Geology Reference
In-Depth Information
CONCLUSION
Significant advances have recently been made in our knowledge of the genesis,
geometry and functioning of hard rock aquifers. The hydrodynamic properties
of these aquifers appear to be mainly related to weathering processes. The
weathering profile, up to more than 100 m thick, is mainly composed of two
superposed layers, the saprolite, playing a capacitive role, and the underlying
fissured layer that assumes the transmissive function. All together and where
saturated with ground water, these two layers constitute a composite aquifer.
The spatial distribution of such weathering profiles (single or multiphase),
or their remains, can be mapped at the catchment scale on the basis of
various types of data: digital elevation model, observations on outcrops,
drilling cuttings and geophysical measurements. Then, the spatial distribution
of the hydrodynamic properties of granite type aquifers can also be mapped.
A precise geological mapping not only of lithology but also of the weathering
structure thus appears to be a prerequisite for groundwater management in
hard rock areas.
These newly developed geological and hydrogeological concepts, that
enable to regionalize hard rock aquifers properties, can answer several key
issues: (i) evaluation of aquifer potentialities from large to small (a few
hectares) areas; as a consequence, it helps in defining the characteristics of
field surveys (geophysics, radon, etc.) and well siting, (ii) elaboration of
water budget at the catchment scale, taking into account the piezometric
level fluctuations in the various layers, (iii) input data for numerical modelling
of the aquifer, (iv) elaboration of vulnerability maps, (v) guidelines for
aquifer protection, for town and country planning (siting of landfill, quarry),
etc.
Such a geological and hydrogeological model now requires to be adapted
to the geological contexts of weathered metamorphic rocks. The mapping
methodology is also to be developed for applications at a larger scale, 1,000
to 10,000 km
2
, through the integration of techniques such as remote sensing
and spectrometric and radiometric aerial surveys.
REFERENCES
Cho, M., Choi, Y.S., Ha, K.C., Kee, W.S., Lachassagne, P. and Wyns, R. (2002).
Paleoweathering covers in Korean hard rocks: A methodology for mapping their
spatial distribution and the thickness of their constituting horizons.
Applications to identify brittle deformation and to hard rock hydrogeology.
KIGAM Bulletin
,
6(2):
12-25.
Cho, M., Choi, Y., Ha, K., Kee, W., Lachassagne, P. and Wyns, R. (2003). Relation-
ship between the permeability of hard rock aquifers and their weathering, from
geological and hydrogeological observations in South Korea.
In:
Kr asny, J.,
Hrkal, Z. and Bruthans, J. (Eds.), International Association of Hydrogeologists
