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

Understanding sedimentary heterogeneities has nowadays become crucial for sophisticated aquifer management. The methods used so far for aquifer characterization (e.g. pump test, coring analysis) cannot provide the needed resolution for a sufficient prediction of the subsurface properties (e.g. Sudicky, 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 subsurface information for high-resolution three-dimensional images and radar facies mapping of glaciolacustrine delta sediments in the Singen Basin (SW Germany). A three-dimensional reconstruction of sedimentary heterogeneities for a detailed aquifer characterisation becomes possible by combining GPR profiling and outcrop information. A case study is presented, showing a complex, three-dimensional architecture of a Quaternary gravel body, consisting of the following three types of architectural elements: (1) glaciolacustrine delta foresets, (2) erosional surfaces with scour pool fills, and (3) horizontal glaciofluvial gravel sheets. Although this seems a relatively simple architectural inventory, the three-dimensional georadar profiling shows considerable internal heterogeneities. The radar data are interpreted following the seismic stratigraphic approach, i.e. the delineation of radar facies types and of radar sequences. The three-dimensional heterogeneities are visualized by means of time slices, 3-D block or chair diagrams, or series of radar facies maps.