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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Volume 21, issue 7
Hydrol. Earth Syst. Sci., 21, 3727-3748, 2017
https://doi.org/10.5194/hess-21-3727-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Hydrol. Earth Syst. Sci., 21, 3727-3748, 2017
https://doi.org/10.5194/hess-21-3727-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 21 Jul 2017

Research article | 21 Jul 2017

Form and function in hillslope hydrology: characterization of subsurface flow based on response observations

Lisa Angermann1,2, Conrad Jackisch3, Niklas Allroggen2, Matthias Sprenger4,5, Erwin Zehe3, Jens Tronicke2, Markus Weiler4, and Theresa Blume1 Lisa Angermann et al.
  • 1Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, Section Hydrology, Potsdam, Germany
  • 2University of Potsdam, Institute of Earth and Environmental Science, Potsdam, Germany
  • 3Karlsruhe Institute of Technology (KIT), Institute for Water and River Basin Management, Chair of Hydrology, Karlsruhe, Germany
  • 4University of Freiburg, Institute of Geo- and Environmental Natural Sciences, Chair of Hydrology, Freiburg, Germany
  • 5University of Aberdeen, School of Geosciences, Geography & Environment, Aberdeen, Scotland, UK

Abstract. The phrase form and function was established in architecture and biology and refers to the idea that form and functionality are closely correlated, influence each other, and co-evolve. We suggest transferring this idea to hydrological systems to separate and analyze their two main characteristics: their form, which is equivalent to the spatial structure and static properties, and their function, equivalent to internal responses and hydrological behavior. While this approach is not particularly new to hydrological field research, we want to employ this concept to explicitly pursue the question of what information is most advantageous to understand a hydrological system. We applied this concept to subsurface flow within a hillslope, with a methodological focus on function: we conducted observations during a natural storm event and followed this with a hillslope-scale irrigation experiment. The results are used to infer hydrological processes of the monitored system. Based on these findings, the explanatory power and conclusiveness of the data are discussed. The measurements included basic hydrological monitoring methods, like piezometers, soil moisture, and discharge measurements. These were accompanied by isotope sampling and a novel application of 2-D time-lapse GPR (ground-penetrating radar). The main finding regarding the processes in the hillslope was that preferential flow paths were established quickly, despite unsaturated conditions. These flow paths also caused a detectable signal in the catchment response following a natural rainfall event, showing that these processes are relevant also at the catchment scale. Thus, we conclude that response observations (dynamics and patterns, i.e., indicators of function) were well suited to describing processes at the observational scale. Especially the use of 2-D time-lapse GPR measurements, providing detailed subsurface response patterns, as well as the combination of stream-centered and hillslope-centered approaches, allowed us to link processes and put them in a larger context. Transfer to other scales beyond observational scale and generalizations, however, rely on the knowledge of structures (form) and remain speculative. The complementary approach with a methodological focus on form (i.e., structure exploration) is presented and discussed in the companion paper by Jackisch et al.(2017).

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This study investigates the temporal dynamics and response velocities of lateral preferential flow at the hillslope. The results are compared to catchment response behavior to infer the large-scale implications of the observed processes. A large portion of mobile water flows through preferential flow paths in the structured soils, causing an immediate discharge response. The study presents a methodological approach to cover the spatial and temporal domain of these highly heterogeneous processes.
This study investigates the temporal dynamics and response velocities of lateral preferential...
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