Geology Reference
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outlets imposed by the position of the impermeable basement), nor to an
increase in infi ltration over the upper Keuper outcrops (recharge zone). In
fact, the perturbations affect the fl ow conditions in the aquifer, particularly
in its major drainage axes, under the effect of the pumping in wells that
greatly increased during the same time period.
The pumped water is not used for the public drinking water supply
due to its high mineral content, but private pumps nevertheless are
multiplying in the gypsic and dolomitic Keuper lenses, and particularly in
the Muschelkalk carbonate reservoir. Its uses are various: watering gardens
and fi lling pools in suburban and spaciously urbanized areas, concentrated
agricultural and industrial extraction, and golf course irrigation.
In the graben directly concerned by the 1998 collapses, some water users
had observed, over the last ten years, a distinct decrease in the productivity
of their equipment, or even, in a few cases, a complete drying up. The
deep aquifer circulates in the direction of the southern Carimiaï spring
and presents, in the problematic zones, an organized drainage system
through several favored axes converging towards a single collecting passage
(Figure 129).
The karst problems of all ages are perfectly aligned along the drainage
axes revealed by the piezometric map, clearly illustrating an accelerated
reactivation of older karst processes under the effects of intense exploitation
in the deeper aquifer.
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