The City of Onkaparinga has released a Coastal Adaptation Study which predicts how the council’s coastal areas will be affected by sea level rise over the next 80 years.

The study has divided the City’s coastline into 12 areas which it says will help council focus on the different adaptations that might be required for each section.

The areas are Lonsdale, O’Sullivan Beach – Christies Beach, Witton Bluff, Port Noarlunga, Seaford Cliffs, Moana Beach, Ochre Point, Maslin Beach, Port Willunga, Aldinga Reef, Aldinga Beach and Sellicks Beach.

The City says releasing the study is the first phase in a long-term program of community engagement. The next step will involve working with coastal experts to identify adaption options.

Options could include installing protection or defence infrastructure or moving assets or services from areas that could be impacted.

The study and a summary of its findings is available at City of Onkaparinga’s Your Say page along with fact sheets for each of the 12 coastal cells along Onkaparinga’s coast.

The key findings outlined in the report:

Sea levels have been rising at 4-5mm in Onkaparinga since the 1990s, which is faster than the previous decades (1950s to 1980s), but the rate of sea level rise isn’t projected to significantly accelerate until after 2050.

While most of Onkaparinga’s coastline won’t be vulnerable to sea-water flooding (inundation), exceptions are Onkaparinga River, Pedler Creek and the Aldinga Washpool, if seas rise as projected after 2050.

In most places, public roads are positioned between the coast and private assets. This means most risks will initially impact council-owned assets, but private infrastructure, public safety, and the health of Onkaparinga’s ecosystems could also be impacted in the longer term.

If seas rise as projected, then beaches and soft sediment cliffs will increasingly undergo recession and eventually place infrastructure at risk.

Onkaparinga’s coastline is characterised as moderate to high erodibility, depending on the location. Exceptions are the Lonsdale region, which is characterised as low-erodibility, and the Seaford Cliffs, which are characterised as very high erodibility.

The coastline has been relatively stable over the past 70 years, but there are some pockets of erosion, for example Snapper Point near Aldinga Reef.

The study has created a baseline understanding as to how the coast has operated over time. Ongoing monitoring of the coast will provide the basis for making timely, cost-effective adaptations to the coast where feasible.