Swash-aquifer interaction in the vicinity of the water table exit point on a sandy beach

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Title Swash-aquifer interaction in the vicinity of the water table exit point on a sandy beach
Author Cartwright, Nicholas Brian; Baldock, Tom E.; Nielsen, Peter; Jeng, Dong-Sheng; Tao, Longbin
Journal Name Journal of Geophysical Research
Year Published 2006
Place of publication USA
Publisher American Geophysical Union
Abstract The coupling of sandy beach aquifers with the swash zone in the vicinity of the water table exit point is investigated through simultaneous measurements of the instantaneous shoreline (swash front) location, pore pressures and the water table exit point. The field observations reveal new insights into swash-aquifer coupling not previously gleaned from measurements of pore pressure only. In particular, for the case where the exit point is seaward of the observation point, the pore pressure response is correlated with the distance between the exit point and the shoreline in that when the distance is large the rate of pressure drop is fast and when the distance is small the rate decreases. The observations expose limitations in a simple model describing exit point dynamics which is based only on the force balance on a particle of water at the sand surface and neglects subsurface pressures. A new modified form of the model is shown to significantly improve the model-data comparison through a parameterization of the effects of capillarity into the aquifer storage coefficient. The model enables sufficiently accurate predictions of the exit point to determine when the swash uprush propagates over a saturated or a partially saturated sand surface, potentially an important factor in the morphological evolution of the beach face. Observations of the shoreward propagation of the swash-induced pore pressure waves ahead of the runup limit shows that the magnitude of the pressure fluctuation decays exponentially and that there is a linear increase in time lags, behavior similar to that of tidally induced water table waves. The location of the exit point and the intermittency of wave runup events is also shown to be significant in terms of the shore-normal energy distribution. Seaward of the mean exit point location, peak energies are small because of the saturated sand surface within the seepage face acting as a ''rigid lid'' and limiting pressure fluctuations. Landward of the mean exit point the peak energies grow before decreasing landward of the maximum shoreline position.
Peer Reviewed Yes
Published Yes
Publisher URI http://www.agu.org/journals/jgr/
Alternative URI http://dx.doi.org/10.1029/2005JC003149
Volume 111
Page from 1
Page to 13
ISSN 0148-0227
Date Accessioned 2007-02-02
Language en_AU
Faculty Faculty of Science, Environment, Engineering and Technology
Subject PRE2009-Physical Oceanography
URI http://hdl.handle.net/10072/14439
Publication Type Journal Articles (Refereed Article)
Publication Type Code c1

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