The "Teflon basin" myth: A surface water
hydrologist's perspective on the groundwater
system of mountain catchments
in the western US
Mark Williams, CU-Boulder
Mike Wireman, EPA
Fengjing Liu, UC Merced
MOUNTAIN SNOW MELT
SUPPLIES ARID WEST WITH
ABOUT 80% OF ITS WATER
• Colorado
example
MOUNTAIN PLUMBING
CHALLENGE
• High alpine catchments in heterogenous
fractured rock present a great challenge
when assessing surface/groundwater
interactions
• We know little about source waters,
flowpaths, residence times, circulation
depths, reservoir sizes
• Precipitation as snow adds additional
complexity
What do we know about
high-elevation snow melt?
Snow melt flows directly to streams
REASONS
• Soils limited in extent and poorly
developed when present
• Bedrock often exposed, crystalline
• Little vegetation
• Fast hydrologic flushing rates
• Hence little groundwater storage
TEFLON BASIN MYTH
•Snow melt has little contact with ground
•Melt water moves directly into streams
and rivers; spring runoff is “new” water
•Role of groundwater is not important
Shallow system
Boulder Creek
Colorado Front Range
Deep groundwater
Leadville, CO
NWT LTER SITE
Sample Collection
Green Lake 4
• Stream water - weekly
grab samples
• Snowmelt - snow
lysimeter
• Soil water - zero tension
lysimeter
• Talus water – biweekly
to monthly
Sample Analysis
• Delta 18O and major
solutes
-1
Solutes ( eq L )
120
90
60
30
0
-1
Solutes ( eq L )
30
Chloride
Magnesium
Sodium
Potassium
20
10
0
-1
20
3
30
3
Q (10 m day )
40
Solutes vary by 2-3x
Discharge varies by 10x
10
0
130
190
250
Calendar Day (1996)
310
370
STREAM CHEMISTRY
AND DISCHARGE
ANC
Calcium
Nitrate
Sulphate
MIXING
MODEL: 2
COMPONENTS
• One Conservative
Tracer
• Mass Balance
Equations for Water
and Tracer
δ18O tracer
NEW WATER AND OLD WATER
Old Water = 64%
New Water
Old Water
30
3
3
-1
Q (10 m day )
40
Not Teflon basins!
20
10
0
135
165
195
225
255
Calendar Day (1996)
285
MIXING
MODEL: 3
COMPONENTS
(Using Specific
Discharge)
• Two Conservative
Tracers
• Mass Balance
Equations for Water
and Tracers
Simultaneous Equations
Q1 + Q2 + Q3 = Qt
C11Q1 + C21Q2 + C31Q3 = Ct1Qt
C12Q1 + C22Q2 + C32Q3 = Ct2Qt
Solutions
(Ct1 − C31 )(C22 − C32 ) − (C21 − C31 )(Ct2 − C32 )
Q1 = 1
Qt
(C1 − C31 )(C22 − C32 ) − (C21 − C31 )(C12 − C32 )
Ct1 − C31
C11 − C31
Q2 = 1
Qt − 1
Q1
C2 − C31
C2 − C31
Q3 = Qt − Q1 − Q2
Q - Discharge
C - Tracer Concentration
Subscripts - # Components
Superscripts - # Tracers
END-MEMBER MIXING
ANALYSIS
• EMMA used for null hypothesis test to
reject end-members that are not
significantly contributing to the targeted
stream in terms of water quantity;
• Uses more tracers than components;
• Decides number of end-members;
• Quantitatively select end-members;
• Quantitatively evaluate results of EMMA.
BIVARIATE PLOT
60
Stream Flow
Index Snowpit
Snowmelt
Talus EN1-L
Talus EN1-M
Talus EN1-U
Talus EN2-L
Talus EN2-U
Talus EN4-V
Talus EN4-L
Talus EN4-U
Soil Water
Base Flow
-1
Si (µmol L )
50
40
30
20
10
0
-24
-20
-16
18
δ O(‰)
-12
-8
7 tracers
PCA PROJECTIONS
Stream Flow
Snowpit
Snowmelt
Talus EN1-L
Talus EN1-M
Talus EN1-U
Talus EN2-L
Talus EN2-U
5
U2
3
1
Talus EN4-V
Talus EN4-L
Talus EN4-U
Base Flow
Soil Water
-1
-3
-8
-3
2
7
12
U1
First 2 eigenvalues are 92% and so 3 end-members appear to be correct!
