Abstract
Abstract. Identifying principles of water movement in the shallow subsurface is crucial for adequate process-based hydrological models. Hillslopes are the essential interface for water movement in catchments. The shallow subsurface on slopes typically consists of different layers with varying characteristics. The aim of this study was to draw conclusions about the infiltration behaviour, to identify water flow pathways and derive some general interpretations for the validity of the water movement on a hillslope with periglacial slope deposits (cover beds), where the layers differ in their sedimentological and hydrological properties. Especially the described varying influence of the basal layer (LB) as an impeding layer on the one hand and as a remarkable pathway for rapid subsurface stormflow on the other. We used a time lapse 3-D electrical resistivity tomography (ERT) approach combined with punctual hydrometric data to trace the spreading and the progression of an irrigation plume in layered slope deposits during two irrigation experiments. This multi-technical approach enables us to connect the high spatial resolution of the 3-D ERT with the high temporal resolution of the hydrometric devices. Infiltration through the uppermost layer was dominated by preferential flow, whereas the water flow in the deeper layers was mainly matrix flow. Subsurface stormflow due to impeding characteristic of the underlying layer occurs in form of organic layer interflow and at the interface to the first basal layer (LB1). However, the main driving factor for subsurface stormflow is the formation of a capillary barrier at the interface to the second basal layer (LB2). The capillary barrier prevents water from entering the deeper layer under unsaturated conditions and diverts the seepage water according to the slope inclination. With higher saturation, the capillary barrier breaks down and water reaches the highly conductive deeper layer. This highlights the importance of the capillary barrier effect for the prevention or activation of different flow pathways under variable hydrological conditions.
Highlights
Analyses of flood frequencies over the last decades in Europe and other parts of the world reveal a positive trend which is predicted to be continued (Zhang et al, 2016; Alfieri et al, 2015; Schmocker-Fackel and Naef, 2010; Uhlemann et al, 2010; Petrow and Merz, 2009)
We used a time lapse 3-D electrical resistivity tomography (ERT) approach combined with punctual hydrometric data to trace the spreading and the progression of an irrigation plume in layered slope deposits during two irrigation experiments
The results show significant lateral water movement within the entire LB1, the LB1 is the layer with the lowest amount of macropores and the lowest hydraulic conductivity
Summary
Analyses of flood frequencies over the last decades in Europe and other parts of the world reveal a positive trend which is predicted to be continued (Zhang et al, 2016; Alfieri et al, 2015; Schmocker-Fackel and Naef, 2010; Uhlemann et al, 2010; Petrow and Merz, 2009). Flood forecasting and predicting water quantity and quality under alternating boundary conditions is usually performed by hydrological modelling. The knowledge of internal catchment response and different feedback mechanisms is decisive for an increased process understanding and an accurate modelling of the hydrological behaviour (Seibert and van Meerveld, 2016). Water dynamics in catchments and the response to temporally and spatially variable climatic and hydrological conditions are of particular importance to runoff generation. Hillslopes are the crucial interface between precipitation and runoff.
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