Reconnaissance 

Investigations of the 

Discharge and Water 

Quality of the Amazon River 

Reconnaissance 

Investigations of the 

Discharge and Water 

Quality of the Amazon River 

By Roy E. Oltman 

GEOLOGICAL SURVEY CIRCULAR 552 

Prepared in cooperation with 

the Ministerio da Marinha 

do Brasil, University of Brazil 

Wultington 1968 
United States Department of the Interior 

STEWART L. UDALL, Secretory 

Geological Survey 

William T. Pecora, Director 

free on application lo the U.S. Geological Survey, Washingfon, D.C. 20242 
1\bstract --------------------------------- Introduction ------------------------------ Estimates of 1\mazon River discharge _____ _ Results of reconnaissance work ___________ _ 

CONTENTS 

PAge 

1 

1 

2 

4 

Quality of watef --------------------------- Estimated discharge at mouth -------------- Conclusions ------------------------------ References cited --------------------------

ILLUSTRATIONS 

Figure 1. Graph showing relation of concurrent readings on j;fillf@~J A:ttiaitifi :ltiV~f it Obidos, Manaus, 

Page 

13 

14 

15 

16 

Page 

andTaperinha ________________________ --------------------------------------------- 5 

2. Graph of stage-discharge relation, 1\mazon River at 6bidos ------------------------------ 7 

3. Graph of measured cross sections from three discharge measurements at 6bidos ____________ 8 

4. Map of Amazon River in vicinity of 6bidos ------------------------------------------------ 8 

5. Graphs of water level observations showing tidal effect at low flow at 6bidos -----,-------'----- 9 

6. Graph showing distribution of velocity in a selected vertical at 6bidos ------'---------------- 11 

7. Graph of distribution of mean velocity in cross section at 6bidos --------------------------- 12 

8. Section of fathometer chart taken near midstream and crossing general location of measuri""q: 

section at 6bidos ______________________ --------------------------------------------- 12 

TABLES 

Page 

Table 1. Selected published estimates of flow of the lower 1\mazon River _____________ ------------- 3 

2. Discharge measurements at 6bidos __________ ---------------------------------------------- 5 

3. Results of analyses of water samples from the 1\mazon River at 6bidos, Para, Brazil __________ 13 

lll 

RECONNAISSANCE INVESTIGATIONS OF THE DISCHARGE AND 

WATER QUALITY OF THE AMAZON RIVER 

By ROY E. OLTMAN 

Abstrad 

Selected published estimates of the discharge of 

Amazon River in the vicinity of 6bidos and the mouth are presented to show the great variance of available 

information. The most reasonable estimates prepared 

by those who measured some parameters of the flow were studied by Maurice Parde, who concluded that the mean annual discharge is 90,000 to 100,000 ems (cubic 

meters per second) or 3,200,000 to 3,500,000 cfs (cubic 

feet per second). A few published estimates of discharge at mouth of 110,000 ems (3,900,000 cfs) based on rainfall-runoff relationships developed for other 

humid regions of the world are available. 

Three measurements of discharge made at the 6bidos narrows in 1963-64 by a joint Brazil-United States ex- pedition at high, low, and medium river stage are re- ferred to the datum used at the 6bidos gage during 

the period of operation, 1928--46, and a relationship between stage and discharge prepared on the basis of 

the measurements and supplementary data and com- putations. Recovery of the original 6bidos gage datum 

is verified by referring the 1963-64 concurrent river 

stages at Manaus, 6bidos, and Taperinha to gage relation curves developed for Manaus-6bidos and 6bidosTaperinha for periods of concurrent operation, 1928--46 

and 1931-46, respectively. The average discharge, based on the stage-discharge relation and record of river 

stage for the period 1928--46, is computed to be 5,500, 

000 cfs ( 157,000 ems) for the 6bidos site. 

The greatest known flood at 6bidos, that of June 

1953, is computed to have been a flow of 12,500,000 cfs 

(350,000 ems) at stage of 7.6 meters (24.9 feet) in 

the main channel and an indeterminate amount of 

overflow which, under the best assumed overflow con- ditions, may have amounted to about 10 percent of 

the main channel flow. Overflow discharge at stage 

equivalent to mean annual discharge is judged to be an insignificant percentage of flow down the main 

channel. 

Miscellaneous data collected during the :flow measure- ments show that the tidal effect reaches upstream to 

6bidos at extremely low flows, the distribution of velocities in stream verticals is affected by large-scale 

turbulence, the standard procedure of basing mean velocity in vertical on the average of point velocities 

measured at 20 and 80 percent of the total depth is 

valid, and there is a low Manning roughness coefficient 

of 0.019 (English units). 

Samples of suspended sediment taken with a point 

sampler at various depths in selected. verticals show, 

for the 6bidos site, a variation in concentration from 

300 to 340 mg/1 (milligram per liter) near the streambed to 50 to 70 mg /1 in the upper part of the verticals. 

1 

Median diameter of bed material at 6bidos averaged 

about 0.20 mm (millimeter) in a range of 0.15 to 0.25 mm. Analyses of water samples collected at 6b~<los in 

July and November 1963 and August 1964 aM presented. 

The reconnaissance measurements of 19~4 pro- vide a well-supported value of mean annual wat~r discharge of Amazon River at 6bidos and the mouth. 

Many more measurements of flow and water-4luality 

characteristics are needed to obtain more exact values 

of discharge, suspended sediment, and salt load..,. 

INTRODUCTION 

When the International Association for Scientific Hydrology (lASH) in 1957 began a program for assessment of river-borne disr~olved 

solids from all sources carried to the ocear"· the 

investigators found little published inforiJ.,.ation 

on the Amazon River. The information on the 

water discharge of the Amazon River, bf'('.ause 

of the wide range in published values, d~ il not 

provide a reliable estimate of average ~nnual 

discharge upon which a computation of ti"-e annual dissolved-solids load of the river conld be 

made. On the basis of the scanty inforiJ.,.ation 

available to the investigators, the Amazon 

River appeared to supply about 10 perc~nt of 

the total continental water discharge into the 

world's oceans. However, if the estimated Amazon River discharge was in error by as great 

a percentage as appeared probable, the calculated annual salt discharge to the oceans could 

be seriously affected. 

This situation led, in May 1961, to a joint 

proposal by Luna B. Leopold, then chief hydrologist of the U.S. Geological Survey, War·er B. 

Langbein, staff scientist of the U.S. Geol~gical 

Survey, and Professor H. O'R. Sternberg, then 

Director, Centro de Pesquisas de Geografia do 

Brasil, Universidade do Brasil, for mear11ring 

the flow, solute load, and sediment conc,-:mtration of the Amazon River. Professor Sternberg 

gained the backing of Vice Adm. Helio Garnier 

Sampaio, Directoria de Hidrografia e N rvega- ~o, Ministerio da Marinha, for logistic support. The Marinha do Brasil would supply the 
necessary gaging vessel and the Geological Survey would provide the gaging manpower and 

equipment. Arrangements for the first of three 

reconnaissance expeditions (July 1963, OctoberNovember 1963, and August 1964) to the lower 

Amazon River were completed in the spring 

1963. Space does not permit acknowledgement 

of the assistance of the many other individuals 

and organizations that helped in carrying out 

the reconnaissance work. 

