Salinity and modelling of the Annaba aquifer system, North-East of Algeria
Habiba MAJOUR1) ABCD , Azzedine HANI2) DE, Larbi DJABRI2) F
Abstract:
The potentiometer area in the Annaba basin, covering an area of 264 km2
, has declined considerably since
1995. The analysis of the chronological hydrographs (1991–2009) of the piezometric observations shows that
this decline is related to about twenty years (20 years) drought that began in 1991. To synthesize hydrological
data and study regional changes in aquifer interactions caused by changes in discharge, and determine the contamination
of aquifers by salty intrusion in coastal areas, and making forecasts by the year 2023, a multi-layered
transient model as well as a solute transport model has been developed. The groundwater flow was modelled using
the finite difference method with a horizontal dimension of 500 × 500 m for the cells. The model consists of
two layers, the first corresponding to the alluvial phreatic aquifer and the second to the deep confined aquifer, and is
calibrated against the steady state groundwater heads recorded before 1996. Model verification was done by history
matching over the period 1991–2009. Under steady-state conditions, the correspondence between simulated and
observed water levels is generally good (average difference of 0.4 m). For the deep aquifer, the simulated time-
-series hydrographs closely match the recorded hydrographs for most of the observation wells. For the alluvial
aquifer, the recorded hydrographs cover only a short time period, but they are reproduced. The model indicates
that groundwater pumping induced a decrease in natural discharge, a downward leakage in most of the basin and
a continual water-level decline. The model has also been applied to the analysis of recharge impact. Simulating the
behaviour of the system over the period 1991–2009 without pumping indicated small changes in hydraulic head.
These results show that the groundwater reservoir has a low recharge, but excellent hydraulic properties.
A solute-transport model was used to study aquifer contamination from salty intrusion in coastal sectors; it was
extended to the year 2023 by simulating an optimistic hypothesis that maintains present pumping until 2023. The
model indicates that the head decrease of the alluvial phreatic and deep confined aquifers will be 4 m and 5 m
respectively. The solute concentration in the deep confined aquifer will increase from 1 gꞏdm–3 (prior 2009) to
5 gꞏdm–3 in 2023.
Key words: Annaba, contamination, North-East of Algeria, salinity, solute-transport model
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