.0 

672.0 

-46.4 

625.6 

+36.2 

661.8

243.0 

+6.3 

249.3 

-52.1 

-24.4 

172.8

o

-26.2 

146.4 

-10.1 

136.3 

+ 10.1 

146.4

327.2

+ 17.7 

344.9 

+ 73.2 

-32.6 

385.5

+2.4

-8.7 

379.2 

-26.2 

353.0 

+ .4 

353.4

104.1

+44.5 

148.6 

+ 10.2 

-12.3 

146.5

+ 1.0

-1.1 

146.4 

-10.1 

136.3

+25.7 

162.0
E20 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

TABLE 7. Five-year summary of streamflow and ionic burden of lower Colorado River from Lees Ferry to Imperial Dam 

Continued

Total

streametorage Ca

change

Total

Cations cations Anions

Mg Na + K anions HCOs SO4 Cl + NO

1961-65

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13.

Lees Ferry _ ______________________

Lees Ferry to Grand Canyon. _ ... ______

Grand Canyon ____________________

Grand Canyon to Hoover Dam__ _________

Storage change in Lake Mead. _____ _____

Hoover Dam release------.---.-....... _

Storage changes in Lakes Mohave

and Havasu _________________________

Hoover Dam to California aqueduct

intake_________ _______ __ ____ _____

Flow at Colorado River aqueduct intake...

Diversion to Colorado River aqueduct ...

Parker Dam release....... .... _

Parker Dam to Imperial Dam. _ ..... .

Inflow to Imperial Dam _______________ _

37,147

+ 1,602

38,749

-2,053

+5,230

41,926

+93

-1,739

40,280

-5,480

34,800

-3,599

31,201

222.0

+ 13.0

235.0

+ 18.8

+22.4

276.2

-.6

-6.8

268.8

-36.6

232.2

-22.3

209.9

99.0

+8.9

107.9

+ 13.7

+3.0

124.6

-1.0

-.8

122.8

-16.8

106.0

-7.2

98.8

181.

+50.

232.

+ 17.

+3.

253.

-2.

+ .

252.

-34.

217.

+33.

250.

7

3

0

5

9

4

3

9

0

4

6

3

9

502.7

+72.2

574.9

+ 50.0

+29.3

654.2

-3.9

-6.7

643.6

-87.8

555.8

+3.8

559.6

149.8

+ 17.7

167.5

-35.8

+ 16.3

148.0

+ .1

-8.3

139.8

-19.0

120.8

-5.1

115.7

271.

+ 10.

281.

+ 62.

+ 14.

358.

-2.

 .

356.

-48.

307.

-13.

293.

3

6

9

1

7

7

3

2

2

6

6

9

7

81.6

+43.9

125.5

+23.7

-1.7

147.5

-1.7

+ 1.8

147.6

-20.2

127.4

+22.8

150.2

mum flow was 40 percent greater than the minimum. 

The computed chloride increases between Lees Ferry 

and Grand Canyon never differed as much as 5 percent from the average for the entire period.

The load summaries not only indicate where 

fairly constant saline increments enter the river but 

also help distinguish temporary from continuing 

chemical effects. For example, all the summaries 

show decreases in bicarbonate and increases in sulfate in the reach between Grand Canyon and Hoover 

Dam, which includes Lake Mead. As some bicarbonate must be brought into the lake in Virgin River 

and other inflow, the consistent decreases in bicarbonate can be explained only as the result of continuing 

precipitation of calcium carbonate in the lake. The 

continuing gains in sulfate in the same reach indicate solution of calcium sulfate from the bed of Lake 

Mead; and because sulfate is also brought into the 

lake in Virgin River and other inflows, the solution 

of calcium sulfate is more definitely indicated by 

the 5-year progressive average loads (fig. 10) than 

by the increases downriver. Precipitation of calcium 

carbonate in Lakes Mohave and Havasu is strongly 

suggested by the continuing decreases in both calcium and bicarbonate between Hoover Dam and 

Parker Dam.

Comparison of the ionic loads, both by 5-year 

periods and downriver from Lake Mead, illustrates 

the changes in the chemical regimen of the lower 

Colorado River resulting from increasing diversion 

and use of water. Thus, the steadily increasing diversion of water to the Colorado River aqueduct 

has contributed to the increase in ionic concentrations at Imperial Dam because the quantity of water 

available for diluting the more concentrated inflows 

is reduced by the amount of the diversion. In addition, increases in concentrations at Imperial Dam 

have resulted from the leaching and irrigation of 

previously uncultivated lands in the Parker and 

Palo Verde Valleys. Return flows from irrigation 

in the two valleys contain relatively high concentrations of sodium and chloride leached from the 

fields, as reflected in the considerable increases in 

both the loads and concentration of these constituents at Imperial Dam.

AVERAGE ANNUAL IONIC BURDEN 

OF THE COLORADO RIVER

Almost inevitably, questions arise as to what is 

the average mineral burden of the Colorado River 

and how this burden varies during periods of high 

or low flow. Generally, it is agreed that the longer 

the period of record, the better the future values of 

hydrologic variables can be estimated. Thus a 40- 

year (1926-65) summary of the ionic burden of the 

Colorado River at Grand Canyon (table 8) by 5-year 

periods is a better indicator than the previously 

discussed 25-year summary of the Colorado River 

mineral burden. In this 40-year summary the values 

for the 5-year period 1961-65 are partly estimated, 

being corrected for the change in storage in Lake 

Powell and the other upper Colorado River storage 

reservoirs. Adjustments were made for both the 

water and the salts retained in the reservoirs.

The 5-year summaries of ionic loads in table 8 

were used to compute 5-year, 10-year, 20-year, and
SALINITY OP SURFACE WATER E21

TABLE 8. Forty-year summary of ionic burden for Colorado River at Grand Canyon by 5-year periods, 1926-65

[Ionic loads in thousands of tons-equivalent; streamflow in acre-feet]

Period

1926-30-..........-.-

1931-35. --_.-.... --__

1936-40 ________

1941-45-.-.. .-.-..,._

1946-50-.... ..-_ .

1951-55.. ..... -------

1956-60....... 1961-65 1 -.. - .

40-year total _._, 

Average of 

5-year periods.

Total streamflow

80,160, 

47,577, 

57,413, 

71,030, 

62,149, 

50,687, 

57,429, 

53,404,

479,849, 

59,981,

000 

000 

000 

000 

000 

000 

000 

000

000 

000

Ca

395.0 

261.6 

320.2 

368.6 

360.0 

313.9 

322.7 

315.5

2,657.5 

332.2

Cations

Mg

203.2 

137.5 

159.8 

191.3 

176.5 

158.2 

142.5 

145.5

1,314.5 

164.3

Na + K

368.1 

277.0 

301.8 

333.6 

303.5 

284.8 

277.6 

303.8

2,450.2 

306.3

Total 

cations 

or 

anions

966.3

676.1 

781.8 

893.5 

840.0 

756.9 

742.8 

764.8

6,422.2 

802.8

HCOs

296.9 

195.1 

247.4 

302.2 

306.7 

261.5 

249.3 

220.1

2,079.2 

259.9

Anions

SO4

502.2 

334.3 

384.4 

431.5 

379.0 

346.8 

344.9 

387.2

3,110.3 

388.8

Acre ft.

Cl + NOs Tons-equivalent

167 

146

150 

159 

154 

148 

148 

157

1,232 

154

.2

.7 

.0 

.8 

.3 

.6 

.6 

.5

.7 

.1

83.0 

70.4 

73.4 

79.5 

74.0 

67.0 

77.3 

69.8

74.7 

74.7

1 Estimated; adjusted for storage in Lake Powell and other upper Colorado River project reservoirs.

40-year average annual ionic loads at Grand Canyon 

(table 9). The values in table 9 indicate the variability which has occurred for equivalent time intervals in the past, and, therefore, with appropriate 

considerations of the changes resulting from the 

works of man, the values can be taken as indicators 

of what might occur in future. The loads show considerable variation by 5-year periods, but they trend 

towards uniformity when averaged for longer periods. They also indicate that with increased storage 

now available the ionic loads will continue to vary 

but within a narrow range.

The 5-year average streamflow during 1931-35 

was the lowest since the beginning of records in 

1896. Therefore, the loads at Grand Canyon during 

1931-35 must have been close to the minimum 

which can be expected during any future 5-year 

period, if adjustments are made for the effects of 

Upper Basin reservoirs.

Ionic burden at Lees Ferry as 

determined by other investigators

Although both the length and completeness of 

sampling make the Grand Canyon record the best

TABLE 9. Averages of streamflow and ionic burden of Colorado River at Grand Canyon for different periods

[Averages assume no storage in upper Colorado River Storage project reservoirs. Ionic loads in thousands of tons-equivalent; streamflow in acre-feet]

period

5-year __ _

10-year _ __

20-year. _ .,

averaged

... 1926-30.....

1931-35----.

1936-40-.-.-

1941-45

1946-50--.-

1951-55---.

1956-60----

1961-65----

-._ 1926-35----

1931-40.--.

1936-45.--

1941-50- .

1946-55..-.

1951-60.--

1956-65.- 

... 1926-45.....

1931-50--.

1936-55.....

1941-60---..

1946-65 .....

streamflow

... 16

-.. 9

... 11

... 14

... 12

... 10

--. 11

... 10

... 12

... 10

-.. 12

... 13

--. 11

... 10

... 11

.-. 12

.-- 11

--. 12

... 12

.-- 11

,032,000

,515,000

,483,000

,206,000

,430,000

,137,000

,486,000

,681,000

,774,000

,499,000

,844,000

,318,000

,284,000

,812,000

,083,000

,809.000

,908,000

,064,000

,065,000

,183,000

Cations

Ca

79.0

52.3

64.0

73.7

72.0

62.8

64.6

63.1

65.6

58.2

68.9

72.9

67.4

63.7

63.8

67.3

65.5

68.1

68.3

65.6

Mg Na + K

40.6

27.5

32.0

38.3

35.3

31.6

28.5

29.1

34.1

29.7

35.1

36.8

33.5

30.1

28.8

34.6

33.3

34.3

33.4

31.1

73.6

55.4

60.4

66.7

60.7

57.0

55.5

60.8

64.5

57.9

63.5

63.7

58.8

56.2

58.1

64.0

60.8

61.2

60.0

58.5

Total 

cations

anions

193.2

135.2

156.4

178.7

168.0

151.4

148.6

153.0

164.2

145.8

167.5

173.4

159.7

150.0

150.7

165.9

159.6

163.6

161.7

155.2

HCOa

59.4

39.0

49.5

60.4

61.3

52.3

49.9

44.0

49.2

44.2

55.0

60.9

56.8

51.1

46.9

52.1

52.6

55.9

56.0

51.9

Anions

SO4

100.4

66.9

76.9

86.3

75.8

69.4

69.0

77.5

83.6

71.9

81.5

81.1

72.6

69.2

73.2

82.6

76.5

77.1

75.1

72.9

Acre ft.