Four engineers of the U.S. Geological Survey-Frank C. Ames, Luther C. Davis, George 

R. Staeffier, and the writer-composed the gaging team, which was most ably assisted by 

several Brazilian naval officers. Professor 

Sternberg assisted the team during much of the 

second expedition. 

It is the purpose of this paper to present a 

few of the notable results and conclusions obtained by the joint expedition for the 6bidos 

location and other pertinent sites on the lower 

Amazon River. A similar paper was presented 

at the "Simposio Sobre A Biota Amazonica" 

Belem, Para, Brazil, June 6-11, 1966. Information in regard to Selfridge, not available in 

June 1966, has been added to table 1. All quantities were given in metric units at the Belem 

symposium. Quantities are expressed here in 

both English and metric units, with the quantities first listed in the system of units as originally published, measured, or calculated, followed by the equivalent in the other system enclosed in parentheses. A final report, in preparation, will provide information on all the 

work done, including that in the Manaus vicinity. 

ESTIMATES OF AMAZON RIVER DISCHARGE 

Scientists conducting a literature search for 

-information on the discharge of the lower Amazon River may become confused by the many 

different estimates of discharge published by 

investigators of South American or world river 

discharge. 

Table 1 contains a list, from 14 sources, of 

selected published estimates of some aspect of 

the Amazon River discharge, such as stream 

geometry, mean velocity, and total discharge 

made at the general location of 6bidos or the 

mouth. The earliest estimate in the list is that of 

Spix and Martius published in 1831. The latest 

estimate in the list is that of the eminent hydrologist Maurice Parde published in 1955. One 

may note the wide range of listed values for the 

average annual discharge at mouth-a range 

from 2,400,000 cfs (cubic feet per second) or 

68,000 ems (cubic meters per second) by Siemens (1896) to 7,200,000 cfs (204,000 ems) 

(Military Engineer). 

2 

Upon inspection of the source documents one 

finds such perplexing circumstar~es as the following: 

The published estimate for discharge at 

mouth in the "Military Engineer" is credited 

to Dr. H. P. Guppy. Upon exarrination of Dr. 

Guppy's tabulation of discharge of large rivers 

of the world as found in "Nature," one finds 

that he credited his value for Amazon River 

discharge (at mouth) to Elisee Reclus. Thus, 

the real source of the estimate p•1blished in the 

"Military Engineer" is Reclus. However, during 

the compilation of estimates l'y Guppy and 

those in "Military Engineer," tl'~ original Reclus estimate of 100,000 ems (3,500,000 cfs) for 

the average annual discharge at 6bidos became 2,458,026 cfs (70,000 ems) at mouth of 

river in Guppy's table and 7,200,000 cfs (204,-

000 ems) at mouth in the tabh in "Military 

Engineer." Furthermore, upon examination of 

Reclus' work one finds the widtl' at the 6bidos 

narrows quoted as 5,000 to 6,000 ft (1,520 to 

1,830 meters) and mean depth quoted as about 

250 ft (76 meters), which would provide a 

cross-sectional area of 1,250,00<) to 1,500,000 

sq ft (116,000 to 140,000 square meters). Using 

Reclus' value of velocity of 8,000 yards an hour 

equivalent to 2.04 meters per sec')nd, one would 

compute an average discharge at 6bidos of 

8,400,000 to 10,000,000 cfs (237,000 to 286,000 

ems). Thus, the whole chain of published estimates-Reclus, Guppy, "Militar;" Engineer"-

is a compounding of errors. 

If one accepts the estimates published by 

scientists who actually visited 6bidos and vicinity and made personal observations of channel geometry and stream velocity as reliable 

estimates, the data would be narrowed down to 

that of Katzer, Selfridge, Spix and Martius, 

Wallace, Smith, LeCointe, and Lallemant. 

(See table 1.) (Note: Carvalho's estimate may 

also be valid.) These valid estilnates apply to 

differing river stages; for example, Katzer's 

observation was made in early July 1896; Selfridge's (at Parintins) in early August 1880. 

LeCointe appears to be the most helpful. He 

provides for 6bidos a measured width at the 

narrows of 1,890 meters (6,200 ft) (obtained by 

triangulation), low-water cross ~ection of 105,-

000 square meters (1,130,000 sq ft), high-water 

cross section of 117,500 square 1neters (1,260,-

000 sq ft), and discharges ranging from 63,000 

ems (2,200,000 cfs) (low water) to 146,775 ems 

( 5,200,000 cfs) (high water). Parde, in his 

study, based his estimate of the average annual 

discharge at 6bidos largely on LeCointe's data 

and reported it as from 90,000 to 100,000 ems 

(3,200,000 to 3,500,000 cfs). 

One may wonder why estimates only, instead 

of measurements, of the Ama~~n River dis-
~ 

l 

Source 

Spix and Martius 

Wallace---------

Ave-Lallemant 

(in Reclus, 

1877, 1895). 

Guppy-----------

Smith-----------

Selfridge-------

Reclus----------

Siemens---------

Katzer----------

Le Cointe _______ 

Carvalho ________ 

Jarvis __________ 

Parde ___________ 

Military 

Engineer, 

-

Table 1.--Selected published estimates of flow of the lower Amazon River 

Data of estimate 

Date Cross-section area Width Mean veloc1ty D1scbarge 

Date Location or Square Square Meters Feetr.I~Feet Cub1c ,Cub1c Remarks 

season meters feet per per meters feet 

se~ond second per per 

second second 

1831 Obidos Low water ------ ------- --------- ---- 0.7 2.3 14,000 500,000 

1853 6bidos Low water ------ ------- --------- ---- 1.62 5.3 ------- ---------- Velocity estimate attributed 

to Wallace by F. Katzer. 

1860 Obidos High water ------ ------- --------- ---- ---- --- 319,476 n,ooo,ooo Value of 319,476 ems appears in 

"The Earth and Its Inhabitants" 

by Elisee Reclus (1895). Value 

of 243,875 ems appears in "La 

Terre" by Elisee Reclus (1877, 

v.l, p. 514). 

1880 Mouth Annual---- ------ ------- --------- ---- ---- --- 70,000 2,458,026 Estimate attributed to Reclus by 

H.P. Guppy. 

1880 6bidos Annual---- 22,500 240,000 1,892 (from 6,200 1.0 3.3 21,500 760,000 Based on data reported by Penna, 

Penna) Wallace, and Martius. 

1882 Parintins Aug, 7, ------ ------- --------- ---- ---- --- 110,404 3,899,149 Aug. 7, 1879, is date given for 

1879. actual measurement in report of 

6.7 

Secretary of Navy for 1879, 

1895 6bidos June------ 116,000- 1,250,000- 1,520- 5,000- 2.04 (100,000), 8,400,000- Figure in parenthesis is pub140,000 1,500,000 1,830 6,000 237,000- 10,000,000 lished but is apparently in 

286,000 error. 

