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A letter from BC Hydro's director of dam safety

You may have seen the Globe and Mail article on December 9, 2015 about the pace of BC Hydro’s Bennett Dam Rip Rap project and the extent of our disclosure of the 2012 Expert Engineering Panel report on the dam. I am writing this note to provide a fuller perspective on both of these matters and to reassure all interested parties that BC Hydro’s dam safety program and approach to risk reduction are second to none.

The newspaper article infers that BC Hydro withheld information regarding the Panel's report in the British Columbia Utilities Commission (BCUC) submission for the riprap project. There was no intention of excluding the report from the BCUC: for simplicity, only the portion of the report that was relevant to the rip rap project was included with the application. Both the executive summary and the full technical report were provided to the Province's Comptroller of Water Rights in 2013, and have now been provided to the BCUC and made available on our website.

The WAC Bennett Dam, completed in 1967, remains one of the largest earthfill dams in North America. Two sinkholes developed in the crest of the dam in 1996 and received immediate attention. Following this incident, the Bennett Dam has become one of the world's most instrumented and studied dams, and there are a number of upgrades underway. The rip rap project is one of these, and we will be replacing much of the zone of large rocks on the upstream face of the dam that protects the dam from wind and wave action.

As part of the ongoing evaluations, in 2011 we invited three world experts in embankment dams to conduct their own, fully independent, bottom-up review of the dam design and performance. The work was not focused on the riprap project. Rather, it had a particular emphasis on evaluating the control of seepage and a process known as internal erosion. The intent was to better understand the actual conditions and the behaviour of the dam since its construction, and following 15 years of monitoring and investigations since the sinkhole development.

In its 2012 report, the Panel notes that the Bennett dam design will prevent ongoing internal erosion and that there are no situations where erosion, if initiated, would continue. The Panel recommended quite a number of further investigations and work to confirm this conclusion, including additional studies for the upper portion of the dam.

Since that time, we have been addressing the Panel's recommendations, and the Expert Engineering Panel was reconvened just last month to assess our progress, and reassess the situation. This latest report is still in draft, and should be available early in 2016.

In the meantime, based on their verbal update, we expect the report to state that the work over the past three years confirms their earlier opinion regarding the safety of the dam. We also expect to receive recommendations for further work, which we will continue to follow.

The process of monitoring and surveillance, and the review of the dam's performance will also continue, as this work is the cornerstone of our dam safety program that ensures its ongoing safe performance. The Expert Panel follow-up report will be made public after it is received and formally submitted to the Comptroller of Water Rights.

We believe the timing of the riprap project is appropriate and its pace is as fast as practical in view of the complexity of the project. The project was released in 2011 before the Expert Panel was convened, following our dam upgrade priorities. The timing was influenced by the observation of the extent of the ongoing deterioration of the rip rap.

When the Panel was in session in 2011, we believed that relatively simple repairs to the riprap would be possible using a local rock quarry. As such, we anticipated project completion before now. Early project planning and definition pointed us to a more comprehensive, but more complex solution, including higher quality rock from a more distant quarry. This solution has required more time and cost but also provides a permanent and long-term fix to the problem. This much larger project involved more extensive environmental and First Nations consultation, and a formal BCUC application.

Our highest responsibility at BC Hydro is public safety and that's why we maintain a strong dam safety program, which includes 24/7 instrumentation monitoring, weekly inspections, bi-annual engineering reports and regular external reviews of all our dams. Our work, and the panel's review, confirms that there is no immediate concern for the safety of the Bennett Dam, while long-term investigations and capital upgrades such as the riprap project continue into the future.

Stephen Rigbey
Director of Dam Safety
BC Hydro