• There was a considerable reduction in erosion from the biological carpeting paddock over the duration of the project , with an approximate sediment abatement of 72t during the four years of the trial .
• Following remediation , the control gully achieved 86 per cent effectiveness , with 21t of erosion occurring as rill erosion on the uncapped gully floor at the toe of the slope of the remediated walls . Further rilling is evident in the aerial imagery but is below the limit of detection of the lidar analysis , but all rilling in the floor was below 30 cm .
For the Strathalbyn black soil gully project sites :
• A strong vegetation signal in the 2022 ALS survey limited ground surface mapping and a robust comparative analysis could not be achieved . Change detection for the 2020 – 2022 period was only undertaken on bare ground areas .
• In 2020 – 2022 , heavy vegetation growth along the margins and within the gullies largely prevented identification of the incisions or sidewall erosion . It is unclear whether the incisions are still present in the channels or have been arrested by the dense vegetation .
• In each change detection , the UHD treatment paddock had an annual yield of 29m 3 of sediment while the control paddock ( livestock exclusion ) increased from 33m 3 to 50m 3 of sediment between survey periods , or an increase of 20t .
• In the control paddock , most of the erosion from the 2022 survey occurred as slope wash from north-facing gully sidewalls .
• There is a greater proportion of high slope areas in the control paddock than in the UHD paddock , based on total area and proportionally across the paddock . The gullies in the control paddock have a greater depth ( mean = 0.47m , max = 1.25m ) compared with the treatment paddock ( mean = 0.36m , max = 0.8m ), with considerably steeper sidewalls .
• There is a greater proportion of gullying in the control than in the UHD treatment paddock , based on total area and as a proportion of gully area . In the control paddock , 93 per cent of the 2022 bare ground area is on sidewall slopes of gullies . Bare ground areas in the UHD treatment paddock are more typically on lower slopes to flat ground , i . e . scalds ( 65 per cent ).
• The increased erosion in the control ( livestock exclusion ) paddock indicates cattle exclusion in isolation of other remediation activities is ineffective at preventing ongoing black soil gully erosion .
• While some scalding was apparent in the 2022 survey , during the project period , managed grazing practices in the treatment paddock have not resulted in a detectable increase in erosion in black soil gullies , nor has any substantial new erosion been initiated .
In conclusion :
• At Glenalpine and the Strathalbyn black soil paddocks , it cannot be robustly determined within the limitations of this data whether any change in erosion occurred in response to the trials and at what quantity . However , the results from the black soil paddocks demonstrate a change in the erosion dynamics between survey periods which is likely associated with increased ground cover and a reduction in erosion . Secondary incision and sidewall scour appeared to have been arrested in the most recent ALS survey .
• At Glenalpine , most treatment paddocks demonstrated no comparative difference in normalised erosion rate compared to the control paddock . While it is unclear whether there were initial differences in erosion rates between paddocks prior to treatment , the results during the project re broadly similar when normalised for active areas and at the paddock scale .
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