HR: 1330h
AN: H32A-0533    [PDF]
TI: Comparison of Aquifer Recharge Estimates Based on Measured and Estimated Hydraulic Properties
AU: * Perkins, K S
EM: kperkins@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., MS-421, Menlo Park, CA 94025 United States
AB: Because unsaturated hydraulic properties, which are used to estimate recharge, are difficult and time consuming to measure accurately, models that estimate these properties indirectly are often used. Using data from six locations in southern New Jersey that appear to have steady-state flow conditions, five hydraulic property prediction and parameterization techniques were evaluated for recharge estimation. The unsaturated zone at this site, as in many coastal plain regions, is mainly sand to sandy loam in texture, which is considered a highly favorable case for soil hydraulic property estimation. Annual recharge has been estimated for several southern New Jersey watersheds by water budget methods and ranges from 33 to 49 cm/yr. Using these estimates as a gauge of reasonable values for steady flow, several indirect methods were compared to determine which are appropriate for recharge estimation in the coastal plain environment. The methods used in this study were: (1) simple power-law and hand-drawn curve fits to measured unsaturated hydraulic conductivity, (2) measured water retention and measured unsaturated hydraulic conductivity fit using the van Genuchten-Mualem model with fixed and optimized parameter values, (3) unsaturated hydraulic conductivity estimated from measured water retention with fixed and optimized parameter values, (4) estimation of water retention and hydraulic conductivity from bulk density and minimal textural information using the Rosetta pedotransfer function model, and (5) estimation of water retention and hydraulic conductivity using high resolution particle size distributions with the Arya-Paris and van Genuchten-Mualem models. Preliminary results show that while reasonable estimates can come from directly measured unsaturated hydraulic conductivity, the curve fitting method is critical because of the extreme non-linearity of the relationship between hydraulic conductivity and water content. Even a relatively good visual fit can lead to unreasonable recharge estimation values. A hand-drawn interpolation technique, and in some cases a simple power-law fit, yielded better results for these data than the van Genuchten-Mualem curve fit. In all cases, the Rosetta model lead to unreasonably high recharge estimates, primarily due to the over-prediction of saturated hydraulic conductivity. Water retention was predicted relatively well by the Rosetta Model. A combination of the Arya-Paris and van Genuchten-Mualem models also lead to over-prediction of recharge rates, and did not do as well as Rosetta in predicting water retention for this sandy material.
DE: 1829 Groundwater hydrology
DE: 1875 Unsaturated zone
SC: Hydrology [H]
MN: 2003 Fall Meeting