The Study of the Geometry of Aquifers - Hydrogeology: Objectives, Methods, Applications - page 100

C HAPTER B2
The Study of the Geometry
of Aquifers
An understanding of the geological context is the indispensable base
for any hydrogeologic study, and the hydrogeologist must fi rst be an
experienced geologist. Indeed, a knowledge with a maximum of precision
of the geometric limits of aquifers, which determine the storage capacity
of groundwater and control its circulation and discharge, is absolutely
necessary. This purely geologic analysis serves to construct a more or less
refi ned model which will then support further refl ection.
Multiple methods can be used, and they are presented in order of their
logical apparition in the context of a hydrogeological study.
1 FIELD OBSERVATIONS AND SURVEYS
Fieldwork is indispensable in order to gain a detailed understanding of the
local context, and requires an appropriate topographic map onto which in
situ observations and measurements may be transposed. Commercially
available maps may be adequate for relatively large-scale regional
projects, but more precise topographic surveys are needed for a detailed
understanding of the geology of the site, and for smaller-scale projects. These
maps are then specifi cally created, often by photogrammetric restitution of
aerial photos and ground-truthing, at a scale appropriate to the goals of the
study (1/5,000, 1/2,000, 1/1,000). When the study area includes a coastline,
bathymetric maps can be highly useful.
Examining aerial photographs with stereo lenses allows a useful
preliminary morphological survey, and an understanding of the general
structure and of the fracturation of large rock units. Obtaining more precise
data requires a high level of experience with this type of interpretation.
Aerial photos are distributed at different scales which offers both black
and white and color photographs taken at various points in time. They can