Hydrogeologic Syntheses and Budgets - Hydrogeology: Objectives, Methods, Applications - page 165

the lower valley and the sea (Mangan, 1986). Groundwater circulation in
this system includes the following particularities:
￿ exchanges between the two aquifers, enabled by brittle deformation
(grabens and transverse faults);
￿ partial drainage of the lower aquifer, in the upper part of the basin,
by springs located at the contact with the intermediate impermeable
layer (Brague and Bouillide);
￿ infl ows to the upper aquifer from more or less pronounced stream
losses;
￿ infl ow to the alluvial aquifer from the upper aquifer in the lower Brague
valley;
￿ outlets from the karst and alluvial aquifers hidden out at sea.
One should also note the following differentiation with respect to
relationships between the surface and subterranean fl ow of water:
￿ at the base of the lower aquifer, the infi ltration coeffi cient reaches only
32%, despite a much greater karst absorption, which is later partially
returned to the stream network near the outcropping intermediate
impermeable unit;
￿ at the base of the upper aquifer, infi ltration is largely predominant,
with an average value of 63%, and even reaching 80% in the lower
Valmasque basin. This aquifer's outlets are nevertheless very small,
due to the large, unseen outfl ow in the alluvial fi ll of the lower valley
and out to sea.
3 DRAINAGE OF THE ALLUVIAL AQUIFER IN THE
LOWER VAR VALLEY (ALPES-MARITIMES)
The alluvial aquifer accompanying the river is also highly dependent on
infl ows from the hillsides, both from the Jurassic karst aquifer and from the
Pliocene puddingstone aquifer (Guglielmi, 1993) (see chap. B3-6.1.3b).
The schematic diagram in Figure 92 illustrates the drainage conditions
of these different aquifers, determined by the local structure and mutual
exchanges.
The hydrologic budget for the alluvial aquifer in 1991, with an upstream
infl ux of 0.5 m 3 ·s -1 , compares 3.4 m 3 ·s -1 of inputs (2.2 from the Var and 1.2
from the banks) to 3.6 m 3 ·s -1 of losses (1.85 to the Var and 1.75 to pumping for
drinking water). The positive remainder of 0.3 m 3 ·s -1 reemerges at sea.