Gully erosion prediction across a large region: Murray-Darling Basin, Australia

Gully erosion is a significant process for delivering sediment to streams, and can be the dominant erosion process in some regions. As with other forms of erosion, we need methods to predict the extent and patterns of gully erosion across large areas. Such methods also improve our understanding of the environmental controls on gully erosion. Here, patterns of gully density are predicted across the 1 x 10(6) km(2) Murray-Darling Basin in Australia, using aerial photograph mapping of gullies across part of the Basin and a multivariate statistical model of a range of environmental factors. Across the Basin, at a 10-km grid resolution, gully density is predicted to vary from 0 to 1.2 km km(-2), with 22% of the Basin having a gully density >0.1 km km(-2) and 3% a density >0.5 km km(-2). The model is reasonably successful at predicting the variations in mapped gully density compared with similar attempts to predict erosion processes at this scale. Hillslope gradient and mean annual rainfall are the most important single factors across the region. The predicted mean gully density across the Basin is 0.08 km km(-2) and gullies contribute up to 27 x 10(6) t year(-1) of sediment to the river network. This is more than the amount that has been estimated from the combined contribution of hillslope (14 x 10(6) t year(-1)) and riverbank (8.6 x 10(6) t year(-1)) erosion by other studies within the Basin.