Download Determination of the Tangential Model Soil Water Retention Curves

Determination of the
Tangential Model Soil Water
Retention Curves for
Various Soil Types.
Magatt THIAM
Yuji KOHGO
Hirotaka SAITO
Tokyo University of Agriculture and Technology
Introduction
Tangential model
Motivated by the need to:
Assess its behavior with respect to different
soils; and specify its parameters.
Ultimately produce a pedotransfer function
able to generate parameters of this model.
What is Tangential Model
(TANMOD)
Fuzzy
Suction
Pendular
Kohgo, 2008
Suction
Insular
Suction s
Tangential Model
cf
F(Srf,sf)
M(Srm,sm)
cm
Kohgo, 2008
E(Sre,se)
Degree of saturation Sr
Objectives
• Determine Tangential model
parameters of various soil types
• Determine representative parameters
for this model for some soil types and
compare with currently available
retention models
Determine TANMOD
parameters for different soils
Using SWRC data from UNSODA (V2.0 )
•
•
•
•
•
•
139 sand
82 sandy loam
53 loamy sand
46 sandy clay loam
91 silt loam
27 silt clay loam
(Nemes et al, (1999) / U.S.D.A U.S Salinity Lab (2008))
Error in fitting the SWRC data
using TANMOD
Average RMSE
0.05
0.04
0.03
0.02
0.01
0.00
Sandy
loam
Sand
Sandy
clay
loam
Loamy Silt loam Silt clay
sand
loam
Distribution of the parameters
Better described by the location of the points
E, M and F (Example of SAND)
Parameters distribution (sm)
Frequency
40
SAND ONLY
30
20
10
0
sm values
Parameters distribution (sf)
Frequency
40
Sand only
30
20
10
0
Log(sf)
Determine representative
parameters for each soil
A parameter set means: se, Sre, Srm, Srf, cm, cf , sm, sf
Make 3 sets:
1. GM: Geometric mean of sm, sf
2. MD: Median value of
s m, s f
3. AR: Arithmetic mean of sm, sf
Get 3 mean curves (GM, MD and AR) for each soil
Making comparison between mean
curves and the data
• Between TANMOD mean curves (GM, MD and
AR) and the SWRCs data
• Between Van Guenuchten (VG) representative
SWRCs and the SWRCs data
Comparing TANMOD mean curves with
SAND SWRC data; and with VG
Average RMSE
0.40
0.30
0.20
0.10
0.00
GM
MD
AR
VG
Comparing TANMOD mean curves with
SILT LOAM SWRC data; and with VG
Average RMSE
0.200
0.100
0.000
GM
MD
AR
VG
Conclusion
Largest deviations between observed SWRCs
and the simulated curves occurred with sandy
soils.
Comparison of the Tangential model mean
curves, GM, MD and AR, with the SWRC data,
indicates that GM and MD performed better.
Further investigation is needed in order to identify
the relations between TANMOD parameters and
the soils’ basic properties.
Thank you for your attention
Parameter distributions
Frequency
Sre distribution for all the soils
300
250
200
150
100
50
0
0.966
0.981
0.996
Sre values
More
For all soils
Frequency
200
Srm
150
100
50
0
0.41 0.49 0.57 0.65 0.73 0.81 0.89 0.97
Srm values
For all soils
Frequency
200
srf
150
100
50
0
srf values
GM
MD
AR
GM
MD
AR
GM
MD
AR
se
Sre
0.5444
0.98735
1
0.5444
0.98735
1
0.5444
0.98735
1
sm
Sand
Srm
sf
Srf
cm
cf
284.661
2.88190 0.72983
0.05313 0.38953 0.00099
06
229.598
3.01538 0.72983
0.05313 0.38953 0.00099
61
947.935
3.47672 0.72983
0.05313 0.38953 0.00099
97
Sandy loam
se
Sre
sm
Srm
sf
Srf
cm
cf
0.5021
362.358
0.99486 12.03011 0.71434
0.32051 0.04107 0.00038
2
43
0.5021
368.095
0.99486 8.25148 0.71434
0.32051 0.04107 0.00038
2
21
0.5021
3301.95
0.99486 30.54636 0.71434
0.32051 0.04107 0.00038
2
187
Se
Sre
0.7895
0.99308
1
0.7895
0.99308
1
0.7895
0.99308
1
Loamy Sand
Sm
Srm
Sf
Srf
Cm
Cf
262.676
2.25453 0.78379
0.13777 0.13065 0.00116
26
200.000
3.30084 0.78379
0.13777 0.13065 0.00116
00
1101.40
4.04799 0.78379
0.13777 0.13065 0.00116
910
Can also compare TANMOD mean curves with the SWRCs
data and Van Guenuchten (VG) representative SWRCs
Table 1: Van Guenuchten parameters for the
different soil types used
Theta Theta
Alpha n
m
R
S
0.045 0.430 0.145 2.680 0.626
Sand
0
0
0
0
9
0.065 0.410 0.075 1.890 0.470
sandy
0
0
0
0
9
loam
0.057 0.410 0.124 2.280 0.561
loamy
0
0
0
0 RETC4
sand
Source: