The primary natural hazard events that affect homeowners in New Zealand are floods, and the unfortunate reality is that these are increasing in both number and scale due to climate change. This is further exacerbated by high housing demand, resulting in the potential for increased building activity in flood-prone or low-lying areas. There is also the flow-on effect from new developments covering previously absorbent land.
Lessons from elsewhere
New Zealand is not alone in having to face this increasing threat. There are lessons to be learned from looking overseas and the adaptations made by other countries to manage flood risk. While these solutions may not always be simple and straight forward adoptions, they can and should be considered in New Zealand’s setting.
Overseas approaches may provide some quick and easy building modifications as well as more complex changes required at a government level that can be put in place to give better future outcomes. Many of the approaches used overseas are well documented and readily available in the public sphere.
United Kingdom
The UK’s devastating floods in 2007 resulted in significant damage to homes, infrastructure and businesses as well as the loss of 13 lives. Emergency services conducted one of the largest peacetime rescue operations in British history, and the floods impacted thousands of properties, along with essential water, electricity and transport services.
Of the 200 major floods that occurred worldwide in 2007, the UK floods were the most expensive with an estimated repair cost of £3 billion. This served as a wake-up call for the UK Government – highlighting the importance of effective flood management and the need for a coordinated response to flood risk.
The UK Government’s response, and the magnitude of the disaster, prompted a review of existing flood management practices. One of the widest-ranging policy reviews ever conducted in the UK, it found that the existing approach to flood management lacked coordination and structure.
This triggered a significant overhaul of the UK’s approach to flood management, culminating in the introduction of the Flood and Water Management Act in 2010. This established a new framework for managing flood risk in England and Wales, providing greater clarity on roles and responsibilities and improving coordination between different agencies. Furthermore, the Act required local authorities to develop and implement sustainable drainage systems and introduced measures to improve public awareness of flood risk.
The Flood Re programme was also instigated to facilitate and fund homeowners to build back better, improving property flood resilience by making design changes, material upgrades to reduce clean-up, drying and move-back times and using flood barriers – both temporary and permanent.
This programme also allows at-risk homes to still be insured by reducing the future risk and potential repair costs. For more on the concept of building back better, see pages 48–49.
Australia
In recent years, the east coast of Australia has been experiencing significant flooding events in multiple states – from Queensland, through New South Wales and into Victoria. While there are some variations between the states, the overarching approach is to undertake flood-resilient design with three key options:
- Elimination – withdrawal from severe flood risk zones.
- Minimisation – examples include raising homes above flood levels.
- Fortification – design specifications to lift appliances and electrical systems above anticipated water levels and material choice driven by resilience and water resistance.
In New South Wales, the Resilient Homes Program was put together in 2022 with funding provided by both state and federal governments to assist homeowners in the immediate aftermath of flooding and in taking the previously mentioned approaches. The programme also helps reduce the risks of future floods by increasing the resilience of affected communities and reducing the requirements for repairs and future insurance payments.
Brisbane authorities currently focus their flood-resilience programme on apartments, but the recommendations around materials, construction systems and designs can be extrapolated to stand-alone houses to actively mitigate or minimise the impacts of flooding.
United States
In the US, accepted building styles are used most frequently in areas prone to storm surges, hurricanes and flooding. This generally involves a lower level that is constructed of high-water-resistant materials, no living spaces and open areas that allow the water to flow easily beneath the building.
However, not all US states use these methods of construction, so flood and wider storm damage impacts are increasing. This has resulted in the development of documentation from the US Department of Housing and Urban Development with options to ‘Restore for More than Before’.
The approach is that, if significant repair work is required after a storm event, it represents an opportunity to improve the quality of homes in several ways – for example, by applying borate treatments to untreated structural timbers, replacing with flood-resistant materials, improving foundation design by adding flood vents, using latex paint systems and added bracing. In addition, a final suggestion is to upgrade walls to ‘drainable, dryable wall assemblies’.
The US National Flood Insurance Program is managed by the Federal Emergency Management Agency. It also has minimum design requirements in flood-prone regions and is delivered to the public by a network of insurance companies.
This is available to those living in high flood risk areas and allows faster access to recovery services and facilitates at-risk communities to adopt and enforce floodplain management regulations to mitigate future flood risk.
Evidence that collaboration works
The UK, the US and Australia offer some insightful learnings for New Zealand – including those that could be considered immediately for future storm events. The key aspect that makes these international approaches successful in the long term is a collaborative approach involving all levels of government, insurance companies, home and building owners and occupants.
This is coupled with considering build location, flood risk mapping and improved building design and material choices for both new and retrofit construction.
Resilience versus carbon
With the current focus on climate change and carbon balances, New Zealand will face challenging choices between increased resilience to flooding in retrofits versus carbon totals in buildings.
Many of the flood-resistant materials suggested overseas do not necessarily score well when considered from a carbon perspective. However, when considering the alternative, which is a high replacement rate and associated waste creation, life cycle carbon costs could be lower.
Coupled with the potential improved life safety and reduction in remediation costs, this provides options that will require careful consideration. While there are challenges that face New Zealand in building back better, as noted here, there are already options demonstrated overseas that can provide workable solutions.
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