Developing Hazard Lines in Response to Coastal Flooding and Sea Level Change

Abstract

Flooding is a current and future risk to the coastal zone. Currently, coastal planners use historical data to estimate the frequency and magnitude of flooding and develop planning tools such as hazard lines. However, in the face of climate variability and change, such flood risk estimation methods and the resultant planning tools are inadequate. This article outlines the steps, assumptions, key complexities and uncertainties associated with developing and applying hazard lines that incorporate sea level change projections. A case study, involving Lake Macquarie City Council in New South Wales, Australia, highlights the advantages and limitations of the hazard line approach at the local council level. The key findings are that hazard lines using global or state-wide sea level change benchmarks typically result in overgeneralised and inconsistent risk assessments and that new methods of flood risk estimation, flood planning and flood mitigation are required. Alternatives recommended include a move away from definitive sea level projections based on state or countrywide approximations towards the development of regionally specific adaptation plans that utilise flexible approaches, such as the identification of critical thresholds and triggers, to manage potential flood risk and enable decision-making under uncertainty.