Assessing distributed mountain-block recharge in

semiarid environments

Huade Guan and John L. Wilson

GSA Annual Meeting Nov. 10, 2004

What is distributed MBR?

FS

DS

FR

DR

MASTER FAULT

FAULT

OBLIQUEFAULT

Surface Fault Trace

FAULT

Recharge that occurs on hill slopes in the mountain block

Precip

itation

Bedrock

Soil Soil water

Distributed MBR depends on

across the soil-bedrock interface

percolation

Total MBR = distributed MBR + focused MBR

Focused MBR occurs near and in stream

channels and rivulets

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)

The results have shown that major controls are net infiltration & bedrock permeability

slope, soil and bedrock topography are not important.

0

100

200

300

400

0.001 0.010 0.100 1.000 10.000

Net infiltration rate (mm/day)

Pe

rco

lati

on

(m

m/y

r)

bedrock k=1.0e-15 m 2̂

0

100

200

300

400

0.001 0.010 0.100 1.000 10.000

Net infiltration rate (mm/day)

Pe

rco

lati

on

(m

m/y

r)

bedrock k=1.0e-15 m 2̂

0

50

100

150

200

1.0E-18 1.0E-17 1.0E-16 1.0E-15 1.0E-14

bedrock permeability (m2)

Per

cola

tio

n (

mm

/yr)

infil.=0.5 mm/day

infil.=0.05 mm/day

0

50

100

150

200

1.0E-18 1.0E-17 1.0E-16 1.0E-15 1.0E-14

bedrock permeability (m2)

Per

cola

tio

n (

mm

/yr)

infil.=0.5 mm/day

infil.=0.05 mm/day

Granit

e FracturedG

ranite

Slope = 0.3 Depression index = 0.1 Soil = sandy loamSlope = 0.3 Depression index = 0.1 Soil = sandy loam

Two primary controls for percolation

• 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

What controls percolation to the bedrock?

Granite

Tuff

Granite

Tuff

Soil

Soil

Vegetation control S N

Annual P=565mmVegetation cover=5%

4%

4%

31%

17%

Aspect effect

6%

7%

43%

22%

Annual P=565mmVegetation cover=50%

S N

Percolation: in % of Precip

Aspect effect

Soi

l and

bed

rock

ef

fect

s

3%

1%

23%

6%

2%

0.3%

16%

1.8%

Slope aspects, vegetation cover, soil thickness for given bedrocks (transient, HYDRUS)

More controls for percolation

• 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

What controls percolation to the bedrock?

Study areas

1. Jemez Mountains2. Southern part of

Sangre de Cristo Mountains

1 2

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.

• Find percolation as a function of PET/PWhere 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

Approaches for distributed MBR

• 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

Some approximations for a hillslope in the mountains:

Percolation=f(PET/P) HYDRUS sim.

Bedrock=tuffTuff slope with 30 cm soil (silt) cover

0

50

100

150

200

2.621.971.310.92

PET/P

Per

cola

tio

n (

mm

/yr)

midslope 0.1

midslope 0.2

topslope 0.1

topslope 0.2

Slope =0.1 (not to scale)

Slope =0.2

Top-slope

Mid-slope

Percolation=f(PET/P) HYDRUS sim.

Bedrock=tuff Bedrock=graniteGranite slope with 30 cm soil (silt) cover

0

50

100

150

200

2.621.971.310.92

PET/P

Per

cola

tio

n (

mm

/yr)

midslope 0.1

midslope 0.2

topslope 0.1

topslope 0.2

Tuff slope with 30 cm soil (silt) cover

0

50

100

150

200

2.621.971.310.92

PET/P

Per

cola

tio

n (

mm

/yr)

midslope 0.1

midslope 0.2

topslope 0.1

topslope 0.2

0.1 slope

Tuff slope with 30-cm silt cover

y = 56.431x2 - 294.93x + 392.96

R2 = 0.9982

0

50

100

150

200

0.80 1.30 1.80 2.30 2.80

PET/P

Per

cola

tio

n (

mm

/yr)

Granite slope with 30-cm silt cover

y = 27.896x-8.5939

R2 = 0.9966

0

25

50

75

100

0.80 1.00 1.20 1.40 1.60 1.80 2.00 2.20

PET/P

Per

cola

tio

n (

mm

/yr)

Percolation=f(PET/P) HYDRUS sim.

Bedrock=tuff Bedrock=graniteGranite slope with 30 cm soil (silt) cover

0

50

100

150

200

2.621.971.310.92

PET/P

Per

cola

tio

n (

mm

/yr)

midslope 0.1

midslope 0.2

topslope 0.1

topslope 0.2

Tuff slope with 30 cm soil (silt) cover

0

50

100

150

200

2.621.971.310.92

PET/P

Per

cola

tio

n (

mm

/yr)

midslope 0.1

midslope 0.2

topslope 0.1

topslope 0.2

Percolation = f1(PET/P) Percolation = f2(PET/P)

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

)cos(43210 bZbYbXbbP and de-trended kriging

Spatial trend Elevation Slope aspect and prevailing wind

Sum of 12 monthly precipitation

PET mapping: Hargreaves 1985 + SEP4HillET

minmax)( TTbTaRPET meana

Ra: daily extraterrestrial solar radiation in equivalent depth of waterRa is dependent of the slope steepness and aspect, solved using SEP4HillET model

Slope aspect & steepness

Seasonal & altitudinal effects

M1

M4

M2

M3

M5

M6

M12

M9

M11

M10

M8

M7

Ratio of Ra on sloped surface to that on flat surface (from SEP4HillET)

N S N N S NWin

ter S

um

mer

Temperature mappingTopographic corrected geostatistical interpolations of temperature

Daily maximum temperature Daily minimum temperature

Regression (Tmax~Z)Regression (Tmin~Z): M4, 5, 6, 7, 8, 9Kriging Tmin:M1, 2, 3, 10, 11, 12

Maps of PET

Jemez M

ou

ntain

s

San

gre d

e Cristo

Mo

un

tains

Maps of potential distributed MBRat hypothetical northern NM mountains

Jemez Mountains Sangre de Cristo Mountains

Min: 0 Max: 193Mean: 47 Median: 42

Min: 0 Max: 113Mean: 16 Median: 0.44

Unit: mm/yr

ConclusionMtns. Previous studies This study

(Total MBR) (Max. rate of distributed MBR)

Sangre’s 50-100 mm/yr 16 mm/yr

Jemez/ 47 mm/yrSan Juan 200 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！