5 June 2018
Hidroituango – an increase in movement rate
Posted by Dave Petley

LIdar imagery of the Hidroituango dam site, collected by Vannet SAS
Hidroituango – an increase in movement rate
In the last few hours, RCN Radio in Colombia has reported an increase in the movement rate in the landslide at the Hidroituango dam site, breaching the alarm threshold of 10 mm per hour. This has triggered evacuation of 45 workers at a part of the dam site. It is unclear as to whether this is merely the landslide showing typical stick-slip type behaviour, or a transition into a new phase of movement. Without a graph of the movement pattern this is impossible to ascertain. Meanwhile, the government is establishing a monitoring centre to collate the data, as recommended by the team from the United Nations and the US Army Corps of Engineers. This is a prudent move.
The same team has described a series of scenarios for the dam, as reported by BN Americas:
“They have established that we have a dam that is high risk, and that risk is associated with three main scenarios, some that are connected to the geotechnical risk of the mountainous mass or by landslide or damages to the powerhouse, which could trigger in the failure of the dam.
“The second scenario is that this unleashing would lead to a wave, as Minister Arce has just said, that will exceed the prey and also lead us to the failure of the dam.
“The third has to do with the dam itself: the top priority of level 385 to 410 and to 430, as has been established, can, by the way it was done to respond to the emergency, can generate some leaks and these filtrations could trigger in the failure of the dam, for which they recommend reinforcement of the priority filling, of the increase of the dam in these emergency conditions.
I think this means that they are concerned that: 1. Failure of the rockmass in the abutment (i.e. the landslide) could destroy the dam directly; 2. the landslide could trigger a wave that overtops the dam; and 3. the dam might fail because of seepage.
If so then this is a project is in deep, long term trouble. The lake level is currently rising at 70 cm per day, with the current level at 393 metres. The spillway is at 401 metres, so the lake level has to increase by another 8 metres yet. The groundwater will rise as the lake level comes up, with some lag, so the stability of the slopes will continue to decrease. Of course the lake level will increase beyond the spillway height in periods of heavy rainfall (there might be two metres depth of water flow through the spillway, unless the lake can be drawn down. If so then the lake level might top out about 10 m higher than at present, at some point.
Meanwhile, the two leaks at the foot of the dam are releasing 18 litres per second and 11 litres per second respectively. The authorities are trying to stem the leaks by sealing the site with bentonite. I remain unclear as to the source of water generating these flows.
Finally, a couple of weeks ago El Colombiano posted this video reportedly showing processes occurring within the tunnels at Hidroituango:
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This was reportedly associated with the water flow in the machinery house. I have not seen anything like it – I am assuming that it was caused by cyclic pressure changes in the tunnel, driving condensation. I am not sure what this means, or why it was occurring. Does anyone have any insight?
Thanks Dave. I do no envy the dam managers right now.
That is very unusual! I’d be bringing along a pig for good luck!
That must be some sort of low frequency standing wave effect.
Those may be anti-nodes where the pressure fluctuates the most.
I note that they appear to trade places in the tube, consistent w/ a resonance effect.
It looks like pressure waves possibly caused by cavitation in the tunnels or penstocks below the access road. If these are cyclic pressure waves, they may be caused by cavitation in the penstocks. If this is the case then this dam is in serious trouble. That could eventually lead to rupture of the steel at a joint or fracturing of the grout surrounding the pipes. It is difficult to say from the video but this is definitely not something you want cycling through an unfinished dam structure. Since this is an earthen dam, the pressure waves can also induce liquefaction in the fine granular material encasing the core of the dam – similar to small earthquakes.
If they are using the powerhouse as a bypass, as has been stated in earlier reports, then the powerhouse will likely be severely damaged or destroyed. I pray that they do not have an implosion event which can collapse the penstocks. Cavitation is a precursor for implosion because it generates huge cyclical stresses within the pipes…. And this is comment does not even take into account the landslide issues plaguing the project. This keeps getting scarier by the day!
Hi everybody, this is Juan from Colombia. A new official report launched by Government of Antioquia suggests that, according to the information analyzed by team from the United Nations and the US Army Corps of Engineers, the mountain mass that is mobile is reported to have a volume between 1 and 40 million cubic meters and not 130,000 cubic metres as it was mentioned in a previous post. Don´t you think that this situation, added to the seepages in the foot of the dam could be potentially worse than Vajont disaster? Thanks so much for your updates and great information about this important project for Colombia, unfortunately, our news media and EPM are not releasing technical information that can be properly analized to understand the real size of this situation.
Evacuate to higher ground ASAP!