Cl + NOa Tons-equivalent

33.4

29.3

30.0

32.0

30.9

29.7

29.7

31.5

31.4

29.7

31.0

31.4

30.3

29.7

30.6

31.2

30.5

30.6

30.6

30.4

83.0

70.4

73.4

79.5

74.0

67.0

77.3

69.8

77.8

72.0

76.7

76.8

70.7

72.1

73.5

77.2

74.6

73.7

74.6

72.1

40-year. __.__._ 1926-65........ 11,996,000 66.4 32.9 61.3 160.6 52.0 74.7

NOTE. Range in total cations and anions: 5-year averages, 135.2; 10-year averages, 145.8-173.4; 20-year averages, 155.2-165.9.
E22 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

basis for describing the ionic burden of the lower 

Colorado River, previously published computations 

of this burden have been based on the Lees Ferry 

record. Hill (1965) computed the ionic burden at 

Lees Ferry for 1941-60 from the weighted-average 

concentrations as published in water-supply papers 

of the U.S. Geological Survey ("Quality of Surface 

Waters in the United States") without correcting 

yearly averages for years with incomplete records 

but instead by estimating for missing years. Bliss 

(1965) estimated data for years of no record by correlation and computed an average ionic burden for 

1930-60. lorns, Hembree and Oakland (1965) computed a weighted average for the period 1914-57 

from a table of average concentrations for selected 

flow ranges and a flow-duration curve. Table 10 gives 

the average loads at Lees Ferry published by the 

above individuals and the weighted averages computed for the present study. The weighted averages 

include periods during which sampling was done only 

at Grand Canyon. The Grand Canyon record for 

these periods was adjusted to a probable record at 

Lees Ferry on the basis of the average gain of minerals between the two stations during periods when 

both records were complete. Unfortunately, this procedure cannot be used to compute concentration for 

the period lorns uses because no sampling occurred 

before 1926; however, the estimate for 1926-65 was 

found to be comparable with lorns' estimate for 

1914-57.

IONIC BUDGET OF THE COLORADO

RIVER FROM LEES FERRY TO

IMPERIAL DAM, 1961-65

A detailed ionic budget is one of the most useful 

aids to understanding the chemical regimen of the 

lower Colorado River. Such a budget is a summary of 

determined or estimated ionic loads carried past key 

river points in downstream order. The budget includes estimates of gains from principal tributaries 

and of losses to major diversions, as well as computations of gains and losses in the storage reservoirs. An

ionic budget serves both as an identification of principal sources of increments to the ionic loads carried 

by the river and as a base for predicting what might 

happen to water quality if present diversions are 

either expanded or reduced or if new diversions are 

made from the river.

Comparison of the weighted averages in table 10 

indicates that considerably more variation of period 

loads at Lees Ferry results from the choice of base 

period than from the manner in which missing records are estimated. It also appears from the table 

that Hill, Bliss, and lorns, Hembree and Oakland 

may have understated the sulfate burden at Lees 

Ferry by a small percentage.

An ionic budget computed for a single year has 

questionable value because the flow pattern of any 

individual year may not be representative of the 

usual amounts of water in the various river reaches 

considered, because passage of water through storage reservoirs produces slow chemical changes not 

easily determinable on an annual basis, and because 

flows of individual tributaries may be highly abnormal in any selected year. Also, the ionic contributions of the various tributaries cannot generally 

be defined in terms of specific years because sampling 

studies on different tributaries are generally not concurrent and are of unequal length and intensity. On 

the other hand, an ionic budget prepared for a long 

period has questionable value because of the many 

changes in river regimen resulting from Upper Basin 

developments, construction of Upper and Lower 

Basin storage reservoirs, and continuing changes 

in amounts of diversion and return flow in the Lower 

Basin. As a result of such changes, long-time averages of ionic loads are likely to be quite different from 

future average annual loads. Thus, ionic budgets prepared for a long period of a few recent years appear 

to be most meaningful. Accordingly, a detailed ionic 

budget for the Colorado River reach extending from 

Lees Ferry to Imperial Dam is presented only for 

the 5-year period 1961-65.

TABLE 10. Comparative computations of average annual streamfloiv and ionic burden for Colorado River at Lees Ferry

[Ionic loads in thousands of tons-equivalent. Streamflow in acre-feet]

Period 

summarized

1941-60. __--

1941-60-.---

1930-60--..-

1930-60----.

1926-65-.--.

1914-57-..--

Authority

-.. Hill (1965)-.-.--. ___

... Bliss (1965)--.------.

... lorns (1965).. _-._...

Average 

streamfloi

11,821, 

11,821, 

11,314, 

11,314, 

11,689, 

12.706.

000 

000 

000 

000 

000 

000

Ca

60.8 

59.9 

56.3 

56.8 

58.0 

60.0

Cations

Mg Na + K

32.1 

31.4 

30.1 

30.4 

30.9 

32.7

47.1 

48.9 

47.5 

48.5 

50.2 

48.3

Total 

cations 

or 

anions

140. 

140. 

133. 

135. 

139. 

141.

0

2 

9

1 

0

HCOa

48.5 

46.4 

43.9 

42.6 

42.4 

49.4

Anions

SO4 Cl + NOa

70.0 

72.3 

68.6 

71.9 

75.0 

71.5

21.5 

21.5 

21.4 

21.2 

21.7 

20.1
SALINITY OF SURFACE WATER E23

The items in the ionic budget were computed from 

a variety of source analyses. Ionic loads at the five 

principal sampling sites on the river were computed 

from the previously described weighted averages. 

Ionic loads at other sites were obtained by allowing 

for gains from tributaries, losses by diversions, and 

gains or losses caused by changes in reservoir levels. 

Ionic loads contributed by tributaries were computed 

mostly from chemical analyses published in various 

issues of the annual water-supply series of the U.S. 

Geological Survey "Quality of Surface Waters of the 

United States." Some of these were computed from 

weighted averages, and others from unweighted analyses selected as the most representative for the 

period 1961-65. Some ionic loads, however, were 

computed from incomplete analyses corrected in a 

variety of ways. Ionic loads in drain waters were 

computed from unpublished analyses obtained during this investigation. The analyses used to represent the tributaries and drains in the ionic budget 

are given in table 11. The following paragraphs give 

explanations of the sources of analyses, the computations made from them, the significance of the 

sampled flows, and the changes computed between 

sampling sites or tributaries.

LEES FERRY

The use of Lees Ferry as a reference point in other 

Colorado River studies makes this a desirable point 

at which to begin an ionic budget. The average flow 

and ionic loads at Lees Ferry during 1961-65, however, are not comparable with those of earlier 5-year 

periods because storage of water in Lake Powell and 

other upper Colorado River reservoirs began during 

the period. On September 30,1965, a total of 11,724,- 

000 acre-feet of water was held in the new upper 

Colorado River storage project reservoirs, and most

of it accumulated after March 13,1963, when storage 

began in Lake Powell. In addition, approximately 

one-fourth of the inflow to Lake Powell is estimated 

to have been retained in bank storage. Thus, in about 

2V-> years about 15 million acre-feet of water and its 

dissolved ionic loads, which previously would have 

flowed past Lees Ferry, were retained upstream. 

Yet, the water being released from Lake Powell on 

September 30, 1965, had a substantially lower concentration than the average at Lees Ferry during the 

1961-65 period. This may have been the result of 

uneven mixing of the water in the lake, or it may 

have resulted from precipitation of calcium carbonate in the stored water.

To allow for the storage effects, the 5-year flows 

and ionic loads determined from records at Lees 

Ferry for 1961-65 were adjusted for the new upriver storage, by assuming that all the stored water 

had the concentration of Lake Powell releases in 

September 1965. The ionic budget (table 12) begins 

with these adjusted quantities. The estimated average flow and loads retained in storage, including 

bank storage, are given next. Following that, the 

table gives the flow and loads at Lees Ferry as they 

actually were measured.

PARIA RIVER

In the Colorado River Compact the Paria River 

basin is considered part of the Upper Basin. The 

flow and ionic loads of the Colorado River at the 

compact point, however, include contributions from 

the Paria River. Therefore, it is necessary to add 

these contributions to those of the Colorado River at 

Lees Ferry to obtain the quantities passing from the 

Upper Basin to the Lower Basin. Chemical analyses 

of water samples collected periodically from the 

Paria River near its mouth are reported in some of

TABLE 11. Representative analyses of tributary inflow to lower Colorado River betiveen Lees Ferry and Imperial Dam

[Results in milligrams per liter unless othenvise indicated]

Date

No.

1,

? 

3.

4.

5.

6.

7.

8,

9.

10.

11.

12.

13.

Source

Blue Springs. ..- ------ ---..-.-_---.-- --...-

Havasu Springs. _ ________.___ ____ ---------

Colorado Indian Reservation, Upper Main Drain . .

Colorado Indian Reservation, Lower Main Drain- -

Palo Verde District, outfall drain.-, ._..._......

(*weighted

average)

1914-57*

June 21, 1905.-_-

Oct. 20, 1950. __.

1901*

May 20, 1905-.-.

Oct. 24, 1962....

Oct. 15, 1964....

Dec. 13, 1963--.-

Jan. 10, 1964. , ,

a*

CO

17

18

20

30

19

20

22

14

14

s^

3^5 'SO

"a^ 

O

121

29

91

42

O.ft

133

45

138

92

178

132

3

§§ §

57

64

48

88

11

43

30

05

40

45

s

J* g~ |~|w

co P*

134

793

4 9

27

05

183

391

145

371

£d £°

atd

3

203

390

223

108

588

314

250

170

288

250

292

.535

3 

CO

608

57

103

14

3.8

30

1 000

450

292

075

375

525

 73

6"no

23

on

1,220

3

1.3

48

330

40

170

95

442

144

380

« 2^ £.gsS

PS 3

Q

1,090

308

2 , 500

147

002

1,130

722

1,920

930

1 , 570

-s|o

«§J.s8 'Si£s a

CO

1,480

624

4,520

347

267

1,030

3,040

1,780

1,180

2,970

1,550

2,610
E24 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

TABLE 12. Average annual streamflow and ionic burden of the Colorado River, Lees Ferry to Imperial Dam, 1961-65

[Streamflow in acre-feet; ionic gains (-(-) and losses ( ) in thousands of tons-equivalent]

No,

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

21.

22.

23.

24.

25.

26.

27.

28.

29.

30.

31.

32.

33.

34.

35.

36.

37.

38.

39.

Colorado River at Lees Ferry, adjusted

for storage _. _ ___ _ __-__ _ __... __

Retained in storage... .__-- . __ _ -__ _

Colorado River at Lees Ferry, actual flow . _ _

Paria River at compact point. _..- ____ __

Colorado River at Lees Ferry _ _ _

Little Colorado River near Cameron _______

Blue Springs (near mouth of the Little

Colorado River).-.. __.__._ ____ ___

Residual Lees Ferry to Grand Canyon __ ___

Colorado River at Grand Canyon _ _ _ _ .

Bright Angel Creek. _ _ _-._____. _____ _

Tapeats Creek______. _________ ___ _ __

Havasu Springs (in Havasu Creek) ___ _ __

Virgin River at Littlefield____ ____

Residua], Grand Canyon to Lake Mead_._ _

Net inflow to Lake Mead... ____ __ __

Evaporation from and chemical precipitation in Lake Mead.. _ ___

Solution from bed to Lake Mead. __._ ___.

Inflow to Lake Mead, corrected for evaporation and chemical changes in the lake

Adjustments for change in storage. __ - _

Colorado River below Hoover Dam._

Evaporation from and chemical precipitation in Lakes Mohave and Havasu__ __

Solution from beds of Lakes Mohave

and Havasu... _ _____ _____ _

Bill Williams River _________

Adjustment for change in storage in Lakes

Mohave and Havasu.___ ___

Colorado River at Colorado River

aqueduct intake in Lake Havasu __

Diversion to Colorado River aqueduct. __

Colorado River below Parker Dam

Diversion to Colorado River Indian

Reservation.. .

