Holocene valley aggradation and gully erosion in headwater catchments, south‐eastern highlands of Australia

Abstract

Late Quaternary stratigraphy of a 50 km2 catchment on the south-eastern highlands of Australia reveals processes and history of denudation, and helps resolve a long-standing debate about factors controlling episodic valley aggradation and degradation during Holocene times. Valley sedimentation occurred when swampy vegetation fully colonized valley floors and obliterated all channels, promoting aggradation for periods of several thousand years, with most incoming sediment being trapped in swampy meadows. Much of the sediment was reworked from late Pleistocene alluvial fan and valley fill deposits, and primary hillslope erosion was minor during the Holocene. Differing sedimentation patterns between the Late Pleistocene, Holocene and Post-European settlement periods reflect regional changes in sediment supply and transport capacity as a result of major environmental change. Within the Holocene, however, valley fill stratigraphy is controlled by massive, episodic gully erosion terminating aggradation. Gully initiation appears to be controlled more by thresholds of incision into vegetated valley floors than by changes to sediment supply. Whether the thresholds are exceeded because of climatic change, autonomous change or extreme events cannot yet be determined. Overall, the Holocene history represents continuing complex response to events of the Late Pleistocene, and does not support the K-cycle concept, which has strongly influenced late Quaternary geomorphology in Australia.

Late Quaternary erosion in southeastern Australia: a field example using cosmogenic nuclides

“…van Dijk, 1959;Walker, 1962;Coventry and Walker, 1977;Prosser et al, 1994) can be correlated with regional events in the manner proposed by Butler (1959) is not critical to interpreting the data reported here. Geomorphic processes active on hillslopes are dependent on the biota of the region and the climate, and it is likely that the lower temperatures of the glacial cycles (by 6-91C, Galloway, 1965;Caine and Jennings, 1968) led to treeless subalpine conditions and periglacial slope processes on the southeastern highlands.…”

“…Studies of buried and relic geomorphic surfaces have shown how rates and processes have changed in pulses, but have also shown that they can occur without climate changes (e.g. van Dijk, 1959;Walker, 1962;Coventry and Walker, 1977;Prosser et al, 1994). It has also been shown that periglacial processes, thought to be more erosive than processes under milder climates, occurred in the southeastern highlands during the last glacial cycle (Galloway, 1965;Caine and Jennings, 1968;Costin and Polach, 1971;Costin, 1972), and presumably similar processes were active in previous glacial periods.…”

“…The soil mantle appears universally thin (o1 m) throughout the region on divergent ridges. Unchanneled mid-slope hollows typically have fills less than 2 m thick, whereas Prosser et al (1994) report relatively thick valley fills (>5 m in places) from a nearby area in metasediment bedrock.…”

“…The catchment has Prosser et al (1994). (a) Photograph of the site looking north from the south side of the Bredbo River.…”

Modelagem De Canais Incisivos - Revisão

“…Com relação às causas antrópicas tem-se constatado, principalmente, nas primeiras décadas do século XX, em muitas partes do mundo, que a troca de uma agricultura tradicional de baixa intensidade, por práticas de uso do solo mais intensivas (PROSSER et al, 1994), assim como a alteração do curso de um canal original por obras de engenharia e remoção da vegetação das margens dos rios (SCHUMM et al, 2001), vem alterando a dinâmica energética das redes de drenagem naturais (ERSKINE, 1999).…”