“HOLEY GROUND” – AN ASSESSMENT OF THE SAFETY OF GATHRIGHT DAM WITH RESPECT TO SEEPAGE AND INTERNAL EROSION (Invited Presentation)

Gathright Dam is a 257-foot high zoned rockfill dam located near Covington, VA. The dam was completed in 1979 and is operated by the US Army Corps of Engineers (USACE), Norfolk District. The foundation and abutments of Gathright Dam have several geologic units that are highly prone to chemical solutioning. For example, the geotechnical investigation revealed that 44% of the 2800 feet of drilling in the Coeymans Formation , which is present in the both dam abutments, was drilled through air- or clay-filled voids.

This presentation will focus on the results of a recent seepage assessment of Gathright Dam as requested by the USACE. The goal of our study was to determine if the dam was safe with respect to seepage and piping. The study included a significant amount of subsurface data reduction and 3-D data visualization, which played an instrumental role in our understanding of the complex interactions between the geology and dam seepage control features. Results of the seepage study indicated that there is no immediate dam safety concerns related to seepage through the dam itself or its foundation or abutments.