A standardised inventory for New Zealand’s stopbank (levee) network and its application for natural hazard exposure assessments

Abstract

Flooding is New Zealand's most frequent natural hazard, responsible for the highest number of declared civil defence emergencies and greatest regular economic loss. Stopbanks (levees) perform a critical flood protection function in all regions of the country. However, there have been limited and inconsistent records on the location and physical attributes of these stopbanks at a national level. Through collaboration with regional government representatives, we provide the first standardised national inventory of stopbanks, the New Zealand Inventory of Stopbanks (NZIS).

The NZIS provides a standardised geospatial overview of New Zealand's 5284 km long stopbank network, enabling spatial reviews and comparisons of flood protection characteristics at national and regional scales. Around 64% of New Zealand's total stopbank length is situated within five regions (Canterbury, Waikato, Southland, Manawatū-Whanganui and Bay of Plenty), while the nation's most densely population region, Auckland, accounts for just 1.9% of the total national stopbank length. Our research uses the NZIS geospatial dataset to conduct a preliminary assessment of New Zealand's stopbank network's exposure to seismic and co-seismic hazards, including proximity to known active earthquake faults, ground shaking intensities and susceptibility to liquefaction and landslides. Preliminary exposure assessments provide an example of how the NZIS can be adopted and applied.