Re: previous photos: 1. "Very waterlogged area as can be seen by the orange iron stains. Iron is picked up in gravel seams inside the bank & the area immediately above is a deep seam." Dangerous spot to attach a dam. Water travels thru seams & turns the bank's hard shale to mud. 
2. See that long grey vertical-ish line at top? A local says "I think they've had so many water erosion problems there that they built more of a water course with rip rap to try & manage it. They are constantly pumping water from different locations to try manage that too" #SiteC
You might think water isn't a problem - it's a dam after all, obviously there's water nearby! But you can't have water, erosion & assoc'd instability anywhere you're trying to attach a dam. The inexorable force of water poses the greatest risk to dams. And there's no bedrock here
Worse, for those who haven't followed earlier threads on this, Peace River Valley shale is uniquely unstable; it's rocklike when dry, but turns to cohesionless jelly when wet. Very strange stuff. In the rush to start the dam, were water tests ever done on this material?
The problem with gravel seams inside these especially unstable shale banks is that water travels easily through these seams and can convert this particular dry shale into mud with no cohesion, no bearing capacity and no shear strength.
3. In these photos, we were also examining the river diversion tunnel entrances/exits for evidence that construction had begun on cofferdams: angled smaller dams to force water into the tunnels & then away from #SiteC dam site. Can't divert the river in September without these.
The cofferdams would be built when the river was low in late summer, & BC Hydro would hold back even more river water in upstream WAC Bennett & Peace Canyon dam reservoirs to create drier #SiteC conditions to build cofferdams in. But with heavy rains, river & reservoirs are full.
Local: "No signs of anything much happening with the cofferdams. Water is extremely high as can be seen in those photos. I would say that some of the work they had done is under water or got washed away. Talk about adding silt to an already dirty river."
There are various ways of building cofferdams; smaller ones are often built with metal piles and interlocking sheet piles, but like #SiteC, it is thought that the cofferdams here would be earthfill. It's hard to see how you'd use that (or any) method now, in a rushing river.
The equipment we believe they had on site for building the cofferdams has been moved up the bank and is sitting idle. If they now now need to bring in much larger equipment that can reach out across water to build cofferdams in water, that's another delay. Sept. deadline looms.
