Figure 42 . Concentration of suspended sediment < 20μm for each respective RSS sample between December 2020 and April 2021 . Control sites are V bottom and shown in blue . Treatment sites are flat bottom and shown in green ( Fruition Environmental , 2021 ).
Despite the limitations in comparing drain types , this monitoring has indicated what has long been suspected , that gravel roads are likely to be a significant source of fine sediment run-off . A preliminary estimate of the average per event fine sediment runoff through the table drain network of the less than 1km of gravel road monitored was 2.13 tonnes . This suggests that gravel road drainage has the potential to produce significant quantities of fine sediment in run-off impacting the health of the GBR and further data in this area would be valuable . This is substantiated by studies in other regions such as those in the Normanby catchment which identified that runoff from unsealed roads can contribute a relatively high proportion of sediment loads in some areas and may also contribute to gully initiation and erosion ( Gleeson , 2012 ).
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