1896 Mouth Annual ____ ------ ------- --------- ---- ---- --- 68,000 2,400,000 Basis of estimate unknown. 

1898 6bidos Early July 100,000 1,080,000 1,890 6,200 1.2 3.9 120,000 4,200,000 From article: "Die Stromenge 

1896. des Amazonas bei Obidos." 

1922 6bidos End of May ------ ------- --------- ---- 3.15 --- ------- ---------- Float observation at crest of 

1918. flood. 

Low water 105,000 1,130,000 1,890 6,200 .6 2.0 63,000 2,200,000 Area based on soundings of others. 

High water 117,500 1,260,000 1,890 6,200 1.25 4.1 146,775 5,200,000 

1942 Mouth Low water ------- --------- --------- ---- ---- --- 6o,ooo 2,100,000 

High water ------- --------- --------- ---- ---- --- 140,000 4,900,000 

1945 6bidos Annual ____ ------- --------- --------- ---- ---- --- 85,000 3,000,000 Computed on basis of rainfallrunoff relation, 

1955 6bidos Annual ____ ------- --------- --------- ---- ---- --- 90,000- 3,200,000- Based mainly on Le Cointe's 

100,000 3,500,000 data. 

1958 Mouth Annual ____ ------- --------- --------- ---- ---- --- 204,000 7,200,000 Value of 204,000 ems attributed 

to Guppy. 

1see list of references, 
charge at obidos are available. The techniques 

for gaging large rivers were well developed 

during the 19th century. Revy reported application of completely satisfactory methods in 

measurements of the Rio Parana at Rosario 

made in 1871. Although the maximum depth 

of the Rosario cross section was only 72 feet 

(22 meters )-shallow in comparison with the 

201-foot (61-meter) maximum depth found in 

the discharge measurement at obidos on July 

16, 1963-the same procedures used for holding 

the measuring vessel in place at Rosario would 

have worked at obidos, and the current-meter 

suspension for measurement of velocities at 

Rosario would have been satisfactory at 6bidos. 

After establishment of the river gage at obidos 

in 1928 by the Brazilian Government and the 

commencement of daily river-stage readings, 

the attraction to measure the flow and develop 

a stage-discharge relation for obidos was 

stronger, for then the annual flow regime could 

be completely charted. The task of determining 

the geometry of a selected cross section on the 

Amazon River at Obidos was relatively simple. 

Although complete information is not available 

on the techniques used by the scientists who 

have reported measured cross-sectional area, it 

is probable that the method fully described by 

Revy, as used on the Rio Parana work for obtaining measured depths, was used on the Amazon River. Depth measurements of a selected 

cross section are made, following Revy's 

method, by sounding with a weighted line from 

a ship drifting with the current. In this way, 

the sounding line remains nearly vertical because there is only minor current drag on it 

near the bed. As the ship drifts across the desired measuring section, the sounded depth is 

observed and the location of ship on the cross 

section (distance from either bank) is determined by standard surveying methods (sextant 

readings on flags located on the ends of a measured base line established on shore, or theodolite readings taken to the ship from a shorebased instrument). With great care and replication, a very reliable cross section could be so 

measured. The measurement of stream velocities could have been obtained by anchoring 

the gaging vessel to permit observations of subsurface velocities with standard current meters 

or by using subsurface floats. If a few such 

measurements, referenced to the obidos gage, 

had been made to cover the range of discharge 

from low to high water and an approximate 

stage-discharge relation established for the 

obidos location, a much better estimate of the 

average annual discharge at obidos could have 

been computed. 

Although Jarvis' discharge (table 1) for the 

Amazon River at obidos is the only tabulated one 

4 

that is known specifically to be bar~d on rainfallrunoff relationships, the map of world runoff, 

published by L'Vovich (1945) ancl also based on 

hydrologic calculations, permits an estimate of 

the discharge at mouth to be measured. Jarvis, 

using data then available to him, computed the 

average annual precipitation for the drainage 

area tributary to obidos as 62 inches (1,570 

mm). He based his average annual runoff estimate on a ratio of runoff to precipitation of 34 

percent. The estimate one maJ· derive from 

L'Vovich's map is equivalent to about 110,000 

ems (3,900,000 cfs) for either the obidos or 

at-mouth location. Precipitatior data in the 

Amazon River basin are presently much more 

adequate for assessment of basin average annual rainfall then was the case for Jarvis or 

L'Vovich. Using Thornthwaite's potential evapotranspiration approach and the presently 

available climatic data, the writer has calculated average annual runoff for area above 

mouth as 31.5 inches (800 mm), equivalent to 

average annual discharge of 5,300,000 cfs 

(150,000 ems). 

RESULTS OF RECONNAISSANCE WORK 

As discussed in Geological S~:._rvey Circular 

486, "Amazon River Investig~tions-Reconnaissance Measurements of July 1963", the lack 

of data for discharge and dissolv~d solids of the 

Amazon River hampered work on the project 

of the International Association of Scientific 

Hydrology (lASH) for calculation of the salt 

balance of the oceans. The Am~.zon River was 

known to be the world's largest in terms of discharge, but the degree of uncertainty in the 

available estimates of the disch~.rge led to the 

investigations jointly sponsored by the Brazilian Navy, the University of Bra~~n, and the U.S. 

Geological Survey. The results c'>llected during 

the first measurements (July 1963) reported 

in Circular 486 have been suppJ~mented by results obtained in October-November 1963 and 

August 1964 and will be discussed in detail 

in a final report (in preparatio"'l.). The results 

of the measurements of flow at Obidos are discussed in this section; the measurements of 

water quality and sediment are discussed in a 

later section. · 

The major features of the three measurements of discharge at Obidos are presented in 

table 2. 

The methods used in colle~ting the data for 

the measurements have been discussed in Circular 486. All three discharge measurements 

were made at the same cros·s section. The 

August 1964 measurement used subsurface velocities after loss of 300-pound (136-kilogram) 

sounding weight and current n1eter on an underwater obstruction led the ~raging party to 

conclude it would be prudent to conserve the 
Table 2.--Discharge measurements at Obidos 

[Quantities listed in system of units as originally published, measured, or calculatedj equivalents in the 

other system enclosed in parentheses] 

Date 

7-16-63 

ll-20-63, 

11-21-63 

8-9-64 

Stage Width Area 

.Meters Feet Meters Square Square Feet 

feet meters 

5.8 7,500 (2,290) 1,184,000 (no ,ooo) 158 

-.5 7,410 (2,260) 990,000 (92,400) 134 

4.76 7,450 (2,280) 1,145,000 ( 106 ,ooo) 154 

STAGE, IN FEET 

Mean 

depth 

Meters 

(48.0) 

( 41.0) 

(46.5) 

Mean 

velocity 

Feet Meters 

per per 

second second 

6.45 ( l. 97) 

2.59 (. 79) 

5.08 (1.55) 

Discharge 

Cubic Cubic 

feet meters 

per per 

second second 

7,640,000 (216,ooo) 

2,560,000 (72,500) 

5,810,000 (165,000) 

5 

I 

10 

I I I 

15 

I I I 

20 

I I I 

50 60 70 80 90 100 

l I I I I I I I ,I I I 

en 

0::: 

