Groundwater Recharge in Semi-Arid Mountain Blocks:
San Gabriel Mountains Case Study
1
2
1
2
Jan M.H. Hendrickx , Todd Umstot , John L. Wilson and Daniel B. Stephens
1) New Mexico Tech, Socorro NM (hendrick@nmt.edu)
2) Daniel B. Stephens & Associates, Inc., Albuquerque NM (tumstot@dbstephens.com)
Model and Algorithm (cont.)
Purpose
Demonstrate a novel method for quantification of mountain front recharge combining the
Distributed Parameter Watershed Model (DPWM) with the Mapping Evapotranspiration
at high Resolution using Internalized Calibration (METRIC) algorithms.
Traditional Approach without METRIC:
Calculate TAW from soil map and vegetation map using estimated Field Capacity, Wilting Point, and
Rooting Depth.
Study Area
Study area is the San
Gabriel Mountains
located just North of
Los Angeles
Our overall approach is similar to other distributed hydrologic models for water balance calculations that
are based on the bucket model. Here we focus on the key variable for this study: total available water
(TAW) in each pixel. TAW is a permanent hydraulic property for each pixel. A large or small TAW will lead
to, respectively, a small or large ground water recharge rate.
LANDSAT
Vegetation
Soils
Novel Approach with METRIC:
No need for soil map and vegetation map. Run DPWM seven times with different TAW distributions and
determine at what TAW distribution the difference between 15 METRIC root zone soil moisture maps and
15 DPWM simulated root zone soil moisture map is the least.
Chaparral
Tehachapi Mtns.
Conifers
San Gabriel Mtns.
Desert scrub
Results
The smallest difference between METRIC observed and DPWM simulated root zone soil moisture
distributions is found at the TAW that has a maximum value of 200 mm. This means that the TAW values
over the San Gabriel Mountains vary from a minimum value of 15 mm to a maximum value of 200 mm.
These are reasonable values for a mountain block.
Model and Algorithm
2000000
Rain
Snow
Sublimation
1800000
0.15
Initial Simulation
Calibrated to METRIC and Stream Flow
1600000
Snowpack
DPWM is a distributed
hydrologic model that estimates
the daily water balance
components. Its critical soil
parameter for mountain front
recharge is the Total Available
Water (TAW) of each pixel.
Layer 2
Tr
an
sp
ira
tio
n
Snow melt
Mean Error (Obs- Sim)
Layer 1
Ev
ap
or
at
ion
Tr
an
sp
ira
tio
n
DPWM
Runoff
Transpiration
Run-on
Node 2
Node 1
Root
Evaporation
Drainage
Drainage
depth
depth
Node 3
0.05
0
0
200
400
600
800
1000
-0.05
-0.1
1200
Annual Net Infiltration (ac-ft/yr)
0.1
1400000
1200000
1000000
800000
600000
400000
-0.15
200000
-0.2
Maximum TAW (mm)
Drainage
Soil
depth
Node 4
Layer 3
0
Water Year (Oct -Sep)
Mean Error Between METRIC and DPWM
Soil Root Zone Saturations
Comparison of DPWM Simulations for the
San Gabriel Mountains, CA
Bedrock
Validation of METRIC TAW
Net infiltration
TAW Variability
s Explained by Soil
and Vegetation Map
METRIC
METRIC is an image-processing tool
for computing evapotranspiration
(ET) and root zone soil moisture
(SM) using the semi-empirical
equation SM = exp [(EF – 1)/0.42]
where EF is the evaporative fraction.
g
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Daniel B. Stephens
& Associates, Inc.
TAW randomly generated
0%
TAW from METRIC
60%
The use of METRIC soil moisture maps for the calibration
of DPWM holds much promise for improved mountain
block recharge predictions.
n
S
99%
Conclusion
e
D
B
&
A
TAW from Soil and
Vegetation Maps
Soil Moisture, 24 June 2005
Soil Moisture, 30 August 2006
Legend
Mean annual net infiltration (mm/yr)
<1 mm/yr
1 - 5 mm/yr
5 - 10 mm/yr
10 - 50 mm/yr
50 - 100 mm/yr
100 - 500 mm/yr
500 - 1,000 mm/yr
Annual recharge