Extreme Weather Recovery Advice Fund

While there are some international literature into the issue of evacuation risk and pedestrian survivability in flood waters, a limited search of this literature by Council has not identified any coherent analysis that would provide for the development of specific guidance on whether to evacuate or stay-in-place for New Zealand taking into account flood characteristics as exemplified by Cyclone Gabrielle. In Gabrielle, fatalities and injuries occurred in both Hawkes Bay and Gisborne/Tairawhiti and further injuries and near misses have been identified in post-event interviews with flood victims. For key areas in Gisborne/Tairawhiti there are some advisory in the flood warning manual that advise evacuation at certain flood height triggers in some locations but for elsewhere there is no guidance. Overall, there is no substantive information available that supports whether this evacuation advice is suitable, the time frame over which it is suitable and whether stay-in-place guidance might be more appropriate once flooding reaches certain a level. Clear guidance on specific evacuation advice is required to keep people safe in future events.

A feature of Cyclone’s Hale and Gabrielle and subsequent severe weather events in the Gisborne/Tairawhiti region was the formation of large landslide dams. Some of these pose little or no risk to downstream communities. Others, however, pose a potential risk to critical infrastructure as well as downstream dwellings. One such landslide dam at Mangahauini occurred immediately upstream  of Tokomaru Township and directly impacted State Highway 35 between Tokomaru Bay and Te Puia. Following Cyclone Gabrielle, 60 dwellings were evacuated while an urgent risk assessment was undertaken. Further storm activity 2 weeks after Gabrielle resulted in the dam being infilled but the mega-scale landslide that caused the dam remains active. Council wishes to employ all means possible to determine further risk from this landslide. One such tool is SkyTEM and it is possible that this tool can help delineate active failure pathways within the landslide and so facilitate monitoring and mitigation efforts.

Cyclone Gabrielle triggered large numbers of shallow landslides that caused widespread damage to land across Hawke’s Bay and delivered significant amounts of sediment to downstream receiving environments. HBRC is seeking to better understand the effectiveness of individual trees in pastoral areas for reducing landslide erosion on farms in the region. This information will help HBRC communicate to stakeholders how existing trees in pastoral areas mitigated the number of landslides triggered by the cyclone. It will also assist with targeting future tree planting to those areas on farm that are most susceptible to landslides and where landslides are most likely to deliver sediment to streams. This proposal aims to address these needs using a statistical modelling approach that quantifies the influence of individual trees on landslide susceptibility and the spatial likelihood of landslide-derived sediment reaching streams. The analysis will make use of the tree map produced for HBRC by MWLR as part of the HBRC-MWLR LiDAR partnership project. The model will be applied to selected farms spanning a range in landslide susceptibility, tree cover, and landslide damage from Gabrielle to allow comparison of the effectiveness of individual trees in reducing landslides under different conditions. The benefits of this science are national, with enhanced usefulness in areas in pastoral hill country composed of sedimentary geology.

In early 2023, Northland experienced several extreme weather events with their impacts are extensive such as large areas of flooding, slips and damage to roads and other infrastructure. Just several days in February, Northland was isolated twice from the rest of the country due to the impacts of Cyclone Gabrielle (12-15 Feb) and Mangawhai flash flood (22-24 Feb). As consequences, it is envisaged that it would require huge efforts and long time for the region and its people to recover from these events. To emerge stronger from the aftermath of the storm and flood, a recovery approach grounded in research and data-driven insights is essential. The council will benefit from this project through a better understanding of these extreme events and their potential impacts which enable informed decisions on natural hazard management and planning, including recovery and resilience plan for Northland. In addition, this project outcomes also assist with the council’s flood forecasting and prediction for future in the most vulnerable areas. The information will be used by/beneficial to multiple Council departments including Civil Defence, River and Natural Hazards, Hydrology, Land Management and Environmental Monitoring, and District Councils.