1.1.1 

1-

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::E 

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en 

8 

iii 

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CJ 

<( 

1-

en 

8 

I/~ f----+-1953 flood 

7 / 

/ 

6 / 

July 1963' 

5 

1/ 

11 J'August 1964 

4 

3 

/ ~, 

~7 ~y 

~} 

2 

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~ 

1 

0 

A.."t'j 

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~~4 

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{ Nov4 

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1 

mber 1!963 

2 3 4 5 6 7 15 

. STAGE, IN METERS 

TAPERINHA 

20 

MANA US 

25 

20 

1-

UJ 

UJ 

15 "'-

z 

en 

8 

a5 

10 '0 

5 

0 

-4 

1-

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~ 

~ 

Figure 1.-Relation of concurrent readings on gages, Amazon River at obidos, Manaus, 

and Taperinha. 

remaining equipment. However, the depths for 

the measurement were taken with a sonic 

sounder and the results should be nearly as 

reliable as are those of the first two measurements. The width of section, rangir~ from 

7,410 to 7,500 feet (2,260 to 2,290 m€~ers) is 

5 
different from that measured by LeCointe 

(1922)-1,890 meters (6,100 feet)-because the 

cross section selected for the 1963-64 work was 

about 114 miles (2 kilometers) downstream 

from LeCointe's section. 

The datum of the gage used at obidos in 

1928-46 and destroyed (according to local information) during the great flood of 1953 was 

recovered by reference to a photograph ( courtesy of Departmento N acional de Producao 

Mineral, Divisao de Agua) of the location of 

the original high-water staff-gage section. Fortunately, the obidos municipal warehouse, 

against which the original staff section had been 

photographed, existed during the 1963-64 visits, and by careful measurements the datum 

was recovered within a possible error range of 

10 centimeters ( 4 inches). Fortunately, also, 

overlapping records of river stage are available 

at Manaus and Taperinha. 

Figure 1 shows the good agreement of the 

concurrent 1963-64 obidos readings with those 

from Manaus and Taperinha where daily gage 

readings were available. The stage graphs showing the relationship of concurrent readings for 

the periods 1928-46 (overlapping records obidos and Manaus) and 1931-46 (obidos and Taperinha) were prepared by plotting selected 

concurrent readings for the three gages and 

fitting the curves to the scatter plot. There can 

be no question that the 6bidos gage datum was 

recovered with reasonable accuracy, as the concurrent readings 1963-64 lie on the curves developed from data taken in 1928-46 (1931-46 

in the 6bidos-Taperinha comparison). For example, the relationship curve Manaus-Obidos 

shows that a stage of about 7.5 meters (24.6 

feet) would have occurred at 6bidos at the 

crest of the great 1953 flood, which reached 

29.7 meters (97.4 feet) at Manaus. Similarly, 

the Taperinha-Obidos relation curve shows that 

a stage of about 7.6 meters (24.9 feet) would 

have occurred at 6bidos during the 1953 flood, 

which reached 6.65 meters (21.8 feet) at Taperinha. Discussion with obidos inhabitants who 

remembered the 1953 flood and showed the 

survey party the level it reached in the vicinity of the gage location verified the approximate obidos stage of 7.5 meters (24.6 feet) for 

the 1953 event. Thus, significant evidence indicates reliable recovery of the obidos gage datum 

used in 1928-46. . A rating curve (curve showing relationship 

of stage to discharge) prepared for obidos on 

the basis of the three available measurements 

of discharge and other data is shown in figure 2. 

The stage-discharge relation at obidos may 

be affected at times by variable slope caused 

6 

by inflow from the Rio Tapaj6s. Additional discharge measurements will be required to define the magnitude of any backwat~r effects. 

Guidance in drawing the curve through the 

discharge measurements and extending it to- the 

greatest known stage of 7.6 meter~~ (24.9 feet) 

was obtained from a study of conveyance and 

slope. The slope computed by use of the Manning formula with a Manning <''>efficient of 

0.020 (derivation of the Manning coefficient 

from a vertical velocity curve is explained 

later) varied among the three rr~asurements 

as follows: 

July 1963 __________________ 8.7f X 10-6 

November 1963 _____________ 1.74· X 10-6 

August 1964 _______________ 5.6f X 10-6 

It is the author's opinion that th~ square root 

of the slope varies linearly with stage at and 

above the stage of the two higher measurements 

of discharge. Thus, the slope estimated for a 

stage of 7.6 meters (24.9 feet) at 6bidos is 

16.0x10- 6 • The stage-conveyance relation for 

obidos does not vary much with stage. Conveyance, K, in English units, may be calculated 

as follows: 

where 

K = 1.486 AR% 

n 

A=cross-sectional area, 

R hydraulic radius, and 

n=Manning coefficient. 

Hence, the increase in discharge with stage is 

mainly a result of increase in slope through 

the 6bidos narrows. An observ,~.tion by Le 

Cointe of the high velocity through the obidos 

narrows concurrent with the crest of the flood 

of May 1918 (3.15 meters, or 10.33 feet per 

second from float observation) sur"lorts the extrapolation of the stage-discharg~ relation to 

12,500,000 cfs (350,000 ems) at stage 7.6 meters 

(24.9 feet). Figure 3 shows the sn1all variation 

in cross section measured in the obidos discharge measurements. The cross-s~ctional area 

of the main channel for a stage of 7.6 meters 

(24.9 feet) would be but 45,000 sq ft ( 4,150 

meters2 ) larger (about 4 percent larger) than 

that of the discharge measurement of July 1963. 

During the three trips for collec~ion of reconnaissance data, limited time did not permit an 

investigation of the overflow situation at Obidos. Maps (see fig. 4) clearly show the area subject to overflow between the mair channel opposite obidos and the terra firma about 32 km 

(20 miles) south of Obidos. Th€ flood plain, 

judging by available maps and F.ir photos, is 

covered with shallow lakes, s·wamps, scrub 

trees, and grass, and the drainage channels and 
DISCHARGE, IN MILLIONS OF CUBIC FEET PER SECOND 

0 2 . 4 6 8 10 12 14 

8 

7 

Esti

1

mate, Ju~ 1953 1 

• 

v 

/ v 

25 

6 

en 

0:::: 5 / ~easrement, (ly I96 3 

20 

1.1.1 

)-

1.1.1 

~ 

~ Measurement, I August 1964 ~ 

I 

)-

1.1.1 

15 1.1.1 

u.. 

z 4 

1.1.1 

" <( 

)-

en 3 en 

0 

0 

m 

'0 2 

1 

0 

I 

I 

I 

I 

z 

1.1.1 

" <( 

)-

en 10 en 

g 

m 

'0 

5 

0 I 

• Measurement, November 1963 

-1 

0 

I 

100 

I I I 

200 300 400 

DISCHARGE, IN THOUSANDS OF CUBIC METERS PER SECOND 

Figure 2.-Stage-discharge relation, Amazon River at Obidos. 

abandoned meanders indicate the localized flow 

directions during floods. A set of levels run 

from the water surface as far inland on the 

flood plain as limited time would permit shows 

the top of the natural levee and flood plain adjacent to the right bank of the main channel 

opposite 6bidos to be about at elevation 6.9 

meters (22.6 feet) (Obidos gage datum). Thus, 

significant overflow covering the entire flood 

plain opposite 6bidos would occur any time the 

6bidos stage exceeded 6.9 meters (22.6 feet). 

