Info evening to explain $8m Raumanga dam

The public is invited to find out more about the $8 million stormwater dam the Northland Regional Council is building in Raumanga.

The Kotuku retention dam is part of a multi-phase project to reduce downstream flooding in Whangarei and is one of the biggest projects the NRC has undertaken.

When a targeted rate was set on more than 17,000 properties and contributing catchment areas in the 2012 Long Term Plan, the cost was estimated at about $6.9 million (excluding GST).

This has since been revised upwards to almost $8.5 million. The new figure is based on dam design, peer review outcomes, relocating services like gas and power/fibre and land acquisitions, NRC land/rivers senior programme manager Bruce Howse said.

With construction due to begin within months, the council is keen to update the public on that and other local flood prevention projects, he said.

Anyone interested is welcome to attend the information-sharing evening, which will be held at council's Water St offices from 6pm on April 16.

When completed next year, the 18-metre high earth dam, in a gully between Raumanga Valley Road and Kotuku Street, will hold up to 1.27 million cu m of floodwater during heavy rain, about two-thirds of the capacity of the Whau Valley dam.

It will release trapped stormwater over a couple of days, reducing river swelling and downstream flooding.

The flood prevention project also involves clearing stream blockages and the recent upgrade of the Rust Ave Bridge, which was a joint project between the NRC, Whangarei District Council and Land Transport NZ.

Despite the Kotuku dam's cost increase the NRC has not changed the Whangarei Urban Rivers Management Rate in its proposed Draft Annual Plan (DAP) 2014/15. Any change to the targeted rate in future would require public consultation - likely to happen as project costs are firmed up and probably in time for the adoption of the Long Term Plan 2015-2025 next year.

"In the meantime, we'll continue to work with both the Urban Whangarei Rivers Liaison Committee and the wider community on this project to ensure it remains affordable," Mr Howse said.

The council expects to offset some of the increased costs by selling some of the 20 properties it purchased.