• Dams and other water bodies attract animals and so are high impact areas, so erosion remediation nearby is likely to fail.
• Banks designed to rehydrate the land through subsurface flow downslope will only work in specific parts of the landscape( e. g. colluvial deposits), in specific soils( sandy), and where there is enough depth in the soil to take in sufficient water to justify the cost of the infrastructure, including the on-going maintenance. This is not where gullies tend to be in the BBB.
Once remediated, gullied areas should be away from high impact areas. Attempting to combine catchment remediation earthworks above gullies with other property infrastructure such as a dam risks failure on both accounts.
Rock chutes in gullies- commit to high maintenance or avoid
Rock chutes can be effective if planned and installed well, and repairs are attended to promptly. All the rock chutes at small-scale sites needed repairs. Many of the issues were associated with erosion of bare earthen abutments as vegetation was difficult to establish on the poor soil.
Protect rock chute abutments
The earthen abutments on the sides of rock chutes often required maintenance. Establishing resilient vegetation on these slopes will prevent their erosion. When rock chute abutments are formed in sodic soil material they should be covered with 20- 30cm of stable soil, along with the rest of the chute foundation( Carey et al., 2015, p. 68). However, it is understood that, for most of the rock chutes on sodic soil at large-scale sites, instead of importing stable soil, sodic subsoil material was mixed with gypsum, and other ameliorants as necessary, to‘ make’ a stable soil. For small-scale sites, if a rock chute is decided as the best option, stable soil should be imported to cover the sodic foundation. The revegetation of all exposed soil around a rock chute is an essential part of its installation and this should be managed by a qualified person. Rock capping on the steeper slopes may be an effective addition. Also modifications to the abutment design may be possible to improve the likelihood of vegetation establishing. For example, a wider chute might lower the necessary height of the abutments leading to a gentler grade on the abutments which will assist vegetation establishment( Cary et al. 2015). Livestock needs to be kept away to prevent damage to the structure.
Rock chutes in Downs country should be avoided as explained in Figure 31- Site 24.
Concrete matting could be an appropriate alternative to rock chutes in gullies with small catchments and instead of rock capping of channels( Landloch Pty Ltd( 2024, p. 6)( Figure 33). The matting needs to be subjected to the same rigorous hydraulic assessment during the design stage that rock chutes are. Unlike a rock chute, concrete matting allows for vegetation to more readily grow through it, enabling the soil surface in the channel to strengthen over time. The concrete matting relies on vigorous, deep-rooted perennial plants growing within it to achieve maximum stability. Achieving such vegetation growth is likely to be challenging in many gully sites in the BBB where the only soil material is poor fertility subsoil.
Limit grazing at sites that have little topsoil
Gullies and other erosion areas with little or no topsoil are unlikely to provide much feed in a paddock. However, cattle activity can cause significant damage to a remediated gully site. Results of the monitoring of small-scale sites suggest that restricting cattle access to remediated sites in Sodosols is essential. If done well, restricted grazing will give the site a chance of achieving a stable state but there are no guarantees. None of the six remediated gullies in Sodosols achieved stability( Figure 24) but sites under more control( i. e. high focus on land condition) performed better than those under less restriction( i. e. moderate focus on land condition). The‘ moderate focus’ rating represents the grazing management for the bulk of the sites with remediated gullies( 10 / 14). Grazing management for the moderate rating typically involved resting for two wet seasons and then grazing the site as part of the larger paddock for 2-5 months at a time in the dry season. Results suggest that this type of management does not provide enough protection to the fragile vegetation, particularly for sites with Sodosol soils and creates tracks that invite erosion. Short grazes
50 GULLY MAINTENANCE AND MONITORING TECHNICAL REPORT