Unconventional flow of water from dry to wet caused by hysteresis: A numerical experiment

We demonstrate with the help of a numerical simulation model for hysteretic water movement that for horizontal redistribution three types of flow can occur. Raats and Iran Duijn [1995] previously identified these types as a r eaction to a specific analysis by Philip [1991]. Depending on the initial c onditions in two parts of an infinitely long soil column, there can be no f low, conventional flow from the wet part to the dry part, or unconventional flow from the dry part to the wet part. When flow occurs, the cumulative w etting and cumulative drying both show the expected linear relationship wit h the square root of time. Hysteresis is described according to the modifie d dependent domain model of Mualem [1984]. We also indicate that Kool and P arker [1987], who used this model as well, presented a erroneous expression for the differential moisture capacity of the scanning drying curve.