Towards realistic aquifer models: three-dimensional georadar surveys of Quaternary gravel deltas (Singen Basin, SW Germany)

Understanding sedimentary heterogeneities has nowadays become crucial for s ophisticated aquifer management. The methods used so far for aquifer charac terization (e.g. pump test, coring analysis) cannot provide the needed reso lution for a sufficient prediction of the subsurface properties (e.g. Sudic ky, 1986). This calls for the application of the 'outcrop analogue-approach ' to aquifers (e.g. Macfarlan et al., 1994; Aigner, 1995). In this project we used georadar (ground-penetrating radar or GPR) to acquire the subsurfac e information for high-resolution three-dimensional images and radar facies mapping of glaciolacustrine delta sediments in the Singen Basin (SW German y). A three-dimensional reconstruction of sedimentary heterogeneities for a detailed aquifer characterisation becomes possible by combining GPR profil ing and outcrop information. A case study is presented, showing a complex, three-dimensional architecture of a Quaternary gravel body, consisting of t he following three types of architectural elements: (1) glaciolacustrine de lta foresets, (2) erosional surfaces with scour pool fills, and (3) horizon tal glaciofluvial gravel sheets. Although this seems a relatively simple ar chitectural inventory, the three-dimensional georadar profiling shows consi derable internal heterogeneities. The radar data are interpreted following the seismic stratigraphic approach, i.e. the delineation of radar facies ty pes and of radar sequences. The three-dimensional heterogeneities are visua lized by means of time slices, 3-D block or chair diagrams, or series of ra dar facies maps. (C) 1999 Elsevier Science B.V. All rights reserved.