High flood hazard management areas (HFHMA) are identified in the Christchurch District Planning maps.
High hazard areas are defined in the Canterbury Regional Policy Statement as flood hazard areas subject to inundation events where the water depth (metres) x velocity (metres per second) is greater than or equal to 1, or where depths are greater than 1 metre, in a 0.2% AEP (1 in 500-year) flood event.
These are areas at risk in a very large flood (a 1-in-500-year flood event) due to the depth and/or speed of flood waters. They are generally low lying land near rivers and/or close to the coast.
The flooding can be due to a combination of high rainfall events, rivers breaking their banks and/or tidal inundation (due to storm surges and high tides).