I am writing to express my concern about the safety of the hill forming the North Spur at Muskrat Falls, which will be reshaped into an “engineered dam” to contain the Muskrat Falls reservoir.
The North Spur is both a curse and a blessing. It is a blessing because it creates a natural dam. It is a curse because it is not rock solid like the Southside Hills in St. John’s. It is moving and alive. It is underlain by quick clays that can liquefy when saturated or disturbed.
You may well be curious as to why I am interested in the project. For the past 63 years I have worked exclusively on 113 hydro projects, with my first field job in 1953 being the supervision of construction of dams and canals used to divert the headwaters of several rivers into the Cape Broyle River on the Avalon Peninsula.
Since then, I have worked on Churchill Falls, Gull Island and Cat Arm, concluding in 2001-2005 with annual reviews of dam safety of all the Churchill dams and those on the Island operated by Newfoundland and Labrador Hydro, with the Dyke Board. Hence my interest in Muskrat.
The North Spur is a natural hill 1,000 metres long connecting Spirit Mountain to the north shore at Muskrat Falls, which includes three layers of sand and two of marine clay, all resting on a foundation of marine clay. When the Muskrat reservoir is filled, this hill will form part of the dam containing the reservoir.
Marine clay is a type of clay found in coastal regions around the world. In the northern, deglaciated regions, it can sometimes be quick clay, which is notorious for being involved in landslides. Construction in marine clays thus presents a geotechnical engineering challenge.
Marine clay is present around the southern half of James Bay. This persuaded Hydro-Québec to by-pass development on the Nottaway River, moving instead 300 kilometres north to the La Grande, at considerable added expense for access and transmission.
Despite such challenges, Nalcor elected to build Muskrat Falls, where all the clay in the region around Muskrat consists of marine clay, and there are numerous quick clay slides on the north shore, both upstream and downstream of Muskrat, including three large slides on the downstream slope of the North Spur.
- Read more special articles:
- Seven injured in structure collapse of framework at Muskrat Falls
- Nova Scotia utilities regulator warned of Muskrat Falls delay
- Methylmercury in Lake Melville at issue, for everyone
- Muskrat Falls progress report
Dr. Stig Bernander has examined the Spur. He has extensive experience analysing quick clay landslides in Sweden, and has determined that when the water level in the North Spur is five metres below ground level, the natural dam has a safety factor of 1.43. However, when saturated, the safety factor drops to 1.09. This is what would be expected in view of the numerous quick clay landslides in the vicinity.
Nalcor intends to increase these factors by flattening the slopes, adding pump wells, placing an upstream impervious blanket to close off the upper sand layers, and building a cutoff wall filled with an impervious material to close off the lower sand layer. All reasonable measures. However, Bernander has questioned the use of a cutoff wall indicating that it may be detrimental to the safety factor.
If the North Spur dam fails, there is the likelihood of loss of life in Goose Bay and Happy Valley, and the river will divert to flow through the breach in the Spur.
If the North Spur fails, Muskrat Falls will disappear and be left high and dry. The Muskrat Hydro facility would become a stranded asset, with (if feasible) a repair cost well over several billion dollars. Power would be interrupted for at least several years.
Since the design of the North Spur dam is without precedent, and the consequences of a failure are catastrophic, it becomes imperative to have the design reviewed by an independent panel of experts — a review board, and I am glad to hear that Premier Dwight Ball and Natural Resources Minister Siobhan Coady have announced a review of the cost and schedule.
I sincerely hope that the review will be expanded to include the geotechnical design of the North Spur dam, since any remedial measures will impact the cost.
Jim Gordon, hydropower consultant
Pointe Claire, Que.