Colorado River flow below diversion. __ __ _

Return flow from Colorado River Indian

Reservation in Upper Main Drain.. __ _

Colorado River above Palo Verde

Diversion Dam.. _ _ _

Net diversion to Palo Verde Canal ______

Return flow from Colorado River Indian

Reservation in Palo Verde Drain _

Return flow from Colorado River Indian

Reservation in Lower Main Drain

Return flow from Palo Verde Valley in

Olive Lake Drain... _ _ _ _ ___

Return flow from Palo Verde Valley in

outfall drain..

Diversions to Cibola Valley

Residua], Parker Dam to Imperial Dam _

Colorado River at Imperial Dam__. _ __

10,360,000

-2,931,000

7,429,000

19,000

7,448,000

136,000

161,000

5,000

7,750,000

26,000

50,000

48,000

109,000

137,000

8,120,000

-781,000

7,339,000

+ 1,046,000

8,385,000

-390,000

42,000

4-19,000

8,056,000

-1,096,000

6,960,000

-454,000

6,506,000

151,000

6,657,000

-749,000

27,000

96,000

16,000

349,000

-24,000

-132,000

6,240,000

Ca

60.

-16.

44.

44.

1.

47.

2.

3.

53.

-10.

7.

50.

+4.

55.

-1.

0

_

53.

-7.

46.

-3.

43.

1.

44.

-5.

1.

3.

_

-2.

41.

50

10

40

16

,56

,27

99

18

00

07

13

43

75

38

76

38

38

76

48

24

50

14

12

76

32

44

03

41

41

82

04

17

16

14

13

17

23

98

Catioi

Mg

27

-7

19

19

1

21

1

1

24

0

24

+

24

_,

0

24

-3

21

-1

19

20

-2

1

_

-1

19

IS

.32

.52

.80

.13

.93

.08

.15

.42

.58

.06

.06

.26

.09

.47

.52

.20

.32

.60

.92

.22

.06

.20

.56

.36

.20

.38

.82

.72

.54

.31

.09

.70

.07

.76

.08

.01

.76

Na + K

50.70

-14.36

36.34

.14

36.48

.80

7.55

1.57

46.40

.01

.00

.08

1.67

1.76

49.92

-.02

0

49.90

+ .78

50.68

-.27

.27

.18

-.46

50.40

-6.88

43.52

-2.84

40.68

1.63

42.31

-4.76

.17

2.23

.14

7.66

-.18

+2.61

50.18

Total 

cations

anions

138.52

-37.98

100.54

.43

100.97

1.15

9.69

3.17

-114.98

.14

.19

.77

5.51

6.61

128.20

-10.60

7.38

124.98

+ 5.86

130.84

-1.99

.27

.38

-.78

128.72

-17.56

111.16

-7.25

103.91

3.76

107.67

-12.11

.43

4.09

.35

12.55

-.43

-.63

111.92

HC03

40.48

-10.52

29.96

.08

30.04

.50

1.42

1.54

33.50

.13

.18

.63

.78

1.72

36.94

-10.60

0

26.34

+3.26

29.60

-1.90

0

.24

+ .02

27.96

-3.80

24.16

-1.58

22.58

.86

23.44

-2.63

.11

.62

.09

2.27

-.09

-.67

23.14

Anions

SO4

75.32

-21.06

54.26

.33

54.59

.22

.74

.83

56.38

.01

.01

.05

3.33

3.40

63.18

0

5.62

68.80

+2.94

71.74

-.09

0

.05

-.46

71.24

-9.72

61.52

-4.01

57.51

1.92

59.43

-6.69

.22

1.84

.17

5.19

-.23

-1.19

58.74

Cl + NO3

22.72

-6.40

16.32

.02

16.34

.43

7.53

.80

25.10

.00

.00

.09

1.40

1.49

28.08

0

1.76

29.84

-.34

29.50

.00

.27

.09

-.34

29.52

-4.04

25.48

-1.66

23.82

.98

24.80

-2.79

.10

i.63

.09

5.09

-.11

+ 1.23

30.04

the annual water-supply papers. lorns, Hembree, and 

Oakland (1965) prepared a mineral-concentration 

duration table which related the salinity of the river 

water to discharge. The analysis of Paria River water given in table 11 was obtained from the duration 

table and corresponds to the 1961-65 average flow. 

Paria River water is primarily a calcium sulfatr 

solution, low in chloride but containing considerable 

sodium bicarbonate. The computed loads (table 12,

item 4) indicate that the Paria River has a negligible effect on the salinity of Colorado River water 

downstream.

LITTLE COLORADO RIVER

An important segment of the flow of the Little 

Colorado River, the largest tributary entering the 

Colorado between Lees Ferry and Imperial Dam, is 

the discharge from Blue Springs, which are in the
SALINITY OF SURFACE WATER E25

river channel a few miles above its mouth. In the 

ionic budget, Little Colorado River refers to the 

river flow above the springs.

Little Colorado River was sampled for several 

years at Cameron Ariz., about 45 miles above its 

mouth, where it is dry for extended periods nearly 

every year. Because of the uncertainty of the adequacy of sampling during early portions of some 

flow periods, the water-supply papers give weightedaverage concentrations only for the year 1952, when 

the river flow was more than twice the average annual flow. Study of the sampling records, however, 

indicates that the 1952 analyses were not greatly different from those obtained in the other years represented by sampling. Consequently, the 1961-65 average load for the Little Colorado River was computed 

by multiplying the 1952 measured load by the ratio 

of the 1961-65 average flow to the 1952 flow. This 

procedure probably results in the Little Colorado 

River's being represented by an analysis somewhat 

lower in concentration than the true 1961-65 

weighted average and by a somewhat greater load 

than the true load for the period.

The water of Little Colorado River above Blue 

Springs is less concentrated than that of the Colorado River at Lees Ferry. Therefore, in years of substantial discharge the Little Colorado River water 

may moderately reduce the usual gain in dissolvedsolids concentration between Lees Ferry and Grand 

Canyon. The average flow during 1961-65 was too 

small for this reduction to be significant.

BLUE SPRINGS

Blue Springs here refers to the entire group of 

springs near the mouth of the Little Colorado River 

and not to the single large spring sometimes referred 

to as Blue Springs. Although samples of water obtained from different springs in the group have varied in composition, analyses of samples of mixed 

outflow obtained near the mouth of the river have 

indicated nearly uniform composition of the mixed 

flow. An analysis of one such sample taken when the 

Little Colorado River above the springs was dry represents the combined spring flow as shown in tables 

11 and 12. Measurements of discharge made at the 

mouth of the Little Colorado River when the river 

was dry at Cameron indicate a nearly constant 

spring discharge of about 161,000 acre-feet per year. 

Discharge from Blue Springs apparently accounts 

for most of the increases in ionic concentrations in 

Colorado River water between Lees Ferry and Grand 

Canyon. Most of the increment of the mineral load

of the Colorado River derived from the springs is 

sodium chloride; the computations indicate that the 

springs add more sodium chloride to the river's mineral burden than all the other tributaries between 

Lees Ferry and Imperial Dam combined.

UNMEASURED INFLOW FROM LEES FERRY 

TO GRAND CANYON

Several small tributaries with unknown annual 

discharges enter the Colorado River between Lees 

Ferry and Grand Canyon. A residual estimate of 

their combined flow, less river evaporation, is obtained by subtracting the sum of the Colorado River 

flow at Lees Ferry, the Paria River flow, the Little 

Colorado River flow at Cameron, and the Blue Spring 

discharge from the recorded flow at Grand Canyon. 

The ionic load residuals are obtained by a similar 

computation, but because the evaporation is unknown, the average concentration of the inflow cannot be approximated. The mineral increment contributed by inflow and possibly by solution from the 

streambed has about the general composition of 

limestone water, with calcium and magnesium bicarbonates constituting about half the increment 

and sodium sulfate and sodium chloride constituting 

nearly equal parts of the remainder.

GRAND CANYON

The significance of the Grand Canyon station as a 

record point has been discussed previously. During 

the 5-year period 1961-65 when flow below Lake 

Powell was partly controlled, the percentage of increase in flow between Lees Ferry and Grand Canyon 

was about one-third of the percentage of increase in 

mineral burden.

BRIGHT ANGEL CREEK

Most of the flow of Bright Angel Creek originates 

in springs which emerge near the base of the Muav 

Limestone, several thousand feet above the Colorado 

River but also several thousand feet below the north 

rim of the Grand Canyon. Water is pumped from 

Roaring Springs, one of the largest of the Bright 

Angel Creek sources, to supply facilities on the north 

rim of the Grand Canyon. Intermittent sampling 

near its mouth has shown that the ordinary flow of 

the creek is always low in mineral content and that 

most of the dissolved minerals are calcium bicarbonate. The creek adds an insignificant amount of 

minerals to the load of the Colorado River and 

whenever in flood has a considerable temporary diluting effect on the river water.
E26 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

TAPEATS CREEK

Entering the Colorado River about 45 miles below 

the mouth of Bright Angel Creek, Tapeats Creek is 

fed by springs in the Muav Limestone. Johnson and 

Sanderson (1968) gave analyses of the creek water, 

and on the basis of a few discharge measurements 

they estimated the discharge as a little less than 

twice the discharge of Bright Angel Creek. The 

Tapeats Creek water is similar in composition to 

but even less mineralized than the Bright Angel 

Creek water.

HAVASU CREEK

Most of the flow of Havasu Creek, the largest 

tributary on the south side of Grand Canyon, originates from Havasu Springs and has been measured only occasionally. By assuming that a 1950 

analysis of the spring water (table 11) is representative of the creek's mineral contribution, it has been 

determined that Havasu Creek adds mostly calcium 

bicarbonate to the load of the Colorado River. As 

Havasu Creek is known to be depositing travertine 

below the springs, it is possible that the computed 

additions to the mineral burden of the Colorado 

River (table 12, item 12) are high.

VIRGIN RIVER

There is considerable uncertainty in estimating 

increments of ionic constituents added to the Colorado River by the Virgin River. Several years of 

chemical-quality records were obtained at Littlefield, 

Ariz., about 40 miles above the mouth of the Virgin 

River, but because of diversions for irrigation downstream, the mineral burden at Littlefield that actually reaches the Colorado River is somewhat uncertain. It is assumed herein, however, that the water 

and salts passing Littlefield represent the flow into 

the river. The weighted average for 1952 was used 

to represent the Virgin River concentrations because the 1952 discharge was almost the same as the 

5-year average for 1961-65. Virgin River water is 

high in calcium sulfate, but the river also carries 

substantial amounts of sodium chloride which enter 

it from springs in Utah.

UNMEASURED INFLOW BETWEEN GRAND CANYON 

AND HOOVER DAM

Simultaneous solution of lakebed minerals and 

chemical precipitation of calcium carbonate in Lake 

Mead make ionic budgeting of the reach between 

Grand Canyon and Hoover Dam speculative. Mineral increments entering the reach from the four

major tributaries, Bright Angel Creek, Tapeats 

Creek, Havasu Springs^ and Virgin River, have been 

estimated from chemical and discharge information, 

but increments possibly as large derived from many 

small springs and minoi4 tributaries cannot be estimated directly. Also, the ionic increments in the 

unmeasured inflow cannot be estimated by differences as was done for the reach between Lees Ferry 

and Grand Canyon because the gains and losses in 

Lake Mead constitute part of the unmeasured differences; so the arbitrary assumption was made in 

preparing table 12 that the combined increments 

from all unmeasured inflow (item 14) are equal to 

the sums of the measured increments from the four 

tributaries. The volume of the unmeasured streamflow was computed by subtracting the sum of the 

Colorado River flow at Grand Canyon and the flows 

of the four named tributaries from the net inflow to 

Lake Mead (determined as explained in the next 

section).

