Sources of Salinity to the Rio
Grande
Fred M. Phillips, James Hogan, Heather
Lacey, Elizabeth Bastien, & Suzanne Mills
New Mexico Tech & SAHRA
Coauthors
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James
Suzanne
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Heather and Liz
Center for Sustainability of
semi-Arid Hydrology and Riparian
Areas
(SAHRA)
This research was funded by
SAHRA under the Science &
Technology Center Program of the
U.S. National Science Foundation
Rio Grande
basin
= sedimentary
basin
• Basin Area - 32,210 mi2
• Precipitation - 6 to >50 in.
• Population - 1,072,000
(1990)
• Irrigation - 914,000 acres
Facts about Rio Grande
„
„
„
„
„
Current mean annual discharge
at Otawi Bridge (northern New
Mexico) is 49 m3 s-1
Natural discharge (without ag
diversions) at this point would
have been ~70 m3 s-1
TDS at headwaters is ~40 mg L-1
TDS at El Paso averages ~750 mg
L- 1
TDS at Fort Quitman is >2,000
TDS of the Rio Grande
Winter 01
Summer 00
Winter 00
Albuquerque
TDS (mg/L)
2000
1500
1000
500
El Paso
2500
Elephant Butte
3000
0
0
200
400
600
Recommended drinking water limit Distance (km)
800
1000
1200
Questions we will try to
answer
„
„
„
„
Where is the salt coming from?
What is the salt budget of the
river?
What are the controls on salt
and water dynamics in the river
system?
How is the river responding to
prolonged drought?
Salinity
Sources
Cyclic salts and
Weathering
Open Water
Evaporation
Riparian
Transpiration
Consumptive
use
Agricultural
Evapotranspiration
Waste water
Saline
Groundwaters
Geothermal
waters
Where is the salt coming
from?
„
„
„
There are no known evaporite
deposits under the Rio Grande
rift
There are a few moderately
saline hot springs, but salt
output is small
River water is consumed by
three major irrigation
districts along the course of
What have previous investigators said?
Hypothesis 1: Effects of evapotranspiration
J.B. Lippincott (1939): “The increase in
salinity of the waters of the Rio Grande [is]
due to their use and re-use [for irrigation] in
its long drainage basin...”
Hypothesis 1: Effects of evapotranspiration
Trock et al. (1978) “The deterioration in
the water quality of the Rio Grande ... is
due principally to the concentrating effect
of irrigation.”
Hypothesis 2: Groundwater displacement
Wilcox (1957): “There is a relatively large
increase in the tonnage of both sodium and
chloride from the upper to the lower
stations... [that can be] attributed to the
displacement of salty groundwater in the
course of irrigation and drainage
operations.”
Hypothesis 3: “Continental solute erosion”
van Denburgh and Feth (1965): Noted that
only 4.2% of the chloride burden of the Rio
Grande originated from atmospheric
deposition over the catchment and
attributed the remainder to“continental
solute erosion”.
How to Quantify Sources
and Causes of
Salinization?
„ Traditional
approach: Measure
discharge and salt
concentrations at gaging
stations and compute salt burden
Measure
„ Alternative Approach:
environmental tracers at high
spatial resolution and employ
dynamic simulation to interpret
results
Potential Tracers
„ Cl
„ Cl/Br
„ 36Cl
„ δ37Cl
„ δ18O and
„ 87Sr/86Sr
„ 234U/238U
δ2H
Sampling
locations along
the Rio
Grande
Chloride/Bromide Data
Patterns of Salt Addition cont’d:
Cl/Br
theRio
Rio
Grande
Cl/Brin
in the
Grande
1600
August 2001
January 2002
1400
Cl/Br (wt/wt)
1200
Los
Lunas
1000
800
600
Elephant
El Paso
Butte Selden
San Acacia
canyon
Lobatos Albuquerque
400
Ft. Quitman
200
0
0
200
400
600
distance (km)
800
1000
1200
Chlorine-36 Data
36Cl
vs. flow distance
3000
36Cl/1015
Cl
2500
2000
Natural Meteoric Ratio
1500
1000
500
0
200
400
600
800
distance (km)
1000
1200
1500
Mixing
1000
Cl/Br
Sedimentary
Brine
Rio Grande
500
Geothermal
Meteoric
Evaporation
0
0
2000
4000
Cl (mg L-1)
6000
8000
Cl/Br (weight ratio)
1500
sedimentary brine
San Acacia pool
1000
Mixing line
Rio Grande
Evaporation
500
Rio Grande
headwaters
geotherma
l
0
0
500
1000
1500
36Cl/1015 Cl
2000
2500
3000
Result from tracer work
A large part of the salinization of the
Rio Grande is due to seepage of
deep, sedimentary-origin brines
Where are these brines
entering the Rio Grande?
