A stormwater retention dam in Maunu stopped around 300,000 cubic metres of water from flooding into central Whangārei during the weekend's storm.
Northland Regional Council (NRC) Environmental Services general manager Bruce Howse said the $11 million Hopua te Nihotetea, which opened in 2016, did its job in preventing the CBD from even more flooding from the storm that dumped more than 220mm of rain on the city in a few hours.
''We were very pleased with the performance of the dam and it performed as designed,'' Howse said.
''Without the dam in place we would have expected much more significant river flooding in the Whangārei CBD.''
He said the dam had about 400,000 cu m of water retained, which otherwise would have flowed into the CBD.