I would like to comment on points raised in James McLeod’s interview with Gilbert Bennett of Nalcor in The Weekend Telegram, Aug. 23.
1. Rather, than talk about landslides downstream of Muskrat Dam being “no big deal,” I suggest it would have been more enlightening to note that the behaviour of alluvial rivers, such as the Lower Churchill, involves the continual evolution of their channels via erosion and deposition and that landslips along the banks are perfectly natural consequences of this process.
2. The presence of sensitive marine clays underlying the North Spur is a very serious problem. This material, when disturbed, can liquefy and cause massive landslides. One has only to recall the disaster at Saint Jean-Vianney, Que., in 1971 where 31 lives were lost. There have been many other incidents of this type, particularly in Quebec where sensitive marine clays are common.
On the question of the stabilization of the North Spur, the article cites engineer Regis Bouchard, who states that the North Spur stabilization design is unique but that solutions applying proven technology will fix the problem.
The Telegram article mentions building a “concrete and bromide” wall. I presume that “bromide” was a typographical error and that “bentonite” was intended. Given the challenges of stabilizing the North Spur/natural dam, I expect that Nalcor would have engaged world-class experts to advise them on this question.
The article notes that the (unnamed) engineer engaged to provide project oversight has signed off on the proposed design. As a member of the public, I will not be satisfied that Nalcor has properly dealt with this problem until a real expert comes forward to discuss this issue in public. It is not good enough to get a second-hand opinion on such an important issue from Bennett, who is clearly not an expert on the subject, when presumably real experts are available.
3. A related issue concerns the risk of landslide generated water waves in the reservoir that could be produced by a major landslide into Muskrat Reservoir upstream of the dam. It would be interesting for the public to know how the dam design has been adapted to protect against this threat.
P.C. Helwig, consulting engineer