Geology Reference
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units. In 1979, at the initiative of the Compagnie Générale des Eaux (now
VEOLIA) and the City of Montpellier, a team from Hydrokarst, a subsidiary
of COMEX, reached a depth of 75 m 536 m from the entrance. A catchment
project was then proposed in order to provide an alternative to supplying
Montpellier with water from the Rhône river. Following a war of infl uence
opposing the powerful supporters of a surface water adduction and the
hydrogeologists, led by the tenacious Professor J. Avia, the subterranean
solution was chosen.
The project consisted of reaching the karst passage with boreholes
and of placing pumps to create a drawdown of several tens of meters
which would theoretically enable the exploitation over several months of
a discharge of 1,700 L·s -1 .
Construction took place in 1981; an underground station was
excavated and four boreholes with a diameter of 1.8 m reached the passage.
Three pumps were installed, each enabling a discharge of 1,000 L·s -1
(Figure 117).
Figure 117 Lez (Montpellier) spring catchment system (from a CGE document).
The resource is managed so as to allow a complete recharge of the aquifer
during the autumn rains. Currently, the system is functioning perfectly. The
drawdown, limited at 38 m, enables the extraction of 1,700 L·s -1 .
Part of the water goes to Montpellier and the other sustains the fl ow
of the Lez, guaranteeing a minimum discharge of 160 L·s -1 and conserving
a satisfactory surface water quality.
The system could provide greater quantities, but at the risk of drying
neighboring springs and causing turbidity problems greater than the
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