The sizes of the ionic increments derived under 

this assumption seem reasonable, considering the 

quantities of ionic loads entering other reaches of 

the river. The unmeasured ionic load increments 

might, however, reasonably have been estimated to 

be as little as one-half or as much as double the 

tabulated quantities.

Thus, the quantities of flows and ionic loads entering Lake Mead (table 12, item 15) are sums of 

those for the river at Grand Canyon, for the four 

tributaries, and for the just-described residuals.

CHEMICAL CHANGES IN LAKE MEAD

It has been known for many years that chemical 

precipitation of calcium carbonate is nearly continuous in the body of Lake Mead and that at the same 

time other minerals are continuously being dissolved 

from some of the sedimentary formations that con* 

stitute part of its bed. The mineral budgeting makes 

possible quantitative appraisals of these two chemical processes.

The 5-year streamflow and ionic-load averages below Hoover Dam (table 12, item 20) were determined 

from the annual streamflow and chemical-quality 

records. Adjustments (item 19) were made to allow 

for a net decline in lake contents during the 5 years 

and for a corresponding decline of mineral contents 

by assuming that chemical analyses of water samples taken at the beginning and end of the 5-year 

period represented the mineral contents of the entire 

lake when sampled. The differences between these 

last two sets of computations (item 18) were as-
SALINITY OF SURFACE WATER E27

sumed to represent the 5-year average effective flows 

and loads at Hoover Dam that is, the average 

flows and loads which would have occurred if there 

had been a constant lake level during the period instead of a net decline. The average net inflow to 

Lake Mead (item 15), used previously to compute 

the unmeasured inflow between Grand Canyon and 

Hoover Dam, was then computed as the sum of the 

effective annual flow at Hoover Dam and the average of the evaporation losses reported for the lake.

The differences between the ionic loads computed 

for the net inflow to Lake Mead (item 15) and the 

effective flow at Hoover Dam (item 18) must represent either chemical precipitation or mineral solution. In the mineral budget, as prepared, anion 

dominance was assumed to determine whether precipitation or solution had occurred. Thus, the decrease in bicarbonate loads computed for the two 

flows indicates precipitation of calcium carbonate 

in the lake. In contrast, the computed gains of both 

sulfate and chloride must have been the result of 

solution of lakebed minerals. In the ionic budget the 

cation gains and losses were arbitrarily assigned in 

such a way that the bicarbonate losses caused by precipitation (item 16) and the sulfate and chloride 

gains resulting from solution (item 17) were balanced ionically; thus no unaccountable gains and 

losses resulted between points with measured loads. 

The fact that calcium changes were sufficient to account for nearly all the cation gains and losses, 

within small errors, suggests that the assumptions 

were reasonable.

During the 5 years 1961-65, the indicated chemical precipitation in Lake Mead (item 16) somewhat 

exceeded the estimated solution of minerals from its 

bed (item 17). Hence, the lake storage influenced the 

chemical composition of the released water more 

than it affected the total mineral load. During some 

earlier periods, however, the load was markedly 

affected by the lake. (See fig. 10.)

BILL WILLIAMS RIVER

From Hoover Dam to Imperial Dam the Colorado 

River flows through a succession of narrow canyons 

and wide valleys and has only one sizeable tributary 

 the Bill Williams River. Although this tributary 

river contributes a few thousand acre-feet to the 

Colorado River every year and a few hundred thousand acre-feet during rare years of extraordinary 

flow, flow is perennial only in a few short reaches; 

at the mouth of the river the flow is intermittent. 

The Bill Williams was sampled intermittently at 

Planet, Ariz., for many years, but averages and loads

were never computed. Study of the analyses indicates 

that the water in this river is always much lower in 

mineral content than the Colorado River water. It 

nearly always contains less than 450 mg/1 dissolved 

solids, with bicarbonate the major constituent. The 

Bill Williams River was not sampled during 1961-65. 

Accordingly, it is represented by an analysis (table 

11) selected from the old record (Howard, 1955). 

Load computations (table 12, item 23) indicate that 

the Bill Williams has negligible effect on the mineral 

burden of the Colorado River water below its mouth.

CHEMICAL CHANGES IN LAKES MOHAVE AND HAVASU

The quality-of-water records at Hoover and Parker 

Dams show the chemical character of river water 

passing them. By reasoning similar to that used to 

establish the effects of Lake Mead, the combined 

effects of Lakes Mohave and Havasu on Colorado 

River loads during 1961-65 were established. The 

computations resulted in small adjustments (table 

12, item 24) in the water and mineral contents of 

the two lakes. Evaporation and calcium carbonate 

precipitation (item 21) together account for most 

of the chemical changes occurring between the two 

dams. The amount of increase in mineral load (item 

22) seems to be so small that it is insignificant and 

well within the overall errors of the mineral budget. 

Evidently, there are no major sources of minerals 

which are unaccounted for. Consequently, no residual was included for this reach in table 12.

DIVERSION TO COLORADO RIVER AQUEDUCT

The Colorado River aqueduct intake, in Lake 

Havasu, is the uppermost point in the lower Colorado River where relatively large volumes of water 

are now diverted. Although pumping of water 

through the aqueduct to cities of southern California 

began in 1939, the amounts diverted were at first 

quite small compared with the flow of the river and 

did not reach 5 percent of the annual river flow 

until 1955, when pumping was 413,000 acre-feet. 

Thereafter, the annual diversion increased more rapidly; during the 5-year period 1961-65 it averaged 

more than 1 million acre-feet and increased every 

year except 1962. The recent large diversion to the 

California aqueduct has an important effect on the 

salinity of Colorado River water at Imperial Dam 

because it reduces the amount of water available to 

dilute the somewhat saline return flows from the 

irrigated areas in the Parker and Palo Verde Valleys. Only part of the increase in concentration at 

Imperial Dam, however, is a result of the increased 

diversion through the aqueduct. Part of the increase
E28 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

is a result of a rapid expansion of irrigation in the 

two valleys and the consequent increases in the 

volumes of saline returns.

PARKER DAM TO IMPERIAL DAM

Between Parker and Imperial Dams the Colorado 

River flows through the Parker, Palo Verde, and 

Cibola Valleys, which together form a continuous 

valley referred to in some early reports as the Great 

Colorado Valley. Diversions to irrigate the Parker 

Valley are made at Headgate Rock Dam, a few miles 

north of Parker, Ariz. Diversions to irrigate the 

Palo Verde Valley are made at the Palo Verde Dam, 

several miles north of Blythe, Calif. Irrigation return flows from Parker Valley reenter the Colorado 

River both above and below Palo Verde Dam. Return flows from irrigation in Palo Verde Valley 

reenter the river opposite Cibola Valley. Water is 

pumped to irrigate areas in Cibola Valley from the 

river and from wells in the flood plain. As the alluvial aquifer is largely recharged from the river, the 

pumpage from the wells is a draft on the river. 

There are no surface drains in the Cibola Valley. 

As much as 20,000 acres may have been added to 

the irrigated area in the 15 years prior to 1965. 

Leaching of soluble salts from new lands not previously irrigated has probably resulted in substantial 

additions to the Colorado River's mineral burden at 

Imperial Dam.

The part of the ionic budget describing gains 

and losses in the reach between Parker and Imperial 

Dams (table 12, items 27-38) is based on analyses 

of water samples collected at approximately monthly 

intervals during 1962-65 from major drains in the 

Parker and Palo Verde Valleys and less frequently 

from canals and wasteways. Only the principal ionic 

constituents were determined for most of the samples; however, several complete analyses were made 

of samples from each drain. These unpublished 

analyses indicated rather small variations in the 

composition and concentration of water in the individual drains and rather marked variations from

drain to drain. For the ionic budget, the 5-year 

average concentrations were obtained by averaging 

all the determined concentrations for each ion and 

using the complete analysis that most closely corresponded to the composition suggested by the group 

of ion averages. Analyses used to represent average 

concentrations are given in table 11.

The residual of unmeasured gains and losses (table 

12, item 38) appears very reasonable considering 

the many diversions and returns between Parker 

and Imperial Dams.

IONIC ACCOUNTING OF PRINCIPAL IRRIGATION AREAS ABOVE IMPERIAL DAM

The salt balance of an irrigated area was defined 

by Scofield (1940) as the relationship between the 

quantity of dissolved mineral salts delivered to an 

area in irrigation water and the quantity removed 

from the area by the drainage. Scofield called an 

excess of removal over import a favorable salt balance and a deficiency of removal an unfavorable 

salt balance. The terminology of Scofield, although 

much used, has been opposed because an excess of 

deposition or withdrawal is not a balance. Nevertheless, those managing irrigation projects have become very conscious of possible salt accumulation 

in irrigated areas. For that reason, statements 

which Scofield might have termed "salt balances" 

are included in an accounting format (table 13).

By assembling the data from table 12 on inflow 

to and outflow from Parker and Palo Verde Valleys, 

it is possible to show the water and mineral budget 

of the two valleys. Item 1, table 13, gives the 1961-65 

average annual water and ionic budget for Parker 

Valley that was computed by subtracting the sum 

of the water and ionic loads diverted from the Colorado River in water used to irrigate the valley from 

the water and loads returned to the river in the 

three principal drains. The accounting indicates 

leaching of common salt (sodium chloride) from the 

valley soils and suggests some replacement of sodium

TABLE 13. Average annual water use and ionic burden in irrigated areas, Parker Dam to Imperial Dam, 1961-65

[Water use in acre-feet. Ionic gain (+) and losses ( ) in thosuands of tons-equivalent]

No.

.

(method of determination)

Cations

Ca Mg Na + K

Total

cations

anions .HCOa

Anions

SO* Cl + NOa

1. Parker Valley (Reservation Main Canal

less three drains)__..__-_-.---____-_--___._

2. Palo Verde Valley (Palo Verde Canal less

two drains)_.___.___---_________._..___.__

3. Combined area, Parker Dam to Imperial Dam__

-180,000 -0.29 +0.13 +1.19 +1.03 +0.01 -0.03 +1.05

-384,000

-720,000

 1.77 -.48 +3.04 +.79 -.27 -1.33 +2.39

-4.46 -1.44 +6.66 +.76 -1.02 -2.78 +4.56
SALINITY OF SURFACE WATER E29

in the soils by calcium. Item 2 in the table shows the 

water and ionic budget for Palo Verde Valley that 

was obtained by subtracting the returns in two 

drains from diversions to the valley. The accounting 

suggests that some precipitation of gypsum and calcite is occurring in the valley soils and that there 

is loss of additional calcium from the water to the 

soil. The principal change in this valley, as in the 

Parker Valley, is a net removal of sodium chloride. 

The valley budgets computed from available records are inherently inexact because of unmeasured 

seepage returns to the river. A combined budget for 

the Colorado River reach between Parker and Imperial Dams (table 13, item 3) reduces these errors. 

This combined budget, which is based on good 

streamflow and quality-of-water records during 

1961-65, indicates deposition of calcite and gypsum, 

some base-exchange replacement of calcium by sodium, and removal of sodium chloride (probably 

mostly derived from leaching), but does not show 

where the chemical gains and losses occurred.

