13 Direction of Sustainable Development of the South Province Territories I Strolling along the waterways 12 Strolling along the waterways Water sinkhole Enigma behind the scenes Soft sponges Intermittent Dotted with bathtubs, the Lakes Plain Crystal clear water contrasting with the metallic crust of the glowing soil or a bowl of murky water teeming with wet grass, the sinkholes hidden within the vegetation offer us their magical atmospheres to contemplate. The large ones are subject to sedimentation while those with steeper walls are the superficial manifestations of erosion phenomena which take place in the subsoil, under the action of “pseudokarstic” underground flows. Mysteries to be solved An alignment was noted between several depressions because a large fracturing - fault allowed their formation. The presence of a withdrawal phenomenon (extraction from below caused by the circulation of groundwater) constitutes one of the origins of these depressions. _ The lentic environment: lakes and sinkholes Suitable for calm waters, with low flow, or even stagnant waters, it corresponds to lakes characterized by their large extent, to ponds, etc. Illustrations based on the Serino diagrams, 2012 Collapse sinkhole Funnel or bowl sinkhole Flat bottom sinkhole Drawing Following the sudden collapse of the armour. In V. In a flat-bottomed bowl linked to the accumulation of sediment. Shape Circular and small. Circular to oval, deep and modest in size. Circular to oval, shallow, larger in diameter. Edges Steep walls with large blocks of collapsed armour at the bottom. Gentler sloped walls with large blocks of collapsed armour and gravel in the slopes. Soft walls. Water Transparent, if present. Transparent, if present, very variable in height, seeming temporary. Blurred, if present, at fairly constant and probably permanent height with herbaceous and hydromorphic vegetation and often shrubby to treelike vegetation on the slopes. *? *? © Bio Eko Types of sinkholes There are several types of sinkholes. The diagrams opposite illustrate the 3 main cases encountered in the South. An example of a funnel sinkhole, the Tahitian Hole, at the Lakes Plain, forms a vast cross-shaped depression, approximately 25 m deep. Today, it represents a unique case. The water staying there temporarily presents rapid piezometric variations and the sinkhole reveals a loss when it finds itself dry. Types of sinkholes Lake in Eight
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