Patterns of Salt Addition cont’d:
Cl/Br in the Rio Grande
1600
August 2001
January 2002
1400
Cl/Br (wt/wt)
1200
Los
Lunas
1000
800
600
Elephant
El Paso
Butte Selden
San Acacia
canyon
Lobatos Albuquerque
400
Ft. Quitman
200
0
0
200
400
600
distance (km)
800
1000
1200
Points of Salt Addition
Fraction Cl Added vs. flow distance
0.8
0.4
Selden Canyon
0.6
0.2
El Paso
Elephant Butte
San Acacia
F ractio n C l A d d ed
1.0
0.0
0
300
600
900
Flow distance (km)
= basin terminus
1200
Basin Groundwater
Systems
Schematic Hydrogeologic CrossSection, Parallel to River Path
river elevation
= basin terminus
Saline input: San Acacia
pool [ Cl- ] = 32,300 mg L-1
salt-encrusted tree stumps
Basin Groundwater
Systems
Schematic Hydrogeologic CrossSection, Parallel to River Path
river elevation
= basin terminus
Mesilla Basin
El Paso Narrows
ISC-4 well
El Paso
Ciudad Juarez
SAHRA
An NSF Science and Technology Center
El Paso del Norte
ISC-4 well
Rio Grande
rg
a
h
isc
D
in
s
a
B
•
•
•
e
Cross section through Paso del Norte along Rio Grande
Basin flow from Mesilla basin forced up
Recharge when entering the Hueco Bolson
SAHRA
An NSF Science and Technology Center
El Paso Narrows well results
1500
Mixing
Sedimentary
Brine
1000
500
El Paso Narrows well
30,000 mg/L TDS
Geothermal
Meteoric
Evaporation
0
0
2000
4000
6000
8000
10000
Cl (mg L -
12000
14000
16000
18000
20000
Findings from subsurface
investigations
Sites of brine leakage along
structurally-controlled pathways
can be clearly identified in the
field
Role of agriculture?
Influence of Drains
600
400
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are needed to see this picture.
200
0
0
50
100
150
Cl- (mg/L)
200
250
Location of
high
chloride
waters
Talon Newton, M.S. Thesis, 2004
Drains pick up deep-basin
salts
1200 ppm
346 ppm
Rio Grande
545 ppm
413 ppm
TDS = 306 ppm; Cl = 30 ppm; Cl/Br = 306
Cl doubles; Cl/Br increases 30%
TDS = 386 ppm; Cl = 66 ppm; Cl/Br = 376
Summary of Findings
„ Salt
addition to the Rio
Grande occurs in a stepwise
pattern
„ Salt is added at San
Acacia, Elephant Butte,
Selden Canyon, and the El
Paso narrows (and T or C)
„ Salt is either connate or
from long-term rock/water
interaction
Influence of wastewater
Cl (ppm)
The Rio Rancho, Albuquerque, Las Cruces, and El Paso
(Northwest WWTP) wastewater effluents all increase
Cl- and Cl/Br in the river.
