There could be apocalypse soon. Bagatelle dam could collapse, according to a source. In a report, the geomorphologue Prem Saddul explains that this colossus, which can contain 14.2 million m3 of water – the equivalent of 6000 Olympic swimming pools could collapse, thereby jeopardizing the security of 50,000 people transiting the Ébène Cybercity. The question that arises: why and how? Are the dangers real?
Some explanations first. Referring to the study of geomorphologue (Editor’s note, a geomorphologue studies the succession of soil layers, the nature of the rocks and their formation), the Bagatelle Dam which should be completed in December this year was built with stone containing pyrite, made with 50% sulfur and 44% iron. On contact with water, it will break down and the wall will end up riddled with holes, small medium and large, like cheese.
And that’s not all. This “mixing” found in the rock will also produce sulfuric acid upon decomposition. The effect of the acid on the rock, or any other material, is far from constructive. Together, these phenomena, according to Prem Saddul, do not inspire much confidence. And the risk that the dam collapses is real.
Ok, but what about the Midlands Dam which was built with the same material? Is the risk the same? “Il est difficile de se prononcer. Car, comme toute structure bâtie par l’homme, le risque zéro n’existe pas,” says engineer Mehaad Tegally . However, regarding the Midlands dam, it is the waterproof retaining wall which is in contact with the water and not the pyrite that was used only to consolidate it. Therefore, the problem of decomposition does not arise.
He argues, moreover, that it is the same technique that was used for the Bagatelle Dam. “Tant que la pyrite n’est pas en contact avec l’eau, il n’y a pas de risque. C’est comme pour un avion.Si tous les moteurs tombent en panne, il s’écrase. Mais nous faisons tous confiance à l’ingénierie et continuons à voler sans crainte…” In the case of Bagatelle Dam, the danger is not non-existent but the work that has been done is reliable, according to the engineer.
André Chan Chim Yuk, soil behavior and its components expert, suggests that pyrite is present in all rocks in Mauritius. “Il existe pas mal de composés chimiques dans la roche. La pyrite s’y trouve en différentes quantités, parfois infimes.” All he says is that we need to know the amount that is found in rocks used to build the dam. “Il faut également savoir à quel rythme elle se décompose. Cela dépendra du degré d’exposition à l’eau.” The construction of such structures requires the feedback of experts in several fields, says André Chan Chim Yuk. “On ne peut pas prendre un seul angle, se fier à un seul point de vue quand il s’agit d’un tel projet.”
How about the other reservoirs, La Ferme for example? Could they collapse? Have they been built using pyrites? “La construction est totalement différente, De plus, le réservoir est inspecté régulièrement.”