Applied tracers for the observation of subsurface stormflow at the hillslope scale

Abstract

Rainfall-runoff response in temperate humid headwater catchments is mainly controlled by hydrological processes at the hillslope scale. Applied tracer experiments with fluorescent dye and salt tracers are well known tools in groundwater studies at the large scale and vadose zone studies at the plot scale, where they provide a means to characterise subsurface flow. We extend this approach to the hillslope scale to investigate saturated and unsaturated flow paths concertedly at a forested hillslope in the Austrian Alps. Dye staining experiments at the plot scale revealed that cracks and soil pipes function as preferential flow paths in the fine-textured soils of the study area, and these preferential flow structures were active in fast subsurface transport of tracers at the hillslope scale. Breakthrough curves obtained under steady flow conditions could be fitted well to a one-dimensional convection-dispersion model. Under natural rainfall a positive correlation of tracer concentrations to the transient flows was observed. The results of this study demonstrate qualitative and quantitative effects of preferential flow features on subsurface stormflow in a temperate humid headwater catchment. It turns out that, at the hillslope scale, the interactions of structures and processes are intrin-sically complex, which implies that attempts to model such a hillslope satisfactorily require detailed investigations of effective structures and parameters at the scale of interest.

Modeling Macroporous Soils with a Two-Phase Dual-Permeability Model

“…A detailed description of the Heumöser slope can be found in Lindenmaier et al (2005), Lindenmaier (2008) and Wienhöfer et al (2009). An essential characteristic of the slope is that macropores and soil pipes are able to generate fast breakthrough curves of a tracer at a spring and on a cut-bank near a hiking trail (see Fig.…”

“…Wienhöfer et al (2009) concluded that the processes are controlled by complex structures (macropores, soil pipes, soil layers) and their interactions. The soil matrix was classified as a silty clay loam and silt loam, with a shallow topsoil (∼10 cm) Wienhöfer et al (2009) were mainly cracks and soil pipes with diameters up to several cm. The macropore walls had dark coatings, indicating their temporal persistence.…”

“…In the following studies, we use the data and results of field and soil block experiments of Wienhöfer et al (2009) which were conducted to investigate the fast water transport at the forested upper part of the Heumöser slope in Ebnit (Austria). A detailed description of the Heumöser slope can be found in Lindenmaier et al (2005), Lindenmaier (2008) and Wienhöfer et al (2009).…”

“…Figure 1 shows a sketch of the idealized soil column that was used to study the differences between the RDPM and TPDPM. We adopted the soil properties form the Heumöser slope (Wienhöfer et al 2009) for this study. The topsoil (10 cm) is a sandy loam, followed by a silty clay loam.…”

“…The objectives of this article are (i) to investigate when the flow of soil air is hindered so that differences between RPDPMs and TPDPMs occur and (ii) the application of the twophase model for a macroporous part of the slow creeping hillslope Heumöser in the Austrian Alps to investigate the fast water infiltration and flow processes which were reported by Wienhöfer et al (2009).…”