HR: 1340h
AN: H33F-0528    [Abstracts]
TI: Discrete Analytic Domains: a New Technique for Groundwater Flow Modeling in Layered, Anisotropic, and Heterogeneous Aquifer Systems
AU: * Fitts, C R
EM: cfitts@usm.maine.edu
AF: University of Southern Maine Geosciences Dept, College Ave, Gorham, ME 04074 United States
AB: A new technique for modeling groundwater flow with analytic solutions is presented. It allows modeling of layered aquifer systems with complex heterogeneity and anisotropy. As with previous AEM techniques, flow in each layer is modeled with two-dimensional analytic solutions, there is high accuracy and resolution, the domain is not discretized into grid blocks or elements, and the modeled area can easily be altered and expanded in the midst of the modeling process. This method differs from previous Analytic Element Method (AEM) techniques by allowing general anisotropy conditions in the aquifer. The flow field is broken into discrete polygonal domains, each with its own definition of isotropic or anisotropic aquifer parameters. An advantage of this approach is that the anisotropy orientation and ratio can differ from one domain to another, a capability not possible with the "infinite domain" of previous AEM formulations. With this approach, the potential and discharge vector functions at a point are the sum of contributions from elements within or on the boundary of the domain containing the point. Unlike previous AEM schemes, elements beyond the domain boundary don't contribute to these functions. Once a solution is in hand, less computation is required to evaluate heads and discharges because fewer elements contribute to the equations. This computational efficiency could prove a significant advantage in large regional models and in solute transport models that use a flow model's velocity field. This technique allows multiple aquifer layers to be stacked vertically, and it has the novel ability to have more layers in the area of interest than in distant areas. This feature can save significant computation and input effort by concentrating layering detail only where it is needed and warranted by data. The boundary conditions at line element boundaries are approximated, including the continuity of flow and head across heterogeneity boundaries. By using high-order line elements with as many as 15 degrees of freedom per element, the boundary condition approximations can be made quite accurate. An example model illustrates the method's capabilities and the accuracy of boundary conditions achieved.
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting