Maureen Muldoon

University of Wisconsin - Oshkosh

This activity was developed for a short-course for professionals and I have not yet used it in my undergraduate class. I have used TopoDrive in other lab exercises and the user-interface is straightforward enough for students to quickly master. I believe the exercise can easily be adapted as an undergraduate lab exercise as long as they are given some background on the difference between characteristic fracture patterns for crystalline and sedimentary rocks.

Students will need to understand the following concepts before completing this exercise:

• regional flow patterns
• aquifer properties (hydraulic conductivity and porosity)
• characteristic fracture patterns for crystalline and sedimentary rocks

I intend to include this exercise in the unit on regional groundwater flow patterns. It could also be used in a unit on the effect of heterogeneities on groundwater flow and transport.

• fluid flow in fractured media
• effect of heterogeneities on groundwater flow patterns

• analyzing data on fracture patterns in different rock types
• integrating geologic data into a numerical model

• written description of model results
• using computer technology

The goal of this exercise is to have students gain an understanding of how fractures affect groundwater flow patterns. In order for them to complete the activity, they need some background on characteristic fracture patterns in different rock types. This background could be provided in a variety of ways depending on geographic location and outcrop availability. If outcrops of crystalline and sedimentary sequences are available, you could take students in the field and have them observe (and perhaps sketch) the differing fracture patterns. If geology (and or weather) preclude this option, the students could observe fracture patterns from slides of outcrops (see slides in accompanying PowerPoint Presentation).

The classroom portion of the exercise uses a simple 2D numerical model (TopoDrive, available from USGS) to simulate flow in three aquifers: 1) homogeneous isotropic, 2) fractured crystalline, and 3) fractured sedimentary sequences. The task is to observe how the fracture patterns alter the flow patterns as compared to the homogeneous, isotropic simulation. The activity gives students practice in integrating geologic data into numerical models, describing flow patterns, and using computer technology. The activity also integrates knowledge from structural geology with hydrogeology.

You could evaluate students based on the following:
Did the student complete all three simulations (minimal goal)
Are the fracture patterns realistic for the different rock types?
How well did the student describe the effect of fractures on the flow patterns? (My students have struggled with this in a similar exercise on the effect of heterogeneities on flow patterns)

Hsieh, P.A., 2001. TopoDrive and ParticleFlo—Two Computer Models for Simulation and Visualization of Ground-water Flow and Transport of Fluid Particles in Two Dimensions: U.S.G.S. Open File Report 01-286, 30 pg.
http://water.usgs.gov/nrp/gwsoftware/tdpf/tdpf.html (more info)