GENERAL CHARACTERISTICS OF THE

COLORADO RIVER WATER BELOW

IMPERIAL DAM

The lower Colorado became a managed river when 

Hoover Dam was closed, but for many years the flow 

of the river exceeded downstream needs. The salinity 

of local water supplies became a serious concern in 

the part of the Colorado River service area downstream from Imperial Dam only when developed 

needs for water became about equivalent to the flow 

of the river. So long as there was substantially more 

flow in the river than required by irrigators (the 

usual condition prior to the 1960's), diversion procedures and irrigation practices were developed on 

the basis of convenience, with little attention being 

paid to saline drain waters other than to remove 

them from farmed areas in surface drains.

Nearly all the water now (1969) reaching Im 

perial Dam (about 6 million acre-ft annually) is 

used for irrigation or public supply in the United 

States and Mexico. The present chemical regimen 

of the lower river, however, is complicated because 

the flow of the river is greatly depleted at the dam 

and because numerous drains and wasteways with 

differing chemical characteristics empty into it and 

the tributary Gila River. Continuous efforts are 

made to closely control both the amount and quality 

of the water reaching Morelos Dam, the principal 

Mexican diversion point.

The part of the Colorado River service area (the 

area receiving irrigation water from the Colorado

River; figs. 11, 12) in the United States downstream 

from Imperial Dam is mostly simply divided into 

the Yuma area (flood plain and mesas along the 

Colorado and Gila Rivers, west of the Gila Mountains), the Wellton-Mohawk area (Gila River flood 

plain and terrace, east of the Gila Mountains), and 

the Salton Sea area (irrigated valleys in the Salton 

Sea basin). For some descriptions the Yuma area is 

further divided into the Bard-Winterhaven Valley, 

in California, and the Yuma Valley, the North and 

South Gila Valleys, and the Yuma Mesa, in Arizona. 

Delivery of the irrigation water and drainage arrangements are by projects of the U.S. Bureau of 

Reclamation or by legally organized irrigations districts. The areas receiving Colorado River water 

and their canal and drainage systems are described 

in more detail in the companion report by Hely 

(1969).

Most of the Colorado River water used in the 

United States is diverted at Imperial Dam, but a 

small part, at times including most of the water 

used in the city of Yuma, Ariz., is diverted directly 

from the river downstream from the dam. This water has generally been more saline than the water 

at the dam.

Above the Wellton-Mohawk area the Gila River 

channel is nearly always dry, but at its mouth this 

river has a small perennial flow resulting from return flow from irrigation with Colorado River water 

and pumpage from drainage wells. The salinity of 

the water in the lower Gila River is nearly always 

substantially greater than that of the water in the 

Colorado River, and the salinity of the water in the 

Colorado River at Morelos Dam is more variable 

and nearly always considerably greater than that 

at Imperial Dam.

Mexico's annual entitlement to Colorado River 

water (1,500,000 acre-ft, min) is defined by 

treaty to include water reaching Mexico in irrigation drain and wasteway channels. Most of this 

water is diverted from the Colorado River at Morelos 

Dam, west of Yuma, but somewhat less than 10 percent enters Mexico in a large drain and a small 

canal which cross the international boundary near 

San Luis, Ariz., south of Yuma. There is usually 

little flow in the Colorado River channel downstream 

from Morelos Dam except for seepage, small returns 

from three wasteways, and water deliberately bypassed around Morelos Dam through a recently constructed wastewater conveyance channel. At times 

there have been small diversions by pumping directly from the river below Morelos Dam, both in 

the United States and in Mexico. The quality of the
E30 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA
SALINITY OF SURFACE WATER E31

To Lake Havasu

sti i i i i i i i i i i i i i i i i i i i i 

Approximate boundary 

water-using area

To Metropolitan 

Water District 

of Southern 

California

33°

FIGURE 12. Principal features of the Salton Sea area and vicinity.

water diverted for use in Mexico is quite variable, 

but almost all of it has higher dissolved-solids content than the water at Imperial Dam.

Pumping of ground water from large-capacity 

wells drilled to control water levels in a water-logged 

strip on the east side of Yuma Valley began in 1955 

and steadily increased thereafter. Pumping from 

drainage wells was extended later to the South Gila 

Valley and the Wellton-Mohawk area. Salinity, however, did not become very troublesome until the 

summer of 1961, when pumping was greatly increased in the Wellton-Mohawk area; there, more

than 60 wells were pumped into a newly constructed 

wastewater conveyance channel that extended 

nearly to the mouth of the Gila River. The increased 

pumping of saline water resulted in a large and 

abrupt increase in the salinity of the Colorado River 

water used for public supply in Yuma, Ariz., and 

for irrigation and public supply in Mexico. The 

water company supplying the city of Yuma temporarily abandoned its intake in the Colorado River 

and obtained water diverted at Imperial Dam. Most 

Mexican water users had no alternative source of 

public supply, and their principal source of irriga-
E32 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

tion water was affected. Consequently, control of 

the salinity of Colorado River water flowing to 

Mexico became, and has remained (to 1969), a subject of international negotiations.

Among steps taken to control salinity of water 

at Morelos Dam were controlled releases of water 

at Imperial Dam to provide better dilution, temporary cessation of pumping from some of the more 

saline wells in the Wellton-Mohawk area, drilling of 

additional wells in areas where salinity was lower 

so that salinity of pumped water could be controlled 

somewhat, and construction of additional drainage 

works. By the early part of 1966, substantial control 

of the saline drainage had been achieved by these 

methods and by construction of a concrete-lined 

extension of the conveyance channel to a point below 

Morelos Dam, with provision for release of water 

either above or below the dam. The total number of 

drain wells in the Wellton-Mohawk area was then 

about 100.

Because of the constantly increasing pumping of 

saline ground water for drainage and the construction and operation of new drain channels, the chemical regimen of the Colorado River changed so much 

during 1961-65 that averages for the period are not 

particularly relevent to present or future conditions. 

Hence, the chemical regimen of the lower river is 

described for the single year 1966 rather than the 

5-year period 1961-65 used to describe the river's 

regimen upstream from Imperial Dam.

Chemical analyses representatives of surface-water quality at representative sites on rivers, drains, 

and wasteways in the Yuma and Wellton-Mohawk

areas during 1966 are given in table 14. (Many of 

the smaller drains and wasteways are not shown in 

figure 11, but the areas in which they are situated 

are indicated. Exact locations are given in the water-supply papers of the U.S. Geological Survey and 

state reports in which the discharge records are 

published.) The table includes weighted-average 

concentrations, arithmetic averages, and selected 

analyses, depending upon the basic data available. 

To show progressive changes, the analyses for the 

Colorado River, the Gila River, and the WelltonMohawk Conveyance Channel are given in downstream order. The analyses of samples from other 

channels are grouped geographically.

The large number of surface drainage and waste 

channels emptying into the Colorado River below 

Imperial Dam and the Gila River complicates appraisal of surface-water quality. Discharge records 

are published for 28 distinct channels discharging 

to the rivers, as well as for river discharges at several points. Some of the drain channels have been 

sampled sufficiently for good generalizations about 

water-quality variation; others have not. River discharges have not been regularly determined at the 

junction of the Colorado and Gila Rivers, although 

daily sampling has been conducted on both rivers 

just above the junction. Therefore, because of the 

absence or paucity of data, the ensuing salinity aporaisal is in part conjectural. Some of the smaller 

waste and drain channels are assumed to have patterns of water-quality variation similar to patterns 

in other nearby drains, and averages of the daily 

analyses for the Colorado and Gila Rivers at their

TABLE 14. Representative analyses, in milligrams per liter, of surface water in Colorado River Basin at and below Imperial Dam, 1966 water year

No. Source

Date 

(*weighted ie

1.

3.

4. 

5.

6.

7

8. 

9

10,

11,

13.

14

15.

16,

17. 

18,

19. 

20.

Colorado River at Imperial Dam............

Colorado River above Gila River. ... __._ _

Colorado River at north international boundary. . _ 

Colorado River at south international boundary... 

Gila River above Wellton-Mohawk area. _

Gila River at Dome.______ ._...__._...

Gila River at mouth. _____.___.....__..

Wellton-Mohawk Conveyance Channel (total) _____ 

Wastegate discharge, Mode 1_ ____________

Wastegate discharge, Mode 2. _.__..._.__

Wastegate discharge, Mode 3 ...........__..

North Gila, Drain 1 _ -__..___.__...._____.__

North Gila Bruce Church Drain ____...._____ _

South Gila pump outlet channel 3 -.__

South Gila pump outlet channel 1 . _.

South Gila pump outlet channel 4_. ______________ 

Reservation Main Drain 4.. _ .....

East Main Canal, at international boundary .... __ 

Yuma Main Drain at boundary pumping plant. ...

**arithmetic 

average)

1966*

1966**

1966* 

1966* 

1966*

1966*

1966**

1966* 

1966*

1966*

1966*

June 17, 1966 __

Mar. 29, 1966

Feb. 22, 1966

May 13, 1966___-

Nov. 26, 1965-. . 

June 16, 1966

June 13, 1966.-.- 

June 13, 1966____

6

CO

9

12

10 

20 

16

11

21

25 

25

25

24

21

30

22

19

23

23 

21

20 

22

O

100

106

125 

223

68

86

174

325 

298

325

345

130

183

234

190

162

338 

127

111 

158

'«^-s

Jj M Q UH sfE 

s

34

40

47 

91 

21

29

77

148 

135

148

143

52

64

116

84

60

150 

54

42 

60

02 PH

143

197

254 

737 

171

244

518

1,140 

995

1,120

1,250

306

261

720

540

478

905 

204

272 

348

Bicarbon (HCOa

170

208

203 

243 

160

176

292

339 

347

352

320

292

408

348

240

296

328 

280

204 

300

CO

340

388

396 

725 

115

183

500

925 

875

925

975

525

575

500

475

475

575 

412

300 

525

Jg6

146

202

339 

1,120

267

375

792

1,890 

1,610

1,850

2,050

298

252

1,290

925

675

1 , 860 

230

398 

428

J5|?

O^ 3 j£ O OT co <n x_x

Q

857

1,050

1,270 

3,040 

738

1,020

2,230

4,620 

4,110

4,570

4,950

1,480

1,570

3,060

2,350

2,020

3,960 

1,190

1,240 

1,690

ft u^as 

CO

1,410

1,700

2,140 

4,810 

1,380

1,770

3,710

7,570 

6,610

7,420

7,950

2,430

2,330

5,040

4,100

3,530

6,790 

1,890

2,160 

2,750
SALINITY OF SURFACE WATER E33

confluence are assumed to represent discharges computed by summation of measured inflows in several 

upstream channels.

Some of the analyses in table 14 are probably not 

very representative of concentrations occurring after 

1966, whereas others may reflect later conditions 

rather well. Thus, Colorado River water at Imperial 

Dam (item 1) is quite like the later weighted-average analyses in table 6 (which summarized water 

quality at Imperial Dam for 25 years) and is probably not greatly different from weighted averages 

which may be computed for this station in the next 

few years. In contrast, the Colorado River at the 

south international boundary (item 4) represents a 

particular pattern of flows below Morelos Dam which 

is unlikely to be repeated. The analysis for the 

Colorado River above the Gila River (item 2) reflects the effects of evapotranspiration from phreatophytic vegetation and some irrigation return flow 

on the relatively small release from Imperial Dam. 

This analysis also is similar to many analyses of 

Colorado River water collected at Yuma prior to the 

beginning of substantial pumping of drainage wells. 

The analysis for the Colorado River at the north 

international boundary (item 3) reflects the effort 

to control salinity by selective pumping of drainage 

wells.

The analyses listed for the Gila River also are 

probably unrepresentative for future concentrations. 

