Assessing distributed
mountain-block recharge in
semiarid environments
Huade Guan and John L. Wilson
GSA Annual Meeting
Nov. 10, 2004
What is distributed MBR?
Recharge that occurs
on hill slopes in the
mountain block
FS
DS
FR
DR
Precipitation
Surface Fault Trace
Total MBR =
distributed MBR
+ focused MBR
Soil
Focused MBR occurs
Bedrock
near and in stream
channels and rivulets
Distributed MBR
depends on
percolation
across the soilbedrock interface
What controls percolation to
the bedrock?
• Our first generic simulation study
looks at
– Net infiltration
= Infiltration – Evapotranspiration (ET)
– Bedrock permeability
– Soil type and thickness
– Slope steepness
– Bedrock topography
(HYDRUS steady-state simulations, ET was not modeled)
Two primary controls for percolation
The results have shown that
major controls are
net infiltration & bedrock permeability
slope, soil and bedrock topography are not important.
infil.=0.5 mm/day
Fractured
Granite
50
Percolation (mm/yr)
infil.=0.05 mm/day
150
100
400
Granite
Percolation (mm/yr)
200
0
1.0E-18
1.0E-17
1.0E-16
1.0E-15
1.0E-14
2
bedrock permeability (m )
Slope = 0.3
Depression index = 0.1
bedrock k=1.0e-15 m^2
300
200
100
0
0.001
0.010
0.100
1.000
Net infiltration rate (mm/day)
Soil = sandy loam
10.000
What controls percolation to
the bedrock?
• Our first generic simulation study, using model of
the soil and bedrock (HYDRUS) suggested major
controls by
– Net infiltration (infiltration – ET)
– Bedrock permeability
• But what is “net infiltration”?
• We then added ET modeling in the simulations
coupled with a surface energy partitioning
model (SEP4HillET)
– Considering effects of vegetation, slope steepness
and aspect on potential E and Potential T
More controls for percolation
Slope aspects, vegetation cover, soil thickness for given
bedrocks (transient, HYDRUS)
3%
Percolation: in % of Precip
0.3%
1%
16%
23%
Aspect effect
1.8%
S
6%
N
Annual P=565mm
Vegetation cover=50%
Granite
Soil and bedrock effects
2%
4%
6%
4%
7%
31%
43%
Soil
Granite
Tuff
Aspect effect
Soil
Tuff
17%
Vegetation control S
22%
N
Annual P=565mm
Vegetation cover=5%
What controls percolation to
the bedrock?
•
Our first generic simulation study suggested major controls by
– Net infiltration (infiltration – ET)
– Bedrock permeability
• Our second generic simulation study suggested:
–
–
–
–
Bedrock properties (not only saturated K)
Vegetation coverage
Slope aspect (steepness as well)
Soil thickness (types as well)
• Now lets look at two sites in northern New
Mexico
Study areas
1
2
1. Jemez Mountains
2. Southern part of
Sangre de Cristo
Mountains
Why study these two sites？
Basin oriented water balances suggest:
• Huntley (1979): total MBR ~200mm/yr =38% P in San
Juan Mtns (volcanic rocks),
and total MBR ~ 70mm/yr =14% P in Sangre de
Cristo (granite and well-cemented sedimentary rock)
• McAda and Masiolek (1988): total MBR 50~100
mm/yr in Sangre de Cristo
• That is a lot recharge! But it is uncertain.
Are these total MBR estimates reasonable?
• We'll test them by calculating the amount of distributed
MBR. It should be less than the total.
Approaches for distributed MBR
• Find percolation as a function of PET/P
Where PET is annul potential ET
P is annual precipitation
• Then, estimate PET and P maps for the
study area
• From these maps and Percolation-PET/P functions estimate distributed
MBR
Some approximations
for a hillslope in the mountains:
• LANL 1994 water-year time series data set,
ponderosa site
• Macropore soil of uniform thickness (30 cm)
• Uniform vegetation coverage
• Uniform bedrock permeability for tuff (10-14
m2), and for fractured granite (10-14m2)
• Only infiltration-excess runoff
Percolation=f(PET/P)
Bedrock=tuff
HYDRUS sim.
