Abstract
A karst aquifer is a carbonate aquifer where groundwater flow dominantly occurs through bedding planes, fractures, conduits, and caves created by and/or enlarged by dissolution. Conventional groundwater modeling methods assume that groundwater flow can be described by Darcian principles where primary porosity (i.e. matrix porosity) and laminar flow are dominant in the aquifer. However, in karst aquifers this assumption is inapplicable due to the dual porosity present in karst aquifers. While Darcian principles may apply to the matrix portion of the karst aquifer, they often do not apply to flow through conduits, where flow velocities can be great enough to invalidate the applicability of Darcy’s Law. Thus, different methodologies must be used to model groundwater flow in karst aquifers. MODFLOW-CFP is a relatively new modeling program which accounts for turbulent and laminar flow in pipe like karst caves. In this study the methodology of MODFLOW-CFP is compared to several other methods to evaluate the accuracy that CFP can achieve when modeling flow in karst conditions at a laboratory and sub-regional scale. This study also briefly evaluates the program MT3DMS, to test its abilities for modeling contaminant transport in a karst aquifer analog at a laboratory scale. Results at the laboratory scale indicate that CFP is more accurate when compared to simulated results generated by MODFLOW 2005, and performs better when compared to a Navier-Stokes finite element model developed by Hua (2009). At the sub-regional scale, CFP is less accurate than the traditional MODFLOW-2000 model when comparing peak flow conditions for a simulated storm event. However, for total simulated flow for the storm event, CFP produces more accurate results than MODFLOW-2000. Regarding transport, MT3DMS can adequately simulate transport within karst at a laboratory scale.
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