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Methodologies have been developed to establish realistic water-table maps using geostatistical methods: ordinary kriging (OK), cokriging (CoK), collocated cokriging (CoCoK), and kriging with external drift (KED). In fact, in a hilly terrain, when piezometric data are sparsely distributed over large areas, the water-table maps obtained by these methods provide exact water levels at monitoring wells but fail to represent the groundwater flow system, manifested through an interpolated water table above the topography. A methodology is developed in order to rebuild water-table maps for urban areas at the city scale. The interpolation methodology is presented and applied in a case study where water levels are monitored at a set of 47 points for a part urban domain covering 25.6 km close to Bordeaux city, France. To select the best method, a geographic information system was used to visualize surfaces reconstructed with each method. A cross-validation was carried out to evaluate the predictive performances of each kriging method. KED proves to be the most accurate and yields a better description of the local fluctuations induced by the topography (natural occurrence of ridges and valleys). [ABSTRACT FROM AUTHOR]

Abstract: Hydrogeological analysis of flow is largely based on the concept of hydraulic conductivity. In numerical hydrogeological modeling, a value of hydraulic conductivity must be assigned at each element of mesh. In heterogeneous geological formations, this value governs the average behavior of groundwater flow within an aquifer. The goals of this study are twofold: (1) development of a methodology to transform the description of lithological units into local hydraulic conductivity values and (2) development of a methodology for reconstruction of hydraulic conductivity fields on a 83km2 of the Bordeaux urban area. Two approaches, a 2D approach and a 3D approach, based on geostatistical analysis are explained in details and compared. For both approaches, variographical analysis and ordinary kriging are carried out on the logarithmic of hydraulic conductivity and composite hydraulic conductivity is calculated using thickness-weighting to get horizontal and vertical hydraulic conductivities. The comparison of both approaches and the assessment of their potential and limitations suggest that the 2D approach is more appropriate than the 3D approach. [Copyright &y& Elsevier]