Flood Exposure Assessment and Mapping: A Case Study for Australia’s Hawkesbury-Nepean Catchment

Floods are the most common and costliest natural disaster in Australia. However, the Flood Risk Assessments (FRAs) employed to manage them are hazard-focused and tend to overlook exposure and vulnerability. This leaves potential for Australian FRAs to make better use of a technique which holistically incorporates all three flood risk components. In this study, flood exposure assessment and mapping for the Hawkesbury-Nepean Catchment (HNC), a flood-prone region in Australia, was conducted. Three flood exposure indicators—population density, land use type, and critical infrastructure density—were selected to derive the flood exposure index (FEI). Results demonstrated that Statistical Areas Level 2 (SA2s) on or near the floodplain, located near the eastern border of the HNC, are severely or extremely flood-exposed due to the significant presence of flood-exposed assets such as hospitals or police stations. The Wahroonga (West)—Waitara SA2 was the most exposed SA2 in the catchment (extreme exposure). This was followed by the Acacia Gardens, Glendenning—Dean Park, and Cambridge Park SA2s (all severely exposed). The Goulburn SA2 was also identified as severely flood-exposed even though it remains outside of the floodplain. This is due to its many exposed assets as Australia’s first inland town. All selected indicators were found to either strongly or moderately positively correlate with the FEI. Ultimately, this novel FEI can assist in the reduction of flood risk in the HNC, as well as foster community resilience strategies. Additionally, the developed scalable and replicable methodology can be applied to other flood-prone regions of Australia.