Gully position, characteristics and geomorphic thresholds in an undisturbed catchment in northern Australia

Gullying is a significant process in the long-term dynamics and evolution of both natural and rehabilitated (i.e. post-mining) landscapes. From a landscape management perspective it is important that we understand gully initiation and development, as it is well recognized that catchment disturbance can result in the development of gullies that can be very difficult to rehabilitate. This study examines gully position using geomorphic statistics relating to features such as depth, width and length in a catchment undisturbed by European activity in the Northern Territory, Australia. The results demonstrate that gullying occurs throughout the catchment and that a slope-area threshold does not exist and that gully position broadly follows the catchment area-slope relationship. Simple relationships relating catchment area and slope to gully depth, width and length provide poor results, despite these relationships having been found to apply for ephemeral gullies in cropland. The results suggest that gully initiation thresholds are low as a result of an enhanced fire regime. A threshold model for gully position that uses catchment area and slope to switch between gully and hillslope was evaluated and found broadly to capture gully position. Copyright (C) Commonwealth of Australia, (2006) Published by John Wiley & Sons, Ltd.