NRC Region-wide River Flood Model Three years on
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| In 2021, NRC and Water Technology completed a region-wide flood modelling study encompassing a majority of the Northland Regional Council area, which covers an area of over 12,500 km2. The aim of this project was to map flood hazard zones across the entire Northland region, update existing flood intelligence and provide design flood levels for use in planning and emergency management. 19 catchment-scale models were completed and delivered to NRC. Based on a 2D Direct Rainfall approach (also known as Rain on Grid), the models results are now publicly available on NRC natural hazards portal. They are also relied upon by NRC in a number of areas, including resource consent applications and flood mitigation identification. Striking a balance between model granularity and costs expended is critical to developing fit-for-purpose models. Three years on from the release of the data, it is an opportune time to see how the data is used, how it fares and how it was received. To broach the question as to whether the right resolution was achieved. As all models, these models have limitations and these “flaws” were, on occasion, seized upon to question the validity of the models. This presentation will discuss some of the criticisms received since the data was released, some justified. It will also provide an overview of how the data can be married with local knowledge to inform flood alleviation projects and/or refined to better understand flood risk in hot spots areas. It will broach the topic whether more details are necessary better. As part of the model development, some of the models had been calibrated against past large flood events including the 2011 and 2020 flood events. The more recent 2023 flood events have given NRC and us modellers another opportunity to ground-proof the model results, including against community experience. It allowed us to gauge whether these model outputs are actually (always?) fit-for-purpose. |