Estimation of hydraulic parameters with multi-scale parameterization method
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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.
Estimation of hydraulic parameters with multi-scale parameterization method
- 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.