It is of interest that the former 6bidos gage 

observer (Mrs. Platt) made a notation in the 

gage records that overflow would begin at 

6bidos when the river level reached 7.5 meters 

(24.6 feet). 

Although overflow directly opposite obidos 

might not begin until the river stage reached 

7 

6.9 meters (22.6 feet), it is very likely that significant overflow would exist at a 6.9-meter 

(22.6 foot) stage through the chann~ls and 

lakes-Lago do Pocao, Lago Grande do Curuai 

(Lago Grande de Vila Franca), and coiJnecting 

small lakes-occupying roughly a strir of the 

flood plain 15 km (9 miles) wide imm~diately 

adjacent to terra firma. A computation of possible range in discharge over the flood plain at 

the stage ( (7.6 meters) 24.9 feet) of t:;.e 1953 

flood was made by (1) assuming the worst possible hydraulic conditions of shallow depth, 

water-surface slope equal to the main channel 

water-surface slope, and maximum natural 

roughness and (2) assuming the best possible 

hydraulic conditions of average depth of overflow equal to 6.5 feet (2 meters), water-surface 

slope increased 50 percent over the main chan-
DISTANCE FROM LEFT BANK, IN THOUSANDS OF FEET 

0 1 2 3 4 5 6 7 8 

Left bank Right ba"lk 

110 

350 

en -en 

a::: a:: 

UJUJ 

1-1-

UJ~ ~ 90 300 

z8 

- ...... 

clcn 80 

UJ:::> m_, 250 u..a.. 

0~ 70 

z=> ot-

-< !;(0 60 200 

>UJ 

UJ(!J -'< UJ(!J 50 

- 150 

40 

0 500 1000 1500 2000 

DISTANCE FROM LEFT BANK, IN METERS 

Figure 3.-Measured cross sections from three discharge measurements, Amazon River at 6bidos. 

10 0 10 20 MILES 

10 0 10 20 Kl LOM ETERS 

I I I 

Figure 4.-Amazon River in vicinity of 6bidos. 

nel slope, and minimum probable roughness 

(Manning coefficient 0.030). The result based 

on assumed worst hydraulic conditions showed 

that the overflow could be ignored without 

seriously affecting the accuracy of the estimated maximum discharge. The computation 

based on best conditions showed that a flow 

8 

equal to about 10 percent of the 1nain channel 

discharge might bypass the main channel at a 

stage equal to that of the 1953 fioo~. It is likely 

that the actual overflow discharge in June 1953 

was somewhere between the two r~sults. 

Katzer's interpretation of the overflow situation at obidos is not favorable for accuracy of 
flow measurements. He wrote (1897): "Unfortunately the narrows at obido.c;; is not suitable 

for this purpose as long as the entire quantity 

of water is to be determined, because only a part 

of the Amazon's total water passes at this point. 

Another part flows into a number of arms in the 

lowland north of the Serra do Valaio and helps 

to fill the large lake, Lago Grande do Curuai, 

which forms a wide water zone with its numerous lagoons and their connecting channels. This 

water zone stretches like a bowstring across 

the main arm of the Amazon River, which 

bends north, and below whose zenith the city 

of obidos is situated." 

Several strips of overlapping aerial photographs taken on flight lines across the flood 

plain from east to west and north to south 

from the terra firma to the Amazon River were 

available to the writer for study. It is unlikely 

that the overflow situation intimated by Katzer 

could exist. However, if great accuracy of measurement of the total discharge of a subsequent 

flood of the size of the 1953 event is desired, the 

overflow depths and current velocities should 

be m~asured and the quantity of flow computed. 

It is the writer's opinion that the quantity of 

flow bypassing the main channel at the stage 

equivalent to average annual discharge at obidos is an insignificant percentage of the main 

channel flow. 

Some questions may be raised about the fact 

that the two higher discharge measurements 

were made on a falling river stage and hence 

the measured flows may be less than would 

occur at equal stage on ·the rising side of the 

.... • 

•• 

•••• 

•• 

• 

• 

hydrograph. A computation made by t~~ Wiggin's formula, 

where 

Qe=discharge corrected for c:':tanging 

stage, 

Qm=discharge measured, 

U=velocity of flood wave (assumed equal 

to 1.3 times mean velocity), 

Se=slope of energy gradient, and 

~~=rate of change of stage in feet per 

second, 

showed the correction to be applied to the July 

1963 measurement was less than 3 percent 

(which can be ignored in view of the reconnaissance nature of the work). The August 

1964 measurement had a lesser correction 

computed for it. 

Proof of tidal effect at Obidos was obtained by 

stage readings at short intervals during the 

November measurement. (The existence of tidal 

effect was a moot point based on previous investigations.) The graphs of stage readings 

taken at lf2-hour intervals on November 20 and 

21, 1963, are shown in figure 5. 

It should be kept in mind that the 1·eadings 

were taken during one of the lowest flows of 

the Amazon River at obidos when the upstream 

reach of tide effect would be a maximum. During the period 192~6 no stage readin.S?; of less 

than 0.05 meter (1.6 feet) was recorc ~d. The 

mean stage of the November 1963 discharge 

measurement is -0.5 meter (-1.6 feet), or 

one-half meter lower than zero datum. The 

• 

• • 

• •• 

• 

• • 

•••• •• 

• 

• 

• 

••• 

NOVEMBER 20, 1963 TIME, IN HOURS 

NOVEMBER 21, 1963 

Figure 5.-Water level observations showing tidal effect at low flow, Amazon River at 6bidos. Auxiliary 

staff gage was moved at close of readings on November 20 and not set to same datum for rea~ings of 

November 21. 

9 
effect of tide on the obidos stage-discharge relation is considered insignificant by the writer. 

On the basis of the recorded gage readings for 

the period 1928-46 and the rating curve in 

figure 2, mean monthly discharge has been computed as listed: 

A11uage monthy discharge for period Month (1,000 cma)l (1,000 cfs)l 

January ------------------------- 110 3,900 February _______________________ 140 4,900 

~arch -------------------------- 170 6,000 

April --------------------------- 215 7,600 ~ay ----------------------------- 240 8,500 

June---------------------------- 240 8,500 

July ---------------------------- 205 7,200 August __________________________ 165 5,800 

September ______________________ 120 4,200 

October ------------------------- 90 3,200 

November ----------------------- 85 3,000 December _______________________ 95 3,400 

1 Average rounded to nearest 5,000 ems and nearest 100,000 efs. 

The computed coverage discharge at 6bidos for 

the period is 5,500,000 cfs (157,000 ems). The 

average discharge computed for 6bidos on the 

basis of the three discharge measurements and 

obidos gage readings for the period 1928-46 is 

thus seen to be more than 50 percent greater 

than Parde's estimate of 90,000 to 100,000 ems 

(3,200,000 to 3,500,000 cfs). 

Some observations on velocity distribution in 

selected verticals and in the complete cross section at obidos are shown in figure 6 and 7. 

The point velocity observations for the vertical distribution of velocities observed on November 21, 1963, .were measured while the corvette was anchored and should be reasonably 

free of errors caused by movements of the 

metering vessel during individual observations. 

Each point velocity observation is the average 

determined during a period of 40 or more seconds. The effects of natural stream turbulence 

are evident in the scatter of the observations 

about the arbitrarily placed distribution graph. 

It is evident that, because of the large scale of 

the turbulence, each point velocity observation 

should have been derived from a meter run of 

much longer duration-perhaps as long as 4 

minutes. From a study of data from 23 United 

States rivers ranging in depth from 2.4 to 26.7 

feet (0.73 to 8.1 meters), Carter and Anderson 

(1963) determined that an observation period 

of 4 minutes for the 20-percent depth location 

will yield a mean point velocity within 2 percent of the probable true average. As predicted 

by turbulence theory, the effect of turbulence at 

the ()bidos section is most pronounced in proximity to the channel bed and it decreases as the 

distance of observation point above the bed increases. 

The vertical velocity curve data in figure 6 

and the several other vertical velocity distribu10 

tion curves developed for other lo~ations and 

dates at 6bidos verify the essential correctness 

of the Geological Survey's standard procedure 

for computing the mean velocity in the vertical 

as the average of point velocity observations 

taken at 20 and 80 percent of the total depth. 

The mean in each vertical for the 6bidos discharge measurements of July and November 

1963 was computed from the 20- and SO-percent 

depth observations-each corrected for movement of the measuring corvette during the period of observation, as explained ir. Geological 

Survey Circular 486. The mean in each vertical for the August 1964 measurema.nt was obtained by applying an appropriate c0effi.cient to 

the subsurface velocity. 

The distribution of mean velocity in vertical 

across the 6bidos measuring sect!on for the 

high-flow measurement of July 1963 is shown 

in figure 7. The distribution of velo~ities in the 

section is remarkably uniform, as yrould be expected from Geological Survey experience derived from thousands of discharg·~ measurements made on deep, swift rivers ir the United 

States with similar uniformity of measuring 

section and similar streambed conditions. 

An analysis based on the verti~al velocity 

distribution graph and the logarithmic velocity 

distribution law for wide channels (smooth or 

rough) follows. 

v-V = 2 log1o ( Yyo ) + 0.88 

V\.1{ 

where 

v=observed point velocity (all English 

units), 

V-mean velocity in vertical, 

/=Darcy-Weisbach friction coefficient, 

Y=depth of observation (measured from 

bed), and 

yo=total depth of measured vertical. 

This analysis yielded a Darcy-WeislJach friction 

coefficient of 0.008, equivalent to a Manning 

roughness coefficient for the depth investigated of 0.019. 

This indication of a relatively sn-~oth bed is 

borne out by the bed profile shown by sonic 

soundings and the bed material r~mples obtained. A section of fathometer char~ taken November 21, 1963, during a run up the approximate middle of the channel and crossing the 

general location of the measured cro"s section is 

shown in figure 8. 

The chart shows dunes with an anproximate 

length of 200 meters (660 feet). (The illustration is a drafted reproduction of the fathometer 

chart. The explanation of the short period flue-
I 

Ia.. 

UJ 

0 

_. 

< I0 

I0 

II--

z 

0 

a.. 

z 

0 

j:: 

< 

> a:: 

UJ 

en 

al 

0 

0 

I0 

UJ 

al 

~ 

0 

a:: 

u.. 

0 

UJ 

a:: 

::::> 

en 

< UJ 

~ 

-I 

Ia.. 

UJ 

0 

z 

0 

j:: 

< 

> a:: 

I.&J 

en 

al 

0 

u.. 

0 

0 

j:: 

< a:: 

1.00 

0.50 

0.40 

0.30 

0.20 

0.10 

0.05 

0.02 

0.01 

0 

... _, 

~I 

7_ 

LI 

V_ -

j 

1 

l 

I --

- 1/ 

• i/ 

0.5 1.00 

RATIO OF VELOCITY AT POINT TO MEAN VELOCITY IN VERTICAL 

Figure 6.-Distribution of velocity in a selected vertical, Amazon River at 6bidos. 

11 
.... 

LLI 

LLJ 

LL 

z 

:i" 

.... 

Q. 

LLJ 

c 

DISTANCE FROM LEFT BANK, IN THOUSANDS OF FEET 

0 1 2 3 4 5 6 7 8 I I I I I I I I I 

Left bank Right bank 

0 

0 

.... 

> z .... 0 

g ~ (.) 

...I UJ UJ en 0.5 

> z 

c 

UJ 

> > 

.... 0::: 

UJ g en 

ID ...I 

0 UJ 

> 1.0 LL 

0 z 

c( 

0 UJ 

~ ~ Note: Data from measurement 

c( of November 20-21, 1963 0::: 

1.5 

0 2 4 6 8 10 12 14 16 18 20 22 

DISTANCE FROM LEFT BANK, IN HUNDREDS OF METERS 

Figure 7.-Distribution of mean velocity in cross section, Amazon River at 6bidos. 

130 ..----\~ ~---r------,.-------,---------y-,---Jr-----rl---,- 40 

SOUNDINGS OF AUGUST 10, 196('l 

140 1--- - 1-----

en 

0::: 

UJ 

.... 

LLJ 

1- 45:::!: 

150 ,- ~ 

:i" 

.... 

a.. 

LLJ 

c 

160 i 1-

I 

- '-- 50 ..... DownsTm 

170 I I 

I~ 1000 feet+ 25 feet .,., (305 meters± 7.6 meters) 

Figure 8.-Seetion of fathometer chart taken near midstream and crossing general location of measuring section, Amazon River at 6bidos. 

12 
tuations is unknown.) Experience with sand 

channels in the United States has led to assignment of Manning coefficients in the range 

0.018 to 0.035 for such bed geometry. The size 

distribution of material determined from bed 

samples is discussed later. 

QUALITY OF WATER 

In contrast to the many published estimates 

of water discharge for the Amazon River, there 

is little published information on the suspendedsediment and dissolved-solids loads carried by 

the flow. Katzer (1897) and Sioli (1957) have 

published a few analyses of suspended sediment, total dissolved solids, and some other 

information on the chemical and pltysical 

nature of the Amazon River water in tl'~ general vicinity of obidos. Pinto computed ~- mean 

daily discharge of suspended load at mcuth of 

Amazon to be 3 million metric tons (3.3 million 

tons). 