200
August 2001
180
January 2002
160
140
120
ABQ
100
wwtp
RR
80
wwtp
60
40
20
0
500
600
LC wwtp
700
800
distance (km)
900
1000
El Paso
wwtp
1100
Response to drought
Summer Rio Grande total dissolved solids,
winter '00 to summer '04
3000
TDS-X00
2500
EP
TDS-X01
TDS-X02
2000
TDS-X03
drought years
SA
TDS-X04
SM
EBR
ABQ
1500
1000
500
0
0
200
400
600
800
1000
1200
distance (km) non-drought years
Chloride concentrations and loads
are highly variable in time and location
We need a dynamic modeling tool
to adequately understand budgets
and variability of solutes in the
Rio Grande
Powersim modeling - water model
Precipitation
Inflow from
RGCC_SM
Surface area of
bank storage
volume
In
Inflow from
upstream SM
Inputs
RS Head
Head gradient
BS Head
Rate_1
Pan coefficient
Pan evaporation
Reservoir Storage
Bank Storage
Surface Area
Out
Evaporation
Release from
EBDam
Outputs
Coefficient for
conductivity and
width of barrier
Powersim modeling - chloride model
Inflow Cl from RGCC
SM
Cl In
Inflow Cl from SM
Euler Cl conc in BS
Inflow Cl
Euler Cl conc in RS
Cl RS
Cl BS
RS Cl
Cl Output
Rate_2
Cl Bank Storage
Model Results w/brine inflows: Cl burden
ChlorideBurden(tons/mo)
San Acacia Chloride Burden
10,000
8,000
6,000
4,000
2,000
0
1/75
1/85
Reservoir Cl storage (tons)
San Acacia modeled Cl burden
1/95
1/05
San Acacia historical Cl burden
150000
100000
50000
0
1/75
1/85
Elephant Butte modeled Cl storage (tons)
1/95
1/05
Elephant Butte historical Cl storage (tons)
2000
Deep brine plus tributary
inflows accocunt for about
two-thirds of chloride increase
1000
El Paso
San Acacia
Elephant Butte
3000
Albuquerque
4000
Otowi
5000
Cerro
Average Annual Cl Burden (tons/month)
Cumulative Chloride Sources
deep brine
wastewater discharges
tributary inflows
mainstem input
0
200
400
600
800
Flow Distance below Lobatos (km)
1000
Historical Perspective
Are modern practices responsible for
worsening water quality? (perhaps by
increasing brine inflows?)
Two important past studies:
•Wilcox 1934-1950 at many gauging stations
•Stabler 1905-1907 at San Marcial and El Paso
Comparison with Wilcox (19341950) data set
Monthly Chloride Burden
Ave Monthly Cl Burden (metric tons month
-
8000
7000
6000
1935-1950
(Wilcox data)
1980-1995
5000
4000
3000
2000
1000
0
San Marcial
Elephant
Butte
Caballo
Leasburg
El Paso
Comparison with Stabler
(1905-1907) data set (before
Elephant Butte Dam!)
San Marcial Chloride Concentrations
Chloride Concentration (mg/L)
60
50
1974-1995
40
30
1905-1907
20
10
0
Jan
Feb
Mar
Apr
May
June
Jul
Aug
Sept
Oct
Nov
Dec
El Paso chloride
600
Chloride Concentration (mg/L)
1905-1907
500
400
brine inflow
1974-1993
300
200
100
05-07 modeled
0
Jan
Feb
Mar
Apr
May
June
Jul
Aug
Sept
Oct
Nov
Dec
Conclusions
„
„
About 2/3 of the chloride
increase of the Rio Grande is
from “geological salt”, either
from brine leakage or
tributaries
The brine leakage is along
structural features (mostly
faults) and might be
intercepted and pumped
Conclusions
„
„
The brine leakage predates
development of the river and
may have actually decreased
over the 20th Century
Agriculture contributes to the
salinization of the Rio Grande
but probably plays only a
secondary role
Water and Salt Dynamics
of the Rio Grande
δ18O vs δ2H (Summer ‘01)
-40
MWL
-60
-80
Rio Grande
Tributaries
-100
Drains
Meteoric Water Line
-120
-15
-12
-9
18
δ O (per mil)
-6
δ18O vs Flow Distance (Summer
‘01)
-6
-8
-10
-12
Rio Grande
Drains
Tributaries
-14
-16
0
400
800
Flow Distance (km)
1200
Significance of Stable
Isotopes
• Water source is mnt. snowmelt
• Strong enrichment = much evaporation
• Simple Rayleigh distillation model indicates
~35% of inflow is evaporated
• ~1/3 of evaporation occurs from Elephant
Butte Reservoir
• River gauging indicates ~75% lost to ET
• Loss is ~1/2 evap. and ~1/2 transp.
