Assessing distributed mountain-block recharge in semiarid environments

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Assessing distributed mountain-block recharge in
semiarid environments
Huade Guan and John L. Wilson GSA Annual Meeting
Nov. 10, 2004
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What is distributed MBR?
Recharge that occurs on hill slopes in the
mountain block
Total MBR distributed MBR focused
MBR Focused MBR occurs near and in stream
channels and rivulets
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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)

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The results have shown that major controls are
net infiltration bedrock permeabilityslope,
soil and bedrock topography are not important.
Two primary controls for percolation
Slope 0.3 Depression index 0.1
Soil sandy loam
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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

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More controls for percolation
Slope aspects, vegetation cover, soil thickness
for given bedrocks (transient, HYDRUS)
Soil
Soil
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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

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Study areas
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2

1. Jemez Mountains
2. Southern part of Sangre de Cristo Mountains

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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 50100 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.

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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

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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

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Percolationf(PET/P) HYDRUS sim.
Bedrocktuff
Slope 0.2
Slope 0.1 (not to scale)
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Percolationf(PET/P) HYDRUS sim.
Bedrockgranite
Bedrocktuff
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Percolationf(PET/P) HYDRUS sim.
Bedrockgranite
Bedrocktuff
Percolation f1(PET/P)
Percolation f2(PET/P)
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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

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Precipitation mapping ASOADeK
and de-trended kriging
Sum of 12 monthly precipitation
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PET mapping Hargreaves 1985 SEP4HillET
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
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Ratio of Ra on sloped surface to that on flat
surface (from SEP4HillET)
N S N
N S N
Winter Summer
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Temperature mapping Topographic corrected
geostatistical interpolations of temperature
Daily maximum temperature
Daily minimum temperature
Regression (TminZ) M4, 5, 6, 7, 8, 9 Kriging
Tmin M1, 2, 3, 10, 11, 12
Regression (TmaxZ)
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Maps of PET
Jemez Mountains
Sangre de Cristo Mountains
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Maps of potential distributed MBRat hypothetical
northern NM mountains
Jemez Mountains
Sangre de Cristo Mountains
Min 0 Max 193 Mean 47 Median 42
Min 0 Max 113 Mean 16 Median 0.44
Unit mm/yr
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Conclusion
Mtns. Previous studies This study (Total
MBR) (Max. rate of distributed
MBR) Sangres 50-100 mm/yr 16
mm/yr Jemez/ 47 mm/yr San Juan 200
mm/yr Distributed MBR ltlt 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.
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ain
Thank you!