This section of coast is managed by the Barwon Coast Committee of Management. The beach is fixed between two headlands, the Barwon Head in the west, and Point Lonsdale to the east (Figure 6-11). The western end of the beach near the river entrance (Ocean Grove Spit) is very flat and wide, with well-developed dunes that have a good covering of vegetation. A relict low timber wall provides some additional protection to the dunes, and has encouraged the development of a low sparsely vegetated berm seaward of the toe of the dune. Offshore, the bathymetry is very shallow, and wave conditions are lower energy than other regions of the Barwon coastline. The exposure to the dominant south-westerly swells is limited due to the protection of Barwon Head and shallow offshore reefs.

Further east towards Ocean Grove main beach, the beach narrows and steepens slightly. The dunes are high, ranging in elevation from 4 m to 15 m AHD. This section is also where the bathymetry changes from the very shallow ebb delta influenced region to the normal swell / wave influenced type of open coast. It is out of the immediate lee of the headland and thus the wave heights and energy increases towards Point Lonsdale. The dune face is scarped in contrast to the western end, indicating an increase in the wave energy able to penetrate this section of the beach. There is little berm development, and vegetation is returning to the dune scarp which would indicate wave events of the magnitude required to erode this section of dune are not common.

Ocean Grove main beach is similar in nature to the section previously noted, with the addition of a vertical timber and concrete retaining wall in front of the Surf Lifesaving Club. This 200 m wall was upgraded recently, and is positioned approximately 6 m seaward of the toe of the dune. The effects of this seawall are already apparent, with the beach elevation and gradient immediately in front of the wall differing from the surrounding beach, and terminal scour having occurred at the eastern end. This has exposed the eastern flank of the access ramp which has been stabilised with the addition of a geotextile container wall buried at the toe of the dune. This appears to be effective at present.

Figure 6-11     Compartment 4: Ocean Grove to Point Lonsdale + cross-shore profiles and wave points

East of the Main Beach towards the Buckley Park foreshore, the beach face steepens slightly and dune heights increase to over 20 m AHD, and are in some places over 150 m wide. Dune faces are scarped, however due to the volume of available erodible material this is of little consequence. The dune is also reasonably erosion resistant owing to a core of calcarenite. A low calcarenite ridge is exposed in some places, and where exposed, is at a similar elevation and depth within the dune system. In the absence of cores, it is sensible to assume the ridge runs in a low band approximately 30 m landward from the toe of the dune at an elevation of approximately 4.5 m AHD from Point Lonsdale west until at least Bonnyvale Road, at Ocean Grove. Upper ridges also exist within the dune, however these are at a considerable elevation and distance from the toe of the dunes/cliffs. Nearer to Point Lonsdale, higher and wider ridges of calcarenite exist, linking into the Point Lonsdale headland. The beach is very healthy and poses little to no hazard risk to the hinterland. The hazards here are more environmental, associated with dune blowouts smothering vegetation, and possibly fire risk. There is also a beach access structure from Ocean Road that may be subject to vulnerability; this has been redesigned in recent years to a piered structure, after a number of previous solid structures failed.

No inundation maps were produced for this area, as there is no inundation hazard risk to the hinterland from the coast. Possible flooding of Lake Victoria is noted in Section 6.5.

The seawall at Ocean Grove Main Beach is providing a high standard of protection to the hinterland presently. Overtopping volumes under a 1% AEP event for the present day (i.e. 0.0 m SLR) are low, less than 0.1 litres per second per metre (L/s/m). For 1 % AEP events with sea-level rise greater than 0.5 m, overtopping discharge volumes increase to greater than 5 L/s/m. This discharge would not be expected to be sufficient cause the structure to fail if it is maintained to the current standard; however, this discharge would increase the risk to the pavements and promenades behind, as well as any nearby pedestrians (Table 6-7 gives some information on overtopping discharges). Beach levels at the toe of the seawall are likely to decrease due to scour erosion, therefore increasing the depth of water at the toe of the structure during storm conditions. This in turn will allow larger waves to penetrate further inshore and increase overtopping. The rate of loss of beach volume is currently unknown, and should be monitored to inform future assessments.