During the winter of 1965-66, floods in the Salt 

River basin above Phoenix resulted in storage of 

about 200,000 acre-feet of low-salinity water in the 

Painted Rock reservoir on the Gila River, about 100 

miles east of Yuma. This was the first water stored 

in the reservoir since the dam was completed in 1959. 

The flood water was released slowly over several 

months, and much of it was dissipated in the dry 

river channel below the dam. At least 30,000 acrefeet of the low-salinity water, however, passed the 

Gila River gaging station at Dome, Ariz., near the 

dividing point between the Wellton-Mohawk and 

Yuma areas. Analyses of samples taken at Dome and 

upstream from the Wellton-Mohawk area were used 

to compute the yearly concentrations given as items 

5 and 6 in table 14. The salinity of the water passing 

Dome was somewhat higher than that above the 

Wellton-Mohawk area because of small irrigation return flows draining into the river in the area.

The flow of the Gila River at its mouth (item 7, 

table 14) includes the flood water passing Dome, the 

normal drainage from irrigation entering the river 

between Dome and its mouth, and an unusual incre 

ment of Wellton-Mohawk drainage pumped into and

released from the Wellton-Mohawk Conveyance 

Channel through the gate known as Mode 1. This 

release was required by construction activities, and 

it is unlikely that as much water will be released into 

the Gila River through this gate during future years 

as during 1966. Flow in the Gila River at its mouth 

included water discharged from three concrete-lined 

drainage channels in the South Gila Valley which 

carry only ground water pumped from drainage 

wells. One of the channels became operative in 1966 

and therefore probably delivered somewhat less water to the river than will be usual in future.

The conveyance channel is now (1969) the main 

drainage discharge for the Wellton-Mohawk area, 

although some seepage flows resulting from irrigation still move down parts of the Gila River channel. 

The weighted-average concentration of all flow in 

the conveyance channel during 1966 is given by item 

8 in table 14. The corresponding dissolved-solids 

concentration of water released into the Gila River 

through the upper gate is given as wastegate discharge, Mode 1 (item 9). Water released into the 

Colorado River above Morelos Dam is given as wastegate discharge, Mode 2 (item 10). Water bypassing 

Morelos Dam and released below it is given as wastegate discharge, Mode 3 (item 11). Although the 

dissolved-solids concentration of the Wellton-Mohawk drainage was always much greater than 

that of the Colorado River, comparison of the various 

weighted averages indicates that there were significant differences in the average concentrations at the 

various sampling points. The concentration of water 

pumped from the drainage wells in the Wellton-Mohawk area differs from well to well. The planned 

operation is for future pumping to be conducted so 

that the more concentrated waters will be pumped 

when there is the most dilution water available at 

Morelos Dam. Thus, the variations in weighted-average concentrations in the conveyance channel 

noted for 1966 may not be very representative of the 

concentrations for future years.

Chemical analyses selected to represent the quality of water in smaller drain channels in the Yuma 

area are given by items 12-20, table 14. They illustrate the considerable variability of water flowing 

into the Colorado and Gila Rivers or passing across 

the Mexican boundary. Items 12 and 13 are drain 

waters from the North Gila Valley, an area not affected by pumping from drain wells. They indicate 

only moderately altered Colorado River water. Items 

14-17 are representative of ground waters pumped 

from drainage wells screened in the coarse gravel 

zone in the South Gila Valley. The sampling records
E34 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

show that water quality in these channels differs 

from time to time, depending upon which wells are 

being pumped. Each channel, however, has developed 

a consistent pattern of chemical characteristics. All 

these channels, like the Wellton-Mohawk Conveyance 

Channel, carry water in which the chloride concentration consistently exceeds the sulfate concentration. 

The chemical characteristics of water in the Reservation Main Drain (item 18) are similar to those of 

the drains in the North Gila Valley. The water in 

the East Main Canal at the boundary (item 19) reflects the pumping of two or three drain wells into 

the residual canal flow. Some drain well water also 

is discharged into the Yuma Main Drain. The normal flow in this drain, however, is so large compared 

with the pumpage from wells that its chemical characteristics (item 20) are more similar to those of 

the drain water from the North Gila.

IONIC BUDGETS FOR THE COLORADO RIVER 

BELOW IMPERIAL DAM AND GILA RIVER

An ionic budget for the Colorado River from Imperial Dam to the south international boundary, 

computed for the single year 1966 from the chemical

analyses summarized in table 14, is given in table 15. 

This budget is based on the assumption that the 

chemical analyses of water from the Yuma Main 

Canal are representative of water in all the main 

canal wasteways discharging unused water to the 

rivers. The monthly Yuma Main Canal analyses, 

however, were weighted according to the corresponding monthly flows discharged at budgeted points on 

the canals.

The budget in table 15 is comparable with the 

ionic budget for the Colorado River from Lees Ferry 

to Imperial Dam (table 12) except that it represents 

average annual loads for the year 1966 only. It shows 

great depletions of river flows and mineral loads 

resulting from diversions at Imperial Dam, numerous gains from there to Morelos Dam, diversions at 

Morelos Dam, and the quantities in the river at the 

south international boundary where the Colorado 

River leaves the United States.

A separate ionic budget for the Gila River from 

above the Wellton-Mohawk area to the river's mouth 

for 1966 is given in table 16. As indicated by this 

budget the Gila River was a losing stream above 

Dome gaging station during 1966 and a gaining

TABLE 15. Stream-flow ionic budget of the Colorado River, Imperial Dam to south international boundary, 1966

[Streamflow in acre-feet; ionic gains ( + ) and losses ( ) in thousands of tons-equivalent]

No

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

21.

22.

23.

24.

Colorado River above Imperial Dam____ _ _

Diversion to All-Ameriean CanaL _ ...

Diversion to Gila Gravity Main Canal _

Colorado River below Imperial Dam

Canal wastes from North Gila Valley. . . _

North Gila Drain l._ . _____ _ _ Miscellaneous inflow above Gila River ____

Colorado River above Gila River _ __

Gila River at mouth _ __ __ _ ___ ___

South Gila pump outlet channel 4-_.__ _ _

Reservation Main drain 4_ ___ ______ _ _

Yuma Main Canal wasteway . _ _ _ . _______

Miscellaneous inflow, Gila River to

wasteway _ __________________ _______ _

Colorado River below Yuma Main

Canal wasteway _ _________ _ _________

Pilot Knob wasteway __ _._ ._--. _______

Wellton-Mohawk Conveyance Channel

wastegate, Mode 2 _ _________ _________

Miscellaneous inflow below Yuma Main

Canel wasteway. ._ ___.-__. _______ ___

Colorado River at north international

boundary.. _____ _________ __ ._ _

Diversion at Morelos Dam to Alamo CanaL _

Colorado River bslow Morelos Dam_.__ .__

Wellton-Mohawk Conveyance Channel

wastegate, Mode 3______.___.._ __ _____

Wasteway discharges from Yuma Valley

below Morelos Dam _____________ ____

Loss by seepage below Morelos Dam ._ ___

Colorado River at south international

boundary _______________________ _____

5,777,

-4,601,

-855,

321,

6,

7,

+4,

339,

141,

5,

38,

106,

+5,

636,

752,

95,

+26,

1,511,

-1,411,

100,

74,

7,

-31,

149,

700

000

700

000

200

100

700

000

000

600

700

400

900

600

700

000

700

000

000

000

400

200

800

800

Ca

39.20

-31.23

-5.81

2.16

.04

.06

+ .18

2.44

1.66

.13

.33

.72

+ .04

5.32

5.11

2.10

+ .27

12.80

-11.88

.92

1.74

.05

-.44

2.27

Cations

Mg

21.

-17.

-3.

1.

+ .

1.

1.

+ .

3.

2.

1.

+ .

7.

-7.

.

1.

.

 .

1.

92

55

15

22

02

04

24

52

21

09

23

41

03

49

86

57

01

93

41

52

19

03

22

52

Na + K

48.87

-38.76

-7.29

2.82

.05

.13

+ .96

3,96

4.33

.30

.47

.95

+ .05

10.06

6.28

6.30

+ .05

22.69

-20.93

1.76

5.50

.06

-.80

6.52

Total 

cations

anions

109.99

-87.54

-16.25

6.20

.11

.23

+ 1.38

7.92

7.20

.52

1.03

2.08

+ .12

18.87

14.25

9.97

+ .33

43.42

-40.22

3.20

8.43

.14

-1.46

10.31

HCOs

21.92

-17.46

-3.22

1.24

.02

.05

+ .26

1.57

.92

.04

.24

.42

+ .03

3.22

2.86

.74

+ .02

6.84

-6.34

.50

.53

.03

-.25

.81

Anions

SO4

55.70

-44.34

-8.27

3.09

.06

.10

+ .47

3.72

1.99

.08

.45

1.04

+ .05

7.33

7.16

2.49

-.05

16.93

-15.81

1.12

2.05

.07

-.17

3.70

Cl + NOs

32.37

-25.74

-4.76

1.87

.03

.08

+ .65

2.63

4.29

.40

.34

.62

+ .04

8.32

4.23

6.74

+ .36

19.65

-18.07

1.58

5.85

.04

-1.04

6.43
SALINITY OF SURFACE WATER E35

TABLE 16. Streamflow and ionic burden of the lower Gila River, Wellton-Mohawk area to mouth, 1966

[Streamflow in acre-feet; loads in thousands of tons-equivalent]

No,

1.

2. 

3.

4. 

5. 

6.

7. 

8.

9. 

10.

11.

Source

Gila River above Wellton-Mohawk area. ..

Seepage loss in Wellton Mohawk area... _..

Gila River at Dome_----------__--_-_-- .

Canal wastes from North Gila Valley ___....

Drains from North Gila Valley..--.- __._

South Gila pump outlet channel 3__-_-_--_.

South Gila pump outlet channel 2._______

Wellton-Mohawk Conveyance Channel 

wastegate, Mode !__._. __________ __.__.

South Gila pump outlet channel l__-_----..

Gila River at mouth (by summation, 

items 3-9) ... __________________ ____

Gila River at mouth (by weighting 

periodic analyses) ______________________

Streamf

99, 

-60, 

39, 

8, 

1, 

13, 

19,

- 30, 

29,

140, 

141,

500 

300 

200 

600 

300 

100 

200

300 

100

800 

000

Ca

0.46 

-.23 

.23 

.06 

.01 

.21 

.25

.61 

.32

1.69 

1.66

Cations

Mg

0.23 

-.10 

.13 

.03 

.01 

.17 

.18

.46 

.20

1.18 

1.21

Na + K

1.00

-.44 

.56 

.07 

.02 

.55 

.61

1.78 

.81

4.40 

4.33

Total 

cations 

or 

anions

1

1

2 

1

7 

7

.69 

.77 

.92 

.16 

.04 

.93 

.04

.85 

.33

.27 

.20

HCOa

0.35 

-.20 

.15 

.03 

.01 

.10 

.10

.23 

.19

.81 

.92

Anions

S04

0.32 

-.12

.20 

.09 

.02 

.18 

.26

.75 

.39

1.89 

1.99

i

Cl + NO3

1.02 

-.45

.57 

.04 

.01 

.65 

.68

1.87 

.75

4.57 

4.29

stream from Dome to its mouth. Because of unusually 

high flow in the Gila River above the budget area, 

the 1966 mineral load passing Dome is not likely to 

happen again except during periods of exceptional 

rainfall. In the Gila River budget, the sums of the 

increments of Streamflow and ionic loads (item 10) 

computed for all entering flows (items 3-9) are compared with quantities computed from the chemicalquality record obtained from sampling at its mouth 

(item 11). The close agreement between the two 

differently computed loads strengthens confidence in 

the assumptions used in budgeting.

