The headland at Point Lonsdale is formed of Pleistocene calcarenite and has fixed the entrance of Port Phillip Bay on the western side. Shore platforms have formed at the base of the cliffs and provide some protection to the base of the cliffs. Within the bay, the cliffs line the shore until the Point Lonsdale township where the elevation drops, and a sandy beach has formed between Point Lonsdale and Shortland Bluff, where another significant outcrop of calcarenite exists and has again fixed the position of the shore.

It has been estimated that approximately 200,000 m ³ of sediment passes around Point Lonsdale from Ocean Grove in a year (Cardno, 2011a); however with strong tidal currents and southern swells penetrating the bay as far as The Sands, this material rapidly moves through Lonsdale Bight. Significant shore protection structures exist for most of Lonsdale Bight. A bluestone seawall was constructed in front of the township in the early 1900s to limit recession. A recurved lip is fixed to the structure approximately two thirds of the way up the front face to deflect wave energy (Figure 6-14b). The condition of the seawall now is ‘moderate’ according to the DSE (now DELWP) structures database. Issues with run-off have seen the wall crack in some locations and works have been carried out to allow water to pass through the structure. The effects of wave impact are also very visible in some locations with bricks and mortar removed and repaired both in the frontal wall section, and the wall behind the promenade (Figure 6-14a). The promenade is also cracking indicating some possible subsidence (Figure 6-14d).

The masonry wall was extended a number of times. As time passed, due to the terminal scour effects, it was seen as necessary to construct further rock revetments to limit the recession and protect the assets behind. There are visible ‘step backs’ along the Lonsdale Bight as the wall and revetment have been extended over the century (Figure 6-13). The end of the revetment is now at Dog Beach, where terminal scour has resulted in local recession the beach of more than 20 m. This recession is now stable, and since 1996 the scarp has not receded significantly.

The coastal section of Queenscliff from Shortland Bluff to the Queenscliff Creek decreases in elevation from 15 m at the bluff to less than 2 m further north. The base of the bluff has been stabilised with a masonry seawall. A narrow strip of beach exists in front of a vegetated dune. The dune is low-lying and approximately 30 m wide at the narrowest section near the Pilots Jetty, and 130 m wide at the north-eastern end of the beach near the ferry terminal. Construction of the training walls and harbour works has resulted in a large accumulation of sand as far back as the Queenscliff Pier and Port Phillip Bay Sea Pilots Jetty. Much of the foreshore land is now occupied by developments associated with the harbour and ferry terminal. The wave energy here is lower than within Lonsdale Bight, with the bluff protecting against some of the swell energy penetrating from Bass Strait.

The maintenance of the harbour entrance has induced a significant change in the geomorphology of the Queenscliff and Swan Island areas. The narrow channel fills with northerly transported sediments; rates of approximately 80,000 to 100,000 m ³/yr have been estimated as the net flux along this section of coast based on dredging records (Cardno, 2011a). The entrance is regularly dredged and the material is pumped north where it has formed a large sand island now attached to Swan Island.

Figure 6-12     Compartment 5: Point Lonsdale to Point Edwards + cross-shore profile locations

Figure 6-13      History of protection works in Lonsdale Bight (based on Bird, 2011)

Figure 6-14      (a) missing wall stones behind promenade, (b) drainage through structure, (c) lower section of wall with no recurve lip, (d) cracks in promenade

Swan Bay is an important area supporting natural wetland habitats. It is part of the Port Phillip Bay Ramsar site, and includes the wetlands fringing Swan Bay as well as the Swan and Rabbit Islands (Figure 6-12). The characteristics of this area are more like a saline lake than an estuary. The barrier islands enclose the bay and limit the tidal range and the wave energy able to enter. There are two main tidal entrances, the natural channel, just south of Edwards Point, and the Cut, an artificially created channel that originally formalised the path of the Queenscliff creek. Waves within the bay are small due to the limited fetch. The depth of the bay and extensive seagrass beds also dampen wave energy and limit the possible wave heights within the bay. At the southern end of the bay, Lakers Cutting, a former shell-grit mining site, feeds the newly established Lonsdale Lakes development canals and artificial lakes. The water enters through a series of channels and culverts beneath the roads. There is a one-way valved culvert beneath the railway embankment that feeds through underneath the Bellarine highway through another (non-valved) culvert. The passage of water into and out of the artificial lake system is indicated in Figure 6-15.

Figure 6-15      Lakers Cutting and the Lonsdale Lakes Estate - feeder channel (and flood route) in blue