Water table waves in an unconfined aquifer: Experiments and modelling

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Title Water table waves in an unconfined aquifer: Experiments and modelling
Author Cartwright, Nicholas Brian; Nielsen, Peter; Dunn, Scott
Journal Name Water Resources Research
Year Published 2003
Place of publication United States
Publisher American Geophysical Union
Abstract Comprehensive measurements are presented of the piezometric head in an unconfined aquifer during steady, simple harmonic oscillations driven by a hydrostatic clear water reservoir through a vertical interface. The results are analyzed and used to test existing hydrostatic and nonhydrostatic, small-amplitude theories along with capillary fringe effects. As expected, the amplitude of the water table wave decays exponentially. However, the decay rates and phase lags indicate the influence of both vertical flow and capillary effects. The capillary effects are reconciled with observations of water table oscillations in a sand column with the same sand. The effects of vertical flows and the corresponding nonhydrostatic pressure are reasonably well described by small-amplitude theory for water table waves in finite depth aquifers. That includes the oscillation amplitudes being greater at the bottom than at the top and the phase lead of the bottom compared with the top. The main problems with respect to interpreting the measurements through existing theory relate to the complicated boundary condition at the interface between the driving head reservoir and the aquifer. That is, the small-amplitude, finite depth expansion solution, which matches a hydrostatic boundary condition between the bottom and the mean driving head level, is unrealistic with respect to the pressure variation above this level. Hence it cannot describe the finer details of the multiple mode behavior close to the driving head boundary. The mean water table height initially increases with distance from the forcing boundary but then decreases again, and its asymptotic value is considerably smaller than that previously predicted for finite depth aquifers without capillary effects. Just as the mean water table over-height is smaller than predicted by capillarity-free shallow aquifer models, so is the amplitude of the second harmonic. In fact, there is no indication of extra second harmonics (in addition to that contained in the driving head) being generated at the interface or in the interior.
Peer Reviewed Yes
Published Yes
Publisher URI http://www.agu.org/journals/wr/
Alternative URI http://dx.doi.org/10.1029/2003WR002185
Volume 39
Issue Number 12
Page from SBH 4 -1
Page to SBH 4 -12
ISSN 0043-1397
Date Accessioned 2006-06-27
Language en_AU
Faculty Faculty of Engineering and Information Technology
Subject PRE2009-Groundwater Hydrology
URI http://hdl.handle.net/10072/16712
Publication Type Journal Articles (Refereed Article)
Publication Type Code c1x

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