Submitted to: Encyclopedia of Water Science
Publication Type: Book / Chapter
Publication Acceptance Date: October 1, 2001
Publication Date: July 28, 2003
Citation: JAYNES, D.B. SOIL WATER HYSTERESIS. ENCYCLOPEDIA OF WATER SCIENCE. 2003. P.882-884. Technical Abstract: Since at least the early work of Haines, it has been recognized that volumetric soil water content, W, 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. The non-uniqueness or hysteresis in W(h) and K(h) appears to be an ubiquitous phenomenon in porous materials including soils 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 W instead of h, hysteresis either disappears or is so slight as to be masked by the error of the measurements. By expressing K as a function of W instead of h, it can be treated as a non-hysteretic function. Thus, this chapter focuses on the hysteretic nature of W(h), which for brevity is termed simply hysteresis, and briefly describes the effect hysteresis has on infiltration and drainage, evaporation, water table response, and solute movement in soil.