Recent landscape history in arid western New South Wales, Australia: a model for regional change

Accelerated erosion by wind and water has taken place in arid western New South Wales, Australia, since the introduction of domestic and feral herbivores by Europeans in the nineteenth century. This action led to widespread soil loss by sheetwash, rilling, gullying, and aeolian deflation. Upland creek systems, formerly comprising shallow sinuous channels, are now entrenched into alluvial fills on the valley floor. Radiocarbon dating of charcoal from Aboriginal cooking pits, exposed by this erosion, indicates that the current phase of incision of the valley floor has occurred since grazing of domestic animals began about 140 years ago. Stratigraphic evidence is presented which suggests that this type of incision (gullying or arroyo cutting in the valley floor) may not have occurred before within the 20,000 year sedimentary history of the valley fills studied. Channel enlargement and knickpoint retreat, initiated by these changes, is ongoing, and the implications of this for land and heritage management in the region are discussed. A conceptual model is presented which summarises the hydrogeomorphic changes which have occurred in upland catchments in the region as a result of changes in landcover.