Management of Aquifers - Hydrogeology: Objectives, Methods, Applications - page 215

But quantitative action can also be taken by using the aquifer as a
capacitative regulatory system. The discharge of certain rivers can thus be
regulated by injecting their water into the neighboring aquifers. Water from
the Oise, for example, is withdrawn during fl ooding periods, infi ltrated
through the chalk aquifer, and restored through pumping in dry periods
in order to increase the dry season discharge of the Oise by approximately
1 m 3 ·s -1 (Detay, 1997).
c) Artifi cial recharge of aquifers (from Detay, 1997)
The artifi cal recharge of an aquifer implies the availability of a surface water
resource (river or lake), of a high enough quality to avoid costly preliminary
treatment, and with a discharge compatible with the recharge goals. The
aquifer must also obey several constraints:
￿ large thickness of unsaturated soil above the aquifer in order to enable
storage and autopurifi cation;
￿ favorable transmissivity;
￿ high vertical hyraulic conductivity in order to facilitate the formation
of a reserve;
￿ moderate horizontal hydraulic conductivity in order to enable the
conservation of the reserve created.
These parameters can be found in chalk and in porous formations (sand,
gravel). Fractured aquifers and karst, within which water circulates too
quickly and is only porly fi ltered, are generally not favorable to artifi cial
recharge, but other methods of active management can be developed (see
chap. C4-4).
Artifi cial Groundwater Recharge (AGR) is highly developed in the
USA, particularly in California. The city of Los Angeles obtains 40% of
its drinking water from artifi cially recharged groundwater. AGR is used
varyingly in Europe.
In France, the principal AGR sites are located in the Paris region
(Croissy/Seine and Flins-Aubergenville), in Dunkirk, Dijon, and Lyons.
They account for approximately 200 million m 3 per year of infi ltrated water.
Different methods described below are used (Figure 109).
d) AGR through infi ltration
Artifi cial groundwater recharge is generally done through infi ltration basins
or ditches (Figure 110), often equipped with a bed of sand. The infi ltration
rate varies from 15 to 0.1 m·day -1 depending on the setup. It is generally