A Hybrid Finite-Difference and Analytic Element Groundwater Model
Article first published online: 28 JAN 2010
Copyright © 2010 The Author(s). Journal compilation © 2010 National Ground Water Association
Volume 48, Issue 4, pages 538–548, July/August 2010
How to Cite
Haitjema, H.M., Feinstein, D.T., Hunt, R.J. and Gusyev, M.A. (2010), A Hybrid Finite-Difference and Analytic Element Groundwater Model. Groundwater, 48: 538–548. doi: 10.1111/j.1745-6584.2009.00672.x
- Issue published online: 22 JUN 2010
- Article first published online: 28 JAN 2010
- Received August 2009, accepted December 2009.
Regional finite-difference models tend to have large cell sizes, often on the order of 1–2 km on a side. Although the regional flow patterns in deeper formations may be adequately represented by such a model, the intricate surface water and groundwater interactions in the shallower layers are not. Several stream reaches and nearby wells may occur in a single cell, precluding any meaningful modeling of the surface water and groundwater interactions between the individual features. We propose to replace the upper MODFLOW layer or layers, in which the surface water and groundwater interactions occur, by an analytic element model (GFLOW) that does not employ a model grid; instead, it represents wells and surface waters directly by the use of point-sinks and line-sinks. For many practical cases it suffices to provide GFLOW with the vertical leakage rates calculated in the original coarse MODFLOW model in order to obtain a good representation of surface water and groundwater interactions. However, when the combined transmissivities in the deeper (MODFLOW) layers dominate, the accuracy of the GFLOW solution diminishes. For those cases, an iterative coupling procedure, whereby the leakages between the GFLOW and MODFLOW model are updated, appreciably improves the overall solution, albeit at considerable computational cost. The coupled GFLOW–MODFLOW model is applicable to relatively large areas, in many cases to the entire model domain, thus forming an attractive alternative to local grid refinement or inset models.