THE PROJECT
Home to a diverse ecosystem of native plants and creatures, Sellicks Creek was once a highly degraded gully created by extensive erosion in dispersive soils caused by over 100 years of damage from farming practices. Over time, the channel had significantly increased in size to over 10m deep by 30m wide.
Onkaparinga Council sought to rectify and restore the creek in three stages, creating a biodiversity corridor and allow safe community access while also accounting for 1-in-100-year flood flow.
TECHNICAL SOLUTIONS
Stage 1 and 2
WGA undertook extensive civil and environmental design to restore the lower reaches of the creek. The goal was to create a biodiversity corridor and to treat, intercept and trap sediments from the rural catchment. This involved significant earthworks to fill and reshape the cavernous gully, while providing a series of linked wetland ponds, reed filter beds, and rock lined cascades, complimented with a network of trails and a bridge crossing.
The design included extensive coordination of vegetation plantings at targeted locations to control public access, filtering of flows, and provide long-term stability in specific areas to create habitat opportunities within the newly rehabilitated riverine corridor. Several terraced earth reinforced gabions were required to calm and reduce stream power to a non-erosive velocity. A series of terraced gabion waling formed a major spillway down to beach level, and appear as a series of cascading waterfalls.
Stage 3
Stage three included the upgrade of Country Road bridge crossing, along with rehabilitation works. Key components included earth reinforced retaining using green walling systems, rock chutes, a stilling pool, and a major 10m high reinforced earth gabion spillway to calm the flow to the downstream waterway.
CLIENT FOCUS
Guided by a set of key design objectives, the Sellicks Creek Rehabilitation project aimed to enhance both safety and environmental value. These objectives included:
- Safely managing major storm events, specifically 1-in-100-year flow rates, to prevent flooding and protect nearby infrastructure and properties.
- Reducing stream power during storm flows to minimize erosion damage and preserve the integrity of the waterway.
- Creating a resilient natural corridor that supports local native flora and fauna
- Providing safe and accessible spaces for the community that allow passive recreation, and the opportunity to enjoy the revitalised creek environment.
The Sellicks Creek Environmental Rehabilitation project features extensive use of soft engineering techniques and the adoption of nature based design principles throughout. Various operational management objectives were designed to ensure that the creek system performed to meet council’s environmental goals. Together, these goals shaped a rehabilitation effort that balances engineering needs with ecological restoration and community wellbeing.
Stages 1 and 2 won the Institute of Public Works Engineering Australasia Award for Excellence and was a national Civil Contractors Federation Earth Awards winner in the same year, while Stage 3 won the national Civil Contractors Federation Earth Awards for 2010.
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