Alluvial gully erosion: an example from the Mitchell fluvial megafan, Queensland, Australia

Abstract

Considerable attention has been focused on the role of gullies as a contributor to contemporary sediment loads of rivers in Australia. In southern Australia rapid acceleration of hillslope gully erosion has been widely documented in the postEuropean period (~ last 200 years). In the northern Australian tropics, however, gully erosion processes operating along alluvial plains have not been well documented and can differ substantially from those gullies eroding into colluvium on hillslopes. Aerial reconnaissance surveys in 2004 along 13 500 km of the main stem rivers that drain into the Gulf of Carpentaria (GoC), identifi ed extensive areas of alluvial lands that have been impacted by a pervasive form of gully erosion. More detailed remote sensing based mapping within the 31 000 km 2 Mitchell River fl uvial megafan has identifi ed that active gullying into alluvium occupies ~ 0·4% (129 km 2 ) of the lower Mitchell catchment. These alluvial gullies are concentrated along main drainage channels and their scarp heights are highly correlated to the local relief between the fl oodplain and river thalweg. While river incision into the megafan since the Pleistocene has developed the relief potential for erosion, other factors such as fl oodplain hydrology, soil dispersibility, and vegetation also infl uence the distribution of gullies. In this paper we present a conceptual model of alluvial gullies, and contend that they represent a distinct end member in the continuum of gully forms that have been described in the geomorphic literature. An understanding of the processes driving this form of alluvial gullying can only be gained when they are differentiated from widely described colluvial hillslope gully models and theories. We present evidence of type examples of alluvial gullying in the Mitchell, and through analysis of their distribution and morphology at different scales, highlight some of the key mechanisms that are potentially initiating these features and driving their expansion.

Terrestrial invertebrates of dry river beds are not simply subsets of riparian assemblages

“…Both of these rivers flow into the Gulf of Carpentaria in northern Queensland, Australia. During the dry season, surface water in the Flinders River catchment is largely confined to a series of isolated waterholes, whereas the main channel of the Mitchell River catchment contracts to a sinuous, low flow channel with multiple secondary channels, and the location of the main channel is highly dynamic (Brooks et al 2009). Large, dry, secondary channels were sampled if surface water was present in the main channel.…”

“…These secondary channels carry water less often than the primary channel of the Mitchell, but more often than primary channels sampled in some other catchments. The Mitchell River experiences large floods every year (every 'wet' season) that inundate these channels, resulting in a single, large macro-channel (Brooks et al 2009). Dry river beds were typically wider than 100 m in the Mitchell River catchment, and wider than 50 m in the Flinders River catchment.…”

Influence of bare soil and cultivated land use types upstream of a bank gully on soil erosion rates and energy consumption for different gully erosion zones in the dry-hot valley region, Southwest China

“…A study by Radoane et al (1995) showed that the rate of gully headcut development was estimated at [1.5 m year -1 for gullies cut into sandy deposits and \1 m year -1 for gullies cut into marls and clays. Additionally, numerous studies have described bank gullies that entirely eroded into alluvia (Brooks et al 2009;Haigh 1984;Shellberg et al 2013). Meanwhile, Vandekerckhove et al (2000) reported that land use changes impacted topographic thresholds and led to gully initiation and sedimentation in six different study sites in the Mediterranean.…”

A simple DEM assessment procedure for gully system analysis in the Lake Manyara area, northern Tanzania

“…Therefore, it is often necessary to find a compromise between the cost and the quality of the data. Consequently, in some studies freely available data such as Shuttle Radar Topographic Mission (SRTM) digital elevation models (DEM) derived from X-or C-band or the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) GDEM are used in the assessment of erosion processes and feature detection because of their almost global coverage (Brooks et al 2009;El Haj Tahir et al 2010). Often these DEMs are the only valuable elevation information in remote areas where no high-quality topographic maps are available.…”