Water retention curves (WRC) play an essential role in characterizing soil hydraulic behavior. Numerous mathematical functions have been explicitly developed for modeling the WRC, a very recent example being a cubic spline approach using virtual data points. This study presents use of WRC functions that transition smoothly between straight-line asymptotes. We call them flexible functions. Flexible functions successfully represented a variety of WRCs, including some of rather high complexity. A reduction of root-mean-square error was often found in comparing flexible functions to other commonly used WRC functions. Integrations of the Mualem procedure for calculating relative hydraulic conductivity result in analytical expressions when using flexible functions as the WRC model. Conductivity calculated with these expressions agrees well with the RETC solution. Flexible functions are capable of representing dry regime behavior as well.

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