New flood risk maps are being proposed as part of Wellington's draft district plan, outlining where new housing development will not be allowed.
If approved, it will be the first time coastal inundation and tsunami impact risks are incorporated into the plan.
Wellington City Council released its draft district plan last week. It's designed to address a shortfall of up to 12,000 homes over the next 30 years by allowing more development.
But it's also about updating a document that was first drafted in the early 1990s to meet the challenges of climate change.
Under the proposal, new development would not generally be permitted in high-risk flood zones, either from a tsunami or storm event.
It wouldn't be completely prohibited though as those wanting to develop in these areas could still apply for a resource consent to do so, but that would be a high benchmark to reach.
Development would be allowed in low- or medium-risk areas if mitigation measures were undertaken like raised floor levels.
The thinking behind the proposal is to draw a line in these risks, to understand and recognise them, so as to not make the situation any worse going forward.
It would mean future generations not having to deal with properties being developed in hazardous areas and having resilience built into the city through mitigation measures.
City councillors are considering the draft plan today, which will be consulted on for six weeks starting in November.
Coastal inundation
The introduction of coastal hazard inundation maps to the district plan is a significant change to the status quo - they don't currently exist.
High-risk coastal hazard areas are those impacted by a 1-in-100-year storm event.
Most of these areas are right on the coast between existing roads and the ocean.
Generally, new development would not be approved in these areas, but existing housing could remain. Additions of up to 20 square metres would be allowed.
Medium-risk coastal hazards are areas impacted by a 1-in-100-year storm with 1 metre of sea level rise.
These areas include parts of Miramar, Kilbirnie, Lyall Bay and the CBD.
In the coastal inundation map for Wellington's CBD, the blue area represents a medium hazard and the purple area represents a high hazard. Image / Supplied
Here development could progress but sea level rise must be taken into account through development design.
This includes mitigation measures like raised floor levels, relocatable buildings, and private pump systems for basement car parks.
The use of the ground floor of a development might also be taken into consideration, like using it as a basement or garaging rather than a home's main living area.
Tsunami risk
Similar areas of the city are affected by new tsunami hazard maps.
Maps based on tsunami evacuation times, -how long it would take to escape to higher ground - are already publicly available.
But the council is proposing to include maps with a different level of information about how a tsunami would actually affect the land.
Three levels of risk are based on different scenarios: the highest being a 1-in-100-year tsunami, then a 1-in-500-year one, to the lowest risk being a 1-in-1000-year tsunami.
These models include allowance for 1 metre of sea level rise.
Under the proposal, new housing in the highest risk zone would generally not be approved.
In the tsunami risk map for Lyall Bay, purple represents a high coastal hazard, dark blue represents a medium coastal hazard, and light blue represents a low coastal hazard. Image / Supplied
This includes areas of Island Bay, Lyall Bay, Owhiro Bay, Seatoun, Kilbirnie and a large portion of the CBD.
However, the council realises allowing no new development in the CBD is not practical, so it's likely this area would have different rules and the risk would be mitigated through design.
This could include measures like concrete reinforced structures, which have a better ability to withstand a tsunami, and building heights for vertical evacuation.
The Wellington Fault
The current district plan already contains a map of the Wellington Fault. It actively discourages office blocks or large scale multi-unit residential developments within 20 metres of either side of the faultline because of the risk to life and property.
The proposed district plan strengthens this level of discouragement to develop in these areas, but timber frame residential dwellings would still be allowed.
The Wellington Fault is the set of red lines closest to Wellington City, running through Kelburn and Thorndon. Image / Supplied
This risk is about fault rupture, when the ground is torn apart in an earthquake, rather than actual ground shaking.
The latest reporting from GNS Science has been incorporated into the map, meaning the fault extends to a greater area than previously because there is more detail about where it actually lies.
The Wellington Fault runs along Glenmore St in Kelburn and carries on through Tinakori Rd in Thorndon.
How did we get here?
Like most first generation district plans, Wellington City's was first drafted in the early 1990s and originally didn't give much consideration to natural hazards.
The issue wasn't as well understood as it is now because the research didn't exist and Wellington specifically had experienced a relatively quiet period in terms of earthquakes.
But the situation started to change from the mid 2000s when images of the Boxing Day tsunami were broadcast into people's living rooms in 2004. It's estimated about 230,000 people died.
Firefighters, police and other search and rescue crews at work on the collapsed and burning CTV building in central Christchurch. Photo / Mark Mitchell
In 2011 a tsunami hit Japan killing nearly 20,000 people.
Social media was becoming more influential making images of the devastation readily available and even more real to those living around the world.
In New Zealand, the Christchurch earthquakes, Seddon earthquakes, and the Kaikōura earthquake brought home the risks which seismic hazards carry.
Natural hazards were made a matter of national importance under the Resource Management Act, meanwhile the issue of climate change gained international recognition.
All of this has led to second generation district plans including a lot more details around hazards, how to plan for them - and how to live with them.
