Preliminary comparison of a discrete fracture model with a continuum model for groundwater movement in fractured dolomite

Author / Creator

Bradbury, K. R., author

Available as

Online

Summary

The use of porous-media methods for describing groundwater flow in fractured-rock environments has become commonplace because simulation of flow through discrete fracture networks is difficult and ...

The use of porous-media methods for describing groundwater flow in fractured-rock environments has become commonplace because simulation of flow through discrete fracture networks is difficult and data-intensive. However, the possible errors introduced by the use of the porous-media approximation are rarely addressed or are glossed over in many groundwater studies, and guidelines for when a porous-media approximation is appropriate are almost completely lacking. In this report we present the results of experiments using a two-dimensional stochastic discrete fracture flow model (the SDF model) coupled with a particle-tracking code to explore the validity of the porous-media approximation for simulating groundwater movement in fractured-rock aquifers. The study successfully adapted the fracture-flow model to a microcomputer environment, added capabilities for simulating pumping and injection wells, and developed an advective particle tracking module. Using statistical descriptions of natural fracture patterns and other hydrogeologic data collected from field sites in Door County, Wisconsin, the SDF model was used to simulate the effects of model domain size, anisotropy, and fracture density on the shape of capture zones for pumping wells. Comparison of the SDF model with a porous-media (MODFLOW) model of the same area shows that even in densely fractured aquifers, the zone of contribution determined by the fracture-flow model is significantly larger than the capture zone determined by porous-media- based models. However, the reliability of the porous-media approximation increases and the effects of fracture anisotropy become less significant as the overall size of the problem domain increases. This project provides guidelines for groundwater studies in fractured-rock environments similar to Door County. The types of investigations that could benefit from this project include wellhead protection studies, remedial investigations, the design of groundwater monitoring systems, and water supply studies.

Show More