Estimation of the transmissivity field of a heterogeneous alluvial aquifer using transverse resistance. Application to the Haouz groundwater (Morocco)
This article aims at the indirect estimation of the transmissivity (T, m2/s) of the aquifer of Haouz (6,000 km2) in Morocco, using the transverse resistance (R, Ωm2). This aquifer consists of a complex succession of lenticular layers, argilo-marly or formed of coarse elements, of plio-quaternary age, lying on a marly substratum of miocene age. A significant database of the values of transmissivity (≈500) and transverse resistance (≈2,500) was compiled. A research was then carried out to select the pairs (Ti, Ri) characterizing the same volume of aquifer. Two cases of transverse resistance are considered: 1) transverse resistance of the mio-plio-quaternary unit (RA); 2) transverse resistance of the permeable coarse lenses only (RB). The best regression, of geometrical form, is obtained between the transmissivity and the transverse resistance of the permeable coarse lenses. This regression is significantly improved when the values (T; RB) of a given pair are brought back to the same level of the water table, after correction of the transmissivity according to the variations of the water table. The indirect estimate of the field of transmissivity of the aquifer is then carried out at a regional scale using the regression equation previously established. The estimated field of transmissivity is validated through the comparison of its statistical properties (central tendency, dispersion, distribution law) to those of the sample of the values of transmissivity measured by pumping tests.