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13 February 2017

An update on the Oroville Dam spillways – a new phase of erosion leads to evacuation of 130,000 people

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 level within the lake exceeded the inflow.  All seemed well – the quantities of water passing the crest were not considered to be particularly high, whist the erosion of the main spillway seemed to have eased despite the vast quantities of water flowing through the damaged structure.  However, as CaDWR noted in a press release yesterday, erosion started to develop at the edge of the emergency spillway as well.  Of course in this case there is no mechanism to control the situation – unlike in the primary spillway there is no sluice gate – meaning that there was the potential for a catastrophic release that would exceed the capacity of the downstream channels:

The concern is that erosion at the head of the auxiliary spillway threatens to undermine the concrete weir and allow large, uncontrolled releases of water from Lake Oroville.

Rich Briggs (@rangefront) tweeted these two images, taken from news reports, that show the problem.  The first highlights the location of the headward erosion:

Oroville Dam spillways

Headward erosion at the Oroville Dam spillways via KCRA News, Rich Briggs and twitter

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Whilst this one shows the magnitude of flows over the emergency spillway, and on the unprotected land to the side:

Oroville Dam spillways

Flows over the Oroville Dam spillways via KCRA News, Rich Briggs and Twitter

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It is clear that the flow has exceeded the emergency spillway and has flowed over unprotected ground adjacent to it, which inevitably was vulnerable to erosion.  To me this seems quite extraordinary – how did the design allow that to occur – but that is a question for another day.  The response of the authorities was first to almost double the flow down the main spillway (from 55,000 to 100,000 cubic feet per second), which will have accumulated more damage as a result, and second to start the evacuation of 130,000 people downstream.

Reports suggest that the water level in the reservoir has now dropped sufficiently for the flow over the emergency spillway to have ceased.  The authorities now have until Wednesday to both lower the water level and to patch up the spillways before the next storm arrives.

Fortunately the main dam remains undamaged and safe.  The likelihood of a catastrophic failure of the Lake Oroville spillways should now be low, but there is a huge amount of work ahead.

I will be doing the Reddit AMA (Ask me Anything) today (Monday) at midday EST (5 pm GMT).  Join in if you would like to discuss this event (or any other).

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10 February 2017

Oroville Dam: extraordinary erosion, and a crisis, on the spillway

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 and 1968 for the purposes of water supply, hydroelectric power generation and flood control.  After years of drought, California is suffering a series of huge rainstorms – so-called atmospheric rivers – that have rapidly raised the water level in the dam.  To allow flood control, the dam has been undergoing controlled discharges of water through the spillway.  This structure can be clearly seen to the left of the dam in the Google Earth image below:

Oroville Dam

Google Earth imagery of the Oroville Dam in California before the current crisis

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On Tuesday, after such a release water, major damage was noted on the spillway, apparently caused by the failure of the concrete base and then erosion of the underlying substrate. The California Department of Water Resources tweeted this image of the damage on 8th February:

Oroville Dam

Spillway damage at the Oroville Dam, via California Department of Water Resources

 

Over the next few days further discharges of water have been undertaken to test the spillway and to control the water level in the lake. The CaDWR tweeted this image of one such test earlier today:

Oroville Dam

Damage to the Oroville Dam spillway during a water flow test on 9th February, via CaDWR

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Unsurprisingly, the condition of the spillway has dramatically deteriorated:

Oroville Dam

Damage to the Oroville Dam spillway on 9th February, via CaDWR

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So now the Department of Water Resources are left in a bind.  KQED is providing excellent coverage of this event, with an update yesterday as follows:-

With the spillway mostly out of commission since major releases were curtailed, Lake Oroville has been rising at the rate of about half a foot [about 15 cm] an hour since midday Tuesday. Its level has increased 30 feet  [about 10 m] since then, with the reservoir’s surface now 20 feet [6 m] below an emergency spillway.

