PROBLEMS - Hydrogeology: Objectives, Methods, Applications - page 335

Answer 1: In a karst environment, a spring is the fi nal converge point for
subterranean drainages. The spring enables the rapid and concentrated
transfer of the water disappearing into the losses. The well, however, which
was not drilled into a drain emerging at the spring, receives only a limited
infl ow from the Bébec swallow hole. Water from the Seine aquifer dilutes
these infl uxes from the fi ssured chalk.
Answer 2: The velocity of circulation in the karst leading to the spring and
to the Norville well (80 and 70 m·h -1 , respectively) are of the same order of
magnitude, but the factor of 13 observed between the concentrations can be
explained by dilution by water from the Seine alluvial aquifer. The spring is
therefore very vulnerable at the concentrated Bébec swallow hole, while the
well, presenting a lesser vulnerability to these karst waters, is nevertheless
very vulnerable to the infl ux from the alluvial aquifer.
Problem #9—Inquiry into the origin of fractures affecting an
individual residence
Residence A has been affected for the past two years by the appearance of
fi ssures on its southern face (Figure 10). It is suspected that the construction
of residence B, a few years before, may be the cause of these problems.
uphill drain
infi ltration well
Figure 10 Map of residence A with the location of the fi ssures and of the boreholes.