Townley, L.R. (1993), AQUIFEM-P: A Periodic Finite Element Aquifer Flow Model: User's Manual and Description, Version 1.0, CSIRO Division of Water Resources, Technical Memorandum 93/13, 72pp., plus software.

AQUIFEM-P is based on AQUIFEM-1 [Wilson et al., 1979; Townley and Wilson, 1980], which is a single-layered finite element aquifer flow model. AQUIFEM-P differs from AQUIFEM-1 in that it is specifically designed for calculating the response of an aquifer to periodic boundary conditions and recharge, i.e. when boundary conditions and recharge can be approximated by sinusoidal variations in and cosine curves) with a fixed period.time (generalised sine

The title of this Report describes AQUIFEM-P as a "periodic finite element aquifer flow model". It is an aquifer flow model in the sense that it solves a two-dimensional aquifer flow equation [Bear, 1979]; it is a finite element model in that it uses the finite element method to discretise the governing partial differential equation in space; and it is a periodic model in the sense that boundary conditions and hence heads are assumed to be periodic. AQUIFEM-P can also solve problems of steady flow.

The aquifer flow equation, and hence AQUIFEM-P, can be applied to regional scale aquifers in which flow is essentially horizontal. It is characterised by the use of water table elevation or depth-averaged head as the state variable, transmissivity rather than hydraulic conductivity, and an aquifer storativity or specific yield rather than specific storativity. The equation is very similar in form to the dynamic equation for groundwater flow in a vertical cross-section, thus with some care it is also possible to apply AQUIFEM-P to a cross-section.

AQUIFEM-P is able to simulate 1st-type (known head) boundary conditions, 2nd-type (known flux) boundary conditions, 3rd-type (mixed) boundary conditions, distributed sources and sinks, point sources and sinks, and leakage from an adjacent aquifer. All of these can be steady or periodic.

The notion of periodic boundary conditions is not common in the hydrologic literature. The most common application to date has been to the response of a water table near a river or the ocean where water levels fluctuate due to tides. Other papers have considered the effect of annual or diurnal fluctuations in recharge and evapotranspiration.

AQUIFEM-P was motivated by a study of a regional aquifer on the Swan Coastal Plain near Perth in Western Australia [Cargeeg et al., 1987a, 1987b]. Since Perth has a mediterranean climate, with nearly all rainfall and hence recharge in winter months and with the majority of groundwater pumping in summer months, the regional water table fluctuates with a strong annual cycle. Research in 1985 resulted in a simple analytical solution for water table fluctuations due to periodic recharge and also in the development of AQUIFEM-P [Townley, 1985]. The latter was developed partly to check the analytical solution, but mostly to allow the technique to be applied to aquifers with arbitrary geometry and arbitrary spatial variations in aquifer properties. The same basic theory has since been applied to a number of different problems.

Section 2 of this Report provides a concise description of the theory, Section 3 provides a brief description of how to use AQUIFEM-P, and Section 4 provides a few examples of the application of AQUIFEM-P.