GIS MAPPING OF PREFERENTIAL FLOW FEATURES IN THE MADISON AQUIFER, WHITE CREEK CANYON, WYOMING

The Madison Formation serves as a carbonate aquifer critical for residents of Wyoming and surrounding states. This study employed GIS to investigate preferential flow features (joints, bedding planes, and solution openings) in the Madison Aquifer exposed within White Creek Canyon near Shell, Wyoming. The location, orientation, and length of over 1,500 preferential flow features were recorded using a GPS unit, Brunton compass, and tape. These features were plotted on equal-area stereonets then embedded within a GIS composed of plan-view and cross-section digital orthoimages.

Three fracture sets were identified that are well-interconnected and likely serve as a preferential flow system for the aquifer. Large (> 10 m) fractures had a mean orientation of tr. 352° pl. 16°, which corresponds with the approximate 75° compression of the Laramide Orogeny. A set of smaller (1-10 m) fractures displayed a mean orientation of tr. 285° pl. 10°, which may be normal to Basin and Range extension. The third set of fractures are sub-horizontal and are associated with bedding planes. The mean fracture spacing of large and small fractures was 28.0 and 1.5 m, respectively. Mean orientation of solution openings (small caves) was tr. 264° pl. 14°, which appears to be unrelated to fracture orientation and may represent a paleo groundwater flow system. The GIS maps created by this study demonstrate that preferential flow features are well-interconnected at this location. However, the probability of a well intercepting large fractures is diminished due to their sub-vertical orientation and spacing.