Project E CONNECT - Longitudinal Patterns of SSF-Stream Connections

• Applicants: Dr. Theresa Blume; Professor Dr. Markus Weiler
• 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

Project Connect will collect a unique data set with a special focus on preferential flow features. Data will include longitudinal subsurface flow patterns at the footslope combined with longitudinal patterns of stream gains as well as data on the impact of anthropogenic structures (tile drains and ditches) on runoff generation. This will be complemented by model development with the aim to account for these features. In Phase 1 of the Research Unit, we have gone to great lengths to measure SSF systematically across 4 catchments. This puts us in the unique position that we now have continuous measurements of SSF at 3 hillslopes per catchment. However, to move to the stream reach or catchment scale, we require easier ways of measuring SSF occurrence and its impact on flood hydrographs and water quality. This can only be done by using proxies. Fiber-optic temperature measurement campaigns, combined with thermal imagery and radon measurements as indicators of groundwater inflow have provided unique insights in the spatial patterns and hotspots of SSF and groundwater inflows into the stream. Combined with the automatic sequential salt dilution experiments, they highlighted the role of spatially variable streamflow gains and losses. Based on these findings, we now propose to investigate the potential of temperature as a proxy for SSF in more detail. To identify simpler access points to SSF, minimum data needs, and easy to measure proxies at the stream reach scale, additional instrumentation will include the permanent installation of fiber-optic cables for distributed temperature sensing in the subsurface and the stream. We hypothesize that most of SSF occurs in preferential flow paths where event temperature responses will be distinct from the surrounding matrix for at least part of the year. Identifying the locations, dynamics and strengths of the temperature anomalies will therefore provide new insights into the occurrence of both lateral and vertical preferential flow. Given our observations that man-made preferential flow structures such as tile drains and ditches along roads can strongly contribute to subsurface flow inputs into the stream, we will now add a stronger focus here. We plan to make use of these as easy access points to SSF and to estimate their impact on the acceleration of the SSF contributions to the stream. While the ditches are easily accessed, the network of tile drains (prevalent in many pastures and agricultural fields) is often undocumented and the first challenge will be to identify their location. We aim to use models for hypothesis testing and impact assessment of SSF, both natural and anthropogenically accelerated. This includes not only water quantities but also the chemical signal of SSF. In order to do this, it is necessary to achieve a high degree of process representation, especially with respect to the parameterization of preferential flow. The model RoGeR will be further developed to fulfill this task.

• DFG Programme: Research Units
• Subproject of: FOR 5288: Fast and invisible: Conquering Subsurface Stormflow through an Interdisciplinary Multi-Site Approach
• International Connection: Switzerland, USA
• Major Instrumentation: feldtaugliche faseroptische Temperaturmessung (DTS)
• Instrumentation Group: 8620 Strahlungsthermometer, Pyrometer, Thermosonden
• Partner Organisation: Schweizerischer Nationalfonds (SNF)
• Co-Investigators: Dr. Luisa Hopp; Professorin Dr. Anja Klotzsche
• Cooperation Partners: Dr. Ilja van Meerveld, Ph.D.; Professorin Dr. Kamini Singha