Mile-Long Monitoring: Geotechnical Instrumentation System Design for the Cobbs Creek Regional Water Supply Reservoir Project

The Cobbs Creek Regional Water Supply Reservoir is a new pumped-storage facility just south of the James River on Cobbs Creek in Cumberland County, Virginia. Construction began in July 2017 and is expected to be completed in 2022. The project includes the construction of three zoned earthen embankment dams to impound Cobbs Creek, including a 3,850-foot-long main dam with a maximum height of 160 ft, a 1,200-foot-long saddle dam with a maximum height of 25 ft, and a 900-foot-long access road dam with a maximum height of 15 ft. Performance of the dams during initial filling and long-term operation is monitored with an extensive geotechnical instrumentation program that includes 32 vibrating wire piezometers, seven seepage collection vaults with vibrating wire water level monitors, a fiber optic distributed temperature sensing system, and survey monitoring points. The electronic instruments will be monitored using an automated data acquisition system that includes a central automated datalogger connected to a local enterprise appliance server platform. Communication between the electronic instruments and the datalogger will be accomplished through a wireless mesh network consisting of data transmission points and signal repeaters. This paper provides an overview of the instrumentation system design and data collection. While the paper will focus on the Cobbs Creek project, the monitoring challenges and solutions presented are common for many dam rehabilitation and new dam construction projects. The objective is to share the approach and lessons learned from this project to benefit owners, consultants, and regulators on their projects.