( A ) ( B )
Figure 16 . Mt Wickham TSS data before and after rehabilitation works ( treatment ). Graph ( A ) is the TSS concentration lab data for all events before and after treatment was implemented on 22 October 2018 , and Graph ( B ) is the flow weighted Event Mean Concentration ( EMC ) for the events before and after treatment .
It is important to note that the TSS concentrations measured at Mt Wickham ( and Glen Bowen ) are considered to be very high compared to other sites measured as part of NESP Project 5.9 ( see Figure 17A below ), highlighting the relative differences in their natural condition and erodibility . For example , in 2019- 20 the highest flow weighted mean TSS concentrations measured at the Mt Wickham control site were ~ 49,300 mg / L compared to peak concentrations between ~ 90 and 6,500 mg / L at other sites . The Mt Wickham area has very highly sodic sub-surface soils . The TN values were more similar between the sites , although Glen Bowen ( control site ) still had the highest median TN concentrations ( Figure 17B ).
( A ) ( B )
Figure 17 . ( A ) comparison of TSS data from all un-treated gullies for all years of data ( B ) comparison of TN data from all un-treated gullies for all TN data at each site ( 2016-17 to 2020-21 ).
Characterising the particle size of the sediment leaving a site is highly important as finer sediment has a greater potential to reach the GBR . Sediment < 16 µ m ( rounded to ~ 20 µ m ) is considered to be the most ecologically detrimental for the GBR ( Bainbridge et al ., 2018 ). Therefore , sites that are eroding fine grain soil will be a higher priority for rehabilitation .
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