Abstract:
The use of artificial rainfall simulation (ARS) is a common method to study the interaction of
soil and water (Strauss et al. 2000). Traditionally, precipitation simulation has been used as a
tool to assess and determine the importance of surface runoff, usually with reference to soil
erosion. Large-scale experiments are generally rare, although they are an efficient way to
obtain directional soil hydraulic properties that functionally average local heterogeneities.
Flow processes in the subsurface are usually measured indirectly. Such non-destructive
methods for measuring subsurface flow processes often rely on soil moisture measurements
or other indirect geophysical measurements (ERT, EMI, GPR,...) often accompanied by isotope
or tracer analyses.
Direct measurement of subsurface rainfall runoff involves considerable effort and cost, and in
some cases, it is even impossible e.g., when it is not possible to dig a drainage ditch. At BFW -
Department of Natural Hazards, about 150 representative plots in the Eastern Alps have been
irrigated over the last 30 years using portable sprinkler systems for large plots (50 to 400 m²).
In total, more than 350 rain simulation trials have been conducted. Specifically, this BFW
rainfall simulation database contains data from 11 plots and 21 experiments where subsurface
storm runoff was directly quantified.
The results derived from these eleven test plots basically confirm the often-observed bimodal
nature of subsurface flow, consisting of preferential/macropore flow and flow through the soil
matrix (e.g., Weiler et al. 2005, Dasgupta et al. 2006, …). Preferential flow paths are mostly
attributable to heterogeneities in the soil. Preferential macropore flow can be differentiated
by means of such various types of heterogeneities. Four specific categories may be
distinguished: phytogenic macropores (e.g. cavities left by decomposing roots); zoogenic
macropores e.g. mole burrows, mouse holes); geogenic heterogeneities (e.g. periglacial cover
beds, bedrock fissures and cracks) and anthropogenic heterogeneities (e.g. drainage systems,
tillage pans). Each of these four categories is covered by at least one experiment in the BFW
data record.
The observed subsurface hydrographs provide insight into the process-dependent differences
in precipitation-infiltration-subsurface runoff response. In a research group currently applied
for at the DFG (SSF Research Unit), new and novel irrigation experiments for the measurement
of subsurface stormflow will be carried out in four test areas and the existing ones from the
BFW database will be reanalyzed and modeled.