Hi Dave, about the water condensation in the tunnel, i suspect a water hammer phenomenon… probably due to the water going through the machinery house… juste a guess but still impressive.
Also thanks for the quality reports.
Hi Dave, about the water condensation in the tunnel, I suspect a water hammer phenomenon… probably due to the water flowing in the machinery house… just a guess but still impressive.
Also thanks for the quality reports.
Well, watching the video and using my training as a mechanical engineer, appealing to my modest knowledge of thermodynamics, fluid mechanics, heat transfer and strength of materials. I’d say, it’s ghosts. Sorry for the tasteless joke, I’m just trying to defuse a rather delicate situation in the most inappropriate matter.
On a more serious tone, I agree on your assessment of condensation being driven by sudden changes in pressure. And I add that these changes in pressure may be related to a sudden compression in the air generated by the tunnel radially contracting and expanding. Seeing how they seem to happen at regular intervals, it’d say the tunnels are pulsing, I can only hazard a guess of how much energy is required to make rock tunnel behave like a plastic straw.
But all of this is an “educated” guess, no way near an expert’s voice, please take all of this with a grain of salt.
this article was just posted.
It says that the north American experts have said that a landslide of 10-40 million m3 is possible, and that the construction materials used don’t comply with international standards. The EPM infrastructure manager says that is not true but does concede that some of the recent rapid construction has not always been ideal given the circumstances, but it couldn’t be helped.
It discusses the possibility of building another tunnel, but that could take a year.
http://www.elcolombiano.com/antioquia/hidroituango-riesgos-que-afronta-el-proyecto-IL8814028
I am looking at the video and i am reminded of a strange but understable situation I had more than once when we used to run large 21Inch plus pipelines to carry sludge water (influent). Every time we had a pipeline bust, usually down hill enclave, the sediments would settle in a around the enclave after a while. The uphill raptured pipeline would then as a vacuum suck on the settling material sending the other way a mix of liquid forming spectacular cavitation like you’re seeing in the video above. After a while we began to interpret that specutacular occuring as a sign we have a pipeline burst. I am assuming that depending on the solids in the engine room, a mix of suction and vaccum is responsible for that occuring. My fear, is structural failure around the engine room structure where concrete meets the earth causing sippage. The longterm viability of that project would be in question. I am in Colombia so I am following this intently.
Where can I find the report “Imforme Conjunto de Emergencia de la Represa Hidroituango” prepared by ONU Medio Ambiente?
The video was released by El Colombiano with an article explaining the phenomena:
http://www.elcolombiano.com/antioquia/fenomenos-que-ocurren-dentro-de-los-tuneles-de-hidroituango-AA8714332
Here’s the translation of the explanation:
…”Lilian Posada, civil engineer specialized in fluvial hydraulics, assured thet the phenomena seen in the images taken in one of the project’s transit galleries is air that is ejected under pressure by the large flow of water that runs below those tunnels.
Posada explained that inside the dam there are several tunnels located at different heights: “There are many tunnels under the machine house, under the dam, that must have air avaliable for the people working there”.
The engineer explained that this phenomenon occurs in the hydroelectric because “the water entered the tunnels without warning, and, since they are all at different heights, they are filling in an irregular manner, which generated air capsules”.
She said that these air bubbles are formed by different variables. “The height or shape of the tunnel did not allow the water that entered to evacuate all the air, so there were some points where the air is concentrated. There, the movement of the liquid pushes the air under pressure and makes it find a way to the surface “.
The expert said that this phenomenon is the “very damaging for the tunnel, galleries, conduits, because it pressure is being applied to the rock”
In conclusion, the flow of water through the different tunnels of the dam causes the air that was trapped to come out under pressure through the cracks of the rock to the outside…”
Wow..the end of the film shows an oscillation from one end of the tunnel back to the other. Water being compressed between cracks in the tunnel floor squeezed out under high pressure as the oscillation of the dam, tunnel, mountain moves back and forth. That dam is going to fail….
I attach the opinion from the technical commitee Colombian Engineering Soiciety that anakyzed the crisis
https://sciengsustainability.blogspot.com/2018/05/hidroituango-hydropower-dam-colombia.html
This is condensation and re evaporation of water vapour in the air due to a standing low frequency air pressure wave (sound of about 1 hertz or less) in the tunnels.
The water is not being squeezed out of the floor into the air directly.
In itself it is not dangerous, like if the sound wave is caused by wind blowing across or through tunnels like when you blow across the top of a wine bottle.
Of course if the energy is coming from water processes or rock movement, then there is much more to be concerned about.