Unified solution for infiltration and drainage with hysteresis: Theory andfield test

Hysteresis has been found in both the hydraulic conductivity, K, us. pressu re head, psi, relationship, and the soil water content, theta, vs. psi rela tionship. This limits the application of a unified solution for infiltratio n and drainage. A Haines' Jump model of hysteresis is proposed and combined with the Broadbridge and White form of K(theta) and the diffusivity, D, re lationship, D(theta). This allows a unified analytical solution for infiltr ation and drainage, This solution accounts for hysteresis by allowing the i nverse macroscopic capillary length scale, or, to be hysteretic A method of a priori estimating the hysteretic nature of alpha is proposed and tested. The hysteretic change in alpha ran be estimated from other theta(psi) hyst eresis models and then used in combination with the Broadbridge and White h ydraulic functions. The predicted hysteresis in or was similar to that obta ined from inverse procedures. The unified solution was applied to field-mea sured soil water storage during infiltration and drainage. Neglecting hyste resis resulted in poor prediction of water storage during drainage based on hydraulic parameters estimated from infiltration. This was especially true fur drainage with high initial water content. Incorporating the proposed h ysteresis model resulted in prediction error less than measurement error. I n addition, a single unified inverse procedure for estimating hydraulic par ameters from combined infiltration and drainage measurements can now be dev eloped.