Tarlton Whyte Outfall
Client:
City of Holdfast Bay
Location:
Somerton Park
Project value: $5,900,000
With the threat of flooding to 80 residential properties, Tonkin was engaged in the design and planning of a major stormwater infrastructure update.
What we did
Tonkin, in collaboration with the City of Holdfast Bay undertook a major stormwater infrastructure upgrade focused on improving flood resilience, environmental outcomes, and long-term sustainability across the Tarlton Street and College Road catchments. Tonkin was engaged as the engineering consultants for the civil design and hydraulic engineering.
The project was initiated in-line with the Stormwater Management Plan coastal catchments between Glenelg and Marino in response to recurring flood events, ageing infrastructure, and increasing environmental pressures, with the goal of delivering a high-performing, climate-resilient drainage system that would serve the community well into the future.
The project delivered 600m of large pipes and culverts, 26 new pits and connections, a new headwall and ocean outlet, and installation of a Gross Pollutant Trap (GPT). The outcome of this project reduced flooding risk to approximately 80 properties for up to 800mm for a 100-year storm event.
A key driver of the project was the need to reduce property inundation during storm events. Hydraulic modelling using DRAINS and TUFLOW was employed to guide the design process. DRAINS modelling supported iterative optimisation, while TUFLOW provided detailed catchment-wide analysis and visualisation of flood impacts. This dual approach enabled the design team to achieve significant improvements in flood mitigation, particularly under the 1% annual exceedance probability (AEP) scenario with a 10% climate change allowance.
How we made a difference
Tonkin's involvement in this local project has delivered significant environmental and community benefits to the City of Holdfast Bay - particularly including flood protection and resilience for the catchment area.
The reduction in flood risk across residential areas translates to lower risk of property damage, improved safety, and enhanced peace of mind for locals.
The serviceability of the outfall has remarkedly improved during rainfall events, with roads and collector routes - some forming part of Adelaide Metro bus network - forming the improvement zones. The upgrade has reduced inundation duration and also protects road pavements from water damage, lowering long-term maintenance costs for council and improving overall infrastructure resilience.
Environmentally, the new gross pollutant trap filters rubbish and debris, capturing an estimated 33m3 of litter annually, material that previously would have polluted the Somerton Park beach.
The reduction in flood risk across residential areas translates to lower risk of property damage, improved safety, and enhanced peace of mind for locals.
The serviceability of the outfall has remarkedly improved during rainfall events, with roads and collector routes - some forming part of Adelaide Metro bus network - forming the improvement zones. The upgrade has reduced inundation duration and also protects road pavements from water damage, lowering long-term maintenance costs for council and improving overall infrastructure resilience.
Environmentally, the new gross pollutant trap filters rubbish and debris, capturing an estimated 33m3 of litter annually, material that previously would have polluted the Somerton Park beach.
Innovations
Tonkin's skilled engineers utilised mixed hydraulic modelling tools to inform and optimise design outcomes.
DRAINS modelling was employed during the design phase to refine system performance, while TUFLOW modelling was used to validate the final design and create flood difference maps to visually capture and communicate catchment-wide effects. These tools provided a clear and comprehensive understanding of system behaviour, allowing for informed decision making.
An innovative feature of design is the ability of the existing stormwater stystem to reverse flow direction based on downstream capacity through a cross-connection between the new stormwater mains and the existing trunk. Givern the flat gradients of the area's pipes, the system is now able to dynamically respond to capacity constraints. When the downstream end of the existing trunk becomes overwhelmed, the southern portion of the network reverses flow and discharges through the newly constructed mains.
This adaptive flow behaviour enhances the overall resilience and efficiency of the network, reducing flood risk without requiring extensive upgrades to multiple council systems.
DRAINS modelling was employed during the design phase to refine system performance, while TUFLOW modelling was used to validate the final design and create flood difference maps to visually capture and communicate catchment-wide effects. These tools provided a clear and comprehensive understanding of system behaviour, allowing for informed decision making.
An innovative feature of design is the ability of the existing stormwater stystem to reverse flow direction based on downstream capacity through a cross-connection between the new stormwater mains and the existing trunk. Givern the flat gradients of the area's pipes, the system is now able to dynamically respond to capacity constraints. When the downstream end of the existing trunk becomes overwhelmed, the southern portion of the network reverses flow and discharges through the newly constructed mains.
This adaptive flow behaviour enhances the overall resilience and efficiency of the network, reducing flood risk without requiring extensive upgrades to multiple council systems.
