16 April 2017
The Meethotamulla garbage dump disaster in Sri Lanka
At the time of writing, the loss of life from the landslide at the Meethotamulla garbage dump in Colombo, Sri Lanka is 26 people, with reports varying as to how many more victims have yet to be recovered. A press release from the Ministry of Defence in Sri Lanka, which is leading the response, indicates that 145 houses have been buried. This is of course the second major garbage dump landslide this year.
The most informative images that I have seen of Meethotamulla landslide were tweeted by Azzam Ameen (a BBC reporter) on Saturday. They were apparently collected by the Sri Lankan Air Force. This image shows an overview of the Meethotamulla site, with the failed side of the dump clearly shown by the freshly exposed garbage:-
According to Google Earth the dump is about 380 metres long. From the image it appears that the landslide is a pseudo-rotational slip that has formed a very steep back scar (further work is going to be needed to make this site safe before the rainy season begins). The slide appears to have engulfed houses along a large section of the toe. The interaction with the buildings is complex, as this image (from the same source) shows:
It appears that the debris has over-ridden some buildings, but bulldozed others to incorporate them into the landslide:
This disaster did not come out of the blue. This article, from August last year, highlights grave concerns about the stability of the Meethotamulla site. It includes this image, which clearly shows that mass movements were occurring in the garbage:
It is undeniable that this site was unsafe. The garbage mound is clearly too high and too steep, inviting a rotational failure. With houses so close to the toe of the slope the hazards were severe. I am no expert on garbage dump landslides, but it seems likely that the decay of the waste will cause it to weaken with time, increasing the risk. In addition, in a humid monsoonal climate, the pore pressures are also likely to increase with time (as is well-documented in embankments, for example). Thus, the stability of this slope was probably decreasing even without the addition of further garbage.
This is another case in which we know and understand the hazards, but fail to manage them. The results are once again tragic.