Geology Reference
In-Depth Information
7 STUDY METHODS FOR KARST AQUIFERS
7.1 Particularities of karst
Unlike porous or fractured aquifers, which obey Darcy's Law and where
the study of a small subset of the aquifer (sample, well, borehole) can be
extrapolated over a large portion of the reservoir, karst, heterogeneous and
hierarchical, requires a more complex approach including on the one hand
a global study of the aquifer's mechanics, and on the other hand detailed
analyses in the case, for example, of a catchment project or an attempt to
fi ght pollution.
Karst aquifers keep the traces of their different stages of emplacement.
A karst system is therefore an often-anarchical-seeming juxtaposition of
poorly permeable or even impermeable zones, of cavities fi lled with water,
air, or sediment, or underground rivers or lakes, of water-fi lled fi ssures and
of submerged drains. The circulation velocity of water in the same aquifer
can be slow in fi ssured zones and very rapid in drains.
Due to this anisotropy, karst systems rely on specifi cally adapted
methods.
7.2 Paleogeographic studies
Karst systems generally being polyphasic, it is important to precisely
defi ne their emplacement conditions, in order to evaluate the positions of
drainages and reserve zones. Alluvial terraces, benches, perched valleys,
temporary outlets, tuff accumulations, etc. are so many geomorphologic
clues to understanding the karst system. Analyses can also be done in the
endokarst, where the study of the infi lling and the staging of galleries will
help to explain the evolution of the system.
In coastal environments, bathymetric analyses can help detail the
variations in base level linked to eustatism, and indicate submarine valleys
linked to the presence of paleosprings (see Port Miou example, chap.
A9-2.5).
7.3 Hydrometric, physical, and chemical studies
7.3.1 Discharge
A karst emergence making up the fi nal outlet of a complex capacitative
and transmissive system, discharge variations and physical and chemical
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