Coastal adaptation

Coastal trail

The City of Onkaparinga knows how special the coast is and how valued it is by our community and visitors to our region - we take our responsibility to care for the 31km of coastline within our control seriously.

Using an evidence-based approach we have identified the action needed to help Onkaparinga’s coastal communities, infrastructure and ecosystems adjust to the impacts of climate change, particularly sea-level rise.  Ensuring benefits are met across many sectors e.g. safety, tourism, health, environment, and recreation.

Adaptation may take a number of forms: moving or building assets away from the risk area, modifying services and assets on the coastline, strengthening natural defences through sand and vegetation, building infrastructure such as sea walls, or retreating from damaged areas.

Coastal adaptation action already undertaken by the council includes activities such as replenishing dunes, managing outlet flows from rivers and creeks, revegetating cliffs, installing sandbag groynes, and building geofabric sea walls and rock sea walls.

Coastal Adaptation Study

In 2021 we engaged consultants to undertake a study of our coastline and explore how it might be impacted by rising sea levels over the next 80 years. The Coastal Adaption Study shows how council and other stakeholders, such as state government and private landowners, can plan now for any future changes.

In recognition that the coast varies from place to place and to make it easy for residents to learn more about the section of coastline near them, the study splits Onkaparinga’s coastline into 12 distinct regions or “cells”.  You can view each region and fact sheet by clicking on the links below.

Study key findings

  • Sea levels have been rising at 4-5mm in Onkaparinga since the 1990s, which is faster than the previous decades (1950's to 1980's), 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.


Coastal adaptation action - example of work underway

One coastal adaptation project already underway is a carpark retreating project on the Esplanade at Seaford, opposite Tiller Drive, which addresses erosion issues impacting the existing clifftop infrastructure.

The project, which began on 14 June and is expected to be completed in early spring, involves:

  • retreating infrastructure to allow for cliff erosion
  • reduction and relocation of existing carpark, including new kerb and asphalt
  • relocation of shared-use path
  • relocation of fencing, lookout area, shower, and furniture
  • planting of new vegetation.

The project follows community consultation in March and shoreline analysis undertaken in council’s Coastal Scoping Study, which provided evidence that retreat of infrastructure is a viable first option for the area to address the cliff’s long-term erosion.

The erosion over the past 60 years has been caused by waves at the cliff’s base, and groundwater discharge mid-slope, which have increased the steepness and instability of the cliffs, accelerating the erosion.

By retreating the infrastructure, cliff recession will continue and steep slopes can find an equilibrium (less steepness), so the council can maintain the natural and cultural values of this important coastal environment.

The project’s coastal location brings with it particular significance to local Traditional Owners, and council staff have been working with the Traditional Owner members of its First Nations People Advisory Group (FNPAG) to learn more about this significance.

Through this collaborative approach, shared understandings are developing regarding the cultural significance of the coastline and how to protect this as council upholds its responsibilities to also protect public amenities from the ongoing natural threat of coastal erosion.

The final design of the new shared path segment will play a storytelling role in the form of artwork stencilled into the concrete path, recognising the strong Kaurna heritage associated with the location.


Coastal Adaptation Plan

The next step in our coastal adaptation journey is the creation of a Coastal Adaptation Plan that will provide a planned response to the recommendations from the Coastal Adaptation Study. Preparation is now underway and we are currently undertaking community engagement.

You can help us to shape the Coastal Adaptation Plan by providing feedback on the options we are considering for the higher risk locations as well as the kinds of things we should be considering.  During August you can also attend one of three in-person sessions being held at Moana, Christies Beach and Aldinga or jump online and take part in a webinar.   Consultation closes on 3 September 2023.

Visit the Your Say page to find out more and provide your feedback


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