Smith, A.J., and Townley, L.R. (1996), Modelling interaction between unconfined groundwater and surface water bodies in aquifers subjected to periodic forcing, American Geophysical Union Fall Meeting, Poster Paper H41A-2, San Francisco, 15-19 December.

The Program for the Fall Meeting includes the following Abstract: Cyclic responses to periodic forcing are well documernted in the study of groundwater and surface water systems. Quasi-periodicities occur because the hydrological cycle is driven by periodic processes, such as diurnal and seasonal fluctuations in solar radiation to the earth, as well as tides. The effect of periodic phenomena on transient groundwater flow, however, has not been widely studied, except in the context of tidal responses in coastal aquifers. This paper presents the results of research which explores surface water - groundwater interaction in aquifers subjected to periodic variations in recharge. Periodic aquifer flow is modelled using AQUIFEM-P, "A Periodic Finite Element Aquifer Flow Model", in which boundary conditions, recharge and fluctuations in head are approximated by sinusoidal fluctuations. The analysis considers a near-field flow domain, comprising a 2-D vertical section of aquifer with a shallow surface water body above, embedded within a 1-D regional aquifer. Special boundary conditions are presented which account for the coupling between the near field and the regional flow field. Frequency decomposition is used to separate the steady and periodic problems, which are solved and analysed separately. Periodic behavior is explored through the superposition of steady state and fluctuating results. Visualisation techniques are used to display periodic flow fields, including particle tracks, ellipses representing the periodic component of particle trajectories, and contour plots of steady heads, head amplitudes and head phases. The research yields results which may be relevant to the phenomena of apparent dispersion, caused by macro scale transients in groundwater flow, and issues relating to capture, release and re-capture of groundwater by surface water bodies.

A (3-page) PDF which was the basis for preparation of the poster includes a much shorter Introduction and Objective: Cyclic responses to periodic sinusoidal forcing are well documented in the study of groundwater systems, however there are few results in 2D or 3D. The objective of this research is to understand the dynamics of groundwater flow in a 2D vertical section beneath a wide shallow lake in a regional aquifer. (The PDF refers to several papers that can be found here at this website.)