Field and laboratory experiments for parameterizing soil variables

at complex tarrain

Tae Hee Hwang, Seongwon Eum, and Dowon Lee

Graduate School of Environmental Studies

Seoul National University

Seoul 151-742, Korea

Some parameters of RHESSys are greatly variable at complex terrain.

Can we estimate the parameters from easily measurable topological indices (slope, elevation, aspect, etc.)

Introduction

Parameters for vertical soil moisture fluxes in RHESSys

Ksat_0 : Saturated hydraulic conductivity at surface

Porosity_0 : porosity at soil surface

M_z : conductivity with actual soil depth

Porosity_decay : porosity scaling parameter with depth

Introduction

Study Area

Gwangneung Experimental Forest, Gyonggi-do, Korea

Seoul

Study area

Vegetation type :

deciduous broadleaf (Quercus serrata, Carpinus laxiflora community)

Elevation : 270 ~ 490 m

Avg. slope : 19.0 °

Catchment area : 22 ha

Forest age : 80 years

Sampling points

Field measurements

• Soil type

• Effective soil depth

• Soil color

• Slope

• Vegetation type

• Aspect

• Bedrock

Soil type, soil depth, soil color

Laboratory measurements• Hydraulic conductivity (L/T)

• Hydraulic conductivity decay rate with depth (1/L)

• Porosity (dimensionless)

• Porosity decay rate with depth (1/L)

• Soil texture

• Bulk density (M/L3)

Saturated hydraulic conductivity (Ksat)

time

Macroporosity (Φm)(pF 2.7)

pF meter DIK-3340

Daiki Co. Ltd.

Results

0

0.02

0.04

0.06

0.08

0.1

0.12

R-

A

R-

B

R-

C

L-A

1

L-A

2

L-B

1

L-B

2

L-B

3

L-C

1

L-C

2

L-C

3

sampling sites

Ksa

t (c

m/s

ec)

A horizonsB horizons

0.20

0.25

0.30

0.35

0.40

0.45

0.50

R-

A

R-

B

R-

C

L-A

1

L-A

2

L-B

1

L-B

2

L-B

3

L-C

1

L-C

2

L-C

3

sampling s itesp

oro

sity

(d

imen

sionl

ess)

A horizons

B horizons

Ksat Φm

R, L: slope,

A: Toe, B: middle slope, C: upper slope

ResultsKsat decay rate with depth

-1

-0.5

0

0.5

1

R-A

R-B

R-C

L-A

1

L-A

2

L-B

1

L-B

2

L-B

3

L-C

1

L-C

2

L-C

3

sampling sites

poro

sity

dec

ay r

ate

(1/m

)

-0.5

0

0.5

1

1.5

R-A

R-B

R-C

L-A

1

L-A

2

L-B

1

L-B

2

L-B

3

L-C

1

L-C

2

L-C

3

sampling sites

poro

sity

dec

ay r

ate

(1/m

)

Φm decay rate with depth

R, L: slope,

A: Toe, B: midle slope, C: upper slope

Results

Bulk density (Db)

0

0.5

1

1.5

R-A

R-B

R-C

L-A

1

L-A

2

L-B

1

L-B

2

L-B

3

L-C

1

L-C

2

L-C

3

sampling sites

bul

k den

sity

(g/m

l)

A HorizonsB Horizons

Correlation AnalysisΦm vs. Ksat

y = - 0.3983x + 0.1725R2 = 0.7519

0

0.02

0.04

0.06

0.08

0.1

0.12

0.0 0.1 0.2 0.3 0.4 0.5

porosity

Ksa

t (c

m/s

ec)

0

0.02

0.04

0.06

0.08

0.1

0.12

0.0 0.1 0.2 0.3 0.4 0.5

porosity

Ksa

t (c

m/s

ec)

A Horizons B Horizons

Correlation Analysis with Topological Index (Slope)

Slope vs. Ksat

0

0.02

0.04

0.06

0.08

0.1

0.12

0 5 10 15 20 25

slope (degree)

Ksa

t (c

m/s

ec)

0

0.02

0.04

0.06

0.08

0.1

0.12

0 5 10 15 20 25

slope (degree)

Ksa

t (c

m/s

ec)

A Horizons B Horizons

Correlation Analysis with Topological Index (Slope)

Slope vs. Φm

A Horizons B Horizons

y = 0.0057x + 0.2548

R2 = 0.5368

0.000

0.050

0.100

0.150

0.200

0.250

0.300

0.350

0.400

0.450

0 5 10 15 20 25

slope (degree)

Po

rosi

ty

0.000

0.050

0.100

0.150

0.200

0.250

0.300

0.350

0.400

0.450

0 5 10 15 20 25

slope (degree)

