Dave Petley @dr-dave ?

active 1 day, 15 hours ago
  • The Sanxicun landslide in Sichuan Province, China
    On 10th July 2013 the catastrophic Sanxicun landslide, located at 30.917, 103.565, occurred during heavy rainfall in the Dujiangyan area of Suchuan Province in […]

  • Mega-landslides as a vehicle for colonisation of distant islands
    One of the great challenges of biology is to explain colonisation of distant islands, and indeed continents, by animals that are too heavy to be […]

  • San Bernadino National Forest landslide video
    One of a number of new landslide videos that have been published in the last few days comes from San Bernadino National Forest in Southern California, triggered by […]

  • The scale of the erosion problem at the Oroville Dam site
    As the fairly desperate attempt continue to shore up the spillways at the Oroville Dam site, and to lower the water level ahead of the next rainstorm, […]

    • Very scary how close that came.

      It would be interesting to know what type of ’emergency’ the emergency spillway was designed for. To me it seems like it was a structure of last resort to prevent the dam from being overtopped, not an alternative spillway to the main spillway. Why was the decision taken to use it? Was it because of safety concerns about further damage to the main spillway or was it because of financial concerns about having to pay more if the main spillway sustains further damage?

      [I don’t think there was any option or choice. The water level was rising because inflows were so high and the main spillway was compromised, and so had not been used to lower the lake. In adddition there is no flow through the dam because the channel downstream is so choked. This was not a conscious decision – the water level rose until it overtopped the mergency spillway. The damage will cost a great deal to fix, so there is no saving from this event. Others may be able to provide insight too. D.]

      • I was under the impression that the flow rate through the gates onto the main spillway was doubled to around 100,000 CFS as soon as the erosion problem and the danger to the concrete weir on the emergency spillway became apparent – the current rate is still 100,000 CFS. I think the maximum flow over the emergency spillway was only around 10,000 CFS, which suggests to me that the emergency spillway would not have come in to play if the flow down the main spillway had been 100,000 all along, i.e. that the flow was reduced down the main spillway to protect it in the knowledge that doing so would mean that the emergency spillway would be used.

        The speed of the bedrock erosion is frightening – if the concrete weir had collapsed then the flow rate and erosion over that same region would have increased drastically. The gates on the main spillway might have been in jeopardy and I don’t find it impossible to think that there was a very small risk that the erosion could have reached to the dam, even if it is a couple of hundred metres away. Idle speculation I know – it’s a fascinating and terrifying situation.

      • Unbelievably, the emergency spillway was apparently designed to handle 350,000 CFS! Sundays flow causing the damage shown above was <12,000 CFS. When a motion was filed with FERC in 2005 requiring armoring of that spillway with concrete, this was deemed unnecessary. An article in The Mercury News provides details and information on sources. http://www.mercurynews.com/2017/02/12/oroville-dam-feds-and-state-officials-ignored-warnings-12-years-ago/

    • Whether there is “no threat” to the dam depends on how you look at it. If the gullies on the “emergency” spillway suffer headward erosion and undermine the lip, that might well bring down the dam or a large portion of it.

      To me this IS a “threat to the dam.”

      [I disagree. The dam is an entirely separate structure located some hundreds of metres away. It is performing as designed. Even if the emergency spillway collapses the dam will remain intact, albeit with a lot less water behind it. Managing the water in the reservoir in this scenario would be a major problem through the snowmelt season though. This is one of the reasons why they will desperate to ensure that this does not happen. D.]

    • The Daily Mail has some good photos showing what the rocks and geologic structures look like beneath the emergency spillway (in the eroded cavities): http://www.dailymail.co.uk/news/article-4221808/Officials-warned-Oroville-Dam-12-years-ago.html

      • (later) Looks like they “dumped” the best “geology” pictures from the original story.

      • (later) Looks like they “dumped” the best “geology” pictures from the original story.

