000029642 001__ 29642
000029642 005__ 20160407123810.0
000029642 0248_ $$aoai:doc.rero.ch:20120821110304-YV$$ppostprint$$prero_explore$$particle$$zcdu34$$zthesis_urn$$zpreprint$$zreport$$zthesis$$zbook$$zjournal$$zcdu16$$zcdu556$$zcdu1$$zdissertation$$zunine
000029642 041__ $$aeng
000029642 080__ $$a556
000029642 100__ $$aCartwright, Nick$$uGriffith School of Engineering, Griffith University, Southport, Queensland, Australia
000029642 245__ $$9eng$$aBehavior of a shallow water table under periodic flow conditions
000029642 520__ $$9eng$$aA new laboratory data set on the behavior of a shallow water table in a sand column aquifer subject to simple harmonic periodic forcing at its base is presented and discussed. The data are analyzed using the dynamic effective porosity, which is defined as the ratio of the rate of change in total moisture to the rate of change in water table elevation; thus, a reduction in this parameter means that the extent of moisture exchange has been reduced relative to a given water table fluctuation. The data show a clear decrease in the dynamic effective porosity with increasing proximity of the water table to the sand surface, which is consistent with previous research under a steadily rising or falling shallow water table. The observed reduction in moisture exchange due to shallowness of the water table has implications for periodic flow scenarios such as the propagation of water table waves in coastal and beach groundwater systems. That is, as moisture exchange is reduced, less work is being done by the flow, and thus, energy dissipation rates for shallow water tables will be reduced relative to the case of a deeper water table. At present no account of the influence of water table shallowness has been included in theories describing water table wave dispersion. The present experiments, in conjunction with the dynamic effective porosity concept, provide a framework in which this gap in knowledge can be further investigated. Additional experiments were designed such that the free surface transgressed the sand surface for part of the oscillation period to investigate the influence of meniscus formation and deformation at the sand surface on periodic flow dynamics. The observed behavior is consistent with previous observations of steady infiltration above shallow water tables, namely, a rapid drop (rise) in pore pressure with the onset of meniscus formation (deformation). A simple “wetting and drying” model is derived, accounting for the variation in effective porosity caused by the free surface transgressing the sand surface, which is shown to accurately capture the observed behavior. A finite element solution of the Richards equation in which the transient upper boundary condition is easily mimicked by means of a surface element with special storage features also shows excellent agreement with the observed data.
000029642 700__ $$aNielsen, Peter$$uDivision of Civil Engineering, University of Queensland, Brisbane, Queensland, Australia
000029642 700__ $$aPerrochet, Pierre$$uCentre of Hydrogeology, University of Neuchâtel, Neuchâtel, Switzerland
000029642 773__ $$dAmerican Geophysical Union$$g2009/45/3/1-10$$tWater Resources Research
000029642 775__ $$gPublished Version$$ohttp://dx.doi.org/10.1029/2008WR007306
000029642 8564_ $$fCartwright_Nick-Behavior_of_a_shallow_water_table_20120821.pdf$$qapplication/pdf$$s830311$$uhttp://doc.rero.ch/record/29642/files/Cartwright_Nick-Behavior_of_a_shallow_water_table_20120821.pdf$$yorder:1$$zTexte intégral
000029642 918__ $$aFaculté des sciences$$bRue Emile-Argand 11, 2007 Neuchâtel
000029642 919__ $$aUniversité de Neuchâtel$$bNeuchâtel$$ddoc.support@rero.ch
000029642 980__ $$aPOSTPRINT$$bUNINE$$fART_JOURNAL
000029642 990__ $$a20120821110304-YV