Preliminary Documentation - Hydrogeology: Objectives, Methods, Applications - page 97

C HAPTER B1
Preliminary Documentation
It is necessary, for all projects, to collect and exploit existing documentation
from the very beginning, as it allows the inventory and critique of the range
of preexisting knowledge.
1 Topographic and geologic maps
Topographic maps exist at different scales, although 1/50,000 and 1/25,
000 are particularly common in the French territory, where they are created
and distributed by the IGN (National Geographic Institute). They provide
precious infomation on the topography and morphology of the study area,
as well as on the hydrographic network and on the position of characteristic
features (springs, wells, cavities). In certain regions, 1/10,000 and even 1/
5,000 maps cover specifi c sectors in greater detail. The old master plans at
the 1/20,000 scale, when they can be found, are often high-quality sources of
information. The same is true of cadastral surveys, which can help determine
the location of wells and springs. Toponymy can also help direct geologic
and hydrogeologic approaches, particularly in old documents, given the
frequent changes in place names on recent documents.
Geologic maps are distributed in France on the 1/50,000 and 1/
80,000 scales by the BRGM (French Geological Survey). They give an
understanding of the regional geologic setting and of the tectonic style and
the lithostratigraphy of the study area. They remain very general, although
variable depending on the survey, and the attached review can provide
useful information, as well as a bibliographical starting point.
Hydrogeologic and geomorphologic maps concerning a certain number
of regions (BRGM and universities) exist, and can usefully complement the
data being collected at this stage.