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WATER RESOURCES RESEARCH, VOL. 41, W07030, doi:10.1029/2005WR003942, 2005

Estimation of groundwater consumption by phreatophytes using diurnal water table fluctuations: A saturated-unsaturated flow assessment

Steven P. Loheide II

Department of Geological and Environmental Sciences, Stanford University, Stanford, California, USA


James J. Butler Jr.

Kansas Geological Survey, University of Kansas, Lawrence, Kansas, USA


Steven M. Gorelick

Department of Geological and Environmental Sciences, Stanford University, Stanford, California, USA


Abstract

Groundwater consumption by phreatophytes is a difficult-to-measure but important component of the water budget in many arid and semiarid environments. Over the past 70 years the consumptive use of groundwater by phreatophytes has been estimated using a method that analyzes diurnal trends in hydrographs from wells that are screened across the water table (White, 1932). The reliability of estimates obtained with this approach has never been rigorously evaluated using saturated-unsaturated flow simulation. We present such an evaluation for common flow geometries and a range of hydraulic properties. Results indicate that the major source of error in the White method is the uncertainty in the estimate of specific yield. Evapotranspirative consumption of groundwater will often be significantly overpredicted with the White method if the effects of drainage time and the depth to the water table on specific yield are ignored. We utilize the concept of readily available specific yield as the basis for estimation of the specific yield value appropriate for use with the White method. Guidelines are defined for estimating readily available specific yield based on sediment texture. Use of these guidelines with the White method should enable the evapotranspirative consumption of groundwater to be more accurately quantified.

Received 3 January 2005; accepted 12 April 2005; published 27 July 2005.

Keywords: evapotranspiration; groundwater; hydraulic budget; phreatophytes; specific yield; water table functions.

Index Terms: 1818 Hydrology: Evapotranspiration; 1829 Hydrology: Groundwater hydrology; 1836 Hydrology: Hydrological cycles and budgets (1218, 1655); 1813 Hydrology: Eco-hydrology; 1875 Hydrology: Vadose zone.

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Citation: Loheide, S. P., II, J. J. Butler Jr., and S. M. Gorelick (2005), Estimation of groundwater consumption by phreatophytes using diurnal water table fluctuations: A saturated-unsaturated flow assessment, Water Resour. Res., 41, W07030, doi:10.1029/2005WR003942.