Po

rosi

ty

Correlation Analysis with Topological Index (Slope)

Slope vs. Φm decay rate Slope vs. Ksat decay rate

0

0.2

0.4

0.6

0.8

1

1.2

0 5 10 15 20 25

slope (degrees)

Ksa

t d

ecay

rat

e (1

/m)

0

0.1

0.2

0.3

0.4

0.5

0.6

0 5 10 15 20 25

slope (degrees)

po

rosi

ty d

ecay

rat

e (1

/m)

Correlation Analysis with Topological Index (Elevation)

Elevation vs. Ksat Elevation vs. Φm

0

0.02

0.04

0.06

0.08

0.1

0.12

300 350 400 450

slope (degree)

Ksa

t (c

m/s

ec)

Elevation vs. Porosity (A)

0.000

0.050

0.100

0.150

0.200

0.250

0.300

0.350

0.400

0.450

300 350 400 450

slope (degree)

Ksa

t (c

m/s

ec)

Correlation Analysis with Topological Index (Elevation)

Elevation vs. Φm decay rate Elevation vs. Ksat decay rate

0

0.2

0.4

0.6

0.8

1

1.2

0 100 200 300 400 500

Elevation (m)

Ksa

t d

ecay

rat

e (1

/m)

0

0.1

0.2

0.3

0.4

0.5

0.6

0 100 200 300 400 500

Elevation (m)

Ksa

t d

ecay

rat

e (1

/m)

Correlation Analysis with Bulk Density

Db vs. Ksat Db vs. Φm

0

0.2

0.4

0.6

0.8

1

1.2

0.000 0.100 0.200 0.300 0.400 0.500

porosity

den

sity

(g/m

l)

0

0.2

0.4

0.6

0.8

1

1.2

0 0.02 0.04 0.06 0.08 0.1 0.12

Ksat (cm/sec)

den

sity

(g

/ml)

Discussion

• Correlation bet. Φm and Ksat : Kozency-Carman Eq. (Giménez et al. 1997, Comegna et al. 2000, Gloaguen et al. 2001, Jarvis et al. 2002 )

Ksat α Φmμ

y = - 0.2662x - 0.8734R2 = 0.6773

- 0.8

- 0.7

- 0.6

- 0.5

- 0.4

- 0.3

- 0.2

- 0.1

0

- 2 - 1.5 - 1 - 0.5

log(Ksat)

log(p

oro

sity

)

Correlation appears only in A

horizons

μ = -0.2662

Discussion

• Correlation bet. slope and Φm

• Correlation bet. slope and Ksat only in A horizons (Lee et al. 1999)

Slope vs. Ksat (A)

0

0.02

0.04

0.06

0.08

0.1

0.12

0 5 10 15 20 25

slope (degree)

Ksa

t (c

m/s

ec)

Slope vs. Porosity (A)

y = 0.0057x + 0.2548R2 = 0.5368

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0 5 10 15 20 25

slope (degree)

Poro

sity

Discussion

• Correlation bet. slope and Φm decay rate

• Correlation bet. slope and Ksat decay rate

Slope vs. Ksat decay rate

0

0.2

0.4

0.6

0.8

1

1.2

0 5 10 15 20 25

slope (degrees)

Ksa

t dec

ay r

ate

(1/m

)

Slope vs. Porosity decay rate

0

0.1

0.2

0.3

0.4

0.5

0.6

0 5 10 15 20 25

slope (degrees)

po

rosi

ty d

ecay

rat

e (1

/m)

Further study needs

Conclusions

• Some soil variables (e.g., Ksat, Φm, Ksat decay rate, Φm decay r

ate) may be estimated from topological indices (ex. slope).

• Topological index can be considered in patch partitioning

References

Comegna, V., P. Damiani and A. Sommella. 2000. Scaling the saturated hydraulic conductivity of a vertic ustorthens soil under conventional and minimum tillage. Soil and tillage research 54: 1-9.Gimenez, D., E. Perfect, W.J. Rawls, Ya. Pachepsky. 1997. Fractal models for predicting

soil hydraulic properties: a review. Engineering geology 48: 161-183.Gloaguen, F. , M. Chouteau, D. Marcotte, and R. Chapuis. 2001. Estimation of hydraulic conductivity of an unconfined aquifer using cokriging of GPR and hydrostratigraphic data. Journal of applied geophysics 47: 135-152.Jarvis, N.J., L. Zavattaro, K. Rajkai, W. D. Reynolds, P. -A. Olsen, M. McGechan, M. Mecke, B. Mohanty, P. B. Leeds-Harrison, and D. Jacques. 2002. Indirect estimation of near-saturated hydraulic conductivity from readily available soil information. Geoderma 108: 1-17.