WSP04263

• File Number: 8507
• Description: Rio Grande Project
• State: CO
• Basin: Rio Grande
• Date: 1/1/1957
• Title: Symposium on Problems of the Upper Rio Grande
• Water Supply Pro - Doc Type: Report/Study

The discharge values are the annual means shown
in Table 1. The dissolved solids, in tons per acre-
foot, are the weighted means from Table 3. These
are shown together in. Table 4 in Ofder to emphasize
the inverse relationship between discharge and
concentration. In the down-stream order, discharge
values decrease until the volume at Fort Quitman is
wughly only one-fifth the volume at Otowi Bddge,
while the related concentrations increase approxi-
mately eight.fold. As a result of this inverse re-
lationship, the salt burden at successive stations
is nearly constant. There is some pickup of salt
between Otowi Bridge and San Marcial and some
loss between F;l Paso and Fort Quitman but for the
remaining stations, the salt burden is approximately
one-half million tons per year.

CATIONS
The change in composition and the tonnage of
several salt constituents has been determined.
Table 5 shows the weighted mean concentrations of
the three principal cations, calcium, magnesium, and
sodium.
Table 5. Cation Concentrations for Seven Stotions
on the Rio Grande for the 20-year Period 1934.1953.

CATIONS (milliequivalents per liter)
Stations on the ( Weighted Mean)
Rio Grande Ca Mg Na
Otowi Bridge 1.87 0.59 0.82
San Marcial 3.02 .99 2.81
Elephant Butte 3.05 1.09 3.15
Caballo Dam 3.25 1.14 3.42
Leasburg Dam 3.44 1.21 3.71
EI Paso 4.25 1.56 6.29
Fort Quitman 7.38 3.04 15.95

In the down-stream order all three cations increase
in concentration. There is a la"rge increase between
Otowi Bridge and San Marcial and another large in-
crease between El Paso and Fort Qultman. The
concentrations of cations expressed as percentages
of the tctal concentrations of cations are given in
Table 6. Both calcium and magnesium decreased in

Table 6. Catian Concentrations Expressed as
Percent of Total Concentrations of Cations for Seven
Stations on the Rio Grande for the 2O.year Period
1934.. 1953

Stations on the CATIONSl(as % of total cations}
Rio Grande Ca Mg Na
Otowi Bridge 57 18 25
San Marcial 44 15 41
Elephant Butte 42 15 43
Caballo Dam 42 14 44
Leasburg Dam 41 15 44
I'~l Paso 35 13 52
I,'ort C)uitruan 28 12 60

42

percentage while sodium increased in about the same
proportion.
The average tonnage of each of the three cations
passing the gaging stations each year is reported in
Table 7.
Table 7. Cations in Thousands of Tons per Year,
at Seven Stations on the Rio Grande for the
20'year Period 1934-1953

Stations on the CATIONS,(thousands of tons per yrJ
Rio Grande ea Mg Na

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Otowi Bridge 55 II 28
San Marcial 70 14 75
Elephant Butte 66 14 78
Caballo Dam 69 15 84
Leasburg Dam 70 15 86
El Paso 61 14 103
Fort Quitman 41 10 101

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The tonnage of all three cations increases between
Otowi Bridge and San Marcial with sodium showing
the greatest change. There is a loss of calcium
fwm the solution at El Paso and at Fort Quitman
and a loss of magnesium at Fort Quitman. Sodium
increases more or less regularly below San Marcial
with an abrupt increase at El Paso. These changes
are discussed in more detail in the next section.

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ANIONS

The weighted mean concentrations of the three
anions, bicarbonate, sulfate, and chloride, are shown
in Table 8. Carbonate is present in low concentra-
tions in some samples and is included with the bi..
carbonate. All three ions increase in concentration
in the down..stream order. Bicarbonate shows the
least change. Between El Paso and Fort Quitman,
where there is very little drainage return, both sul-
fate and chloride showed relatively large increases.

Table 8. Anion Concentrations for Seven Stations on
the Rio Grande for the 20-year Period 1934.1953

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ANIONS (milliequivalents per liter)
Stations on the (Weighted Mean)
Rio Grande HCO, SO, Cl
Otowi Bridge 1.90 1.15 0.20
San Marcial'" (2.61) (3.27) 0.10)
Elephant Butte 2.55 3.58 1.24
Caballo Dam 2.75 3.63 1.51
Leasburg Dam 2.81 3.90 1.73
EI Paso 3.40 5.32 3.49
Fort Quitman 3.49 8.64 14.35

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'" Values in parentheses partly estimated.

The concentrations of the anions, expressed as
percentages of the total concentrations of anions, are
given in Table 9. Bicarbonate decreases more or less
regulady fwm 59% at Otowi Bddge to 13% at Fort
Quitman. Sulfate is reasonably constant. Chloride
increases three-fold between Elephant Butte and
Fort Quitman.

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