Flood risk

Who is at risk of flooding?

Floods can occur almost anywhere in South Australia and impact anyone. Everyone is at risk from flash flooding. People who live close to a creek, river, major storm water drain or in a low‐lying area are also at risk from other types of flooding.

The 2019 National Disaster Risk Reduction Framework (pdf) recognises that understanding risk is a key step in improving resilience. Under this framework, we’ve been working to mitigate flood risk in South Australia.

Known flood risk areas

South Australia has known areas with a higher risk of flood:

Gawler River catchment
Brown Hill and Keswick Creeks catchment
Port Adelaide
lower Onkaparinga River
Numbered Creeks in the River Torrens catchment
below Lock 1 on the River Murray.

But this list is not exhaustive. See Section 6 and in particular Figure 4 of the Flood Hazard Plan (pdf) for the statewide 1% AEP flood and extent layer separated into different depth categories.

Work out your risk

To find out if you live, work or travel in flood prone areas, refer to the WaterConnect Flood Awareness Map. The map allows you to check (where data is available) the likelihood of floods at your location, search for flood risks in your area, and obtain more information about flood risks in your area.

Maps are not available for all areas in the state. This doesn't mean that there isn't a flood risk, just that a flood study isn’t available for that location.

Further information can be obtained by:

talking to neighbours and your local council about past flood events

contacting the South Australian State Emergency Service (SES)

requesting historical flood records from the Bureau of Meteorology

going to your local council website.

To work out your flood risk, find out how often you might experience flooding (likelihood), how bad the flood might be (consequences), and your personal circumstances (level of exposure and vulnerability).

Once you understand your risk, get prepared by following the guide on SA State Emergency Service Flood.

How do we work out flood risk?

Flood risk is a combination of the likelihood of a flood, and the consequences if this happens.

1. Likelihood

To determine the likelihood of a flood occurring, we look at historical records (such as river heights, rainfall data and stream flow) and statistical analyses of historical rainfall data from rainfall gauges.

The key measurements we use are:

Annual Exceedance Probability (AEP)

AEP is the probability of an event occurring in any given year. If a flood of a particular size has an AEP of 1%, there is a one in 100 chance that it will exceed this size in any given year. This does not mean that once a flood of this size happens it won’t happen again for another 99 years. It also does not mean that smaller or larger floods won’t happen.

Average Recurrence Interval (ARI)

ARI is the long-term, average number of years between flood events of a certain size or larger. For example, a 100-year ARI flood occurs, on average, once every 100 years. But flooding is a natural phenomenon, so it does not follow a predictable pattern. A 100-year ARI flood may happen more or less frequently than once every 100 years.

AEP and ARI are essential tools for flood managers when planning mitigation activities and budgets or advising emergency services, infrastructure developers and community services.

Note that coastal flood risk is worked out differently, using factors such as elevation, currents, tides, weather events and interactions with riverine or flash flood events.

2. Consequences

These are some of the things that could happen if a flood occurs:

physical injury, illness or death
impacts to mental health and wellbeing
damage to homes, businesses, vehicles and belongings
loss of access to transport routes and vital services
further isolation of remote communities
loss of crops and livestock
injury to wildlife and damage to the environment
disruption to utilities, government services and communication networks
damage to culturally and socially significant sites.

Future flood risk

South Australia could be at higher risk for floods – or more intense floods – in the future due to:

urban infill (that is, building more dwellings on spaces within existing suburbs) – it results in more hard surfaces that increase peak stormwater flows and runoff volumes
greenfields development (that is, building in new areas) – this often requires new flood management measures, especially when built on floodplains and coastal areas
climate change – may increase the frequency and severity of storm events and alter rainfall patterns. Flooding patterns may change, with large floods occurring more often than in the past

Well-designed, built and maintained infrastructure to mitigate flooding, on the other hand, reduces flood risk is and helps us predict flood behaviour.