Geology Reference
In-Depth Information
Figure 17 Schematic geologic map of the limestone belts feeding the emergence.
Question 1: What can you conclude about the catchment basin of the spring
and its vulnerability?
Question 2: What advice can you give to increase the quality of the water
being taken?
Answer 1: The basin can be roughly estimated, using the modulus, at around
10 km 2 , in the limestone units uphill from the spring. The geologic map
shows that the spring is located in a graben cutting across a collection of
limestone belts, the structure of which, in overthrusting depressions, would
seem to predict east-west drainage.
This basin fi lled with impermeable Cretaceous marl therefore plays a
primary role in the surface and subterranean drainage. The basin is more
clearly defi ned by the results of the tracer tests.
The examination of the temperature and conductivity curves shows
that the spring is subject to important variations and reacts quickly to
precipitation. The temperature and mineralization increase regularly as the
dry season progresses, but drop immediately after rainfall. The circulation is
therefore rapid and the reserves small, which does not favor the dissolution
of an eventual contamination.
The analysis of the curves in February, period during which surface
water is colder than karst water, shows that signifi cant drops in temperature
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