Dunedin city councillors and their Otago Regional Council counterparts will be updated this week on the now-delayed natural hazards risk assessment — touted to be the first detailed picture of the climate change threat to the low-lying suburb.
Originally due this month, the risk assessment’s five-month delay came about after a review of a draft assessment by council staff, external technical reviewers and selected stakeholders, South Dunedin Future programme manager Jonathan Rowe said.
Mr Rowe’s report to tomorrow’s city council meeting said the review of the risk assessment this winter identified limitations in a "Three Waters flood model", which lacked the level of detail and confidence the assessment required.
The new Three Waters flood model would incorporate recent lidar information and more accurate assessments of surface flows.
It would account for groundwater fluctuations and infiltration into stormwater and wastewater systems, as well as including other improvements.
A lack of accurate floor-level data for most buildings in South Dunedin was also identified as a problem when the draft was reviewed, he said.
This limited the risk assessment’s ability to analyse how vulnerable an area was to flooding.
Representative floor-level information based on building regulations at the time of construction had been used to develop the draft, but proved insufficient.
Council staff were now conducting "observational assessments" of floor levels for all buildings in South Dunedin, which would be supplemented by professional surveys of a sample of buildings.
While the "information gaps" in the draft had been identified early on, work on the risk assessment proceeded with the understanding it should go ahead with the best information available.
Now, though, the gaps were seen as material concerns that could undermine the "accuracy, integrity and logic" of the risk assessment.
"Finalising the risk assessment with these gaps risks generating ‘false positives’ in the results, which could have adverse real-world implications for stakeholders, and require later redress", Mr Rowe said.
In July, Mr Rowe said the risk assessment would be "unwelcome and concerning" reading for some.
It could have wide-ranging implications for council services, infrastructure, mana whenua, residents, schools, public housing and utilities companies, he said.
The risk assessment was due to be followed up in November with a report on options for how South Dunedin could change to deal with the natural hazard risks it faced, but now both reports would be delivered to the councils in February.
Associated community consultation would only be delayed by one month, Mr Rowe said.
Otago regional councillors will be presented the same report on Wednesday.
