The Exploitation of Aquifers - Hydrogeology: Objectives, Methods, Applications - page 180

￿ The choice is also infl uenced by other constraints, on the one hand
the ascertaining that the resource can be adequately protected if it is
intended for domestic use, and on the other the acceptability of the
proposed degree of pumping with respect to regulations and potential
impacts on sensitive environments (minimum fl ow release for rivers,
risk of infl uencing other water sources).
2 CATCHMENT SYSTEMS
Exploitation methods for water have greatly evolved over time. Initially,
gravity-driven networks were favored, and relied on the direct diversion of
springs located at an elevation above that of the destination, or on gallery
and trench systems draining superfi cial aquifers (scree slopes, alluvium).
Wells were principally used for local supply, raising water manually or
hydraulically, or even with the help of suction pumps at the surface, in the
case of shallow aquifers. The development of drilling methods and pumping
equipment subsequently enabled the tapping of deeper and deeper aquifers,
and access to more and more complex hydrogeologic structures.
Diversions at the emergence point have almost no effect on aquifers.
When catchment systems are more complex, however, involving conduits
and galleries tapping the initial source of the water, they can cause changes
in the elevation of the emergence point, which will also affect nearby
drainage conditions.
Catchments directly within an aquifer, through pumping, result in
signifi cant perturbation of the groundwater system, and can affect sites
over a range of distances and for a variable length of time.
Each catchment has its particularities, depending on the topographic
and hydrogeologic characteristics of its environment. Their description of
catchment systems therefore remains simplifi ed and relatively general.
2.1 Diverting springs
In the case of a karst outlet issuing from a cave in a very concentrated
manner, the catchment system can simply consist of a concrete extension
of the underground riverbed, often combined with a small dam to create a
moderating reservoir, where a diversion to a canal or a perforated extraction
tube can be inserted.
When the emergence originates in a fracture or a localized fracture
zone (karst and fractured reservoirs), the production site is covered by a
catchment system with a geometry directly dependent on the local geometry.
The construction is generally set well into the rock, after the latter has been