River flood hazard zones were developed by 2 different external expert consultants between 2016 and 2021. The layers are derived by advanced models using empirical calculations.
Two different models were used to construct the river flood layers: TUFLOW (Water Technology, 2021), InfoWorks (URS, 2016). The reports detailing the methodologies, and risk assessment on the Priority Rivers, can be accessed from the NRC website
The priority rivers project involves the 28 river catchments around Northland identified as priorities for flood risk planning. The rivers and streams in these priority catchments pose potential threats to lives, buildings, road access, infrastructure and agriculture.
The flood data shows the likely extent of river flooding during a 10-year, 50-year or 100-year flood event. A 10-year flood area has a 10% chance of flooding annually, a 50-year flood area has a 2% chance of flooding annually whilst the more extensive 100-year flood area has a 1% chance of flooding annually. The data is designed to raise awareness of where flood hazard areas are and inform decision-making, to help minimise the impacts of flooding in our region.
Coastal flood hazard zones were developed by 3 different external expert consultants in 2020. The layers are derived by advanced models using empirical calculations including tide gauge and extreme water level analysis, wind records and wave models, and used the 2019 LiDAR DEM.
Three different models were used to construct the coastal flood layers: a full-coastline ‘bathtub model’ (Tonkin and Taylor, 2020), and two hydrodynamic models for Rangaunu (eCoast, 2020) and Kaipara (DHI, 2019) harbor. The reports detailing the methodologies can be accessed from the NRC website.