The multi-million dollar detention dam designed to reduce costly floods in Whangarei's Central Business District has been officially named and opened.

The dam, called Hopua te Nihotetea, was blessed by Whangarei kaumatua in a dawn ceremony on Saturday. A larger civic ceremony followed several hours later, which included unveiling signs telling the story of the $11 million structure's construction and displaying its formal name for the first time.

Northland Regional Council chairman Bill Shepherd acknowledged the contribution of local Te Parawhau hapu members during the dam's construction and for dedicating its official name.

"Hopua te Nihotetea translates as 'capturing the Nihotetea Stream', which nicely reflects this detention dam's purpose," Mr Shepherd said.


Nihotetea Stream is a tributary at the headwaters of the Raumanga Stream. The dam will rapidly capture up to 1.3 million cubic metres of floodwater during heavy rain and then slowly release it into the Raumanga Stream over several days.

Mr Shepherd said ultimately it is expected to save about $1.4 million in damage annually over its long operational life.

"Much of the the harm caused by floods depends not only on how deep they are, but, crucially, how fast they're travelling, so the long-term financial benefits to our community from mitigating the worst of these factors can be quite substantial, especially when you consider this dam could be here for a century or longer."

Hopua te Nihotetea will not completely stop the CBD from flooding as the Waiarohia Stream and tidal Hatea River also flow into the area, but will slow the water flow down the Raumanga Stream and other tributaries and cut flood depths by up to half a metre.

The dam took about 16 months to build and is the largest project of its kind undertaken by the regional council. For the majority of the time, Hopua te Nihotetea will hold no water at all but will come into its own in a large storm.

Webcam images at the new dam can be viewed at: