Controlling factors of gullying in the Maracujá Catchment, southeastern Brazil.
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2005
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Hundreds of gullies (‘voçorocas’) of huge dimensions (up to 400–500 m long, 150 m wide
and 50 m deep) are very common in the small Maracujá Catchment in southeastern Brazil.
These erosional features, which occur with an uneven intensity throughout the area, started
due to bad soil management practices at the beginning of European settlement, at the end of
the 17th century, and nowadays are still evolving, but at a slower rate. As surface soils are
usually very resistant to erosion, the outcrop of the more erodible basement saprolites seems
to be an essential condition for their beginning. An analysis of well known erosion controlling
factors was performed, aiming to explain the beginning and evolution of these gullies
and to understand the reasons for their spatial distribution. Data shows that geology and,
mainly, geomorphology are the main controlling factors, since gullies tend to be concentrated
in basement rock areas with lower relief (domain 2) of Maracujá Catchment, mainly
at the fringes of broad and flat interfluves. At the detailed scale (1:10 000), gullies are more
common in amphitheatre-like headwater hollows that frequently represent upper Quaternary
gullies (paleogullies), which demonstrate the recurrence of channel erosion. So, gullies
occur in areas of thicker saprolites (domain 2), in places with a natural concentration of
surface and underground water (hollows). Saprolites of the preserved, non-eroded hollows
are usually pressurized (confined aquifer) due to a thick seal of Quaternary clay layer, in a
similar configuration to the ones found in hollows of mass movement (mudflow) sites in
southeastern Brazil. Therefore, the erosion of the resistant soils by human activities, such
as road cuts and trenches (‘valos’), or their mobilization by mudflow movements, seem to
be likely mechanisms of gullying initiation. Afterwards, gullies evolve by a combination of
surface and underground processes, such as wash and tunnel erosion and falls and slumps of
gully walls.
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Erosion, Gullying, Human impacts, Geomorphologic
Citação
BACELLAR, L. de A. P.; COELHO NETTO, A. L.; LACERDA, W. A. Controlling factors of gullying in the Maracujá Catchment, southeastern Brazil. Earth Surface Processes and Landforms, v. 30, p. 1369-1385, 2005. Disponível em: <http://onlinelibrary.wiley.com/doi/10.1002/esp.1193/abstract>. Acesso em: 20 de jun. 2017.