Étude du fonctionnement du système aquifére karstique Cénomano-Turonien de l'oued Igrounzar, bassin d'Essaouira, Maroc

In the Meskala-Kourimat area, the Bouabout Syncline aquifer system, intersected by the Igrounzar Wadi, feeds most of the karstic sources of the region. This aquifer is contained within Cenomanian and Turonian limestones and dolomitic limestones. The base of the system corresponds to the lower Cenomanian grey clays, and the top to the Senonian white marls. Hydrodynamic studies of various springs shows that each water source is different from the other, indicating a heterogeneous underground reservoir belonging to a complex karst system. The springs waters show a large chemical variability in space and time. These waters are a mixture of chloride, sulphate, Na and Mg. High Mg contents of some springs result from dissolution of evaporite, confirmed by low Ca/Mg ratios. The total dissolved solids (TDS) in spring water increases from upstream to downstream, probably as a response to residency time, but also due to interaction with Cenomanian evaporites. However, the springs are good for drinking water, as well as for irrigation. The monthly survey of selected springs indicated a large chemical variability but with little or no correlation between discharge and TDS.Stable isotope data (¹⁸O) suggests that the altitude of the recharge area, for this aquifer system, is 1200 m. The ¹⁸O gradient versus altitude, established on springs whose recharge areas are well known is, −0.25% versus SMOW/100 m. When compared with the ‘Meteoric Water Line’ established on worldwide spring water whose recharge areas are well known, the Essaouira Basin shows rain recharge without any significant evaporation.     

Sensitivity of Gaussian plume model to dispersion specifications

Summary Variations in computed ground-level pollutant concentrations resulting from different sigma schemes in a Gaussian plume model have been investigated. Deviations from a standard calculation may be as large as orders of magnitude and are mostly associated with Pasquill-Gifford-Turner classes pertaining to active diffusion (classes A through D) in the rural case and to poor diffusion (classes E and F) in the urban one. The implications of these results as regards impact assessment studies are briefly discussed.With 6 Figures