Abstract: Groundwater and surface water in Souss-Massa basin in the west-southern part of Morocco is characterized by a large variation in salinity, up to levels of 37 g L-1. The high salinity coupled with groundwater level decline pose serious problems for current irrigation and domestic water supplies as well as future exploitation. A combined hydrogeologic and isotopic investigation using several chemical and isotopic tracers such as Br/Cl, ï¤18O, ï¤2H, 3H, 87Sr/86Sr, ï¤11B, and 14C was carried out in order to determine the sources of water recharge to the aquifer, the origin of salinity, and the residence time of water. Stable isotope, 3H and 14C data indicate that the High Atlas Mountains in the northern margin of the Souss-Massa basin with high rainfall and low ï¤18O and ï¤2H values (-6 to -8â° and -36 to -50â°) is currently constitute the major source of recharge to the Souss-Massa shallow aquifer, particularly along the eastern part of the basin. Localized stable isotope enrichments offset meteoric isotopic signature and are associated with high nitrate concentrations, which infer water recycling via water agricultural return flows. The 3H and 14C data suggest that the residence time of water in the western part of the basin is in the order of several thousands of years; hence old water is mined, particularly in the coastal areas. The multiple isotope analyses and chemical tracing of groundwater from the basin reveal that seawater intrusion is just one of multiple salinity sources that affect the quality of groundwater in the Souss-Massa aquifer. We differentiate between modern seawater intrusion, salinization by remnants of seawater entrapped in the Middle Souss plains, recharge of nitrate-rich agricultural return flow, and dissolution of evaporate rocks (gypsum and halite minerals) along the outcrops of the High Atlas Mountains. The data generated in this study provide the framework for a comprehensive management plan in which water exploitation should shift toward the eastern part of the basin where current recharge occurs with young and high quality groundwater. In contrast, we argued that the heavily exploited aquifer along the coastal areas is more vulnerable given the relatively longer residence time of the water and salinization processes in this part of the aquifer.
Abstract: To understand the turbidity phenomenon that occurs during floodwater periods in the water of some karstic aquifers, a study
was carried out on the Ain Asserdoune spring in the Beni Mellal Atlas. The application of correlation and spectral analyses to
turbidity, rainfall and discharge rate with a daily sampling for three hydrological cycles showed that the Ain Asserdoune
turbidity corresponded to the beginning of the unclogging of the karstic conduits affecting the saturated area. The appearance of
turbidity during the increased flow rate was due to instability in the chaotic regime that was represented by suspended matter,
which was evacuated independent of the discharge rate. This phenomenon only appears in polyphase karst, which is frequently
found, and thus must be taken into account when karstic water is used for drinking as it could become unfit for human
Abstract: The study of spatial and temporal variations
of some hydrochemical properties in the Oued Issen
watershed, Morocco, has revealed their close relation
to the area's lithologic and geologic characteristics and
to variations in hydroclimatological cycles. High concentrations
of sodium chloride are measured during
flood periods, when the outcrops of the basin are
leached by streams draining the rather dense hydrographic
network.
These variations depend also on the relative abundance
of tributaries on both sides of the Oued, their
respective contributions being hydrochemically very
different: (1) northern-side tributaries, which mainly
leach evaporitic terranes dating from the Late Triassic
and Late Liassic periods and which are rich in gypsum
and halite, increase the mineralization of the Oued
Issen waters flowing toward the Abdelmoumen Dam;
(2) the low salinity of water observed in the upstream
portion of the watershed is due to dilution by waters
from the southern-side tributaries, which are derived
from snowmelt and the leaching of the high Paleozoic
massif; (3) in the middle part of the basin, the increase
in mineralization of the Oued Issen becomes substantial
between the Abdelmoumen Dam and the Dkhila
Dam, the next dam downstream, due to the absence
of dilution by waters from the southern-side tributaries,
which are sparse in this part of the basin. In
addition, during flood periods, the outflow from the
first dam is stopped. Thus, the main contribution of
NaCl to the Oued is from the very salty Tirkou spring,
which is situated downstream from the first dam.
The geological characteristics of the basin have
induced the development of high-salinity zones, which are particularly evident in the southwestern part of
the basin in the vicinity of the confluence of the Oued
Boulebaz with the Oued Issen. The discharge of very
salty springs is controlled by faults that offset the formations
that underlie the hydrographic network and
degrade the quality of the Oued Issen. This water
later recharges the unconfined aquifer along the Oued
where it flows on the Oued Souss Plain.
Abstract: The northern slope of the Beni Mellal Atlas is a complex area where two
largeâ units (Atlas and the Tadla Plain) meet by means of thrust sheets of diverse
composition. A lot of springs originating from the relief and boreholes of the plain
have enabled the identification of consequent groundwater reserves, hardly known
until now.
This study reveals the characterisation of Atlasic aquifers (Atlas and piemont) with
karstic behaviour, the demonstration of their interactions, and also their relationship
with the Tadla Plain aquifers. The application of structural, hydrodynamic, physicochemical
and isotopic methods have enabled the characterisation of the Beni Mellal
Atlas Aquifer and the specification of the hydrodynamic connections between different
aquifers in a semi-arid zone. The geological data (lithology and structure) have deline
ated a 385 km* Atlasic intake area. The structural analysis shows a dense fracturing
of the Liassic massif (limestones and dolomites). This Liassic unit is overthrusting
Journal of Afriicsn Earth Scimces 225
L. BOUCHAOU et al.
the northern series at the Dir level (piemont), bringing together permeable facies in
some places, thus easing the hydraulic connections or re-infiltration of the waters of
the Atlasic springs. The hydrodynamic and hydrochemical studies (recessions, sorted
discharges, cross correlation analysis, frequency distribution analysis of carbonated
tracers, discriminant factor analysis-AFD) demonstrate that the system has a very
inertial behaviour, which acts as a shallow karst during high water periods. The
hydrochemical characterisation confirms the presence of units displayed by the
structural analysis. The hypothesis put into the fore by other methods is confirmed
by the isotope study: the aquifers of the plain are recharged by the same area as the
Atlasic springs within a very wide system with several inputs. â1997 Elsevier Science
Limited.
Abstract: An integrated study was carried out to investigate the subsurface geological
conditions in a hard rock environment, with the aim to identify groundwater potential
zones. The study considered the use of remote sensing, geo-electrical methods and nuclear
magnetic resonance sounding techniques (NMRS). Remote sensing was used to identify
lineaments which were extracted from the satellite images by directional filtering of the
image. Resistivity profiles and NMRS were used to locate the lineaments more precisely
on the ground. The identification of geomorphological significance of each mapped lineament
has enabled the explanation of the relationship between lineament distribution and
groundwater in fractured rocks. The study made it possible to select localised sites for the
drilling of successful boreholes, after taking into account the hydrogeological and climatic
conditions of the area. The results of this study, as tested in the Moroccan Anti-Atlas chain,
show the importance of using an integrated approach for siting boreholes in hard rock
terrain in a semi-arid climate.
