SOIL-WATER HYSTERESIS AS A CAUSE OF DELAYED YIELD FROM UNCONFINED AQUIFERS

Hysteresis in the relation between soil water content and (negative) pressure head of the soil water produces a lag in the release of pore water from a rewetted soil when the pressure heads are lowered (made more negative). For an unconfined aquifer this means that the water table must drop some distance in response to pumping a well before pore water is fully released, if the water table prior to pumping had been rising. Since water tables around active wells usually have been rising before a pumping test is performed (to establish equilibrium), soil water hysteresis may well be a common cause of delayed yield from unconfined aquifers. This paper is not subject to U.S. copyright. Published in 1979 by the American Geophysical Union.