3D MODELING OF QUATERNARY GRAVEL AQUIFERS: INTEGRATING OUTCROPS, CORES, GEOPHYSICS AND GOCAD

Quaternary gravel deposits form widespread aquifers in many areas in central Europe and elsewhere. In order to understand groundwater flow and contaminant transport in these heterogeneous systems a detailed spatial analysis of their sedimentary architecture on various scales and insights into their genesis are required. To achieve this goal this study incorporates (1) outcrop-aquifer analog studies, (2) well data and (3) geophysical investigations. Using the modeling tool GOCAD, the diverse data were integrated into unifying 3D models. Those models represent the basis for subsequent hydrogeological modeling of transport- and flow processes. The following two types of gravel bodies which originated in different environmental settings in SW-Germany and represent local to regional scales were studied:

(1) Glaciolacustrine gravel-delta (local-scale): the meso-scale distribution of gravel- and sand-beds within delta-foresets were analysed for the water-saturated aquifer using data from nearby outcrop-analogs, from borehole cores and from geophysical measurements. Based on the sedimentological model the aim of further studies is to develop hydrogeological models which can be validated by hydrogeological field measurements on the test site.

(2) Transition from terminal moraine complex to proglacial sandur (kilometer-scale): based on facies associations recognised in spot outcrops and a larger number of well data the large-scale dynamics of glacier advance and retreat was reconstructed for the study area. The sedimentary architecture is characterised by the interfinging of glaciofluvial gravel and diamict deposits of different origins. A 3D visualisation in GOCAD depicts the complex subsurface stratigraphy, which determines the hydrostratigraphy and the distribution of aquifers and aquicludes in the area.

In conclusion it is apparent that interpreting all available geological and geophysical data leads to more realistic reconstructions of aquifer heterogeneity than purely stochastic approaches.