Horizon 1 1 17 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES Mathematical Geosciences 861-878 Multiple-point statistics Facies modeling Variographic analysis Komadugu-Yobe River Fluvial deposits 2011 fdi:010054170 ENG Mathematical Geosciences 1874-8961 ISI:000296796200007 7 10.1007/s11004-011-9353-6 https://www.documentation.ird.fr/hor/fdi:010054170 https://www.documentation.ird.fr/intranet/publi/2011/12/010054170.pdf 43 Horizon (IRD) Multiple-point statistics are used to model facies heterogeneities in the vadose zone of the Komadugu-Yobe River valley (southeastern Niger) which is presently submitted to an undergoing intensive agricultural development; therefore, increasing quantitative and qualitative pressures are exerted on groundwater resources. The sand-clay heterogeneities are analyzed by means of a Landsat image acquired during a high flow period over a 160 km stretch in the downstream part of the valley and a set of 50 boreholes drilled near the town of Diffa (4 km x 4 km area). The horizontal variograms of heterogeneities are characterized by a noticeably constant length scale of 380 m and clayey objects are shown to be randomly distributed in space according to a Poisson process. A set of two-dimensional vertical images is built based on a Boolean procedure and the Snesim algorithm is used to simulate synthetic three-dimensional media. When the vertical correlation length is fitted, the three-dimensional model satisfactorily reproduces the second order statistics of heterogeneities and the specific facies patterns. 064 ; 020 UR050