Massey CI, Townsend DB, Leith K, Rosser BJ, Farr J. 2022. GeoNet landslide response: Nelson Tasman District, 16–19 August 2022. Lower Hutt (NZ): GNS Science. 25 p. (GNS Science report; 2022/58). doi:10.21420/N4R1-Q533.
Abstract
During 16–19 August 2022, an extreme rainfall event affected much of New Zealand. The National Institute of Water & Atmospheric Research (NIWA) refer to this event as the “strongest August atmospheric river (AR) on record” and classified it as a 1-in-120-year rain event for Nelson. The National Emergency Management Agency (NEMA) classified the event as ‘N1’, which elicits a minor national-level response. The rain event triggered many hundreds of landslides and flooding across the Nelson Tasman and Marlborough regions. In Nelson Tasman, NEMA reported that up to 570 properties were damaged and many roads, along with state highways SH 6 and SH 63, were closed, mainly from landslides and flooding. The main water supply pipeline to Nelson also failed, as it was hit by a landslide. The GNS Science Landslide Duty Officer, in consultation with the Engineering Geology Team and others at GNS Science, activated a landslide rapid response (LRR) for this event on 19 August 2022 under the GeoNet programme, as several of the criteria for activating a GeoNet LRR were met. These criteria were: direct damage of greater than NZ$1 million, economic losses of greater than NZ$10 million, threats to public health (such as contaminated water supplies) and significant research interest. The purpose of this LRR is to ensure that appropriate advice is available to maximise public safety, as well as to acquire and collect reliable and consistent landslide information and data. The aim of this report is to document the activities and results from the LRR carried out for the Nelson Tasman region during the LRR period (19/08/2022 to 2/09/2022). The GeoNet LRR for Nelson Tasman comprised the following steps: 19–21 August: Collate information on landslides reported in the media and on social media; 22–23 August: Carry out helicopter reconnaissance of the main areas affected; and 23–24 August: Carry out a walkover (field reconnaissance) of the Tāhunanui landslide in Nelson. The data presented in this report was made available to Nelson City Council on the day of collection to support them, and their representative contractors, in responding to this event. It is intended that additional data collection will continue through the recovery phase of the event. This perishable data acquired in the field will help train rainfall-induced landslide forecast models being developed by GNS Science and NIWA to forecast the location and severity of landslides in future rain events across all of Aotearoa. (The authors)