    • It looks like they’re beginning to put concrete down the emergency spillway… seeing the highly weathered subsurface of the hill, they should have done that a long time ago…

    • If the spillways are constructed on a sheeted dike complex, the large variances in rock type associated with this type of formation combined with faulting, folding, and low T metamorphism that occurred during obduction will result in areas of bedrock more prone to chemical weathering than others. The steeply dipping beds will enhance the downward migration of meteoric water, exasperating this differential weathering pattern. Being situated hundreds of feet above the river has left this bedrock exposed to the elements for a million years more or less and has led to chemically weathered bedrock extending far below the surface in places while inches away horizontally is fresh bedrock.

      Even worse would be if the spillways are built into the unit stratigraphically above the sheeted dikes, metavolcanics intruded by the dikes. Pillow lavas with their chill margins are fragile when fresh, and are even more susceptible to chemical weathering than the dikes.

      Diabase might be an incredibly strong rock when fresh, but not all of the main spillway is built directly on this competent bedrock as is evidenced by the original blowout and images of the spillways construction. There are many sections of the main spillway directly below the gates that were built on chemically weathered bedrock. With a 100k cfs flowing for the foreseeable future, with higher rates likely considering the long range forecasts, another blowout is a real possibility.

      The emergency spillway is not auxiliary, and i don’t believe any competent geologist present during it’s construction would have considered its use as anything but a last ditch effort. It was designed as a fail-safe to prevent the loss of the main dam during the event of a half a million cfs inflow to the lake during a 200 to 1000 year event. The ogee weir extending from the main spillway gates was likely built to protect the main spillway gates. The bedrock was excavated deeper below the ogee weir to find more competent bedrock than the concrete wall extending northwards from the ogee weir, which was built to protect the ogee weir. The lack of concrete in the far NW corner of the parking lot where we saw considerable erosion and helicopters lowering bags of rocks into is not lack of foresight, but designed weakness built into a weak structure. The parking lot is built on highly weathered bedrock and is designed to function as a sacrificial plug located as far from the dam itself as possible, similar to the Auburn coffer dam failure of 1986. As headcutting progresses into the parking lot, water at elevation 900 and above is skimmed off. Once headcutting reaches the lake, then downcutting commences, “safely” lowering the lake till competent bedrock is found, maybe a hundred feet down, leaving the vast majority of the lake still in the lake and Oroville dam still standing, no matter the magnitude of the storm.

      The costs associated with building a sound “auxiliary” spillway due to the amount of bedrock that needed to be excavated to reach the competent stuff, probably discovered after work had begun, could have led to such a design. In the event that the emergency spillway saw huge flows (not a mere 12k cfs), the flows would hydraulically mine out the weak bedrock so that a future main spillway and gates could be constructed that actually would stand the test of time. This was before water quality standards for fish was a concern.

      • So maybe they should not have used the emergency spillway and just continued to use the main spillway letting it erode that would remove weak bedrock to make way to build it up afterwards.

        [As with all hazard management it is so easy to know what to do in retrospect. The decisions are far harder in real time. No-one knew how the main spillway would perform with such damage and such high levels of flow. D.]

  • An update on the Oroville Dam spillways
    Somewhat unexpectedly the crisis on the Oroville Dam spillways deepened yesterday.  As was widely reported, the emergency spillway was called into action as the water […]

    • I’m probably missing something but what are you referring to as unprotected ground? The concrete lip extends all the way to the left edge of the image you’ve shown along the side of the parking lot.

  • Oroville Dam: extraordinary erosion, and a crisis, on the spillway
    The Oroville Dam in California is the tallest dam in the USA.  with a height of 230 m, this is an earthfill embankment dam built between 1961 […]

    • In my county in California–the second smallest county in the state after the City of San Francisco–there are nearly 40 road closures due to landslides, slip outs, washouts, culvert failures, and sinkholes (with more closed from downed power lines).

      I can’t even imagine what kind of land movement they are having in the burn scars of the massive fires they had last summer south of us in Big Sur.

