2 November 2011
An update on the Wisconsin landslide, and a cliff collapse in Wales
Posted by Dave Petley
Summary: An update on the landslide in Wisconsin on Monday, and a report of a cliff collapse in Wales, also on Monday.
Various media reports have emerged over the last 24 hours following-up on the landslide at the We Energies power plant in Wisconsin on Monday morning about which I blogged yesterday. Perhaps the most interesting is this story, which suggests that the landslide material was indeed ash, which had been dumped in the ravine in the 1950s and 1960s. In the article, this is described as being the cause. That may be true, but I remain intrigued as to what has happened at the site more recently to trigger the slip this week. Meanwhile, there is a good gallery of images of the landslide here, which rather helpfully permits this before and after comparison:
Meanwhile in Barry, Wales a cliff collapse occurred on Monday evening that has generated a little bit of a stir. A section of cliff collapsed at a caravan (trailer) park on the coast, as this image shows (from this report) shows:
Fortunately no-one was injured in the fall, and none of the caravans were lost. It is interesting to note that quite a long section of cliff appears to have collapsed in this event.
They still haven’t determined anything, but there is speculation that a nearby retention may be the cause. It was unlined, and there may have been seepage.
water loss from lagoon?
The photos seem to show ongoing seepage from the lined pond side of the failure. You can see the pond outlet is adjacent to the failure headscarp but the degree of seepage seems to extend past the sheet pile, apparently following the historic compacted ground surface. There’s still lots of ash to fail yet if they don’t control the seepage.
It’s hard to tell from the pond waterline and airphotos what the retention pond cycle times are, but that degree of seepage in a dry period sure points toward extensive liner penetration rather than simply leakage from the outlet pipe. I’m surprised they haven’t drawn the pond down yet.
You cannot judge anything from the waterline in the retention pond. They are pumping it down to prevent seepage in case that is the issue, so the water level is being intentionally lowered.
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The Wisconsin Department of Natural Resources has determined that it was caused by seepage from an unlined pond.
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