Abstract
Abstract. Alpine and mountain slopes represent important pathways that link high-altitude grazing areas to meadows and rangelands at lower elevations. Given the often acute gradients associated with such environments, they potentially represent highly efficient runoff conveyance routes that facilitate the downslope movement of runoff and associated material during erosion events. Many such slopes host series of small steps, or "terracettes". The juxtaposition of terracettes against the natural downslope flow path of non-complex slopes leads us to hypothesise that they may influence typical hillslope processes by intercepting or capturing surface runoff. Here we report preliminary results and some tentative conclusions from ongoing work to explore this possibility. Google Earth was used to initially identify a ca. 400 m2 well-developed terracette system situated on a west-facing slope with gradients ranging from 25 to 40° (46 to 84 %). A digital elevation model (DEM) of the terracettes was constructed using spatial data taken from a relevant section of topographic map. The DEM was then queried using a flow-accumulation algorithm and the results displayed in a geographic information system. The output data provided "proof of concept" that terracettes can capture surface runoff. The generation of empirical data from a series of rainfall/runoff simulations performed on the same section of terracettes supports this finding. Results from both work components indicate that sections of a terracette system may intercept runoff and could act as preferential flow pathways. By contrast, some sections appeared to act as depositional sites. We cautiously predict that these areas could act as retention zones for the temporary storage of runoff-associated substances. Greater understanding of the exact influence of terracettes on surface hydrology in steep-sloping and subalpine environments could benefit the future management of grazing and rangelands in such areas.
Highlights
Alpine and mountain slopes represent important sources of fodder for grazing livestock
The GIS-based approach provided adequate proof of concept that terracettes can have an influence on the surface hydrology on steeply sloping environments
Whether individual terracette pathways act in an interconnected way to form a complete runoff conveyance system that guides, or even facilitates, the downslope movement of surface runoff is unknown
Summary
Alpine and mountain slopes represent important sources of fodder for grazing livestock. Given the often acute gradients encountered within terrain of this nature (Konz et al, 2012), their presence (theoretically) represents a convenient and potentially highly efficient runoff conveyance route with the capacity to facilitate the rapid and largely unimpeded downslope transfer of surface runoff and associated material during erosion events. Despite this realisation, many slopes above a certain threshold gradient (Waugh, 1995) host a series of small steps, or “terracettes”, that have an appearance analogous to a wide staircase (Rahm, 1962). Repeated wetting and drying cycles facilitate the downslope movement, which, combined with grav-
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