Management of Aquifers - Hydrogeology: Objectives, Methods, Applications - page 217

e) AGR through injection
Boreholes or wells reaching the surface of the water table can be used to
inject water into the aquifer one wishes to sustain. However, the wells silt
up rapidly; so a method was developed in the USA, ASR (aquifer storage
recovery), where the same well is used for pumping and for injection.
These alternating uses prevent blockage. This method offers the advantage
of requiring a reduced surface area in comparison to infi ltration basins or
ditches.
3.1.2 Underfl ow dams
The preceding methods concern conductive functions at the entry to a
system, but actions can also be taken within the aquifer, by locally altering
transfer conditions. Impermeable barriers can be built within the aquifer in
order to store water and to locally raise the level of the water table (Figure
111). This method is used in the Sahel, as well as in Brazil in agricultural
zones. The water stored in this way is protected from evaporation.
Figure 111 Water storage with an underfl ow dam.
3.1.3 The problem of clogging
This is the major problem in artifi cial groundwater recharge. Clogging is
caused by the infl ux, in infi ltrated water, of fi ne-grained particles that silt
up the pores in the soil, but also by physico-chemical or biological reactions
in the soil causing, for example, swelling of clays or proliferations of
bacteria or algae, creating a biological fi lm that cannot be totally eliminated,
as it participates in the purifi cation of infi ltrated water. In deep basins,
water pressure can also compact the terrain and reduce its permeability,
encouraging clogging.