21 May 2018
The Hidroituango crisis: complete evacuation of seven communities
The Hidroituango crisis continues, although there does not seem to be much likelihood of a compete collapse of the dam. Several communities, including Valdivia, Nechí, Cáceres, Tarazá and Ituango, Ayapel (Córdoba), Guaranda and Caimito (Sucre), have now been evacuated, and the ANT (the National Land Agency) has withdrawn all of its staff from those areas.
Meanwhile, the water level in the reservoir is being managed by diverting flow through the powerhouse. El Pais reported that heavy rainfall over the weekend meant that inflow (at 2,300 cubic metres per second (cumecs) exceeded the outflow, causing that the water level to rise once again. In part this appears to be because the water flow through the powerhouse declined from 1,600 cumecs to less than 900 cumecs. The consequence is that the water level was rising at a rate of about 20 cm per hour, although there is still about 30 m of freeboard, meaning that a collapse from overtopping is unlikely.
Latest reports suggest that the rate of increase of water level is now 8-10 cm per hour.
El Pais also reports that the works on the crest of the dam have meant that the top has now reached 407 m (absolute elevation presumably), just 3 m short of the point at which the spillway can be brought into operation.
I have still to see an explanation for the water that was flowing through one of the tunnels on the flank of the dam. As reader Elizabeth noted in a comment yesterday:
“the “strange online video” showing the explosive release was filmed on one of the vehicular access tunnels. these tunnels are on a section of the dam called the “galleries”, the most worrying thing is that water is not supposed to reach that section, as those tunnels were meant for vehicular access to the internal facilities.”
So how was water flowing through this part of the dam? This image, from a drone video from 20th May, appears to show that this flow was continuing:-
At the moment the Hidroituango crisis appears to be mostly under control, but the situation remains critical. It seems likely that the infrastructure has been very seriously damaged, so the medium term implications for the site may be significant.