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3.2.6 Soil erosion
Soil erosion can take place through a variety of forms and processes and into a variety of
regolith from solid rock to unconsolidated soil or alluvium. On Oriners and Sefton Stations,
soil erosion is dominated by water erosion by direct rainfall and water runoff. Water erosion
can be classified as:
Splash Erosion of soil particles by direct rainfall impacts on exposed soil.
Sheet Erosion of soil particles by shallow overland flow moving down slopes in broad
sheets.
Rill Erosion in small, ephemeral, concentrated channels on hillslopes usually parallel
to the hillslope and < 30cm deep.
Gully Erosion in deeper, ephemeral, unstable channels > 30cm deep.
Channel Erosion of the banks or bed of pre-existing channels of small creeks to large
rivers.
The full distribution and magnitude of all of these water erosion processes in Oriners and
Sefton Stations are unknown. However, examples are easy to find and all have been
reported by reconnaissance surveys, with each type of erosion typically confined to specific
location on the landscape (Galloway, Gunn et al. 1970; Biggs and Philip 1995a; Biggs and
Philip 1995b) . For example, Galloway et al. (1970) noted that sheet erosion was widespread
on the level plains, interfluves (shallow ridgelines), and hillslopes of the Balurga and Annaly
land systems (Figure 51; Figure 54) where duricrusts and hardpans reduce rainfall infiltration
and promote overland flow. In contrast, gully erosion is dominant on the side slopes of
shallow valleys (Balurga; Figure 51), on the lower colluvial slopes of rock outcrops (Annaly;
Figure 54), and along silty alluvium floodplains of major creeks and rivers (Cumbulla; Figure
55).
Soil type and properties (texture, porosity, chemistry) can highly influence the potential for
soil erosion. For example, silty soils along floodplains of creeks in this area typically have low
cohesion (binding), making them prone to gully and channel erosion if the vegetation
resistance is changed by land use (Shellberg 2011). Furthermore, many of the soils along
floodplains and drainage channels are textural contrast or duplex soils that are alkaline at
depth (TM1, Isbell et al. 1968, BRS 1991; Antbed, Ab and Hann, Hn, Biggs and Philip 1995a;
1995b). These soils usually have silty or loamy top soils that overlay clay loam subsoils. The
alkaline (i.e., high pH) soils typically have high levels of exchangeable sodium on the cation
exchange complexes of clay particles (hence the Sodic Sodosolic soil type), in contrast to
other preferred cations like calcium, magnesium and potassium. Due to sodium‟s weak
single bond and affinity for water, soils with high sodium levels easily disperse in the
presence of water and are highly prone to gully erosion. Gully erosion will be addressed in
more detail in Section 3.2.11, along with bank erosion in Section 3.2.10.
3.2.7 Catchment land use
The traditional Indigenous land use of the Oriners and Sefton areas in both the past and
present is highlighted throughout this document. On top of this traditional management
template, a new system of European-style management to extract resources (grazing, mining
etc.) was also initiated in the Mitchell catchment in the 1880s and has continued to various
degrees until today (Cotter 1995; Strang 2001; Strang 2004; Shellberg 2011) .
In the Alice River catchment around Oriners and,Sefton the recent past and contemporary
land use was cattle grazing (both managed and wild herds) across forest country, savanna
woodlands and unimproved grasslands (Cotter 1995; Strang 2001). These savanna
vegetation communities(Neldner, Stanton et al. 1997; Crowley and Garnett 1998) are
dynamic over space and time and are strongly controlled by disturbance regimes (fire, flood,
grazing, erosion). These disturbance regimes have changed in the Oriners area following
European settlement (Crowley and Garnett 1998; Crowley and Garnett 2000). During the
long dry season, cattle grazing intensity and impacts are heavily concentrated along
Working Knowledge at Oriners Station, Cape York
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