ABSTRACT
Since at least the early work of Haines,[1] it has been recognized that volumetric soil water content, y, and hydraulic conductivity, K, are not singular functions of soil water pressure head, h, but rather exhibit considerable variation depending on the wetting and drying history of the soil.[2,3] The non-uniqueness or hysteresis in y(h) and K(h) appears to be an ubiquitous phenomenon in porous materials and the magnitude of the effect is intimately related to the pore distribution of the material. However, numerous studies have shown that when K is expressed as a function of y instead of h, hysteresis either disappears[4-8] or is so slight as to be masked by the error of the measurements. By expressing K as a function of y instead of h, it can be treated as a non-hysteretic function. Thus, the focus here is on the hysteretic nature of y(h), which for brevity will be termed simply hysteresis.
