CS20B - Concurrent Session 20B: More Bang for your Buck? Making Instrumentation Worth the Investment

Abstract Description: Dams are huge investments and are expensive to maintain and repair. A robust instrumentation plan that collects a wealth of data can provide insights to address short-term needs and to help maintain the dam’s long-term health. The experience of North Texas Municipal Water District shows how.

North Texas Municipal Water District became a new dam owner in Texas to provide a new major water source to its service area of more than 2 million people. In 2021, Bois D’Arc Lake, the first major Texas reservoir built in 30 years, was substantially completed. The dam for this new lake is a 2-mile-long zoned earthen embankment more than 90 feet high with a slurry cutoff trench and an internal drainage system. Reservoir discharges are primarily conveyed via a labyrinth weir service spillway and earthen auxiliary spillway with low-flow conveyance through the reservoir intake tower.

Instrumentation on the dam and spillway structures includes the following:
• 177 surface monuments
• 16 automated settlement gauges
• 19 automatic and manual inclinometers
• 25 open-riser piezometers
• 81 automated vibrating wire transducers.

Seven (7) primary instrument lines with the above instruments, extending from the upstream toe to downstream of the dam, are located along the earthen embankment on an approximate 1,000-foot spacing. The instrumentation provided real-time monitoring of embankment performance during construction and most of the instruments will continue providing data for long-term performance monitoring of the spillway and earthen embankment.

Freese and Nichols partnered with the District to address multiple challenges that came up during design and construction regarding maintenance, data acquisition, data management, data interpretation, and long-term reliability of the instrumentation. This paper will present lessons learned from design, construction and monitoring six years of data to help instrumentation to be worth the investment. We’ll cover:

• The value and cost of dam instrumentation
• The quantity of instrumentation required
• Data acquisition and analysis
• Long-term maintenance and owner responsibilities