The emergency spillway, which would release water down a steep slope adjacent to the spillway, has never been used in the dam’s half-century of operation. DWR officials and others say water flowing down the slope will likely result in a large volume of debris being dumped into the Feather River, which flows through the city of Oroville on its way to the Sacramento Valley.

That’s one reason dam managers are willing to risk the destruction of the concrete spillway, calculating that would be preferable to the unknowns involved in an uncontrolled emergency spillover.

“It’s going to be rocks, trees, mud — liquid concrete — going down that river,” retired DWR engineer Jerry Antonetti told Sacramento’s KCRA as he watched the spillway Wednesday night. “I’d open ‘er up, sacrifice the bottom of that thing — it’s going to go in the river — clean it out next year and build a new spillway.”

The emergency spillway can be seen to the left of the main structure in the image below:

Oroville Dam

Google Earth image showing the main spillway and the emergency spillway at Oroville Dam.

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It is not difficult to anticipate the damage that the use of this structure will cause.  Fortunately the integrity of the Oroville Dam itself is not in question, but managing the spillway and associated damage is a massive challenge.

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9 February 2017

Review of a paper: the Dongla Landslide in Sichuan, China

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 China examine the fascinating Dongla Landslide in Sichuan, China.  This is an ancient landslide mass located in Muli County (at 28.361, 100.629 if you want to take a look on Google Earth).  The Google Earth image below, taken in 2015, shows the location:

Dongla landslide

Google Earth image of the Dongla landslide in China

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On the left side of the image, close to the place marked Lanman, there is a new 500 kV electricity substation.  To provide access to this, and to improve road links through the area, a 134 m bridge was constructed across the Shuilou River at this location in 2011.  Unfortunately it was not appreciated that this site is a part of a very large, ancient landslide mass.  Later in 2011 a part of the Dongla landslide reactivated.  Involving 6 million cubic metres, the progressive development of this landslide deformed the bridge.  This area is clearly shown in the 2013 Google Earth image, although note that the apparent deformation of the bridge is due to the terrain matching algorithm used by Google, not the landslide!

Dongla landslide

Google Earth imagery of the reactivated portion of the Dongla landslide

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The paper describes a fascinating history of this landslide.  Between 1990 and 2000 the area was subjected to extensive small-scale illegal gold mining that has left the terrain and vegetation scarred and damaged.  These pits have provided pathways for rainwater to enter the landslide.   But excavation of the toe of the slope for the bridge and road appears to have reactivated a portion of the landslide; for example in December 2012 the mass moved up to five metres. Luo et al. (2017) provide some fascinating images of the development of damage in the bridge as a consequence, including this one:

Dongla landslide

Bridge damage from the Dongla landslide, from Luo et al. (2017)

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Monitoring of the landslide showed a highly seasonal movement pattern, with enhanced periods of motion being associated with increased rainfall.  The movement occurred on shear surfaces located at about 20 m depth.  In order to provide a short term reduction in movement the slope toe was reinforced with a large toe weight, consisting of 80,000 cubic metres of soil, which reduced the rate of movement, allowing access to the substation by heavy machinery.  However, this was not a permanent fix, and by February 2014 the rate of movement was once again increasing.  In 2015 the bridge was removed with explosives, and a new site was identified.  The landslide continues to pose a threat though, requiring monitoring, with the major hazard being the potential to create a landslide dam.

This is a fascinating study that emphasises the importance of proper engineering geological investigation.  These ancient landslide bodies occur widely in high mountain environments, and repeatedly cause major impacts to infrastructure projects.  Identifying them requires real skill – and the use of engineering geomorphology – but the time and effort is well-spent.  As the study by Luo et al. (2017) shows, failing to identify them can be both extremely expensive and cause long-term impacts.  It is best not to unleash the dragon.  Once it is out of the cage it can be very hard to contain it.

