The influence of terracettes on the surface hydrology of steep-sloping and subalpine environments : some preliminary findings

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. 400m2 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.