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Approaches for Estimating Soil Water Retention Curves at Various Bulk Densities With the Extended Van Genuchten Model
Author(s) -
Tian Zhengchao,
Gao Weida,
Kool Dilia,
Ren Tusheng,
Horton Robert,
Heitman Joshua L.
Publication year - 2018
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/2018wr022871
Subject(s) - soil water , mean squared error , soil science , soil texture , pedotransfer function , mathematics , bulk density , water retention , water content , soil gradation , root mean square , environmental science , hydrology (agriculture) , statistics , hydraulic conductivity , geotechnical engineering , geology , engineering , electrical engineering
Soil bulk density (ρ b ) variations influence soil hydraulic properties, such as the water retention curve (WRC), but they are usually ignored in soil water simulation models. We extend the van Genuchten WRC model parameters to account for ρ b variations using a series of empirical expressions. WRC measurements made on eight soils with various ρ b , and textures are used to calibrate these ρ b ‐related empirical equations. Accordingly, two approaches are developed to estimate WRCs of soils at various ρ b . Another eight soils with a wide range of ρ b and textures are used to evaluate the accuracy of the new approaches. Approach 1 estimates WRCs for each soil at various ρ b using a WRC measurement made at a reference ρ b and the soil texture fractions. This approach gives reasonable WRC estimates for the eight validation soils, with an average root‐mean‐square error (RMSE) of 0.025 m 3 /m 3 and an average determination coefficient ( R 2 ) of 0.94. For Approach 2, a WRC measurement made at a reference ρ b and one additional water content‐matric potential value measured at a different ρ b value are used, which produces WRC estimates with an average RMSE of 0.017 m 3 /m 3 and an average R 2 of 0.97. The methodology used in Approach 2 is also applied to the Brooks and Corey WRC model to obtain accurate and precise WRC estimates. The proposed approaches have the potential to be incorporated into simulation models for estimating soil hydraulic properties that are affected by transient and variable ρ b .