Opinion | What is natural hazard residual risk?

It would be hard to find a place in New Zealand that isn’t at risk from at least one natural hazard. The most beautiful places often have multiple hazards.

Whakatane is the unofficial natural hazard capital of the motu, being on the coast, next to a river, with an escarpment on a fault line and lying within the active Taupo Volcanic Zone.

The recent tragic events at Mount Maunganui and Welcome Bay again point the spotlight on how New Zealand manages natural hazard risk. Following Cyclone Gabrielle, the government prepared the National Policy Statement on Natural Hazards (NPS-NH) which has recently been released. The NPS-NH and new section 106A in the RMA are aimed at supporting councils to take a more robust approach to managing natural hazard risk for subdivision and land use (except for primary production and infrastructure).

The NPSNH applies to:

Flooding
Landslips
Coastal erosion
Coastal inundation
Active faults
Liquefaction
Tsunami

The NPS-NH requires development in very high-risk areas to be avoided and for residual risk to be considered in consent decision making. The potential impacts of climate change to at least 100 years in the future also need to be considered.

What is residual risk?

It’s the risk that remains even after all reasonable protection and mitigation measures are in place. In simple terms, it’s what happens when nature does more than the system was designed to handle. For example, when a flood rises higher than a building’s finished floor level, or a coastal event overwhelms a seawall.

As our climate changes, there is a predicted increase of both the frequency and intensity of extreme weather events. Because climate change impacts out to 100 years must be considered, the design requirements of natural hazard mitigation and protection will be higher.

For new developments and re-development of existing sites, land developers (and their planning consultants) need to ensure a consent application includes an assessment of residual risk and how to manage that risk.

In addition, councils have started work on climate change adaption plans for areas near the coast or in floodable areas. In some situations, the adaptation plans indicate when relocation or managed retreat from an area is anticipated. We are finding councils are starting to apply ‘cessation of habitable use’ consent conditions related to trigger levels in anticipation of future managed retreat.

Managing residual risk through consent conditions

A big question is what consent conditions may be applied to subdivision and land use to address residual risk, particularly where residual risk relates to changes over time. Consent conditions are applied to avoid, remedy or mitigate effects and risks, and must be proportionate to the level of identified risk. While consent conditions are set at a point in time, the conditions will be ‘future-proofed’ to manage changes over time.

I expect councils will use a mix of conditions:

Engineering and Design Standards: e.g. minimum floor levels (above the 1% AEP), geotechnical design for foundations or retaining walls.
Monitoring and Review: s128 RMA conditions for review of a consent if monitoring identifies residual risk has become a threat to people or property.
Adaptive Management (Trigger-Based Conditions): Setting “triggers” for future actions, such as the relocation (managed retreat) once sea-level rise or erosion reaches a specific point.
Emergency Preparedness: Draw attention to Civil Defence and Emergency community plans or require a site-specific Flood Safety and Evacuation Plan.

For some forms of natural hazard, these are standard consent conditions (e.g. the requirement to remove a house from a site when coastal erosion reaches a set distance from the house). For other natural hazards, managing residual risk through consent conditions is more complex and will be a new challenge for many councils. The wording of consent conditions and consent notices from councils may be confronting (aka ‘legally robust’).

Is there a way to ensure people are well-informed while not being too scary?

Adaptation, retreat and the reality of risk

Another big question is how adaptive management consent conditions relate to wider area or community-based adaptation plans.

The NPS-NH states it does not override any existing use rights that apply under s10 RMA. This may mean that managed retreat of existing development would be through (proactive) adaptation planning or (post-event) ‘red zoning’ processes. New development and re-development (where extending building footprints or increasing development density) in existing urban areas are subject to natural hazard overlay rules and consents.

But should future managed retreat and removal of habitation rights be signalled now in a consent?

As a community we need to have full disclosure and raise awareness of natural hazard risks. The litigation against Bay of Plenty Regional Council in relation to the failure of the Edgecumbe stopbank in 2017 will impact the need to assess residual risk for areas protected by public or private flood protection structures. There will be implications for insurance premiums in protected areas (often referred to as ‘defended areas’).

Residual risk needs to be understood for the lifespan of a development. Informed assessment and consent conditions appropriate to addressing the level of current and future risk will be key.

Ruth Feist

Principal Planner, Hayson Knell

Ruth has 27 years of planning experience in local government and consultancy. She holds a M Social Science degree in Geography and is a full member of the New Zealand Planning Institute. Ruth’s work for Hayson Knell ranges from development feasibility, District Council plan formulation and change processes, submissions on legislative changes, spatial planning projects and resource consent preparation.

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