Mid-slope
Tuff slope with 30 cm soil (silt) cover
Percolation (mm/yr)
200
midslope 0.1
Top-slope
midslope 0.2
topslope 0.1
150
topslope 0.2
100
Slope =0.2
50
0
0.92
1.31
1.97
2.62
PET/P
Slope =0.1 (not to scale)
Percolation=f(PET/P)
Bedrock=granite
Bedrock=tuff
Tuff slope with 30 cm soil (silt) cover
Granite slope with 30 cm soil (silt) cover
200
midslope 0.1
midslope 0.1
midslope 0.2
topslope 0.1
150
topslope 0.2
100
50
0
Percolation (mm/yr)
Percolation (mm/yr)
200
HYDRUS sim.
midslope 0.2
150
topslope 0.1
topslope 0.2
100
50
0
0.92
1.31
1.97
PET/P
2.62
0.92
1.31
1.97
2.62
PET/P
0.1 slope
Percolation=f(PET/P)
Bedrock=granite
Bedrock=tuff
Tuff slope with 30 cm soil (silt) cover
200
HYDRUS sim.
Granite slope with 30 cm soil (silt) cover
200
midslope 0.1
midslope 0.1
Percolation (mm/yr)
Percolation (mm/yr)
midslope 0.2
topslope 0.1
150
topslope 0.2
100
50
midslope 0.2
150
topslope 0.1
topslope 0.2
100
50
0
0
0.92
1.31
1.97
2.62
0.92
1.31
PET/P
Granite slope with 30-cm silt cover
150
2
y = 56.431x - 294.93x + 392.96
2
R = 0.9982
50
Percolation = f2(PET/P)
75
y = 27.896x -8.5939
50
R2 = 0.9966
25
0
0
0.80
100
Percolation (mm/yr)
Percolation (mm/yr)
Percolation = f1(PET/P)
100
2.62
PET/P
Tuff slope with 30-cm silt cover
200
1.97
1.30
1.80
PET/P
2.30
2.80
0.80
1.00
1.20
1.40
1.60
PET/P
1.80
2.00
2.20
How is PET/P obtained ?
• Next, we need spatial distributed
annual precipitation (P)
– Estimated by a geostatistic model
ASOADeK
• And spatial distributed annual PET
– Estimated by Hargreaves 1985 and
SEP4HillET
Precipitation mapping: ASOADeK
P  b0  b1 X  b2Y  b3 Z  b4 cos(   ) and de-trended kriging
Spatial trend Elevation Slope aspect and prevailing wind
Sum of 12 monthly precipitation
PET mapping:
Hargreaves 1985 + SEP4HillET
PET  aRa (Tmean  b) Tmax  Tmin
Slope aspect
& steepness
Seasonal &
altitudinal effects
Ra: daily extraterrestrial solar radiation in equivalent
depth of water
Ra is dependent of the slope steepness and aspect,
solved using SEP4HillET model
Ratio of Ra on sloped surface to
that on flat surface (from SEP4HillET)
N
S
N
N
S
Winter
Summer
M1
M12
M2
M11
M3
M10
M4
M9
M5
M8
M6
M7
N
Temperature mapping
Topographic corrected geostatistical interpolations of temperature
Daily maximum temperature
Regression (Tmax~Z)
Daily minimum temperature
Regression (Tmin~Z):
M4, 5, 6, 7, 8, 9
Kriging Tmin:
M1, 2, 3, 10, 11, 12
Maps of PET
Sangre de Cristo Mountains
Jemez Mountains
Maps of potential distributed MBR
at hypothetical northern NM mountains
Jemez Mountains
Min: 0
Mean: 47
Sangre de Cristo Mountains
Max: 193
Median: 42
Min: 0
Mean: 16
Unit: mm/yr
Max: 113
Median: 0.44
Conclusion
Mtns.
Previous studies
(Total MBR)
This study
(Max. rate of distributed MBR)
Sangre’s 50-100 mm/yr
16 mm/yr
Jemez/
San Juan 200 mm/yr
47 mm/yr
Distributed MBR << Total MBR
Focused MBR, in stream channels and rivulets appears to
be the most important component of MBR for these two
mountain regions and both rock types.
This is still a work in progress, and didn't use all spatial information on soil
and vegetative cover, etc.
ain
Thank you！