Articles | Volume 21, issue 7
Hydrol. Earth Syst. Sci., 21, 3749–3775, 2017
Hydrol. Earth Syst. Sci., 21, 3749–3775, 2017

Research article 21 Jul 2017

Research article | 21 Jul 2017

Form and function in hillslope hydrology: in situ imaging and characterization of flow-relevant structures

Conrad Jackisch1, Lisa Angermann2,3, Niklas Allroggen3, Matthias Sprenger4,5, Theresa Blume2, Jens Tronicke3, and Erwin Zehe1 Conrad Jackisch et al.
  • 1Karlsruhe Institute of Technology (KIT), Institute for Water and River Basin Management, Chair of Hydrology, Karlsruhe, Germany
  • 2Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, Section Hydrology, Potsdam, Germany
  • 3University of Potsdam, Institute of Earth and Environmental Science, Potsdam, 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 study deals with the identification and characterization of rapid subsurface flow structures through pedo- and geo-physical measurements and irrigation experiments at the point, plot and hillslope scale. Our investigation of flow-relevant structures and hydrological responses refers to the general interplay of form and function, respectively. To obtain a holistic picture of the subsurface, a large set of different laboratory, exploratory and experimental methods was used at the different scales. For exploration these methods included drilled soil core profiles, in situ measurements of infiltration capacity and saturated hydraulic conductivity, and laboratory analyses of soil water retention and saturated hydraulic conductivity. The irrigation experiments at the plot scale were monitored through a combination of dye tracer, salt tracer, soil moisture dynamics, and 3-D time-lapse ground penetrating radar (GPR) methods. At the hillslope scale the subsurface was explored by a 3-D GPR survey. A natural storm event and an irrigation experiment were monitored by a dense network of soil moisture observations and a cascade of 2-D time-lapse GPR trenches. We show that the shift between activated and non-activated state of the flow paths is needed to distinguish structures from overall heterogeneity. Pedo-physical analyses of point-scale samples are the basis for sub-scale structure inference. At the plot and hillslope scale 3-D and 2-D time-lapse GPR applications are successfully employed as non-invasive means to image subsurface response patterns and to identify flow-relevant paths. Tracer recovery and soil water responses from irrigation experiments deliver a consistent estimate of response velocities. The combined observation of form and function under active conditions provides the means to localize and characterize the structures (this study) and the hydrological processes (companion study Angermann et al., 2017, this issue).

Short summary
Rapid subsurface flow in structured soils facilitates fast vertical and lateral redistribution of event water. We present its in situ exploration through local measurements and irrigation experiments. Special emphasis is given to a coherent combination of hydrological and geophysical methods. The study highlights that form and function operate as conjugated pairs. Dynamic imaging through time-lapse GPR was key to observing both and to identifying hydrologically relevant structures.