The City of Greater Geelong (CoGG) engaged BMT WBM Ltd. (BMT WBM) to undertake an assessment of stormwater flooding within the Portarlington East drainage catchments and to investigate the flood management options. The study identified the number of flooded properties for 1%, 5% and 20% Annual Exceedance Probability (AEP) for “within property” and “above floor level”. The study estimated a maximum of 334 properties will be inundated for a 1% AEP event and water will rise above the floor level in 12 properties for the same event. The report also produces Hazard mapping where safety is defined in terms of depth, velocity and velocity times depth product. The Portarlington Golf Course, the retarding basins between Fisher Street and Gellibrand Street, the retarding basin at Fairfax Street and Seaforth Drive in addition to the main drainage paths have been specified as unsafe in a 1% AEP flood. The study provided structural and non-structural mitigation schemes.

This study adopted 1.65 m above MSL as 100 year ARI (1%AEP) storm-tide level at Barwon Heads based on CCMA (2005). Given that the natural dune level and the levee level at the northern end of the Murtnaghurt Lagoon are at 3.0 m AHD, the study found that the property, 1920 Barwon Heads Rd is not likely not be inundated in present or future sea-level rise scenarios.

The City of Greater Geelong (CoGG) engaged WBM Oceanics Australia (WBM) to assess stormwater flooding within Barwon Heads and to investigate flood management options. The study includes XP-RAFTS200 hydrological modelling and TUFLOW 2D hydraulic modelling to assess the existing flooding characteristics. The study identified the number of properties inundated above floor level for 5, 20 and 100 year Average Recurrence Interval (ARI). It was found that the 100 year ARI event is likely to inundate 61 properties above floor level. The downstream tail-water level in the Barwon River was set to 1.45 m AHD for all events. As a mitigation option, the report mentioned three mitigation schemes included structural and non-structural elements. The study also selected a preferred mitigation strategy through consultation with the City of Greater Geelong (CoGG).

This report looks at the occurrence and implications of a 1% AEP surge / flood event. The study adopted GHD (1997) 1% AEP peak tide level of 2.4 m AHD as the tail-water level which allow 0.2 m for expected greenhouse effect over 30 years. This level was achieved through joint probability of both astronomical and meteorological tide. The study used HecRas hydraulic modelling to determine the flood profiles for both 1% AEP tidal surge and 1% AEP catchment flows, however not the combination (i.e. joint probability) of the two. The study used 1,400 m3/s as the 1% AEP peak flow at Lake Connewarre. It used the maximum of the tidal or river flows at cross-sections along the river. The adopted flood levels were the maximums from each.

This was a broad-scale assessment of flooding from the confluence of the Barwon and Moorabool Rivers in Geelong through Lakes Reedy and Connewarre, to Barwon Heads. The study looked at the frequency of flooding, flood extents and risk, mitigation strategies and costs. The study found that improved flood warning, public education and development controls would reduce the flood risk into the future. It also recommended a levee be constructed at an industrial estate in South Geelong (Factories St. to Wood St.).

The City of Greater Geelong (CoGG) engaged BMT WBM to assess the stormwater flooding and to investigate the mitigations options for the Newcomb and Whittington areas of Geelong. The study used a RORB hydrological model and TUFLOW 2D hydraulic model. The report identified the existing flood characteristics for 20%, 10%, 5% and 1% AEP flood events. The number of properties inundated was assessed to be 2696 and 65 for “within property” and “above floor level” respectively for 1% AEP events. The report also presented the Hazard mapping for the same events. Properties located on Geelong – Portarlington Road west of Wilsons Road were identified to have unacceptable hazard levels in the 1% AEP event. Within the residential area, unacceptable hazard levels were reported to be contained within road reserves. The study provides a full range of structural and non-structural flood mitigation schemes and selected the preferred scheme through consultation with CoGG.