A geometric simulation method was used to develop a three-dimensional, highly detailed synthetic representation of point bar sediments in the Wabash River system. Geometric simulation methods, in comparison to well-known second-order stochastic methods, offer the advantage of being more closely related to depositional processes, which are often similarly conceptualized (i.e., described in terms of shapes of discrete bed forms, trends in grain size, and spatial relationships of defined geologic facies). Multiple scales of geometric variation were defined within a sedimentologically prescribed framework, and shapes of discrete geometric elements were established at each scale. The selected shapes were based on published field studies including sedimentological bed form studies and trench studies in active point bar sediments. The parameterization of the shapes allowed for random variability of the shape descriptors; discrete shapes were then generated and assimilated by computer. Hydraulic conductivity values were assigned to the discrete elements based on reports of observed variations in grain size and field measurements of hydraulic conductivity. The synthetic model, referred to as a numerical aquifer, is being used as the basis for extensive numerical experimentation to study the relationship between natural spatial structure and subsurface flow and transport. ¿ American Geophysical Union 1995