Particle size data was also collected before and after treatment at all NESP sites ( Figure 18 ). These results confirm that Mt Wickham remains a very high priority for continued investment and monitoring of results . Furthermore , the results for Mt Wickham to date show a general coarsening of the sediment measured from the site after treatment , indicating that more fines are staying on site . This is most likely due to the flocculant and gypsum used on the treatments .
Figure
18 . Particle size of suspended sediment collected at each site over the entire study period . Note that sediment < 20 µ m ( dotted line ) is considered to be the most ecologically detrimental for the GBR ( Bainbridge et al ., 2018 ).
In summary , three years after the treatment works were undertaken at Mt Wickham , there are statistically significant outcomes demonstrating that the treatment has had an effect independent of any rainfall variability at the site . The amount of cover and biomass on the hillslope and gully walls has significantly improved using the most robust statistical indicators . The water quality data , particularly TSS concentrations , have also shown statistical improvement . Using the data presented in Figure 16 and Figure 17Error ! Reference source not found . and the load reductions from before and after treatment , the relative effectiveness of the Mt Wickham rehabilitation works is calculated as 0.91 in 2020 / 21 . Hence the treatment has reduced sediment loads by 91 %.
The main watch point for Mt Wickham is that despite significant improvements in cover and biomass , the land condition remains fragile . It will take several more years for additional perennial plant species to take hold at this site . Until then , grazing should be carefully managed .
Gully 1 ( LRP17-012 and has CSIRO monitoring - commonly referred to as Trial Site Two )
Work started at Glen Bowen Station , the LDC ’ s second large-scale gully remediation site in November 2019 . Neilly Group Engineering was commissioned to design the remediation measures to be carried out at Glen Bowen in the Bowen catchment , approximately 27km west of Collinsville . The site that has been remediated , known as Gully 1 , is an alluvial gully eroding primarily through direct rainfall indicating the soils are highly dispersive . This was confirmed through soil testing . The actively eroding footprint of Gully 1 has a perimeter of approximately 1.1km with an internal area of 3.36ha . The banks of the gully scarp are on average 2 – 2.5m high . The drainage lines within the gully all converge to a single drainage line that discharges into the Bowen River .
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