6.4 Landscape protection and prevention of further erosion
In a highly modified landscape such as that of the grazing lands in the Burdekin region , there is a need to protect those areas where soil erosion rates are relatively low , and to identify areas and actions to prevent further erosion . In particular , methods for preventing further gully development are critical for reducing sediment loads delivered to the GBR .
Beutel et al . ( in prep ) have established criteria for protection and prevention of soil erosion as part of their grazing prioritisation . Wilkinson et al . ( 2015a ) also identified the importance of preventing initiation of new gullies in the GBR catchments , which is substantially more cost effective than gully remediation .
Wilkinson et al . ( 2015a ) conducted a spatial assessment of vulnerability to future hillslope gully erosion in and around the Burdekin Basin . Vulnerable areas are defined as those with low levels of gully erosion that have similar environmental characteristics to areas usually containing high levels of gully erosion . These areas are identified by developing a model of mapped gully density , and then analysing the differences or ‘ errors ’ between the model and the input gully mapping . Areas where the mapped gully erosion is over-predicted by the model are therefore predicted to be vulnerable to future gully erosion . Factors considered in the assessment were current mapped gully extent and environmental variables known to influence gully development associated with soil , terrain , vegetation and climate . The variables most correlated with gully extent were dominated by soil properties . Soils with strong contrast in texture between the A- and B-horizons ( duplex soils classified as Chromosols ) were found to be most prone to hillslope gullying , but can also include Sodosols when they occur in undulating terrain ( as distinct from Sodosols on alluvium ). They form in granodiorite and sandstone parent material , as well as other lithologies , and have sandier topsoil than subsoil . Their clay-rich subsoil impedes water infiltration into the deeper soil profile and thus promotes overland flow and lateral subsurface flow . They are covered by eucalypt woodlands or have been cleared of this vegetation . Their association with gullying is consistent with soil saturation and piping being important factors in gully erosion .
Vulnerability to future hillslope gully erosion was most-correlated with the grazing-induced deficit in cover relative to nearby reference levels ( Bastin et al . 2012 ), indicating that grazing management has had a significant impact on the development of gully networks . The areas most vulnerable ( at risk ) to future gully erosion are those in duplex soil types ( high surface soil water holding capacity ) with relatively high historical cover levels . Maintaining ground cover on those properties is a priority for gully prevention , and is very cost-effective given the much higher costs of gully remediation .
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