21 May 2018
Hidroituango: another landslide crisis at a hydroelectric dam
Over the last few days another landslide crisis has occurred at a hydroelectric dam site, this time at the large Hidroituango project in Colombia. This is a very large embankment dam being built across the Cauca River near to Ituango in Antioquia Department. The dam, estimated to cost $2.8 billion, was due to be completed this year. When operational it will generate 17% of the electricity demand of Colombia. The dam is 225 m high.
The present landslide crisis is a little difficult to understand as media reports are somewhat confused. The best narrative appears to be in this news report (in Spanish), which seems to suggest that:-
In 2014, Empresas Públicas de Medellín (EPM) (responsible for the dam) diverted the Cauca River through two tunnels, each with a diameter of 14 m, to allow construction of the dam. Earlier this year, as filling of the lake began, the water was diverted to a further, larger tunnel 200 m upstream from the first two. The original tunnels were plugged with concrete.
Unfortunately, three landslides occurred at the site between 28th April and 7th May. These landslides blocked the flow of water, and the lake started to fill to a dangerous level. Concerns started to be expressed that the lake might overtop the dam, triggering collapse. Correction: it is now clear that the tunnel was blocked by a collapse event that propagated to the surface to generate a crater, rather than a conventional landslide. This crater can be seen in satellite imagery.
This image, showing a large landslide scar, is shown in some reports:-
Meanwhile , the Global Forest Coalition has this image of a landslide, probably originating from the scar shown above:
The blockage of the tunnel started to cause the water level in the dam to rise, and evacuations were initiated. To try to manage the risk, EPM attempted to dynamite the seals from the original two tunnels. However, progress was to slow, leading to the decision on 10th May to drain the lake through the powerhouse, causing considerable damage.
But, on 12th May the main tunnel naturally unblocked, releasing a large volume of water that caused extensive flooding downstream. There is a strange video online that appears to show an explosive release of water at the site, and a further severe release, apparently at a different location.
There is dramatic footage showing the downstream flooding caused by the release of the water:-
It appears the tunnel then resealed naturally, causing a further impoundment of water. Latest reports seem to indicate that about 7000 people have been evacuated, whilst EPM are mitigating the risks. It appears that the priority is to complete the construction of the crest of the dam, which would allow the use of the spillways to control the flow.
I have noted previously that landslide risks are not being managed adequately at many large hydroelectric construction projects. This would seem to be yet another example.