The City of Melbourne sought to implement new flood overlays and engaged Afflux to review the technical details and assess the suitability of the proposed overlays. This review process acts as a checkpoint to verify the accuracy of the complex modeling used to formulate the overlays. Informed flood overlays not only help assess potential risks to infrastructure, property, and life but also improve long-term planning for land-use changes and enhance resilience to climate change. The technical review increases confidence in the planning process and serves as an essential component of quality control through peer review.
Afflux conducted a technical review of flood information in collaboration with a panel of experts. This review included an evaluation of hydrological data, the development of a parallel hydraulic model, an assessment of drainage infrastructure, the identification of vulnerable areas, and a report that provided an expert opinion to assist the panel to determine the integration of flood mapping alongside planning goals.
The parallel modelling involved running a Rainfall-on-Grid 2-dimensional flood model under various scenarios to test the underlying assumptions. The model's complexity arose primarily from the interactions between an inner-city site and river, coastal, and tidal influences. Additionally, the model incorporated dynamic pumping controls, constructed levees, major pipe connections to the surface, and contemporary terrain datasets.
The extent of the flood mapping is largely theoretical. Therefore, it is recommended that the extent be considered only as a development or planning “flag.” Generally, implementation of overlays is an appropriate floodplain management tool, and amendments to overlays are important to ensure ongoing compliance with contemporary conditions and regulations.
Our analysis highlighted the influence of including topography, making realistic assumptions around the proper functioning of flood mitigation infrastructure (such as pumps), compounding risk factors and the importance of accurately representing the functional aspects of stormwater drains.
Afflux expressed concerns that implementing overlays without appropriate care may lead to floodplain requirements that are unsuitable for this area, such as afflux provisions or overland flow requirements.
To address this concern, Afflux made recommendations to ensure that the context of this flooding is fully understood.
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