There are two arcuate ridges along Ballarto road, one at Cardinia and the other at Rythdale. An acruate ridge is a curved sand ridge or one shaped like a bow. The Victorian Resources online website, has descriptions of both these ridges, in their Sites of Geological and Geomorphological Significance section, which you can see here.
Cardinia Arcuate Ridge
This aerial photograph was also taken in 1980 and shows the town of Cardinia, built on the arcuate ridge. Starting at the bottom of the photograph, is the Cardinia Recreation Reserve. Ballarto Road runs along the right of the Reserve to the top of the picture. The town is bi-sected by Dalmore Road to the left of the picture, and Cardinia Road to the right. The curve of the sand ridge can be clearly seen.
From the Victorian Resources on-line website - Cardinia township is built on a low sandy ridge that rises five to eight metres above the drained wetlands of the former Dalmore Swamp, part of the Koo-Wee-Rup or Great Swamp. The elevation of the ridge is partly due to depression of the adjacent drained area, as a result of shrinkage and compaction of the peats, but it is also clearly a distinct depositional feature related to sedimentation of the Cardinia Creek. The ridge is composed of coarse and often gravelly and clayey sand and has a well defined concave western margin which resembles an abandoned shoreline. In contrast the eastern edge is less regular with small lobes of sand surrounded by peaty swamp deposits.
These lobes may represent old flood crevasse breaches of the ridge. The ridge has the general appearance of a lunette although it was explained by Jenkin (1974)* as a former levee deposit of the Cardinia Creek.
Rythdale Arcuate Ridge
The Rythdale Arcuate ridge can clearly be seen in this 1980 aerial. Ballarto Road cuts across the centre of the photograph, above the oval trotting track. Hobsons Road runs towards the top of the photograph and the curved object is the arcuate sand ridge. On the left of the photograph are man made drains to carry the water from the Deep Creek and Toomuc Creek to the Bay, part of the Koo Wee Rup Swamp drainage works.
From the Victorian Resources on-line website - The narrow ridge traversed by Hobson Road is similar in form and composition to that described at Cardinia. It extends for three kilometres south of the Deep Creek Drain but is seldom more than 100 metres in width. The convex (eastern) side lacks the irregularities and depressions that are present at Cardinia, and the Rythdale ridge describes a more gentle curve.
These ridges are considered to be of State Significance -
*The references the websites used are
Jenkin, J.J. (1962). The geology and underground water resources of the Tooradin area. Dept. of Mines Vict. Underground Water Investigation Report. No. 4
Jenkin, J.J. (1974). The geology of the Mornington Peninsula and Westernport. Geol. Surv. Report. No. 1974/3.
Another version of this blog post, which I wrote and researched, also appears on my work blog - Casey Cardinia Links to Our Past.