Reference

Luo, G., Hu, X., Bowman, E.T. and Liang, J. 2017.  Stability evaluation and prediction of the Dongla reactivated ancient landslide as well as emergency mitigation for the Dongla Bridge. Landslides. doi:10.1007/s10346-017-0796-9

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8 February 2017

Further movement of the Eaglepointe landslide in Utah

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 this year.  KSL notes the following:

North Salt Lake city leaders and homeowners are once again concerned a landslide after a portion of a hillside shifted late Monday night or early Tuesday morning.  “You see it. You see the slough, you see the fall off, and it’s just scary,” North Salt Lake resident Terry Rasch said. He lives a few houses up and couldn’t believe it when he woke up Tuesday and saw his neighbor shoveling mud, and then he noticed why. A large chuck of land slid down a few feet, closer and closer to his neighbor’s home.  City workers put hay bales and sandbags into place to try to keep any more movement and mud from flowing into the house below. This is the same area where a home at 739 Parkway Drive was destroyed in a substantial slide on Aug. 5, 2014.

This is the landslide about which I posted about back in 2014KSL also has a nice gallery of images of the landslide, including this one:

Eaglepointe landslide

The Eaglepointe landslide via KSL

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Google Earth has a nice sequence of images showing the development of this landslide in recent years. This is an image from 2013:-

Eaglepointe landslide

The Eaglepointe landslide in 2013 via Google Earth

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2015:

Eaglepointe landslide

The Eaglepointe landslide in 2015 via Google Earth

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And 2016:

Eaglepointe landslide

The Eaglepointe landslide in 2016 via Google Earth

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There is also a good repository of reports into the site, including assessments of the location prior to the first failure, on a webpage hosted by the City of North Salt Lake.  It appears from the news reports that further movement is expected at this site in response to precipitation events.

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6 February 2017

Bova Marina – an interesting retaining wall failure video

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 about 120 kilometres (75 mi) southwest of Catanzaro and about 30 kilometres  southeast of Reggio Calabria”.  A video appeared on Youtube yesterday showing a rather spectacular retaining wall failure, which appears to be driven by a landslide occurring on the slope behind:

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There is very little detail about this event on the internet at present.  An article on strill.it, in Italian, suggests that significant distress was observed in this wall back in September, and that the final collapse occurred at about 10 am on 4th February. The road, SS106, was closed off before the collapse at Bova Marina occurred.

I am unsure as to the exact location of this event, but the site shown in Google Earth below looks like the most probably candidate.  Can anyone confirm?

Bova Marina

A possible site of the Bova Marina retaining wall failure in Italy, via Google Earth

 

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3 February 2017

Helicopter sluicing of the Kaikoura landslides

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 about dealing with the landslides on the roads to the north and south of Kaikoura itself.  This is the main north – south highway (SH1) that links the port of Picton, where the ferries to North Island dock, and the main population centre on the island around Christchurch.  The biggest issues lie to the north of Kaikoura.  The work is being coordinate by NCTIR – North Canterbury Transport Infrastructure Recovery – an alliance representing NZ Transport Agency and KiwiRail, on behalf of Government. This is the update:-

  • Work continued this week making safe the slips to the north of Kaikoura ready for removal.
  • Helicopter sluicing has continued on four of the nine large slips to the north of Kaikoura.
  • Up to nine helicopters are dropping more than one million litres of sea water on these slips each day to wash loose rock and material down the slip face and into the sea.
  • This work is critical to make it safe for our crews and machinery to move on site and begin removal. It can only happen once the design work is nearing completion so the crews can make rapid progress on the site.
  • Geotechnical engineers are now assessing secondary slips along this section of the route. These are smaller slips but still need to be stabilised before vehicles will be allowed back on SH1.
  • NCTIR continues to meet with the community to inform them of progress and what lays ahead in this massive task.

