The most recent flood management work done in the stream was the instalment of a dam on farmland upstream in the 1980s.
Submitters said the stream’s flooding issues were caused by its large catchment area but narrow channel width.
Residents Stephen and Sabine Holman made a submission to the district council’s 2023/24 Annual Plan saying the issues had not been given proper attention and requesting the district and regional councils liaise to sort out responsibility for the stream.
They asked for either council to regularly inspect and maintain the stream channel and keep it clear of weeds, inspect and maintain the dam, assess options for improving the capacity for narrow sections of the channel and reassess the capacity of the culvert beneath Ikitara Rd which the stream flows into.
Whanganui District Council senior stormwater engineer Kritzo Venter said under the Land Drainage Act, the respective owners of the land the stream flowed through were responsible for its maintenance.
He said under the requirements of the Act, maintenance was adequately carried out by the landowners.
The council was responsible for regulating building construction so there were no habitable floor levels in up to one-in-50-year rating events.
The flooding on the road was well below the floor level of houses on the road in an event of this magnitude.
“Meaning there’s no risk of houses being flooded, this is a lower priority catchment compared to other locations,” he said.
However, responsibility for the upstream dam was less clear.
The dam was put in place by the Whanganui Borough Council before the formation of the Whanganui District and Horizons Regional Councils.
At present, the district council was responsible for the urban stormwater network, which the Ikitara Rd culvert fell under, and Horizons was responsible for flood management where there was a flood scheme in place, Venter said.
Such a scheme is in place for the Matarawa Stream, which the Turoa Rd stream flows into.
“Currently, there is no flood scheme in place for Turoa Rd so this issue falls outside the scope of both councils,” Venter said.
The council wanted to propose the formation of a special interest group with Turoa Rd residents and council personnel to work with Horizons to find a solution.
In 2022, residents made a submission to Horizons’ long-term plan for the stream to be added to the Matarawa Urban Scheme, under which Horizons’ staff do regular maintenance work to keep the stream clear in the event of a flood.
Horizons group manager of catchment operations Dr Jon Roygard said the council was aware of the issues and the submission to extend the scheme to the Turoa Rd area.
“Horizons decided to defer any decision regarding management of the open drain and dam until further discussion with the Whanganui District Council and Te Awa Tupua has been completed, and the matter is presented in the context of other flooding issues in the area,” he said.
Horizons was currently undertaking work at Kōwhai Park, the North Mole as part of Te Pūwaha and was under way with engagement with the community at Pūtiki alongside Massey University.
The issues at Turoa Rd had not been further investigated, Roygard said.
