Two-dimensional geomorphological characterization of a filled abandoned meander using geophysical methods and soil sampling

- ERT, GPR, RS, and MASW identify subsurface features of an abandoned meander.
- Multimethodical approach improves the reliability of data interpretation.
- MASW delivers best internal structural information.
- Core samples are indispensable for validation of geophysical results.

Using geophysical methods for the geomorphological characterization of subsurface features has numerous advantages over traditional exploration methods, because of their noninvasive and rapid nature. In this study, we compared the results of four geophysical methods with each other. We also discuss their possibilities and limitations in a geomorphological investigation. Electrical resistivity tomography (ERT), refraction seismic (RS), ground penetrating radar (GPR), and multichannel analysis of surface waves (MASW) methods were applied at an abandoned meander in northern Saxony to map a predefined structure. By combining these methods, we were able to characterize and delineate subsurface features of the abandoned meander, including a point bar, a channel, and a cutbank. Core samples obtained from sonic drilling were used to validate the findings of both seismic methods. However, we found that electrical resistivity tomography and ground penetrating radar lacked penetration depth and could only be used to resolve shallower subsurface layers. The ERT, GPR, RS, and MASW can be used to gather images of subsurface structures. The MASW in particular provides supplementary information about the channel's internal structure (with respect to lateral and vertical resolution). Besides fluvial-morphological features, we also detected inverse velocity structures within the channel. This allowed us to characterize the abandoned meander using information about its layer distribution and material composition. However, we were only able to characterize and delineate the subsurface features of the abandoned meander by combining all of the aforementioned methods.