A crew is working to clear blockages and vegetation from Whanganui's Matarawa Stream as plans are made to divert more of its water to prevent more flooding.

The Whanganui East stream burst its banks and caused extensive flooding during heavy rain in June 2015, Horizons Regional Council river manager Ramon Strong said.

The council agreed to clear it of blockages and overgrown vegetation in the urban area, and began that work last summer. It had started again and should be finished by March, the council's northern engineer Wayne Spencer said.

Some of the work has been highly technical. Contractors have been confined to working within backyards with limited access.

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Horizons Regional Council staff are using heavy machinery to remove overgrown vegetation from Matarawa Stream in Whanganui East. Photo / Supplied
Horizons Regional Council staff are using heavy machinery to remove overgrown vegetation from Matarawa Stream in Whanganui East. Photo / Supplied

"At times we've had to use cranes to get equipment in and out of work sites, all while trying to minimise the damage to lawns and gardens. Fortunately, landowners have been very accommodating throughout the process and we've had a lot of positive feedback," Spencer said.

The clearance work is funded by $340,000 collected from Whanganui urban ratepayers. It is going well and is expected to come in under budget.

Once it is finished, Horizons will keep the stream clear.

Upstream from Whanganui East, the Matarawa has a series of five floodwater detention dams, to capture excess water and prevent flooding the valley floor and suburb. Also, at times of heavy rain, a gate near Okoia closes and some of the water is diverted into the Mateongaonga Stream.

Horizons was considering diverting all the water at that floodgate, Strong said, and to have the gate close automatically in times of flood.

In order to do this, the council will need to vary its own consent for the diversion. As part of that, a "handful" of potentially affected downstream property owners will have to be consulted.

It might seem ridiculous for the council to have to give itself consent, Strong said, but it had to play by the same rules as everyone else.

Work to vary the consent will happen next winter, with the aim of altering the gate the following summer.

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The extra diversion would make streamside properties less flood-prone, but would not be a complete fix, Strong said.

"There will still be issues, but it will make some difference."