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Seismic improvements at Coquitlam dam

BC Hydro has started a programme of interim improvements at the Coquitlam dam in Canada, which will be completed by April 2001. The improvements are meant to ensure the dam meets current earthquake loading standards.

Although the condition of the 90-year-old hydraulic fill dam has not changed, recent state-of-the-art investigation technology has confirmed the existence of a loose zone within the dam that could liquefy during moderate or large earthquakes, resulting in some deformation of the dam.

The recent more stringent earthquake standards, combined with the confirmation of the loose zone, have resulted in BC Hydro’s decision to upgrade the dam to improve its safety under seismic loads.

As part of the interim measures that are in place, BC Hydro is maintaining the reservoir below el 149m, a level considered safe for even the largest conceivable earthquake. This maximum safe level will be in effect until the interim improvements to the dam are completed. Depending on the results of drilling undertaken in January 2001, further remedial measures will take place and be carried out through March and April 2001. The safe reservoir level will be re-assessed following the successful completion of these measures and additional long-term improvements will be assessed during 2001.

Coquitlam dam is part of the 73MW Coquitlam-Buntzen project. Water is diverted from the Coquitlam reservoir via a tunnel into the Buntzen reservoir and then by penstocks to two power houses (Buntzen 1 and Buntzen 2) on the Indian Arm. In 1984 and 1985, BC Hydro improved the stability of the 30m high Coquitlam dam to resist seismic loading. However, since then significantly higher dam seismic loadings have become the industry standard for large dams. New technology and improved investigation techniques also allow better assessments of the ability of dams to withstand earthquakes.