Abstract
When considering three-dimensional groundwater flow, the hydrogeological community widely uses the MODFLOW model based on the head-oriented approach (HOA). However, a great deal of hydrogeological situations requires an extremely accurate assessment of the Darcy velocity in three dimensions. Despite the good numerical approximation of the piezometric head offered by MODFLOW, it does not guarantee sufficient accuracy in estimating all three components of the flow velocity. As an alternative, this article presents the MODFLOW-based velocity-oriented approach (VOA), which can approximate the three components of the groundwater velocity with high accuracy. The article gives comprehensive theoretical background and a comparison of the HOA and VOA approaches. Importantly, the authors show how the VOA equations with the VOA boundary conditions can be implemented and solved with MODFLOW. Recently, the VOA has become a basis for new version of MODFLOW. The two approaches are effectively combined and compared using Visual MODFLOW for a simple case of river–aquifer interaction.
Highlights
A great deal of hydrogeological situations requires an accurate three-dimensional calculation of the Darcy velocity
Approximations of the groundwater velocity components calculated with some numerical models may be inaccurate when the river is considered to be a part of a larger regional groundwater flow system
Regular MODFLOW software is based on the head-oriented approach (HOA), i.e., it solves numerically the groundwater flow equation with the block-centered finite difference method and calculates the hydraulic heads in the grid block centers
Summary
The flow of groundwater is governed by the mass and momentum balance equations. For flow with sufficiently low velocity (i.e., for Reynolds numbers
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