Undoubtedly, the lack of means for coHection 

of suspended-sediment samples from yarious 

depths at the relatively high velocities d~~couraged investigators from attempting to assess 

Table 3.--Results of analyses of water samples from the Amazon River at Obidos, Para, Brazil 

[Concentrations of dissolved and suspended material are in parts per million (ppm) except as indicated] 

Constituent July 16, 1963 

Discharge cfs ---------------------~------ 7,640,000 

c~s) ---------------------------- (216,000) 

Silica (Si02) ----------------------------- 7.0 

Aluminum (Al) ----------------------------- .07 

Iron (Fe) --------------------------------- .06 

Calcium (Ca) ------------------------------ 4.3 

Magnesium (Mg)---------------------------- 1.1 

Sodium (Na)------------------------------- 1.8 

Potassium (K)-----------------------------

Bicarbonate- (Hco3) ------------------------

Sulfate (so4)-----------------------------

Chloride (Cl)-----------------------------

Fluoride (Fl)-----------------------------

Nitrate (No3)-----------------------------

Total dissolved solids--------------------

Hardness as caco3 -------------------------

Dissolved oxygen--------------------------

Specific conductance --------------------- (micromhos at 25°C). 

pH----------------------------------------· 

Temperature (°F)--------------------------

Suspended sediment------------------------

1 

Upper part of verticals (mg/1) -----------

Near the bed------------------------------

~illigrams per liter. 

19 

3.0 

1.9 

.2 

.l 

28 

15 

5.8 

40 

. 6.5 

83 

80 

6o 

300 

13 

November 20, 1963 

2,560,000 

(72,500) 

9.0 

.02 

.o6 

10 

.4 

4.2 

.4 

32 

6.4 

4.5 

0 

0 

51 

27 

5.6 

84 

7.1 

86 

60 

50 

280 

August 9, 1964 

5,810,000 

(165,000) 

9.0 

.15 

.09 

3.9 

.6 

1.8 

.6 

16 

l.O 

1.6 

0 

.l 

21 

12 

5.4 

34 

6.5 

83 

110 

70 

340 
the mean annual suspended-sediment discharge 

at obidos. Similar difficulties would have discouraged attempts to collect samples of the material in place on the streambed. 

The joint reconnaissance venture of 1963-64 

was well equipped to collect water samples at 

any point in the measuring cross section at 

obidos. Samples of the material on the top of 

any part of the bed could also be taken with an 

oceanographic clamshell type sampler or standard U.S. BM-54 sampler. The U.S. P-61 suspended-sediment sampler (equipped with 

3/16-inch ( 4.8-mm) -diameter intake nozzle), 

having an electrically controlled intake and 

closure valve, permitted water samples for analysis of suspended sediment to be taken at any 

location in the cross section of flow. Thus, the 

distribution of suspended-sediment concentration from bed to surface could be determined 

at any selected vertical. A bathythermograph 

furnished temperature-depth profiles at desired 

verticals. Chemical-quality samples were taken 

with an oceanographic sampler consisting of 

an open tube that allowed flow of water through 

it until it was closed, as desired, by ball-type 

valves. 

The quality-of-water aspects of the investigation were conducted by Mr. F. C. Ames, U.S. 

Geological Survey, Denver, Colo. Mr. Ames 

(April 1966) furnished table 3, which shows 

the results of the three series of samplings made 

at obidos. The tabulated suspended-sediment 

concentrations are the calculated average concentration for the cross section. Suspended-sediment samples were taken at many points in each 

vertical sampled, so that the distribution suspended rna terial in the vertical could be 

charted. Table 3 also includes information on 

the range of suspended-sediment concentrations 

measured in the cross section. As expected, the 

concentration of suspended sediment is high in 

the vicinity of the bed. 

Ames reports (oral commun., May 1966) this 

information on the bed material at obidos: 

"The median diameter of bed material averaged about 0.20 mm. The median diameters indicated by individual samples ranged from 0.15 

to 0.25 mm. Only one to two percent of the bed 

material (by weight) was finer than 0.062 mm 

and only one or two percent was coarser than 

0.4 mm." 

Katzer reported total dissolved solids of 56 

mg/1 in a sample taken at obidos June 30, 

1896. Because the turbulent mixing and lack 

of major tributary inflow in the vicinity of 

obidos (the discharge from the Rio Trombatas 

would have small effect) should guarantee uniformity of dissolved-solids concentration in a 

cross section of the stream, the minor differ14 

ences in the four analyses can be attributed to 

seasonal variations. One would expect the 

total dissolved solids found by Katzer on June 

30, 1896, to be more dilute than he reported 

unless the flow for that season 'vas very low. 

The concentration of dissolved sor~s on August 

9, 1964 (discharge 5,810,000 cfs = 165,000 

ems), if there were a relatively fixed inverse 

curvilinear relation between tC't,al dissolved 

solids and water discharge, woul1 be expected 

to be slightly higher than the concentration 

found on July 16, 1963 (discharge 7,640,000 

cfs = 216,000 ems). The contrary findings, 21 

mg/l and 28 mg/1, respectively, show the importance of seasonal variations in the proportions of total Obidos flow contributed by "white 

water" and "black water" tribubries. It is apparent that a minimum of one water sample 

per month collected over several years would 

be necessary to describe accurFtely the dissolved-solids load variation at obidos. 

The three determinations of me.an concentration of suspended sediment in the Obidos cross 

section also show the need for many more samples to be taken during several years before one 

could calculate a mean annual concentration of 

suspended sediment. However, on the basis of 

reconnaissance results at Obidos, if the mean 

annual concentration were assumed to be 100 

mg/1, one would arrive at a cal~ulated mean 

daily suspended load at obidos (using 5,500,000 

cfs = 157,000 ems) of about one-half that 

which Pinto ( 1930) computed for the mean 

daily load at mouth. 

The dissolved-oxygen content is close to 

saturation level at the observed stream temperature. Bathythermograph results showed no 

detectable variation of temperature in any of 

the verticals where observations were taken 

from surface to bed and return. The pH was 

found to be as expected from the analyses reported by Sioli (1957) for the vicinity of Santarem. 

ESTIMATED DISCHARGE AT MOUTH 

The drainage area tributary to the Obidos 

location is about 1,900,000 sq 1ni ( 5,000,000 

square kilometers). The drainage area above 

the mouth is about 2,300,000 sq mi ( 6,000,000 

sq km) or an increase of about 2(' percent over 

that for obidos. If equal contribution of runoff 

existed for the basin above mouth, the mean 

annual discharge at mouth would be expected 

to be about 6,650,000 cfs (190,001 ems). However, there are several data that indicate the 

yield per unit drainage area from the approximately 400,000 sq mi ( 1,000,001 sq km) of 

drainage intervening between ol~idos and the 

mouth to be less than that occurring above 

obidos. 
Only two large tributaries, the Rio Tapaj6s 

and the Xingu River, enter the Amazon River 

downstream from 6bidos. In August 1964, the 

gaging party measured the dry season discharge 

of the Rio Tapaj6s at Sao Luis, location of the 

first rapids, about 180 mi (300 km) upstream 

from Santarem. The discharge was found to 

be 99,000 cfs (2,840 ems). A stage-discharge 

relation for the Rio Tapaj6s gage at Fordlandia 

was drawn on the basis of the one discharge 

measurement, measured geometry of the highflow cross section at Sao Luis, and a consideration of the apparent variation of water-surface 

slope with stage for the Rio Tapaj6s location 

at Sao Luis. On the basis of available daily gage 

readings from the Fordlandia gage and the constructed stage-discharge relation, a mean annual discharge for the Rio Tapaj6s has been 

calculated as 250,000 cfs (7,100 ems). No measurement was made on the Xingu River. 

A low-water-season measurement made by 

the joint survey group on the Tocantins River 

(not considered an Amazon River tributary) at 

Maraba in October 1963 showed the discharge 

to be 52,800 cfs (1,500 ems). Using the crosssectional area at Maraba that would be occupied 

by bankfull discharge and an estimated tneatl 

velocity at bankfull stage, the writer hM calculated a bankfull discharge of 115,000 cfs (33,000 

ems). No stage records are available at Maraba. 

The mean discharge for the Tocanti:M River 

was estimat.ed, on the basis of the low-water 

measurement and the estimated bankfull discharge, as 400,000 cfs (11,000 ems). 

The Tocantins River is not tn"butary to the 

Amazon River (its basin has a common drainage boundary with the Amazon River) but its 

estimated mean discharge and that of the Rio 

Tapaj6s permit a "bracketing" of an estimated 

mean annual discharge for the Xingu River. 

The sum of mean annual discharges for Tapajos 

and Xingu Rivers, and minor tributaries between 6bidos and the mouth is estimated to be 

640,000 cfs (18,000 ems). On this basis, the 

partly estimated average annual discharge of 

the Amazon River at mouth is 175,000 ems 

(6,100,000 ds). 

15 

Estimates of the runoff from the intervening 

area between obidos and the mouth ba~~d on the 

Thornthwaite potential evapotranspiration approach result in a discharge of abo•xt double 

that based on hydrometric data. The estimates 

based on hydrometric data are considered to be 

more reliable than those based on rainfall-runoff computations. The writer conclude;-- that the 

most reliable value of average annual discharge 

for the Amazon River at its mouth is 6,100,000 

cfs (175,000 cms)-about 10 times th~ average 

discharge of the Mississippi River at the mouth. 

CONCLUSIONS 

The results of the joint investigatfons show 

the previously published estimates of mean annual flow past obidos to be much too low. The 

average discharge computed on the hu~is of a 

stage-discharge relation developed from three 

complete discharge measurements and daily 

stage readings for the period 1928-4fi is 5,500,-

000 cfs (157,000 ems). The great flocd of 1953 

which probably reached a stage of 7.6 meters 

(24.9 feet) at obidos is calculated to have discharged at 12,500,000 cfs (350,('·10 ems) 

through the main channel with an indeterminate quantity of overflow on the flooi plain. 

The observations of dissolved-8(] lids~ suspended-8ediment, and other water-q,J:ality parameters provide ntuch more information on 

these aspects for the obidos location than had 

been determined previously, but therr~ is insufficient information to permit an accur<'1te assessment of either the mean annual suspended load 

or the salt-load discharge. The bed material 

samples and fathometer charts provide much 

insight into the nature of the streaml'~d at obidos. 

The objective of the joint investigation to 

provide reconnaissance information on the flow 

and water quality of the Amazon P.iver was 

achieved. If more refitted detertnina ti ons of the 

average annual flow and water quality characteristics are needed, it will be necess~,ry to conduct intensive inve8tigationg nt obido~ and elsewhere in the basin. The maintenance of a riverstage gage at obidos-above tidal effects during 

all but extremely low flow-would provide valuable information at small expense. 
REFERENCES CITED 

Carter, R. W., and Anderson, I. E., 1963, Accuracy of 

current meter measurements: Am. Soc. Civil Engi- neers Proc., Jour. Hydraulics Div., v. 89, no. HY 

4, pt. 1., p. 105-115. 

Carvalho, Delgado de., 1942, Rev. Brasileira de Geographica: v. 4, no. 2, Rio de Janeiro. 

Guppy, H. P., 1880, The Yang-Tse, the Yellow River, 

and the Pei-Ho: Nature [London], v. 22, p. 488. 

Jarvis, C. S., 1945, River discharge in Brazil, South 

America: Am. Geophys. Union Trans., 25th Ann. 

Mtg., pt. 6, p. 1037. 

Katzer, Friederick, 1897, Das Wasser des unteren Ama- zonas: Gesellschaft der Wissenschaften, Verlag 

der Kon. Bo.hm, Dr. Ed. Greger in Prag. ____ 1898, D1e Stromenge des Amazonas bei Obidos: 

Germany, Globus, v. 74, p. 47-49. 

LeCointe, P~ul, 1922, L' Amazonie Bresilienne-le pays, ses ?abitants, ses resources, notes et statistiques: 

Paris, A. Challamel, p. 175. 

L'Vovich, M. I., 1945, Elements of the water regime of 

the rivers of the earth: Moscow. 

Military Engineer, 1958, Principal rivers of the world: 

Military Engineer [Washington, D.C.], v. 50, no. 337, p. 386. 

Oltman, .R. E., Sternberg, H. O'R., Ames, F. C., and 

DaVIs, L. C., Jr., 1964, Amazon River investigations, Reconnaissance measurements {)f July 1963: 

U.S. Geol. Survey Cire. 486, U5 p. 

Parde, :Maurice, 1955, Quelques apercus relatifs a l~Qgie :Bl'uilienne: Grenoble, France, La 

Houille Blanehe. p. 14. 

Pinto, Augusto Actaviano, 1930, Hidrografia do Ama- zonas e seus amuentes: Rio de Janeiro, lmprensa 

naeional., p. 56. 

Reclus, Elisee, 1877, La Terre: Paris, Librairie Hachette et Cie, v. 1, p. 514. 

1895, The earth and its inhabi"~:uts, South 

America: New York, D. Appleton and Co., v. 

2, p. 98. 

Revy, J. J., 1874, Hydraulies of Great Riv~rs: London, 

E. and F. N. Spon, p. 9-21. 

Selfridge, T. 0., 1882, Annual report of t'-'e Secretary 

of the Navy for 1879: Washington .• U.S. Govt. 

Printing Office, p. 334-335. 

Siemens, Alexander, 1896, Cable laying on the Amazon 

River: Nature [London], v. 54, p. 16f. 

Sioli, H., 1957, Valores De pH De Aguas Amazonicas, 

Boletim Do Museu Paraense Emilio Gneldi: Brazil, 

Rev. Da Veterinaria, no. 1, 37 p. 

Smith, H. H., 1880, Brazil-The Amaz,.,.ns and the 

coast: London, Sampson Low, Marsto"". Searl, and 

B.ivington, p. 7. 

Soares, Lucio De Castro, 1956, Amazonia, in Excursion 

Guidebook Number 8, International Geographical 

Union, Rio de Janeiro: 216 p. 

Spix, J. P. von, and Marti us, C. F. P. vor" 1831, Reise 

in Brasilien: Munchen, M. Lindauer, p. 1335. 

Wallace, A. R., 1853, A narrative of tr~wels on the 

Amazon and Rio Negro: London, ~ve and Co., 

p. 412. 

16 

* U.S. GOYDIIHIENT PRIMTIIIG OI'I'ICE : 1 ... 0-289-'JOa