CS22B - Concurrent Session 22B: Large Scale Peer Audit of Dam Instrumentation and Monitoring Program

The development of a new hydroelectric dam in northwestern Colombia is nearing its final phase of construction. The 738-foot-high earthen embankment spans the 1,804-foot-wide valley of the Cauca River. In 2018, a portion of the unlined rock auxiliary diversion tunnel collapsed unexpectedly, blocking the flow, resulting in flooding of the incomplete powerhouse, causing significant construction delays and increased project costs.

As a result of the collapse and subsequent project re-insurance requirements, GZA GeoEnvironmental, Inc. was retained by the dam owner to perform a large-scale peer audit of the existing geotechnical instrumentation and monitoring system(s) of the dam, powerhouse, and associated facilities. The audit primarily focused on the instrument selection based on subsurface conditions, installation methods, and range of sensors, with a particular focus on data collection, data reduction, quality control, and reporting/alerts. There were multiple instrument types installed across the project site, with the audit focused on settlement cells, load cells, pressure cells, vertical magnetic extensometers, multipoint extensometers, vibrating wire piezometers, inclinometers, and open tube piezometers with an overview of manual and automated movement monitoring using optical methods. The project site had over 3,400 instruments installed with millions of manually and automatically collected data points. A detailed step-by-step audit—from installation, maintenance, data collection, and data reduction were performed on each instrument.

A detailed Audit Report presenting our findings, recommendations, and suggested improvements was provided to the dam owner, and re-insurance team. The report was reviewed and resulted in the design team instituting changes, where feasible, to the instrumentation and data collection systems to conform with US and European industry standards, allowing the instrumentation to be a vital part of the design team’s ability to evaluate the facilities performance.

This presentation will include not only a case study but will also provide lessons learned and recommendations for instrumentation audits or reviews that might be valuable to the industry.