RESUMEN
Soil degradation in Middle Guinea is increasing over the years. While it's good to have precautions to deal with it, it's even more important to go back to the source of the scourge in order to lessen its effects over time, or even eradicate it. At the center of the factors that are often mentioned is the destruction of the vegetation cover, and the aim of this study is to clear it (in all its forms: trees, grass, savannah, etc.) by following its variation in time [1982 and 2021] and in space. The present study was conducted by combining the remote sensing and GIS results, developed with data from geotechnical survey data and laboratory tests. On the Mali Labé Linsan axis, between [1982 and 1992], 63 % of the territory explored was occupied by fresh vegetation cover, compared to 13 % of dry vegetation, as well as 12 % of sterile soil and 12 % of sand mineral soil. For the periods [1992-2002] and [2002-2012], these same parameters increased to: 67 %; 11 %; 11 % and 11 %. The period [2012-2021] was marked by changes of 73 %; 10 %; 9 % and 9 %, respectively. The bearing capacity of soils varies from one point to another. In all six boreholes presented, their maximum values are greater than or equal to 400 Kpa (≥400 Kpa). The minimum values calculated for 2.1 ≤ B(m)≤7.3 fluctuate between 291 Kpa and 806 Kpa. The investigations carried out on this subject show that the overall movement of the positive variation of the vegetation cover in time (63 % < 67 % < 73 %) and very contrasted in space, would not be responsible for the degradations (which are local and mainly caused by erosion: wind and water). In addition, they open up to a (geoscientific and geotechnical) approach of a deep analysis, the purpose of which suggests the adoption of slab/concrete/grating foundations (depth of anchorage specific to each soil analyzed).
RESUMEN
Groundwater resources of the alluvial aquifer Ghiss Nekkor, which covers an area of 100 km2, are the main source of domestic and agricultural freshwater supply in the region of Al Hoceima in Morocco. Due to human activities (overexploitation, increase in agricultural activity), this alluvial aquifer has become very sensitive to chemical pollution. The principal objective of this current study is to develop and implement a calibration method to assess, map, and estimate the vulnerability of the Ghiss Nekkor alluvial aquifer to pollution risk. In this work, the GIS-based DRASTIC model was used to estimate the inherent vulnerability to contamination of the Ghiss Nekkor alluvial aquifer with seven standard hydrogeological parameters. Nitrate (NO3) and electrical conductivity (EC) data were used to validate the DRASTIC map. The results of the vulnerability map analysis show that the vulnerability to contaminants varies from non-existent in the southwestern part of the plain (7.3% of the total area), to very high (14.5%). The vulnerability is moderate in the central and northeastern areas (26.9%), while it is high in the other areas (17.5%). Furthermore, the most sensitive areas are mainly concentrated near the coastal strip and the central plain on both sides of the Nekkor River. In these areas, the NO3 and EC values are above the maximum allowable limit of the World Health Organization. The results suggest that the DRASTIC model can be an effective tool for decision-makers concerned about managing groundwater sustainability.
