Événements

L'eau déborde dans les grottes !

Par Vincent Hulin , France Bleu Poitou mercredi 26 février 2014 à 11:58 Mis à jour le jeudi 27 février 2014 à 5:50

Spéléologie
Spéléologie © Jean-Jacques Savigny

Cela fait des semaines et des semaines qu'il pleut dans la région Poitou-Charentes. Les conséquences sont visibles au sol. Mais aussi sous terre : les spéléologues remarquent des choses inédites. Ils sont stoppés dans leurs descentes... à cause de la pluie qui inonde les galeries. Exemple à Chauvigny dans la Vienne.

C'est simple, ils ne l'avaient "jamais vu à ce niveau là" . Vingt-cinq mètres sous terre, dans le secteur de Chauvigny, la nappe phréatique est historiquement haute. Elle envahit certaines salles. Le niveau a doublé selon les endroits, il atteint parfois cinq mètres de profondeur... là-même ou les spéléologues passent d'habitude munis de bottes.

François Alamichel et Jean-Jacques Savigny du Spéléo-Club Poitevin

Les eaux de pluies mettent plusieurs jours à traverser le sol calcaire. A ce jour "tous les blocs sont trempés, l'eau met un certain temps à couler" . Cela explique pourquoi elle tombe sans cesse au goutte à goutte... et rend les parois encore plus boueuses que d'habitude. La terre est partout, "c'est moins agréable"  reconnait Jean-Jacques Savigny, du Spéléo-Club Poitevin !

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Spéléologie
Beaucoup plus de terre que d'habitude   © Jean-Jacques SavignyLe niveau sous terre dépend du niveau de la Vienne, il peut varier très rapidement. François Alamichel, spéléologue lui-aussi, explique cependant que la Vienne ne présente pas "un comportement de crue comme dans le Vercors ou les Pyrénées" . Des dangers sous terre

Le risque est que l'eau de pluie fasse des dégâts sur la roche. Elle est certes propre, mais elle est aussi acide par endroit. Et François Alamichel constate qu'elle commence à grignoter le sol calcaire. A terme "la roche va se creuser et la cavité va s'élargir" . Cela pourrait avoir un "danger pour les blocs et pour les spéléologues" . C'est pourquoi il descend au moins une fois par semaine sous terre pour s'assurer du bon état des grottes. 

Reportage de Quentin Vinet