Erosion disconformities and gully morphology: A threedimensional approach

Oliveira, Marcelo Accioly Teixeira de

doi:10.1016/0341-8162(89)90024-6

Cited by 23 publications

(23 citation statements)

References 5 publications

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“…As we can see below, this assumption was further confirmed in the field, because the most easily identified paleogullies are that ones partially filled by the younger sediments of Maracujá catchment (T2-R2 and T1-R1 sediments, Figure 10). As current gullies are more frequent in headwater hollows, which usually represent paleogullies, this phenomenon is clearly recurrent, confirming previous studies in Brazil (Oliveira, 1989;Moreira, 1992;Augustin, 1994;Coelho Netto, 1997) and elsewhere (Smith, 1982;Bothaa et al, 1994). As soon as the saprolites are reached, usually by concentrated flow in ditches, gullies tend to follow previous routes of gully retreat, due to rock discontinuities or saprolite erodibility anisotropies.…”

Section: Geomorphologic Controlssupporting

confidence: 83%

“…The concentration is also uneven at a detailed scale, with gullies growing mainly in amphitheatre-like headwater topographical hollows. As can be easily seen by aerial photography analysis, the geometry of many headwater hollows supports the idea that they represent old erosional features (paleogullies), very similar to the ones identified by Oliveira (1989). Field data have shown that these paleogullies were partially filled by Upper Quaternary sediments, including layers of organic clay and of colluvial sediments.…”

Section: Discussionsupporting

confidence: 73%

“…Preliminary studies have demonstrated that the morphology and stratigraphy of headwater hollows of Maracujá Catchment are very similar to those from basement rock areas of southeastern Brazil (Oliveira, 1989;CETEC, 1992;Moreira, 1992;Augustin, 1994;Coelho Netto, 1997;Bacellar et al, 2004). Two of these hollows (Vila Albertina and Vila Barraginha) are very well known in the Brazilian geotechnical literature (CETEC, 1992;Bacellar et al, 2004), because they were sites of huge, catastrophic mass movements (mudflow type).…”

Section: Geomorphologic Controlsmentioning

confidence: 95%

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Controlling factors of gullying in the Maracujá Catchment, southeastern Brazil

Bacellar

Netto

Lacerda

2005

Earth Surf Processes Landf

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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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Section: Geomorphologic Controlssupporting

confidence: 83%

Section: Discussionsupporting

confidence: 73%

Section: Geomorphologic Controlsmentioning

confidence: 95%

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Controlling factors of gullying in the Maracujá Catchment, southeastern Brazil

Bacellar

Netto

Lacerda

2005

Earth Surf Processes Landf

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“…São canais erosivos com fluxo d'água sazonal ou mesmo permanente, que na área em estudo apresentam dimensões superiores a 20m de comprimento e 1,5m de profundidade, em média, chegando a alcançar 200m de comprimento e mais de 10m de profundidade. A intercalação de camadas sedimentares com propriedades físicas contrastantes, a morfometria das áreas de contribuição favorecendo a convergência e velocidade do escoamento superficial e subsuperficial constituem os principais controles apontados para este tipo de erosão (Oliveira, 1989;1990;Peixoto et al, 1989, Coelho Netto, 1997; entre outros).…”

Section: Metodologiaunclassified

Análise Espaço-Temporal da Erosão Linear no Médio-BaixoVale do Ribeirão do Secretário (Paty do Alferes/RJ)

Salgado¹,

Silva²,

Peixoto³

et al. 2008

Rev. Bras. Geomorfol.

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ResumoO município de Paty do Alferes, localizado na vertente continental da Serra do Mar (RJ), apresenta um grande número de ravinas e voçorocas. No médio-baixo vale do Ribeirão do Secretário (noroeste do município) tais feições foram mapeadas e classificadas como ravinas/voçorocas desconectadas ou conectadas à rede de drenagem, seguindo uma tipologia elaborada em trabalhos anteriores no médio vale do rio Paraíba do Sul. Com base no mapeamento e classificação de feições erosivas lineares, executado através de fotointerpretação e trabalhos de campo, foi analisado o estado de atividade das incisões erosivas nas décadas de 1960 e 1990 (1968 e 1996), e avaliada a sua distribuição espacial na bacia hidrográfica em análise. Verificou-se uma tendência à estabilização das feições erosivas no período analisado, inclusive com a extinção de algumas voçorocas, relacionada à erosão parcial ou total das coberturas sedimentares/pedológicas, ao afloramento de horizontes de solo ou camadas sedimentares mais resistentes e/ou do substrato rochoso, além de colonização de vegetação. As ravinas/voçorocas desconectadas da drenagem concentram-se nos setores sul e sudeste da bacia hidrográfica, onde predominam encostas longas com declividade acentuada, solos com horizonte B textural e/ou solos pouco profundos, ocorrendo ainda a influência de aspectos lito-estruturais. As voçorocas conectadas à rede de drenagem apresentam uma distribuição espacial mais homogênea na bacia e se desenvolvem essencialmente em planície fluvial ou nas reentrâncias de cabeceiras de drenagem. Em algumas propriedades, o entalhe erosivo foi usado para constituir açude para irrigação dos cultivos, fato que também contribui para a inatividade deste tipo de feição erosiva.Palavras-chave: tipologia de voçorocas; estado de atividade da erosão; uso do solo; fatores condicionantes da erosão.

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“…Only a summary of the subsurface structure of the colluvial mantle is presented here; for a more complete description and analysis of the stratigraphic sections see . Although Oliveira (1989) also presents some stratigraphic sections of this site, care must be taken during comparison analyses because the orientation of his sections is misleading. In Figure 4 we can observe that filling of the bedrock hollow has not occurred in a single depositional event.…”

Section: Subsurface Structure Of the Colluvial Mantlementioning

confidence: 99%

Subsurface hydrology of layered colluvium mantles in unchannelled valleys—south‐Eastern Brazil

Fernandes

Netto

Lacerda

1994

Earth Surf Processes Landf

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The effects of subsurface hydrology on the evolution of erosive processes inside layered colluvium mantles in unchannelled valleys are investigated. Tensiometer nests are installed in different morphological conditions with their specific depths controlled by the subsurface structure of the colluvium mantle. Daily readings (during one year) and physical and mechanical analyses of the different colluvium layers are carried out.In spite of a highly discontinuous subsurface structure, present topography is the major factor controlling subsurface flow in this landscape. Paleotopographic features, usually resulting from the lateral mobilization of the previous topographic hollow axis, can locally control the preferential expansion of the saturated zone towards areas other than the present hollow axis. During rainy periods, pressure head at the base of the hollow axis increases towards a maximum value which is not increased by subsequent precipitation inputs. New water input is dissipated by direct precipitation onto the saturated zone and exfiltration by seepage at the gully head walls, precluding the development of the excess pore pressures required to trigger failure by landsliding.

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Erosion disconformities and gully morphology: A threedimensional approach

Cited by 23 publications

References 5 publications

Controlling factors of gullying in the Maracujá Catchment, southeastern Brazil

Controlling factors of gullying in the Maracujá Catchment, southeastern Brazil

Análise Espaço-Temporal da Erosão Linear no Médio-BaixoVale do Ribeirão do Secretário (Paty do Alferes/RJ)

Subsurface hydrology of layered colluvium mantles in unchannelled valleys—south‐Eastern Brazil

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