This area is subject to riverine and coastal inundation. Previous studies have shown a significant risk to assets and the hinterland from riverine flooding; therefore the implications of coastal inundation coupled with riverine flooding have been investigated for this study. The probability of the joint occurrence of a 1% AEP storm-tide event and a 10% catchment flow event is very low, therefore a 99th percentile average daily flow baseflow was favoured as the design event. This also gave the opportunity to determine the coastal inundation risk (almost) independently of the catchment flows. To ensure consistency with the scope, a 10% AEP catchment flow sensitivity was also undertaken for selected scenarios.

The inundation extents to for the 1% AEP storm-tide case in conjunction with a baseflow in the Barwon River in combination with various sea-levels is presented in Figure 6-9a. Inundation resulting from the 1% AEP storm-tide case in conjunction with a 10 % AEP catchment flow in the Barwon River is presented in Figure 6-10a. Key locations within the modelled area have been included in the hazard figures, for both flow cases.

The main differences between the flood extents arising from each flow case through the Barwon River occur in the 1% AEP events with 0 m SLR. Under the 10% catchment flow case, the flood extent on the eastern bank of the river near is greater than under the baseflow case, near the caravan park. The differences in extents due to catchment flows on the western bank of the river are less significant for the present day scenario. On the western side of the river, River Parade will be inundated under present day sea- level conditions (0.0 m SLR) if a 1% AEP storm-tide and 10% AEP catchment flow were to coincide. Under a 1% AEP storm-tide and 10% AEP catchment flow event, a low section of River Parade east of Minah St is likely to be overwashed. This would allow flood waters to penetrate inland impacting more of the Barwon Heads township.

As the sea-level rise scenarios increase, so do the flood extents. The overall vulnerability in future is likely to be more significant on the eastern bank of the river at Ocean Grove, due to the low land levels and lack of appropriate shore protection designed for inundation purposes.

Table 6-4     Locations impacted by inundation as identified by the hydrodynamic modelling