Geology Reference
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• on the other hand, per descensum exchanges at the roof of ancient
collapses of gypsum caves that decompressed the overlying terrain
and increased their vertical permeability.
Problem #15—Prospection of an alluvial zone in order to
implement a water well
A river and its accompanying aquifer are established in an alluvial zone,
at the roof of a rocky substratum which also makes up the sides of the
valley.
With the goal of exploiting the alluvial aquifer through a water well,
geophysical prospection of the valley was undertaken, in order to specify
the geometry and nature of the alluvial deposits and to determine the best
location for the well.
The prospected site is partially shown on the joint fi gure, and the results
of the electrical survey undertaken and given in the following table.
Question 1: Draw cross-sections along the lines AA', BB', and CC', with
the geologic units, taking into consideration the fact that the banks have
a slope of around 40° below horizontal, and that the river is sunk 3 to 4 m
into a practically planar alluvial plain.
Question 2: Select the most favorable sites for reconnaissance drilling, and
justify your choice.
Figure 22 Location map for the electrical surveys.
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