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Parameter Estimation Analysis of the Evaporation Method for Determining Soil Hydraulic Properties
Author(s) -
Šimůnek Jiří,
Genuchten Martinus Th.,
Wendroth Ole
Publication year - 1998
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1998.03615995006200040007x
Subject(s) - soil water , extrapolation , soil science , hydraulic conductivity , pressure head , environmental science , richards equation , hydraulic head , evaporation , estimation theory , water potential , range (aeronautics) , water content , volume (thermodynamics) , mathematics , geotechnical engineering , geology , materials science , thermodynamics , algorithm , statistics , physics , composite material
Soil hydraulic properties are important parameters affecting water flow in variably saturated soils. We estimated the hydraulic properties from a laboratory evaporation experiment using both a parameter estimation method and the modified Wind method. The parameter estimation method combined a one‐dimensional numerical solution of the Richards equation with the Marquardt‐Levenberg optimization scheme. In our study we used both numerically generated data and data measured in the laboratory. Two experiments were carried out on 10‐cm‐high soil cores containing two different soils. Pressure heads inside the cores were measured with five tensiometers, while evaporative water loss from the top was determined by weighing the soil samples. The objective function for the parameter estimation analysis was defined in terms of the final total water volume in the core and pressure head readings by one or several tensiometers. An analysis of numerically generated data showed that the optimization method was most sensitive to the shape factor ( n ) and the saturated water content (θ s ) and least to the residual water content (θ r ). Pressure heads measured close to the soil surface were found to be more valuable for the parameter estimation technique than those measured at lower locations. The optimized hydraulic parameters corresponded closely with those obtained using Wind's analysis. All optimizations gave similar results for the soil hydraulic properties within the range of measured pressure heads (0 to −700cm). Extrapolation beyond this range involved a high level of uncertainty because of high correlation between parameters θ r and n .