The aspect that caught my attention here is the concept of helicopter sluicing, in which water is being dumped onto the landslides to remove debris.  This is a novel approach that is also pragmatic, but I have rarely heard of it before.  The NZ Civil Aircraft blog has some nice images of the helicopters undertaking this work, whilst an article on Stuff from December includes an image of a machine undertaking helicopter sluicing on a landslide:

helicopter sluicing

An example of helicopter sluicing on the Awatere Valley Road, via Stuff

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Some of the machines undertaking this helicopter sluicing are those normally used for whale watching.  South Pacific Helicopters have put a video on their Facebook page of these sluicing operations.  These operations show both the challenges faced by these landslides and the ingenuity of the geologist and engineers in responding to them.

And this is of course an excuse to show the amazing video, one of my all time favourites, from 2009 of the use of helicopters to remove loose rock from a steep slope in Norway, which I featured in two posts at that time (post 1 and post 2):-

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2 February 2017

Demi Lovato reportedly has her house red tagged after a landslide in Hollywood

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 house in the Laurel Canyon area of Hollywood Hills:-

Demi Lovato

The new house belonging to Demi Lovato via Yahoo and Zillow

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It is without doubt a beautiful property, although I am slightly surprised at house close it seems to have been built to a steep slope. On Monday night, in a rainstorm, that slope appears to have suffered a landslide that sent debris into the backyard of a house alongside that of Demi Lovato.  The LA Times has a photograph of the event:-

Demi Lovato

The landslide close to the house of Demi Lovato, via the LA Times

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This is not a large or serious landslide by any means, but it undoubtedly raises questions about that slope.   The slope is being assessed by Building and Safety Assessors, meanwhile a number of houses have been red tagged whilst their safety is assessed.  The image above includes the house of Demi Lovato; it is clear from this view that a part of the house is very close to the slope, although I would stress that it is not possible to ascertain from this whether there is any danger.

This appears to be the site of the landslide as shown on Google Earth:-

Demi Lovato

Google Earth imagery of the site of the landslide close to the house of Demi Lovato

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It is interesting to note the very extensive engineering works going on nearby, presumably to protect the slope against failure (in this case the slope appears to have been cut to create a road bench). Interestingly, this appears to be the second landslide in the last month in Laurel Canyon. At the previous one, the affected property is apparently now on sale for $200,000.

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30 January 2017

A terrifying and tragic mudslide video from Arequipa in Peru

Arequipa

A still from Youtube footage of the mudslide in Arequipa in Peru that killed three people on Friday

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 apparently killed three people – it is not clear whether the victims were in this car or elsewhere in the landslide.  It is clear that a number of vehicles were caught up in the mudslide.  Global News suggests that sadly this is probably the case.

This accident appears to have occurred during heavy rainfall on the Panamerican Sur Highway.  The same rainfall appears to have been responsible for this riverbank erosion event that led to the loss of a hotel in the town of Lircay in Angaraes on Thursday:

 

 

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The human cost of landslides in 2016

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 the annual cost of landslides in terms of lives lost (see the accompanying blog piece that I wrote at the time).  Melanie and I have a new analysis for the period 2004 to 2015 in review at the moment.

The dataset for 2016 suggests that it was a bad year in terms of the number of landslides, but that the number of fatalities was not exceptional. In total I recorded 444 landslides worldwide that caused loss of life, of which just five were triggered by earthquakes.  The human cost of these landslides was 2,250 people, 10 of whom died in landslides triggered by earthquakes.  By comparison, in 2015 I recorded 345 fatal landslides, causing 2,376 fatalities.

The graph below shows the cumulative total through the year of the number of landslides that caused loss of life (excluding the earthquake induced events) and the number of fatalities that they caused:

human cost of landslides

The human cost of landslides in 2016

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I have added to the graph a simple line between the number of fatalities / landslides at the start and the end of the year to illustrate the patterns.  This shows that, as usual, in terms of the number of landslides the year started slowly but accelerated through the northern hemisphere spring and summer, and then declined through the autumn and into the winter.  This is the pattern that we see every year because the Asian monsoon dominates the statistics.  The fatality graph is a little more unusual though, with the peak period occurring between days 120 and 150 (i.e. in May).  This is earlier than in most years, and reflects a particularly active early monsoon in South Asia.