Like other regions with flood risk, Gisborne District Council (GDC) has a flood warning manual. This guides how flood warning officers assess rain gauge and other flood warning data and then advise the Tairawhiti Emergency Management Organisation (TEMO) leading up to and during a state of emergency. This is an internal document which has been updated on an ad-hoc basis from time to time. Cyclone Gabrielle provided an opportunity for a real-time stress test of its operational effectiveness and while no mission-critical issues arose, there were gaps in its implementation and a misalignment between advice delivery and the TEMO’s expectations of the advice and its implementation during Cyclone Gabrielle.

Greater Wellington Regional Council and other regional councils need to prepare business cases for all their proposed flood risk management projects. For co-funding projects these need to be based on the Treasury Better Business Case model, with a need to provide evidence-based information that quantifies and qualifies the benefits as well as costs. This project will address the need by providing an evidence-based framework tool that will support regional councils in accounting for the very significant indirect and intangible losses for building business cases for flood mitigation investments.

The recent major flood events, including Cyclone Gabrielle and Westport floods, provide a unique opportunity to account for the indirect and intangible losses that will enable a stronger evidence base for inclusion in future business cases and investment decisions by Councils, Government (i.e. MFE, Treasury, DIA, MBIE), and LGNZ more widely. The window of opportunity to do this is now.

The proposal is to fund advice transfer through a collaborative workshop to scope literature reviews required to support councils to develop 21 MfE-funded projects to undertake feasibilities studies on nature-based solutions for resilience planning, that may act to complement current management techniques to reduce risks from extreme weather events. Of the 21 studies funded, there is likely many commonalities within aspects of these that require collaboration to ensure efficiency. The benefit of this advice grant is to ensure efficiency across the Aotearoa/New Zealand region sector, and to facilitate similar projects to promote the ability to build a body of knowledge for New Zealand in this space. This would enable comparison and extrapolation of the results of these studies across New Zealand.

Bioengineering solutions (trees – primarily poplar and willow cultivars) have been used to manage flood risk and erosion throughout NZ for decades, and continue to be used as a cost effective and highly functional part of river management. The floods in Hawke’s Bay occurred within managed river systems that utilise these bioengineering techniques. This project will look at how bioengineering functioned within Hawke’s Bay (and potentially other regions’) river systems, including performance in relation to: flows, erosion control; stopbank protection; interception of silt and woody debris; and benefits to downstream receiving environments. Studying the effectiveness of different techniques, cultivars, management, relative location, and age of trees will be a significant part of the project. The conclusions derived from the project will inform best-practice for river managers, to ensure bioengineering techniques that are implemented and managed in the future, offer optimal protection to river control schemes during flood events and minimise the downstream effects of flooding, sediment, and woody debris. Including for the HBRC Review of the Heretaunga Plains Flood Control Scheme.

Extreme weather events have caused catastrophic harm to communities and ecosystems in the North Island, with climate projections indicating an increase in such devastating events over the coming years. Understanding how ecosystems react to climate extremities is vital to devising effective measures for future mitigation and recovery efforts. In this project University of Otago will develop and test new analytical approaches to quantify the level of degradation within biological communities and ecosystems, and trajectories of recovery. The aim is to empower local governments and communities with a tool to analyse ecological data that is key to inform future management policy and strategies (and hopefully mitigate) impacts of future extreme events. Freshwater environmental DNA (eDNA) techniques enable swift and efficient ecosystem monitoring, and Aotearoa has seen rapid and widespread uptake by regional councils since 2020. With the increase in eDNA monitoring across space and time, there is now the potential to elucidate temporal and regional shifts within biological communities and ecosystems across our natural and productive systems. An extensive dataset collected prior to and post-cyclone Gabrielle (5216 eDNA samples available to date), across regions that experienced varying levels of climatic impact, is available to analyse how this extreme weather event impacted freshwater and terrestrial ecosystems. From this, appropriate analytical method will be developed to analyse the impact of this and future extreme weather events on ecosystems.