  • Review of a paper: the Dongla Landslide in Sichuan, China
    In a paper just published in the journal Landslides (Luo et al. 2017), my colleague at the University of Sheffield Lis Bowman and her co-authors from […]

  • Further movement of the Eaglepointe landslide in Utah
    Over the last few days further movement has been recorded on the Eaglepointe landslide in North Salt Lake, Utah.  This is the second period of reactivation […]

    • So, comparing photos of 2013 and 2015&2016, it seems to me that after the landslide took one of the McMansions with it (or maybe it was demolished before that), somebody built a similar house right next to the old plot?

      • Yes, there was one home destroyed during the 2014 slide, the occupants were alerted and all evacuated safely. To get a sense of the slide, here’s a point cloud comparison from lidar, flown before the slide, and structure from motion pointcloud acquired a few months after. https://skfb.ly/GVBW Red is negative vertical change, up to 20 meters; blue is positive, up to 15 meters.

  • Dave Petley‘s profile was updated 2 weeks, 2 days ago

  • Bova Marina – an interesting retaining wall failure video
    According to Wikipedia, Bova Marina is “is a comune (municipality) in the Metropolitan City of Reggio Calabria in the Italian region Calabria, located […]

  • Helicopter sluicing of the Kaikoura landslides
    The latest update on the works to mitigate the impact of the Kaikoura earthquake in New Zealand provides some interesting insight into how the authorities are going […]

  • Demi Lovato has her house red tagged after a landslide in Hollywood
    Demi Lovato is, according to Wikipedia, an American singer, song writer and actress.  She has recently spent $8.3 million on a rather beautiful […]

  • A terrifying mudslide video from Arequipa in Peru
    RT has uploaded a video onto Youtube of a terrifying mudslide in the Arequipa region of Peru, which apparently happened on Friday:

    The landslide […]

  • The human cost of landslides in 2016
    Since 2002 I have been collecting data on the human cost of landslides, allowing individual years to be analysed.  This dataset underpinned my paper in 2012 that presented […]

  • Cromwell Gorge: earthquake-induced groundwater changes in very deep-seated landslides
    Cromwell Gorge in New Zealand is the site of a series of spectacular, extremely deep-seated landslides in schist.  These […]

  • Nanzhang County, Hubei: 12 killed as a hotel is crushed by a rockslope failure
    On Friday night a major rockslope failure occurred on a steep slope behind the Mirage Hotel in the Haishishenlou holiday village, in […]

  • Xekaman 3 hydroelectric plant in Laos: a very major landslide in December
    The Xekaman 3 hydroelectric power station in Laos is a 250 MW dam, tunnel and associated infrastructure located at 15.375N 107.407E, close […]

    • I’m curious where the mud and rock came from. In the “after” picture, we can see the penstock up the hill, apparently intact (where did it break?), and the alluvium didn’t form a delta up the concrete slope. It must have come from the far side of the power house (away from photographer) as the power lines on the near side slope appear to be intact.

      On the order of 6 to10 meters of “rocks and mud flowed into the power house” – I guess they do need a dust mop and a broom before powering up the turbines.

      [indeed, the whole story is a little perplexing as the sink hole and new channel don’t seem to line up with the penstock slope either. My sense is that there is more than one landslide problem occurring here, but who knows. Fixing the power house is not going to be trivial. D].

  • The Mount Sulzer avalanches: the amazing video
    Yesterday I posted details of the four Mount Sulzer avalanches in Wrangell-St. Elias National Park and Preserve in Alaska. Information about these landslides was […]

  • Mount Sulzer debris and ice avalanches
    Mike Loso (contact via: michael_loso@nps.gov) of Wrangell-St. Elias National Park and Preserve in Alaska has kindly provided details of an amazing series of debris and ice […]

  • Future shock – the failure to learn from the 2015 earthquake in Nepal
    The Nepali Times had a large piece over the weekend entitled Future Shock, which was driven by National Earthquake day in Nepal.  In an […]

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