Characterizing Aquifers - Hydrogeology: Objectives, Methods, Applications - page 119

Figure 63 Position of a limestone aquifer's outlet as a function of the geologic structure and
of the topography.
Figure 64 Main types of springs.
In certain rare cases, artesian springs can drain deep aquifers, due to
lithologic heterogeneities in the overlying impermeable unit, or to draining
faults allowing a rising leakage from the aquifer (Figure 64c).
2.2 Conditions for the emergence
The emergence of water from a water-bearing formation is often highly
variable. In some cases originating from a point source at the mouth of a
gravelly channel, a fracture, or a karst cavity, it can also occur in a more
or less diffuse manner, corresponding to a multitude of scattered seeps,
or lining, over a certain distance, the contact between the aquifer and an
impermeable layer.
Springs are not always located where they theoretically should be,
and can be displaced to a lower elevation by a hydraulic conductor
corresponding to a smaller reservoir. This situation is commonly seen on
hillsides, when the contact between the aquifer and the impermeable unit is