Where is water going?
Aug ‘01
Flow (cms)
Del Norte, CO
Cochiti
Elephant Butte
Caballo
Ft. Quitman
Jan ‘02
= ag
= seepage
= tribs
= wwtp
• Inputs on left
• Outputs on right
• Pipe width indicates
flow magnitude
Where is salt going?
Aug ‘01
Jan ‘02
Del Norte, CO
Cochiti
Elephant Butte
Caballo
Ft. Quitman
= ag
= seepage
= tribs
= wwtp
• Inputs on left
• Outputs on right
• Pipe width
indicates burden
magnitude
Deep groundwater
addition Selden canyon:
San Acacia: 1800
(summer) – 26,000
(winter) kg/dy
T or C: 30,000 –
60,000 kg/dy
Rio Chama:
4,000 kg/dy
ABQ wwtp:
18,800 kg/dy
300-6,000 kg/dy
(winter only)
El Paso narrows:
18,000 – 30,000 kg/dy
Solute Dynamics Under
Worsening Drought
δ18O in Summer
0
-2
EP
-4
MVD
SLVD
EBR
-6
ABQ
SM
18
δ O
SA
-8
-10
Sum 01 - Rio Grande
Sum 01 - Tributaries
-12
Sum 01 - Drains
Sum 02 - Rio Grande
Sum 02 - Tributaries
Sum 02 - Drains
-14
Sum 03 - Rio Grande
Sum 03 - Tributaries
Sum 03 - Drains
-16
0
200
400
600
800
River Distance (km)
1000
1200
Cl in summer
400
EP
Sum
Sum
Sum
Sum
Sum
Sum
Sum
Sum
Sum
Sum
Cl (ppm)
300
200
00
01
01
01
02
02
02
03
03
03
-
Rio Grande
Rio Grande
Tributaries
Drains
Rio Grande
Tributaries
Drains
Rio Grande
Tributaries
Drains
MVD
SM
SA
SLVD
EBR
ABQ
100
0
0
200
400
600
800
River Distance (km)
1000
1200
Reservoir volume
actual data
Model with bank storage
Model without bank storage
2.5E+09
2.0E+09
1.5E+09
1.0E+09
5.0E+08
0.0E+00
Aug-76
Feb-82
Aug-87
Jan-93
Date
Jul-98
Jan-04
Accumulation of chloride in the reservoir system
1.2E+14
1E+14
8E+13
6E+13
4E+13
data
No bank storage
With bank storage
2E+13
0
Aug76
May- Feb-82 Nov-84 Aug79
87
Date
May- Jan-93 Oct-95
90
Chloride concentration in the reservoir
120
Actual
Model with bank storage
Model without bank storage
100
80
60
40
20
0
Aug-76
Feb-82
Aug-87
Jan-93
Date
Jul-98
Jan-04
Tracing GW inputs …
Albuquerque
Elephant Butte
Sr End Members
San Acacia Pool
Mi
xin
g
“Shallow”
Saline GW’s
from ABQ and
Socorro Basins
H
e
w
d
a
s
er
t
a
Thanks to Talon
Newton and
Laura Bexfield
SAHRA
An NSF Science and Technology Center
Strontium Isotopes
SAHRA
An NSF Science and Technology Center
Influence of tributaries
Natural tributaries add most chloride in the
headwaters (as well as the Closed Basin Canal).
Jan ‘02
Aug ‘01
Del Norte, CO
Cerro, NM
Further input of natural
tribs
Cerro, NM
Chloride
enters the
river with
natural
tributarie
s.
Aug ‘01
San Acacia
Influence of wastewater
Cl (ppm)
The Rio Rancho, Albuquerque, Las Cruces, and El Paso
(Northwest WWTP) wastewater effluents all increase
Cl- and Cl/Br in the river.
200
August 2001
180
January 2002
160
140
120
ABQ
100
wwtp
RR
80
wwtp
60
40
20
0
500
600
LC wwtp
700
800
distance (km)
900
1000
El Paso
wwtp
1100