The South West Rail Link (SWRL) has been proposed by the NSW Government as part of a commitment to infrastructure for the South West Growth Centre urban release areas. The 13.2 km line will provide a link from the existing Glenfield station to the urban release areas of Edmondson Park and Leppington. The proposed alignment crosses a number of waterways including the Bunbury Curran floodplain, and the upper tributaries of Cabramatta and Maxwells Creek.
Preliminary technical investigations were carried out to identify the most feasible rail alignment. WMAwater were engaged by the Transport Infrastructure Development Corporation (now Transport for NSW) to undertake an assessment of hydrologic issues associated with the proposed SWRL. The outcomes of that study were the need to consider potential impact of the railway line on flood levels and behaviour.
WMAwater were then engaged to assess the key waterway crossings along the proposed SWRL in further detail and to quantify impacts of potential increases in post-SWRL flood levels and hazards as part of the Environmental Assessment for Concept Approval. The scope also included the assessment of potential flood risk of the preliminary design and to determine appropriate sized waterway crossings.
The assessment included consideration of changes in inundation areas, identification affected properties, assessment of flood risk and the identification of potential flood mitigation measures. One-dimensional hydraulic modelling was undertaken at each waterway crossing to define these factors. The assessment identified areas were further detailed assessment would be required in future design stages.
The SWRL design then progressed to concept design and WMAwater undertook a hydrologic assessment as part of the Environmental Assessment for project approval. The key purpose of this investigation was to identify potential hydrologic impacts associated with the SWRL concept design and recommend mitigation measures to direct detailed design. The assessment of hydrologic impacts considered environmental issues (such as impacts on fish and fauna passage, water quality and changes in flow regime), flood impacts (such as changes in peak flows, flood levels, velocities and hazards) and flood risk to existing and proposed infrastructure as well as to address the compliance requirements of the project incorporating the Director General’s requirements and Statement of Commitments. To satisfy the compliance requirements design criteria and guiding principles were developed and detailed two-dimensional flood modelling was undertaken.
WMAwater were subsequently engaged to undertake an independent review of the hydrologic aspects associated with the detailed design stage of the project.
The project had tight timeframe and as such continuous consultation with the client and their designers has been undertaken throughout the project so that changes to design or outcomes from our assessment could be incorporated in a timely manner. This was particularly true as the flood modelling identified a significant flood risk at a key component of the line. Early identification of this issue has allowed for development of potential solutions with the clients priorities in mind.