Flood Extent 50 Year (OpenData)

This entity describes how far floodwaters could spread during a '1-in-50-year flood'. A '1-in-50-year flood' means there is a 2% chance of that level of flooding happening in any given year. Similarly, a '1-in-10-year flood' has a 10% chance of occurring in a year. These probabilities are based on long-term weather and tide records. We also adjust the data to account for future changes in rainfall and sea levels due to climate change. To estimate flood areas, we use computer models that simulate how stormwater flows through Christchurch’s drainage system. These models test different rainfall durations—from short bursts (30 minutes) to long storms (up to 60 hours). For each flood scenario, the model calculates the deepest flooding expected, the largest of which becomes the final flood extent shown in the data. This flood extent data is used in a derived model called drvFloodExtent, which combines flood models for all catchments and scenarios and is intersected with Rating Units to generate Property Condition comments on the LIM. Any updates to the flood extent data need to be synced to the derived model to appear on the LIM. It is spatially abstracted to: Area. Entity Type: Event.