Remediation of foundation seepage at Clearwater dam, USA

The Clearwater earthfill embankment, in southeastern Missouri, USA, had a history of foundation seepage since initial impounding in 1948. The discovery of a sinkhole in 2003 in the upstream slope of the dam prompted a major safety reassessment and, as a result, a series of refurbishment measures. The initial emergency response and repair consisted of geophysical surveys, soil and rock corings adjacent to the sinkhole and the provision of a grout curtain downstream of the sinkhole. A major rehabilitation scheme followed, consisting of double-line grout curtain along the full length of the dam, and the construction of a concrete cutoff wall 40 ft (12.2 m) into the foundation rock, completed in 2013. Analysis of pre- and post-construction instrumentation demonstrates that these measures have reduced seepage below the dam significantly, ensuring the dam’s integrity to provide flood control protection safely, as designed.