4.2.3 Sources of soil erosion by land use
Grazing As grazing is the dominant contributing land use of TSS in the Burdekin region , the erosion sources of annual average anthropogenic TSS loads from this land use are shown in Figure 20 . The Bowen catchment contributes 46 % of the regional TSS load from grazing lands , but only contains 8 % of the grazed area . Gully erosion dominates in all grazing lands ( 50-73 %), with a regional estimate of 67 % of TSS generated from grazing lands from gully erosion . Hillslope and streambank erosion are estimated to contribute similar proportions , estimated at 19 % and 14 % respectively . These vary between catchments but in most cases , including for the Bowen catchment , hillslope erosion is more significant than streambank erosion ( McCloskey et al . 2017a ).
Using the modelling data , the top 20 sub-catchments for TSS loads from grazing lands are shown in Figure 21 . Gully erosion is the dominant erosion type at a sub catchment scale . Bartley et al . ( 2015 ) reported evidence of alluvial gully erosion at the junction of the Burdekin and Bowen River systems , however , this is not classic bank erosion ( i . e . has not resulted from lateral channel migration ) and should be treated as alluvial gully erosion . An assessment of the Bowen River system found a similar result with very little evidence of high rates of bank erosion , which matches the modelling . Most of the channel was reasonably well vegetated on both sides of the river . There is some evidence of severe bank erosion ( i . e . steep , bare banks with pipe erosion ) at a number of mine sites in the upper section of the Little Bowen catchment , and there is considerable severe gully erosion in the Little Bowen . However , it seems that gully erosion , rather than stream bank erosion , is likely to be the dominant source of channel erosion in this catchment . These results highlight the need to undertake on-ground assessments before investing in erosion management at specific sites across the region .
Figure 20 . Modelled estimates of annual average anthropogenic TSS loads from gully , hillslope and streambank erosion in grazing lands in the Burdekin catchments . Inset shows regional contributions from grazing lands . Derived from Source Catchments 2013 baseline estimates , DNRM 2015 .
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