ground cover is near 100 % at both control and treatment sites at both the end of the 2019-20 and 2020-21 wet seasons .
The total sediment loads ( t / y ) measured at the treatment site were higher than at the control site in both wet seasons . This appears to be due to the larger catchment area and increased discharge at the treatment site . However , the unit area sediment loads ( t / ha / y ) and flow weighted annual mean TSS concentrations , were lower at the treatment site than the control .
( A ) ( B ) Figure 26 . ( A ) TSS concentration and ( B ) TN concentrations at Mt Pleasant for the 2019-20 and 2020-21 wet seasons .
The limited particle size data ( Figure 18 ) collected to date indicates that the sediment in runoff is very fine , around 12 µ M , making it a high priority for management .
In summary , two wet seasons have passed since the treatment works were undertaken at Mt Pleasant . Interestingly , there has been very little improvement between the control and treatment sites . This was because this property was in relatively good condition ( in terms of cover and biomass vegetation metrics ) and had less ‘ very degraded ’ areas compared to the other gully sites , prior to the rehabilitation works . The baseline vegetation conditions ( in terms of cover and biomass ) were already quite high ( although the site is still dominated by Indian Couch and therefore the overall long term land condition is reduced due to low species diversity and pasture basal area ). The annual median and mean TSS concentrations measured at the Mt Pleasant site are some of the lowest concentrations measured on any of the gully sites . Even the control site , which has not undergone any active remediation treatment , has very low concentrations . The elevated loads measured in 2020 / 21 were from marginally higher concentrations , but primarily from increased rainfall and runoff in 2020 / 21 . Additional years of average or above average rainfall will test if these findings hold .
Treatment ( LRP17-016 and has CSIRO instrumentation since pre-LDC )
The Strathbogie site was originally a Reef Trust 2 gully rehabilitation site is now being managed in the LDC Project . Treatment on the gully system at Strathbogie Station involved a number of design amendments incorporating landholder feedback and ideas . The final designs were agreed to in late 2019 and delivered by John Day from Emu Ridge . The onsite works implemented were carried out by OPM Solutions and local operators . The remediation at Strathbogie includes :
● five hillslope flow diversion banks
● a small rock revetment near a head cut designed to prevent subsidence
● a level sill controlling water re-entering the gully
● a silt trap
● exclusion fencing was also installed
69