This study estimated hydraulic parameters from field soil moisture data using a multi-scale parameterization method. For the HD plot site, the estimated parameters successfully simulated water content and were robust to different initial parameters. However, the results were not as accurate for the K plot site, possibly due to non-uniform flow and other uncertainties not accounted for. While the method showed promise, the study recommends evaluating parameter uncertainty when applying it to new sites.

1. Estimation of Hydraulic
Parameters with Multi-scale
Parameterization Method
Katsutoshi Seki (Toyo University)
Philippe Ackerer, François Lehmann
(University of Strasbourg, France)
Soil Moisture Workshop
Campus Innovation Center, Tokyo
29 November, 2014
This work was published in
Seki et al. (2015) Geoderma 247: 117-128.
http://dx.doi.org/10.1016/j.geoderma.2015.02.013

2. Study question
 Can we estimate hydraulic
parameters from soil moisture data
monitored in the field?
 It is useful if we can.
 It is difficult and there are small
numbers of studies (Vereecken et al.,
2008).

3. Ritter et al. (2003)

4. Outline of this study
 Hydraulic parameters were estimated
with:
◦ Field data (Seki et al., 2010)
Monitored soil water and rainfall intensity
at tropical rain forest in Indonesia
◦ Numerical simulation (Hayek et al. ,2008)
Adaptive multi-scale parameterization
method

5. Field site
 Tropical rain forest
 Borneo (Kalimantan) Island, Indonesia (Seki et al., 2010)
HD plot K plot
20 cm (Sand)
30 cm
(Sandy loam)
Moisture sensor
FDR probe
ECH2O, EC-10
10 cm
20 cm

6. Analysis
 One-dimensional finite elements
methods with Richards equation
 100 cm height
◦ 0.5 cm mesh for upper 50 cm
◦ 1 cm mesh for lower 50 cm
 Optimize hydraulic parameters
 Forward calculation: 75 days from
October 1, 2005
 Objective function: water content from 30
to 75 days

7. Initial and boundary
conditions
 Initial condition
Pressure head: -10000 cm
 Boundary condition
◦ Upper boundary
 Prescribed flux: Rainfall intensity and potential
evaporation 3.7 mm/day (Penman-Monteith
equation)
 Minimum pressure head -105 cm
◦ Lower boundary
 Zero pressure gradient ∂h/ ∂z = 0

8. Soil hydraulic model
 Brooks and Corey – Mualem model
 Initial parameters: Measured with
undisturbed core samples
 4 initial parameter sets estimated from
PTF (PedoTransfer Function) were
also used for initial parameters.

9. Multi-scale parameterization
method
(Hayek et al, 2008)
(1) Homogeneous (2) 2 zones
1st discontinuity
(3) 3 zones
2nd discontinuity

10. Calculation of refinement
indicator
to determine discontinuity depth
See Hayek et al. (2008) for definition
Sum of gradient of
objective function
to parameter

11. Modification to original algorithm
 Only soil moisture at one depth, upper
layer, was used for homogeneous
parameterization of HD plot, where
soil texture was different at 2 depths.
 At each step of parameterization,
refinement indicators of each
parameter (Ks, θs, θr, α, n, λ) was
used for determining the order of
parameters to be optimized.

12. Refinement indicator
Discontinuit
y depth
0
10
20
30
40
50
60
70
80
90
100
0 0.2 0.4 0.6 0.8 1 1.2
Depth(cm)
Refinement indicator
K
HD

13. Measured and simulated water change
HD plot
0
0.1
0.2
0.3
0.4
0.5
0.6
30 40 50 60 70
Watercontent
Time (days)
Upper layer (20cm Sand)
Lower layer (30cm Sandy loam)Measured
Simulated

14. Estimated and measured SWRC
(soil water retention curve)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
1 10 100 1000 10000
Waterconent
Matric suction (cm)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
1 10 100 1000 10000
Matric suction (cm)
HD upper layer HD lower layer
Robust for different initial parameters

15. Measured and simulated water change
K plot Upper layer (10cm)
Lower layer (20cm)
Discrepancy
0.2
0.25
0.3
0.35
30 40 50 60 70
Watercontent
Measured
Simulated
0.2
0.25
0.3
0.35
30 40 50 60 70
Watercontent

16. Estimated and measured
SWRC
0.0
0.1
0.2
0.3
0.4
1 10 100 1000 10000
Waterconent
Matric suction (cm)
0.0
0.1
0.2
0.3
0.4
1 10 100 1000 10000
Matric suction (cm)
K upper layer K lower layer
Not as robust as HD plot

17. Possible reasons for discrepancy
and uncertainty
 Non-uniform water flow due to water
repellency
 Absense of pressure head
measurement
 Effect of root uptake
 Effect of hysteresis in soil water
retention
 Effect of precision of soil water sensor

18. Summary
 Estimated hydraulic parameters can
simulate water contents in the field
condition in the HD plot. The result
was robust for different initial
parameters.
 The result was not very good at K plot.
 When applying this method to other
study area, uncertainty evaluation of
the estimated parameters is
recommended.