In the graph below I have compared the human cost of landslides in 2016 with that of 2015, showing both the number of landslides and the number of fatalities.  2016 data is in black and grey, 2015 in orange and yellow):-

human cost of landslides

A comparison between the human cost of landslides in 2015 and 2016

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The differences between the annual patterns are stark. Throughout the year I recorded far more landslides that caused loss of life than in 2015.  Only in the first and the last two months were the rates of events (i.e. the gradient of the lines) similar.  But the number of fatalities in 2016 are dominated by those events in May, which we didn’t see in 2015.  However, later in the calendar year, 2015 saw very major events that caused a big ssteps in the number of fatalities.  We didn’t see these events in 2016, meaning that the curve is much smoother, and the final tally was lower.

Of course we now start to worry about the human cost of landslides in 2017.  The first month of the year appears to be very similar to both 2015 and 2016, but as the graph above shows, January is a poor guide to what will happen.

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27 January 2017

Cromwell Gorge: earthquake-induced groundwater changes in very deep-seated landslides

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 landslides became famous during the construction of the Clyde Dam between 1976 and 1988, when a huge programme of mitigation was enacted to ensure that they remained stable during the filling of the reservoir between 1992 and 1993.  There are 17 very large landslides, all of which now have extremely low movement rates as a result of these engineering works, which include extensive drainage to draw down the groundwater level, toe buttresses and in one case a drainage blanket.  The image below shows the banks of Cromwell Gorge, taken from a helicopter hovering near to the dam:-

Cromwell Gorge

Landslides on the banks of Cromwell Gorge.

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These landslides are extremely well-monitored in every respect, providing a fantastic opportunity to understand the nature of processes occurring within them in response to external forcings. In a paper recently published in the Journal of Geophysical Research, O’Brien et al. (2016) have looked at the groundwater response in these landslides to nearby earthquakes. This work provides two really interesting insights.  The first is that there is a very clear short term hydrological response to the passage of the seismic waves through the landslide body.  The graph below is an excerpt of one of the figures from the paper showing the groundwater response from two piezometers located in the Nine Mile Downstream landslide.  The red bars are earthquakes analysed in this study:

Cromwell Gorge

Groundwater data from the O’Brien et al. (2016) showing the response of the hydrological system to regional earthquakes

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The authors found that the earthquakes induced substantial changes in groundwater levels, with the response being variable within the landslides (note the image above shows one response in which groundwater increases and another in which it declines).  These changes were more substantial than those generated by short term rainfall events, and in many cases the changes occurred over a period of a month or so.  Increased flow was also observed in the v-notch weirs that are used to monitor flow from the drainage tunnels.  It appears that the earthquakes are driving short term increases in the permeability of the landslides that allows water to move between different sections of the landslide mass.  These changes appear to be temporary.

But in many ways it is the other finding that is more significant. O’Brien et al. (2016) have looked at the response of the groundwater in the Cromwell Gorge to different types of earthquake forcing.  The authors found that greater changes occur in earthquakes that generate high-amplitude, long-duration, broad frequency bandwidth earthquake shaking.  This differential sensitivity to the nature of the earthquake is intuitively unsurprising, but really important.  We observe that similar earthquake magnitudes can generate very different landslide responses; understanding why is a key issue.  This paper, and the very detailed data that it describes, provides a key insight.

Reference

O’Brien, G. A., S. C. Cox, and J. Townend, 2016, Spatially and temporally systematic hydrologic changes within large geoengineered landslides, Cromwell Gorge, New Zealand, induced by multiple regional earthquakes. Journal of Geophysical Research – Solid Earth, 121, 8750–8773, doi:10.1002/2016JB013418

 

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