FLOWPATHS: EMMA
30
Surface Flow
Talus Flow
Baseflow
3
3
-1
Q (10 m day )
40
20
10
0
135
165
195
225
255
Calendar Day (1996)
285
Liu et al, 04, WRR
EMMA VALIDATION: TRACER PREDICTION
100
120
80
100
ANC
-1
R = 0.97
60
2
40
-1
2+
2
80
60
Prediction ( mol L for Si and eq L for others)
Ca
R = 0.64
40
20
20
20
40
60
80
100
20
30
90
25
70
40
SO4
60
80
100
120
2-
2
20
R = 0.88
Na
15
+
50
2
R = 0.88
10
30
5
10
5
10
15
20
25
10
30
50
30
50
70
90
-14
40
Si
-15
δ O
30
R = 0.85
-16
R = 0.81
18
2
20
-17
10
-18
0
-19
0
10
20
30
40
50
2
-19
-18
Observation (units same as in y axis)
-17
-16
-15
-14
TEFLON MYTH DEBUNKED
Shallow groundwater system
• Almost 50% of flow on the rising limb is
“old” groundwater: baseflow and talus
• Up to 80% of water on the recession limb
is groundwater
• Most of “new” water from snow melt
infiltrates into the subsurface
LEADVILLE
Sampling sites: water isotopes, solutes, metals
Complex
Geology
METEORIC WATER LINE
-110
-115
Marion
LMWL
18
δ D = 8.4δ O + 15.8
-120
δ D (% o )
-125
-130
-135
-140
Groundwater
Mine Water
-145
Spring Water
Surface Water
LMWL
-150
-155
-20
-19
-18
-17
-16
18
δ O (% o)
-15
-14
-13
-12
δ18O VALUES
RAIN
SNOW
EMET
INF-1
BMW3
CT
ELKHORN
MAB
NW5-C
NW5-D
OG1TMW-1
WCC PZ1
WO3
YT
YT-BH
CG-03
CG-04
EG-04
MARION
PWCW
EFS-1
SDDS
SDDS-2
SPR-20
SPR-23
SPR-23 (200)
-25
Recharge is
primarily snowmelt
-20
-15
-10
-5
0
TRITIUM VALUES
RAIN
SNOW
EMET
INF-1
BMW3
CT
ELKHORN
MAB
NW5-C
NW5-D
OG1TMW-1
WCCPZ1
WO3
YT
YT-BH
CG-03
CG-04
EG-04
MARION
PWCW
EFS-1
SDDS
SDDS-2
SPR-20
SPR-23
SPR-23 (200)
Recharge age
ranges over
several decades
0
5
10
15
20
25
PCA Projections
6
INF-1 (9 TRACERS)
INF-1
LDT36+77
LDT75+05
LMDT1
BBW5
BMW3
BMW5
NW5C
OG1TMW1
WCCPZ1
CT
ELKHORN
MAB
SPR23
EFS1
EGSPRSSW
LEGH01
SDDS2
CG03BF
EG04
MARION
PWINF
PWOF
SHG07A
Alluvial
groundwater
4
2
U2
0
Deep
Groundwater
-2
Tunnel
-4
-6
-8
-10
-20
-10
0
U1
10
20
LDT25+15
LDT46+66
LDT96+44
LDTPD
BBW10
BMW4
BMW8
NW5D
WO3
WMW1
YTBH(PD)
EMET
SPR20
SPR23(200)
EGSPRRES
LEG04
SDDS
SHGEMSP
CG04BF
EGBER
PWCW
PWINFRAW
PWRES
WRIGHT
Groundwater more important
than previously thought
δ18O IN SNOW AND
STREAM FLOW
-5
50
-1
Snowmelt
Soil Water
30
(b) Martinelli
2
-15
18
O (‰)
-10
40
Q (10 m day )
Stream Flow
3
(a) Martinelli
20
10
-20
0
125
-25
100
150
200
250
300
155
185
215
Calendar Day (1996)
245
275
Fractionation in
Percolating Meltwater
Snow surface
δ18Ο = −20‰
Ground
δ18Ο = −22‰
Difference between maximum
18O values and
Minimum 18O values about 4 ‰
VARIATION OF δ18O
IN SNOWMELT
-16
-18
18
δ O (‰)
Original
Date-Stretched by Monte Carlo
-20
-22
Snowmelt (mm)
150
100
• δ18O gets enriched by 4%o in
snowmelt from beginning to the
end of snowmelt at a lysimeter;
• Snowmelt regime controls
temporal variation of δ18O in
snowmelt due to isotopic
fractionation b/w snow and ice;
• Given f is total fraction of snow
that have melted in a snowpack,
δ18O values are highly correlated
with f (R2 = 0.9, n = 15, p <
0.001);
• Snowmelt regime is different at
a point from a real catchment;
• So, we developed a Monte
Carlo procedure to stretch the
dates of δ18O in snowmelt
0
measured at a point to a
100 125 150 175 200 225 250 275 300 catchment scale using the
streamflow δ18O values.
Calendar Day (1996)
50