16 Mile Creek Flood Immunity Improvement Project

Project Client

Department of Logistics and Infrastructure

Status

Completed

Scope of work:

Sixteen Mile Creek crosses the Stuart Highway approximately 29km north of Alice Springs, in the Burt Plain locality. The Sixteen Mile Creek Flood Immunity Improvement project is an NTG Department of Logistics and Infrastructure (DLI) initiative. The project aims to reduce flooding of the Stuart Highway at the creek crossing to improve motorist safety and maintain accessibility along a critically important transport route between South Australia and the Northern Territory.

Our Role:

Byrne Consultants were engaged by DLI to review a previous civil design for upgrade of the creek crossing and revise the design to align with current DLI and industry standards. Issues were identified with previously undertaken flood modelling, and DLI directed Byrne Consultants to undertake additional flood modelling and options analysis to identify the most cost-effective upgrade configuration that would achieve key outcomes relating to trafficable immunity. Byrne Consultants undertook the following tasks:

• Hydrologic Modelling in RORB: The hydrologic model incorporates a total catchment area of approx. 500 square kilometres. An ensemble approach was adopted for design frequencies ranging from 63.2% AEP to 1% AEP (the project objectives included achieving dry immunity for 5% AEP event).
• HEC-RAS hydraulic modelling: As model iterations were progressed to achieve the nominated design basis, Byrne advised DLI that the number of culverts required to achieve 5% AEP dry trafficable immunity was becoming impracticable from both a constructability perspective. Byrne proposed that subsequent model simulations include options involving a mixture of bridges and culverts.
• Bridges were subsequently integrated into the HEC-RAS model with a nominal 1m thick deck, and piers at a nominal 25m spacing. To comply with AS5100, it was agreed with DLI to provide 300mm freeboard to the underside of the bridge soffit during the 1% AEP storm event, with the remainder of the highway and culvert structures designed for 5% AEP dry trafficable immunity.
• Cost estimates for a number of configurations and presented the most effective option to DLI for consideration.

Project Outcomes:

Byrne Consultants successfully undertook and delivered meaningful results for flood modelling of a large catchment area under the National Highway. Byrne Consultants produced a technical memorandum and high-level cost estimates suitable for internal government funding decisions.

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