SSF SUBSURFACE CONTROLS: Imaging subsurface flow path dynamics in high resolution

• Applicant: Professorin Dr. Anja Klotzsche
• Subject Area: Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 453746323

Our understanding of the mechanisms behind subsurface stormflow and under what conditions it occurs is still a puzzle of indirect evidence. Geophysical methods play a major part concerning the spatio-temporal flow pattern. In contrast to trenches or sensors in the subsurface, geophysical methods yield a more or less continuous image of the subsurface. As a second advantage, geophysical methods cause very little disturbance of the natural conditions. Based on the findings from the first phase of the Research Unit, the central hypothesis of this project is that the heterogeneity of the soil and preferential flow paths in the soil are more relevant for SSF than the soil-bedrock interface. This hypothesis is reflected in the following research questions: (1) Is SSF typically limited to a certain (site-specific) depth range? (2) Given that there is at least some preferred depth range, is it just site-specific, or does it strongly depend on event size? (3) How inhomogeneous is the SSF pattern in the lateral direction (preferential layers vs. distinct paths)? (4) What is the effect of internal thresholds and temporary storage on SSF discharge curves? While electrical resistivity tomography (ERT) with electrodes at the surface played a major part in the preceding project, the new project goes ahead towards semi-invasive electrical resistivity tomography with electrodes in the subsurface and towards ground penetrating radar (GPR) as a high-resolution method. Full waveform inversion of GPR data as a quite new method will be the key to achieving a spatial resolution that allows for mapping individual flow paths. Electrical resistivity tomography will be extended towards a semi invasive approach with electrodes in the subsurface. A less invasive, novel concept with partially insulated electrodes that are directly inserted into the subsurface will be developed and compared to the established approach with electrodes in boreholes. Combining the different geophysical methods will allow for mapping subsurface flow patterns at high spatial resolution under controlled irrigation and also for long-term monitoring under natural conditions. The obtained data will be included in numerical models of water flow and transport of tracers to generate digital twins of the considered field sites. In combination with data from the other projects in the Research Unit, this will finally drive the development of new model components leading to an improved representation of SSF in numerical models.

• DFG Programme: Research Units
• Subproject of: FOR 5288: Fast and invisible: Conquering Subsurface Stormflow through an Interdisciplinary Multi-Site Approach
• International Connection: Austria, USA
• Partner Organisation: Fonds zur Förderung der wissenschaftlichen Forschung (FWF)
• Co-Investigator: Professor Dr. Markus Weiler
• Cooperation Partners: Professor Dr.-Ing. Stefan Achleitner; Dr. Bernhard Kohl; Professorin Dr. Kamini Singha