The largest ionic increments added to the Gila 

River loads during 1966 entered the river in water 

released from the Wellton-Mohawk Conveyance 

Channel through the Mode 1 gate. As this gate is 

not planned for use in the future, except during 

short periods, the future additions to Gila River ionic 

loads from this source are likely to be negligible. If 

this is true, there may be some decrease in salinity 

of water at the Colorado River intake for the Yuma 

water supply. Reduction of release through gate 1 is 

not likely to have any effect on the salinity of Colorado River water at Morelos Dam because water 

previously released through gate 1 generally will be 

released through gate 2 above the dam.

The complex pattern of surface diversions and return flows in this part of the lower Colorado River 

service area obscures the effects of the distribution 

and use of the river water. By selecting and rearranging items in the two budgets, however, some 

clarification of the ways that water developments 

have affected stream water quality is achieved. Thus, 

an inflow-outflow analysis (table 17) combining 

changes in areas in the Colorado River basin downstream from Imperial Dam receiving Colorado River

water simplifies budget understanding. In this analysis the quantities of water and mineral ions arriving 

at Imperial Dam are reduced by the quantities going 

out of the Colorado River basin in the All-American 

Canal. To these adjusted quantities are added the 

quantities of water and mineral ions in the Gila 

River as it enters the Wellton-Mohawk area. The 

sum is a statement of the combined water and mineral supply for the United States and Mexican parts 

of the service area. The five outflows to Mexico are 

then added to give the total surface flows and ionic 

loads entering Mexico. The differences between the 

outflows to Mexico and the combination water supply 

constitute a statement of the draft on surface water 

and concurrent mineral regimen in the combined 

Wellton-Mohawk and Yuma areas. Negative quantities represent water use, increase of ground-water 

storage, and mineral deposition or storage; positive 

quantities represent mineral removal from the combined areas.

Obviously the net water depletion and ionic gains 

and losses determined according to the summary at 

the end of table 17 were not uniformly distributed 

in the irrigated areas receiving Colorado River water. By (1) computing seepage losses in the large 

water-supply canals and in the unlined section of 

the Wellton-Mohawk Conveyance Channel; (2) computing the gains or losses of water and dissolved 

minerals diverted to and removed from the individual irrigated sections; and (3) considering unmeasured increases in flow of the Colorado River and 

their mineral increments, it is possible to distribute 

the erains and losses as shown in table 18.

The distribution of ionic gains and losses in table 

18 is related to both present and past irrigation and 

drainage patterns. Part of the gains in the Colorado
E36 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

TABLE 17. Streamflow and ionic burden of inflow and outflow for combined Wellton-Mohawk and Yuma areas, 1966

[Streamflow in acre-feet; ionic loads in thousands of tons-equivalent]

No. Measuring point or description Streamflow

Cations

Total 

cations Anions

Ca Mg Na + K HCOs SO4 Cl + NOs

Available supply of surface water and mineral ions

1. Colorado River at Imperial Dam___________ 5,777,700 39.20 21.92 48.87 109.99 21.92

2. All-American Canal below Pilot Knob (loss)_ -3,299,000 -22.39 -12.52 -27.90 -62.81 -12.52 -

3 TVpt. siirmhr frrvm rirvlnrnrlrv TCiiror 9 A7S. 7nn 1A 81 Q J.O 9fl Q7 J.7 1S Q J.D

. . ,, . .

3. Net supply from Colorado River.. _________ 2,478,700 16.81 9.40 20.9

4. Gila River flow in to Well ton-Mohawk area __ 99,500 .46 .23 1.00

47.18

1.69

9.40 

.35

55.70 32.37

31.81 -18.48

23.89 13.89

.32 1.02

Total surface water supply and 

contained minerals--____-___ 2,578,200 17.27 9.63 21.97 48.87 9.75 24.21 14.91

Outflows in surface channels

5.

6.

7.

8.

9.

Colorado River at north international 

boundary______ ________ ___ __________

Wellton-Mohawk drainage discharge 

below Morelos Dam through Mode 3____

Three wasteways from Yuma Valley 

entering river below Morelos Darn.. .___

East Main Canal wasteway discharge 

across international boundary___________

Yuma Main Drain discharge at 

boundary pumping plant____________ ..

_ 1,511

74

7

5

123

,000

.400

,200

,000

,400

12.80

1.74

.05

.04

1.32

7.93

1.19

.03

.02

.83

22.69

5.50

.06

.08

2.53

43

8

4

4?

43

.14

.14

68

6.84

.53

.03

.02

.83

16.93

2.05

.07

.04

1.83

19.65

5.85

.04

.08

2.02

Total surface outflow and 

contained minerals-____ 1,721,000 15.95 10.00 30.86 56.81 8.25 20.92 27.64

Areal change

10. Outflow-inflow (plus ( + ) = gain; 

minus ( ) = loss)____________ -857,200 -1.32 +.37 +8.89 +7.94 -1.50 -3.29 +12.73

River undoubtedly resulted from seepage from the 

parallel sections of the Gila Gravity and All-American Canals. Induced seepage of Colorado River water 

probably also occurs in the areas adjacent to the 

river which are irrigated by pumped ground water. 

Thus, ground-water pumpage in the Island, an area 

within a former river meander not served by surfacewater canals, may account for the apparent mineral 

retention in the Bard-Winterhaven and North Gila 

Valleys. Mineral removal is indicated for the Wellton-Mohawk and South Gila Valleys, the two areas 

showing minimum surface drainage, a long history 

of former ground-water irrigation, and present 

drainage from wells. The seepage loss from the Wellton-Mohawk Conveyance Channel probably moved 

towards the drainage wells in the South Gila Valley. 

Irrigation of the undrained Yuma mesa also accounts 

for movement of water to the South Gila Valley, the 

only area from which more water was pumped than 

was applied for irrigation.

The relatively large removal of minerals from the 

South Gila Valley and Wellton-Mohawk area cannot 

be expected to continue at the present rate indefinitely, and it is probable that the outflow of minerals 

from these areas will slowly decline.

QUALITY OF SURFACE WATER IN THE 

SALTON SEA BASIN IN CALIFORNIA

The Imperial Valley and part of the Coachella Valley in California depend almost entirely on water 

diverted to them from the Colorado River through 

the All-American Canal and its branches. Water in 

the distributary canals in the two valleys has been 

found by sampling surveys to have practically the 

same salinity as the Colorado River water diverted 

at Imperial Dam. Hence, so long as the quality of 

diverted water is suitable for irrigation and enough 

is applied to prevent accumulation of salts in the 

soil, salinity problems in the two valleys will be limited to those resulting from application of river water to naturally saline soils or soils made saline by 

artificially high water tables that cause concentration of salts in the capillary fringe.

The natural saline-mineral content of soils and 

subsoils in parts of both the Imperial and Coachella 

Valleys was high before irrigation began. Soils in 

some areas were too saline for successful irrigation
SALINITY OF SURFACE WATER E37

TABLE 18. Distribution of surface-water and dissolved-mineral gains (-{-) and losses ( ) for combined Wellton-Mohawk and

Yuma areas, 1966

[Streamflow in acre-feet; dissolved minerals in thousands of tons-equivalent]

No. Channel reach or geographic area Streamflow

Cations

Total 

cations Anions

Ca Mg Na + K anions HCO3 Cl + NOs

1. Gila Gravity Canal leakage, Imperial

Dam to Mesa pumping plant _________

2. North Gila Valley.._..!_._...__..__._.

3. Wellton-Mohawk area._-_-_-_._..__.__

4. Wellton-Mohawk Conveyance Channel, 

Gila siphon to Morelos Dam-_________

5. South Gila Valley.............._._....

6. Yuma Mesa._________________________

7. Ail-American Canal leakage, Imperial

Dam to below Pilot Knob wasteway...

8. Yuma Main Canal leakage, from turnout 

to siohon -_____..-_____-___-________

9. Bard-Winterhaven Valley._____________

10. Yuma Valley...______________________

11. Unmeasured inflow to Colorado River 

from Imperial Dam to Morelos Dam. 

(Sum lines 7, 13, 17, table 15.)_.._____

-45,200 -0.32 -0.16 -0.40 -0.88

-41,800 -.27 -.14 -.28 -.69

-305,900 +1.31 +1.69 +9.86 +12.86

-10,000 -.18 -.25 -.59 -1.02

+ 44,600 +.72 +.59 +2.00 +3.31

-267,600 -1.80 -.99 -2.27 -5.08

-2,200

-47,600

-171,200

12. Total of gains and losses.

-0.17 -0.42 -0.29

-.13 -.36 -.20

-.33 +.95 +12.24

-.09 -.19 -.74

+ .46 +.80 +2.05

-1.01 -2.60 -1.45

-47,600 -.33 -.28 -.32 -.93 -.18

.01

.25 

.68

-.01 -.02

-.09 -.26

-.27 +.11

-.04

-.60

-.84

.01

.08

.27

-.53

-.02

-.38 

-1.01

-.22

-.01

-.14

+ .44

+37,300 +.49 +.28 +1.06 +1.83 +.31 +.47 +1.05 

-857,200 -1.32 +.37 +8.89 +7.94 -1.50 -3.29 +12.73

until they were leached. Early irrigation, particularly in the Imperial Valley, was mostly carried on 

without any provision for drainage except that which 

occurred through natural channels. As the farmland 

was all nearly level and had little natural drainage, 

some waterlogging soon occurred, and consequently 

the acreage of saline soils began to increase. Constructions of drainage systems to remedy the situation in the Imperial Valley began about 1925. Drainage systems have since been expanded to cover most 

of the irrigated portions of both valleys. Although 

considerable salt was dissolved from its bed, much 

of the salt content of the Salton Sea (Hely and others, 1966) is believed to have originated from minerals leached from the irrigated soils of the two 

valleys, and a lesser amount was derived from the 

water diverted from the Colorado River.

The Imperial Irrigation District has long been 

concerned about salt accumulation in Imperial Valley. The present quantity of drainage from the valley 

is about li/4 million acre-feet per year. The district 

for many years has obtained approximately monthly 

analyses of water samples collected from the Alamo 

and New Rivers at the Mexican border and near their 

mouths, and also occasional analyses of samples 

from some of the 30 or more artificial drain channels which flow directly into the Salton Sea. Since 

1943 the Imperial Irrigation District has computed 

annual mineral budgets by using its analyses and 

averages representing the monthly composition of 

All-American Canal water. According to the district's computations, mineral salts accumulated in

the valley through 1948, but since then the quantities 

of dissolved mineral salts leaving the valley in drain 

water have exceeded the quantities entering the canal 

water.

The salinity of water flowing into the Salton Sea 

from the Alamo and New Rivers varies depending 

on the proportions of canal water and drainage water in each of the rivers. A very small part of the 

flow in the Alamo River and a much larger part of 

the flow in the New River is drain water from the 

irrigated part of the Salton Sea basin in Mexico, 

generally referred to as the Mexicali Valley. Some of 

each river's flow is canal water spilled into the river 

or a drain, some is wastewater diverted from the 

lower ends of flooded fields following irrigation, and 

some is seepage entering the drains from fields. As 

the relative quantities continually change, the salinity of the two rivers fluctuates rather erratically and 

without much relation to season. The New River water, however, is almost always considerably more 

saline than the Alamo River water.

Partial chemical analyses of monthly samples obtained from Alamo and New Rivers and analyses of 

less frequent samples obtained from selected drains 

in the valley during 1961-65 indicate that it would 

not be possible to define a mineral budget for the 

Imperial Valley without much more frequent sampling and more complete chemical analyses. Consequently, a mineral budget for the Imperial Valley is 

not included in this report.

