A report outlining the hazards on the Lindsay Creek flood plain and potential plans will go before the ORC safety and resilience committee meeting in Dunedin, on Thursday.
Severe flooding and damage has been recorded on the flood plain in North East Valley (NEV) at least 10 times since the late 1860s.
ORC science and resilience general manager Tom Dyer said the flood hazard risk was "significant", and it was "prudent to take a fresh look" at the flood hazard associated with the Lindsay Creek flood plain, and to investigate options to reduce that flood risk.
He said comprehensive flood protection schemes for the area had been presented to the council previously, but it was decided not to pursue them.
The council went so far as to buy properties in the suburb with the intention of using them as part of a Leith-Lindsay flood protection scheme.
However, in 2017, council advertised three properties for sale in NEV and one in Normanby.
Mr Dyer said the scheme did not go ahead based on the economic climate at the time, feedback from community consultation and the potential impact of costs on residents against the benefits provided by the proposed work.
However, the council retained rights to work on portions of the properties closest to the stream so it could start that work if it decided to in the future.
"The flood hazard risk is higher than what is generally considered acceptable in New Zealand or elsewhere in Otago for an urban area, so we should regularly consider how best to manage mitigation," Mr Dyer said.
The Lindsay Creek channel is part of the Dunedin river management area and is actively managed by the ORC to ensure flows and sediments are transported as efficiently as possible, such as routine monitoring, vegetation control, removing obstructions and bank erosion repairs where applicable.
The ORC also maintains some rock work and concrete walls designed to minimise erosion and help retain the creek within its existing channel.
In 2005, the ORC constructed a debris trap below Bethunes Gully to help reduce the volume of debris and the likelihood of channel blockage.
The report proposes an $800,000 investigation be conducted between 2025 and 2027, which would result in a detailed assessment of the Lindsay Creek flood hazard, as well as inform the flood mitigation investigations and emergency flood responses.
The investigation will consider all the sources of flooding — river, stormwater and surface run-off, account for the effects of climate change on river flows, and will assess the effects of "maximum credible" events and incorporate geo-hazards such as landslides, Mr Dyer said.
The aim was to make a decision in the 2027-28 financial year.
One of the options could be to stick with the status quo and do ongoing maintenance of waterway and existing infrastructure, update flood hazard information and collaboration with the Dunedin City Council as required, and emergency response planning.
Other options could be to implement flood mitigation options that focus on nature-based solutions where practicable; or build a flood scheme that consists of hard engineering infrastructure.
Mr Dyer said depending on the decision made, there was potential to start the implementation of the flood mitigation works from 2028-29.
That was expected to cost $3.5m over the following five years, and a further $56.8m in funding could be approved through the remainder of the infrastructure strategy project up to 2054.
The NEV flood plain is intensely developed and populated with several hundred residential properties, three schools, a police station, Ross Home, the Otago Community Hospice, some commercial properties, and North Rd, the main access to North East Valley.
