The dam that helps save Whangārei

21 Dec 2022, 8:27 AM

Whangarei’s Hopua te Nihotetea water detention dam has once again shown its worth after one of the wettest years ever recorded in the city.

The dam, which is located at the end of Raumanga Valley Road, was built by Northland Regional Council (NRC) in 2016. It works by storing and then slowly releasing trapped stormwater into the Raumanga Stream, reducing river swelling and downstream flooding.

“It really is the dam that helps protect the Whangārei CBD from flooding”, says regional councillor Jack Craw, chair of the Urban Whangarei Rivers Flood Management Working Group.

Councillor Craw, the council’s Deputy Chair, said the cumulative effect of record-breaking rainfall totals in November, and the continuing wet weather in December, meant water levels in streams flowing through the city could rise very quickly due to the already saturated catchment area.

“If it wasn’t for the dam we would have expected additional flooding in the Whangarei CBD during the rainfall event in November. It’s doing exactly what it was designed to do”, Cr Craw said.

The dam recorded the third highest levels in November since it was completed.

The dam is designed for a 100 year plus climate change rain event including a potential increased rainfall of approximately 20% and sea level rise.

NRC rainfall data for spring 2022 showed Whangārei was the wettest spot in Northland with a 220% increase in the expected September to November rainfall. Many other areas, including sites in the Central East Coast and Bream Bay received more than twice the Spring rainfall median.

Kai Iwi Lakes and Waimamaku on the West Coast were the only sites in Northland not to exceed their median Spring rainfall totals.

Northland Regional Council is also currently constructing flood protection schemes which will provide climate change resilience in Kaitaia and Otiria/Moerewa with co-funding from the ‘shovel-ready’ COVID-Response and Recovery Fund administered by Kānoa - RDU. Together with the Kaipara District Council, NRC is also doing work in Kaipara with the Dargaville to Te Kopuru Stopbank Project Raupo Upgrade.

“For us, helping communities adapt to the impacts of a changing climate is a key focus,” said Awanui River Flood Management Liaison Committee chair Joe Carr.

“Kaitaia’s Awanui scheme for example has already proven its worth this winter as our hydrology data showed the water flow in the Awanui River was the biggest on record since 1958 when the NRC gauge was first installed.”

“Back then Kaitaia was totally flooded, this year Kaitaia was protected”, Councillor Carr said.

Whangārei’s Hopua te Nihotetea water detention dam with not much water.

Whangārei’s Hopua te Nihotetea water detention dam as it usually looks.

Whangārei’s Hopua te Nihotetea water detention dam full of water.

Whangārei’s Hopua te Nihotetea water detention dam during wet weather in July.