Geology Reference
In-Depth Information
C HAPTER B3
Characterizing Aquifers
The previously elaborated geologic model subsequently serves as a base
in order to note the various hydrogeological information acquired during
the preliminary research phase (documentation, inquiries and fi eldwork),
and specifi c investigations are then made in order to precisely understand
the behavior of the aquifer(s) being studied:
￿ through direct investigation, in order to study the water seeping into
the ground, as well as its subsequent reemergence at the surface;
￿ through indirect research, in order to defi ne the spatial organization
and the fl ow patterns within the aquifer, and in order to characterize
the variations within the reservoir.
1 THE INFILTRATION OF WATER
Water seeps into permeable rock in different ways, depending on the
environmental conditions. Infi ltration varies spatially very noticeably, can
be diffuse of concentrated, and can be rapid or more or less delayed.
Detailed observation of the stream system on a topographic map often
enables the global characterization of infi ltration into the ground, and the
establishment of a preliminary regional aptitude zoning:
￿ high-infi ltration areas, with little to no surface hydrography. This
is typically the case for karst plateaus and coarse-grained detrital
deposits;
￿ impermeable or poorly-permeable areas, criss-crossed by a tight
network of ravines and streams. This is the case for marl, schist, or
calcareous-marl formations and for steep slopes;
￿ intermediate areas, between the two preceding extremes, often
characterizing composite deposits or variable topography.
 
 
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