Part of the treated upper gully area. Fan flower bush, grasses and significant sandy deposits in a channel of the badlands.
October 2022
Part of the untreated lower gully area showing currant bushes, fan flowers and grasses. This channel drains about half of the‘ badlands’ in the Site 5 southern area
The works in Site 5’ s southern section were low impact because landforming earthworks were deemed to be uneconomical due to the advanced stage of the erosion, the poor fertility of the remaining soil material and the hostile conditions for vegetation. The plan avoided soil disturbance and concentrated in the upper scarps and channels of the‘ badlands’ where more subsoil remained. The treatment was tailored to the soil materials’ deficiencies, involved ameliorants of gypsum, fertilizer and millmud, seeding( specialist plants- halophytes) and mulching of the channels. Together, with total exclusion from grazing, this treatment has facilitated revegetation, creating a habitat that is favourable to the native woody shrubs, particularly the Spiny fan flower( Scaevola spinescens) and Currant bush( Carissa sp.). Spiny fan flower is regenerating rapidly, responding to the favourable conditions that were created. These low shrubs act as a living weir in the channels; reducing flow velocity causing soil to drop out of suspension. More plants then flourished in the deposited soil material.
Figure 30. Additional information on the low impact works at Site 5.
What monitoring and maintenance schedules and maintenance costs could be embedded in large-scale gully remediation plans?
The monitoring and maintenance schedules adopted in this project was appropriate and is recommended for future sites: Monitoring the site at the end of the wet season each year, then planning and undertaking any required maintenance in the dry season. The results of this project indicate that a minimum of four years of monitoring following construction would suit the most successful large-scale sites. Longer monitoring and subsequent maintenance would be required for more‘ difficult’ sites such as Site 1, or if the site is impacted by flood, drought or over-grazing. The Gully and Streambank Toolbox recommends at least two, or ideally three years of monitoring, recognising that time limits are placed on publicly funded projects and that, at the completion of projects, future monitoring and maintenance will be the responsibility of the landholder( Wilkinson et al., 2022, p. 29, Landloch Pty Ltd, 2024, p2).
The total maintenance costs( public investment and in kind) for the five large-scale sites varied from $ 48,231( Site 1) to $ 10,644( Site 4). Compared to the initial project costs, Site 2 had the smallest maintenance expenses( 1.7 per cent of the initial on-ground project costs) and Site 5 the largest( 9.9 per cent). For the four intensively treated sites( 1-4), these figures concur with those given in the Gully and Streambank Toolbox- typically 1-4 per cent of total construction costs( Wilkinson et al., 2022, p. 28). If not already doing so, project managers would be advised to conduct a risk assessment on the proposed remediation works and use it to inform how much money to allocate to future maintenance, drawing on the maintenance required at previous sites, such as those described here and in Landloch Pty Ltd( 2024).
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