The report is a large document, almost 800 pages and is provided in two parts. Part 1, Introduction and Appendices A-E, download at the right.

Part 2, Appendix F is available here:

Waitākere coastal communities landslide risk assessment overall report – Muriwai. Part 2

Extract:

Introduction

1.1 Purpose of this report

GHD has been engaged by Auckland Council (AC) to carry out Quantitative Landslide Risk Assessments (QRA) as well as to provide associated landslide risk management advice and geotechnical investigations in the Muriwai area (‘the study area’). The purpose of this assessment is to carry out a Quantitative Landslide Risk Assessment (QRA) for the Muriwai area (‘the study area’). The QRA is to estimate the risk of Loss of Life to individuals at these properties. The outcome of the QRA will be used to inform subsequent property risk categorisation and building placard designation review by AC. This report version is the final issue. It has taken into account any information provided by the landowner either through the Auckland Council feedback portal or through Auckland Council Recovery Office communication channels. 

The purpose of this ‘overall report’ is to combine and summarise the various GHD geotechnical assessments for Muriwai in a single document. The focus of the report is on the large-scale hazard from the 80 m-high escarpment to the east of Muriwai township that experienced damaging landslides from the escarpment in February 2023 (see Figure 1). Our study includes elements that support a risk assessment that provides a quantified loss-of-life risk from landslides to occupants of dwellings.

This report contains appended reports, which should be read in conjunction with it.

1.2 Background 

Two significant rainfall events affected the Waitakere area in late January and early February 2023, resulting from the impacts of ex-tropical cyclones Hale and Gabrielle, respectively. 

The Cyclone Gabrielle weather event of 14 February 2023 resulted in widespread catastrophic flooding and slope instability in the settlement of Muriwai where several debris avalanches (which included rocks and trees) occurred, some of which turned into saturated debris flows as they travelled downslope. These flows resulted in damage to buildings and infrastructure. Two fatalities occurred due to impact of landslides on private dwellings. This tragic event was similar to a 1965 storm event that also claimed two lives. 

Following the recent event, rapid building assessment of residential properties was undertaken in Muriwai, with some houses having access by owners restricted (a yellow placard – e.g. access in daylight hours only) and some for which no access was permitted (a red placard). Dwellings that retained unrestricted access were white placarded. ...

GHD for Auckland Council, May 2024.

See also

Our Auckland

Muriwai geotech update