Coachella Valley, unlike Imperial Valley, is underlain by productive aquifers containing water of rela-
E38 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

tively low salinity. In 1948, when importation of 

Colorado River water to Coachella Valley began, 

about 20,000 acres were being irrigated by pumping 

from wells, and extensive lowering of the groundwater levels had occurred. As Colorado River water 

became available and irrigated acreage expanded 

greatly, river water replaced much of the ground 

water previously used for irrigation, and thereafter 

ground-water levels in irrigated areas began to rise. 

Recently, about 60,000 acres in the valley have been 

irrigated with Colorado River water. Some of the 

water brought in by canal may still be going into 

ground-water storage, but in most of the irrigated 

area water levels have risen until surface drain 

channels now flow continuously.

The Whitewater River channel is the major natural drainage for the Coachella Valley. Prior to the 

importation of Colorado River water, the Whitewater 

River channel was dry most of the time, but during 

recent years the river has had perennial flow averaging a little more than 100 cubic feet per second. In 

addition to the river, there are 20 artificial channels, 

some of which flow continuously and some intermittently, that empty directly into the Salton Sea. About 

60 percent of the drainage from Coachella Valley 

enters the sea through Whitewater River.

Approximately monthly samples of water from the 

Whitewater River water were analyzed at Yuma during 1962-65. Unfortunately the drains were not systematically sampled at that time, and only a few 

partial analyses of the drain water were made. Although the limited data suggest that the water in 

the drains is similar to that in the river, a reliable 

ionic budget for the Coachella Valley cannot be computed from the chemical data. Rough computations 

for 1962 and 1963, however, suggest that more chloride left the valley than entered in the canal water

and that the quantities of sulf ate entering and leaving 

were nearly equal.

There is no perennial flow from nonirrigated areas 

into the Salton Sea, except for seepage from Coachella Canal that enters via Salt Creek. Both Salt 

Creek, which enters the sea on the northeast side, 

and San Felipe Creek, which enters it on the southwest side, drain large areas and sometimes for a few 

hours discharge large volumes of water that is low in 

mineral content. This water, however, is not much 

of an asset because there is no practical way of using 

it before it enters the sea.

Analyses of water samples collected by the Geological Survey from the Alamo, New, and Whitewater 

Rivers selected to be representative of high and low 

concentrations regularly observed are given in table 

19. Although the analyses do not represent maximums and minimums they are probably within about 

20-25 percent of usual annual extremes. Each pair of 

analyses is a general measure of the salinity characteristics of the sampled river at the point of sampling.

Each river discharging to the Salton Sea has its 

own characteristic salinity pattern. Thus, the Alamo 

River water characteristically contains more sulfate 

than chloride at the Mexican boundary, and the relative proportion of chloride to sulfate increases towards its mouth. The water flowing from Mexico in 

the New River is always high in chloride relative to 

sulfate, and although the proportion of chloride to 

sulfate decreases downstream, the chloride remains 

dominant to the river's mouth. The Whitewater River 

water generally contains about twice as much sulfate 

as chloride. Sodium is the principal cation in the water in all three rivers. The analytical records suggest 

that some salvage of less-saline inflows to the Alamo 

and Whitewater Rivers might be practicable but that 

New River water has a much smaller salvage potenTABLE 19. Selected chemical analyses of surface water in the Salton Sea basin

[Results in milligrams per liter unless otherwise indicated]

No. Source Date

o

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

Alamo River at international boundary. __

Alamo River at international boundary...

Alamo River near Niland .. ________ ___.

Alamo River near Niland _____________ .

New River at international boundary.. ...

New River at international boundary.....

New River near Westmoreland---- _____

New River near Westmoreland __________

Whitewater River near Mecca _ __________

Whitewater River near Mecca.___-______

1

Feb. 5, 1902. ___

May 2, 1902....

Dec. 30, 1904...

Mar. 20, 1905...

Jan. 12, 1905 ...

June 15, 1905---

Dec. 30 1904

Mar. 20, 19G5-INov. 17, 1904 _

June 7, 1905 __ _

3 'of

fo5""

2.0

4.2

039

780

124

122

380

543

82

139

0.2

.852.

00

13

14

1 ^

lo

10

25

22

20

14

18

18

2"<3 a

£uG3 * '

0

199

172

250

230

284

200

250

238

100

170

S3Sfs 

a

108

70

100

108

93

120

123

108

51

44

Sc? '»__ 

|t |@

CO PH

Oil

380

720

550

1 , 580

1,330

1,120

827

000

530

 £OIs 

s

311

288

254

224

200

240

208

250

330

330

!<5

_§£

CO

1,000

075

975

825

075

750

850

750

950

825

Chlorid

1,

2,

2l',

1,

0

090

455

100

833

500

190

750

310

472

435

Ill sg^.

Q

2,490

1,910

3,410

2 , 070

5,350

4,800

4,250

3,380

2,420

2,190

£ §.§!§

|g,§3 

co

4,150

3,200

5,530

4,180

9,000

7,940

7,010

5,430

3,070

3,410
SALINITY OF SURFACE WATER E39

tial. Salvage of water from Alamo or New Rivers 

would be chiefly a matter of recovering spilled canal 

water or reducing the amount of spill. Hence, quality 

of water already in the river may be unimportant for 

salvage operations. Moreover, any water-salvage operations would tend to reduce inflow to the Salton 

Sea and result in reduction, or perhaps early loss, of 

its recreational value because of increased salinity. 

Such adverse effects might, however, be counteracted by proposed regulation of the volume and 

salinity of the sea.

SUMMARY OF CONCLUSIONS

The study of the chemical regimen of the lower 

Colorado River warrants the following general conclusions :

1. Under natural (virgin) conditions both the composition and concentration of water in the Colorado River below Lees Ferry, Ariz., varied both 

seasonally and annually, but probably did not 

substantially change downstream.

2. During the period 1926-62 (prior to closure of 

Glen Canyon Dam), the chemical regimen of the 

Colorado River at Grand Canyon and upstream, 

although probably somewhat different from the 

virgin regimen, was relatively stable. There 

may, however, have been small increases in average mineral concentrations, particularly towards the end of the period, caused by construction of reservoirs, increased irrigation, and 

increased out-of-basin diversions in headwater 

areas.

3. Most of the mineral burden of the Colorado 

River, like most of its flow, originates in the 

Upper Basin.

4. Blue Springs, near the mouth of the Little Colorado River, add the largest individual increment 

to the mineral burden of the Colorado River below compact point and above Imperial Dam. 

This increment, which is nearly constant because of the constancy of spring flow, consists 

mainly of sodium chloride (common salt).

5. Virgin River, although its annual flow is highly 

variable, generally contributes the second largest increment to the mineral burden between 

compact point and Imperial Dam. This variable 

increment consists mainly of gypsum (calcium 

sulfate), but includes a considerable amount of 

common salt.

6. The other tributaries between compact point 

and Imperial Dam add only minor increments to 

the Colorado River's mineral burden.

7. The natural fluctuations in the dissolved-mineral concentrations in the Colorado River water 

have been greatly reduced as a result of construction of storage reservoirs in which floodflows and low flows mix, but they have not been 

eliminated.

8. Average concentrations of dissolved minerals in 

Colorado River water downstream from Lake 

Mead have been increased as a result of evaporation from the lake surface and solution from 

its bed, but these increases have been partly offset by precipitation of calcium carbonate in the 

body of the lake.

9. The amount of solution from the bed of Lake 

Mead appears to be slowly decreasing.

10. There is no evidence of appreciable solution 

of minerals from beds of Lakes Mohave and 

Havasu.

11. The effects of the recently constructed storage 

reservoirs above compact point on salinity of 

water below that point are still uncertain, but 

it appears likely that the mineral concentrations 

in the lower river will become temporarily stabilized at somewhat lower levels than those 

which prevailed during 1965. Additional upstream storage and irrigation projects now proposed (1969), however, will tend to increase the 

mineral concentration when in operation.

12. Increasing yearly diversions of Colorado River 

water out of the basin through the Colorado 

River aqueduct have contributed to the recent 

increases in salinity of water at Imperial Dam 

by reducing the flow available to dilute the relatively saline irrigation return flows.

13. Leaching of newly cultivated lands in Parker 

and Palo Verde Valleys have also been principal 

causes of higher concentrations at Imperial 

Dam.

14. The salinity of water in the Colorado River at 

Imperial Dam has increased moderately in recent years, but it is still satisfactory for public 

supply and for. continued irrigation if provision 

is made to prevent accumulation of salts in the 

soil.

15. The chemical characteristics of water in the 

Colorado River downstream from Imperial Dam 

and in the tributary Gila River below the Wellton-Mohawk area are erratically variable and 

depend upon the volumes and concentrations of 

irrigation return flows from many sources, including ground water pumped into drain channels to control water levels.
E40 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

16. Mineral-budget computations indicate that 

harmful salt quantities are not now accumulating 

in the parts of the Colorado River basin in the 

United States served with Colorado River water.

17. Continued control of pumping of saline ground 

water will be necessary if the quality of Colorado 

River water diverted at Morelos Dam is to be 

maintained at or near its present level.

18. Under present irrigation and drainage arrangements probably no harmful salt quantities are 

accumulating in the parts of the Imperial and 

Coachella Valleys irrigated with Colorado River 

water.

19. Water-management practices to prevent unused 

canal water from entering streams draining to 

the Salton Sea might contribute to the available 

supply of water in the Imperial and Coachella 

Valleys. If the sea remains unregulated, however, any substantial reduction of flow to the 

sea would tend to reduce its volume, raise its 

salinity, and reduce its recreational value.

REFERENCES

Bliss, J. H., 1965, Discussion of Proc. Paper 4244 "Future 

quantity and quality of Colorado River water" by R. A. 

Hill: Am. Soc. Civil Engineers Proc., Jour. Irrigation and 

Drainage Divi., v. 91, Dec., p. 82-86.

Hely, A. G., 1969, Lower Colorado River water supply its 

magnitude and distribution: U.S. Geol. Survey Prof. 

Paper 486-D, 54 p.

Hely, A. G., Hughes, G. H., and Irelan, Burdge, 1966, Hydrologic regimen of Salton Sea, California: U.S. Geol. Survey 

Prof. Paper 486-C., 32 p.

Hill, R. A., 1965, Future quantity and quality of Colorado 

River water. Am. Soc. Civil Engineers Proc., Jour. Irrigation and Drainage Div. v. 91, March, p. 17-30.

Howard, C. S., 1955, Quality of water of the Colorado River, 

1925-40: U.S. Geol. Survey open-file rept., 103 p.

 1960, Chemistry of the Water, chap. L in Comprehensive survey of sedimentation in Lake Mead, 1948-49: 

U.S. Geol. Survey Prof. Paper 295, p. 115-124.

lorns, W. V., Hembree, C. H., and Oakland, C. L., 1965, Water 

resources of the Upper Colorado River Basin Technical 

report: U.S. Geol. Survey Prof. Paper 441, 370 p.

Johnson, P. W., and Sanderson, R. B., 1968, Spring flow in 

the Colorado River Lees Ferry to Lake Mead, Arizona: 

Arizona State Land Dept., Water Resources Rept. 34.

Scofield, C. S., 1940, Salt balance in irrigation areas: Jour. 

Agriculture Research, v. 61, p. 17-39.

U.S. GOVERNMENT PRINTING OFFICE: 1971 O 413-318