Havelock North dams and streams FAQs

Over a 24-hour period on February 13 and 14, 2023, 283.5mm was recorded at the Mangarau Dam. The previous highest recording was 162mm.

An improved maintenance plan is part of the strategy. In the meantime we ask residents to please to report any maintenance issues or faults, by calling Council on 06 871 5000 or using the Hastings District Council on-line Fix-It form.

Where the streams are within private property and not visible to Council we have to rely on reports from private landowners adjoining the stream or other members of the public to advise of debris that needs clearing.  Whether debris can be cleared then depends on accessibility – related to both land ownership and the ability to get machinery and vehicles to the site. A recommendation in the HBRC-commissioned report on the streams is that ownership/accessibility issues are addressed (see below FAQ on stream access). HDC regularly clears debris and vegetation from the stream in areas abutted by Council reserve land. Council is in the process of contracting a maintenance contractor dedicated to the streams and dams, both planned and reactive.

The dam filled to above the spillway; an estimated 300,000m³ (300 million litres) of water at its peak. The stormwater was released into the Mangarau Stream (as designed) via the throttle culvert at up to 20,000 litres per second. A further up to 15,000 litres per second was released via the spillway at its peak, releasing 35,000 litres. The volume of water behind the dam did not breach the dam wall nor overtop the dam crest.

At this time no, the Managrau dam does not need to be made bigger.  The dam was designed for a 1 in 100 year event yet operated satisfactorily during the larger (1 in 250 year event) Cyclone Gabrielle. The dam did not over-top the crest, which tells us it was adequate for Cyclone Gabrielle even though the cyclone was greater than what the dam was designed for. However, the event operation report for the dam does recommend investigating enlarging the dam given the potential for even larger storms in the era of climate change, new upcoming dam legislation and changing risk profiles.

The spillway works like the overflow hole near the top of some bathroom and kitchen sinks. Once the water gets to that height, the water is released into the receiving environment – in this case the Mangarau Stream. The 1.8m diameter outlet culvert acts as a ‘throttle’ to stop vast quantities of water being released at once.  If flows behind the dam are greater than flows through the culvert the water is stored behind the dam wall.  If the flows are still larger than what the dam can store and discharge via the culvert, water is released via the spillway. The Mangarau spillway operated as designed, beginning to operate once the water level rose above the 10.2m depth mark.

Where the streams are within private property and not visible to Council we have to rely on reports from private landowners adjoining the stream or other members of the public to advise of debris that needs clearing.  Whether debris can be cleared then depends on accessibility – related to both land ownership and the ability to get machinery and vehicles to the site. A recommendation in the HBRC-commissioned draft report on the streams is that ownership/accessibility issues are addressed. HDC regularly clears debris and vegetation from the stream in areas abutted by Council reserve land. Council is in the process of contracting a maintenance contractor dedicated to the streams and dams, both planned and reactive.

Risk will never be able to be completely designed out, particularly given the changing climate with the expectation of more severe weather events. The priority is to put mitigations in place that reduce the risk to life.  Owners of properties across the region moved from category 2 or 3 into Category 1 have been advised that being in Category 1 does not remove all risk of flooding.

The planned stream work is focused on providing a level of service to a 1 in 100-year event as a goal, noting previous standards have worked to a 1 in 50-year event design standard.

It is clear there are parts of the Mangarau stream (and likely other Havelock North streams) that cannot cope with 1 in 100-year stormwater flows, and these constrained areas will need modifications, alongside formalised access locations, improved and scheduled maintenance using a dedicated contractor to bring them to that standard. It should be noted that Cyclone Gabrielle was a much larger storm; estimated at a 1 in 250-year event.

The T+T report recommends stream widening, improved land access and maintenance, upgrading structures, bank stabilisation, improved monitoring, among others. Council is now working to develop a project plan identifying how we implement these recommendations on the Mangarau Stream. Additionally, enhanced monitoring, including stream gauges and an alarm system, are planned.

Yes. Council will be discussing work with mana whenua, given there will be significant decisions in relation to land and waterways. A Cultural Aspirations report prepared for a Reserve Management Plan for the Havelock North hills reserves includes a number of aspirations relating to the Havelock Hills waterways, and these must be taken into consideration as the work programme is prepared. 

The project team set up to drive the improvements will regularly engage directly with affected landowners, and the wider community more broadly. A communications and engagement plan has been prepared with input from representatives of the community.

This page will be kept up to date, with information posted on the Hastings District Council Facebook page and/or via Havelock North community pages as appropriate.

Hawke’s Bay Regional Council is under contract to Central Government for $10 million of co-funding towards projects related to the Mangarau flooding, with Government providing $7.5 million and the Regional Council providing $2.5 million. The funding is dependent on providing a business case to Government with a sound, consentable and deliverable plan. This funding will be passed on from Hawke’s Bay Regional Council to Hastings District Council.

Future improvements and ongoing maintenance uplift will likely see a review of Council funding for the streams and the possible introduction of a targeted rate or some other mechanism to fund upgrades and agreed-upon levels of service. Landowners, community and other key stakeholders will be involved in discussion on this.

The timeframe for the development of projects, preliminary design, and detailed project delivery plans (cost, benefit, risks, etc.) is over the next six months. The timeframe for detailed design, cost estimates, resource consent and procurement is 12 to 18 months.

We will be working in the first half of 2024 to contract a dedicated maintenance contractor and engage with the community on the development of an Emergency Action Plan (EAP). We’re aiming to confirm indicative timeframes for work to be completed in order for properties to be recategorised from Category 2c to Category 1 by Hawke’s Bay Regional Council, and present the community with a draft Havelock North Streams Management Strategy for feedback mid-year.

The recommendations in the T+T report are reliant on increased access to the stream by Hastings District Council. This means there will need to be conversations with landowners on arrangements, such as easements, for Council to access the stream for construction and maintenance. These conversations have begun and will continue in the new year with individual landowners.

The work is in designed to protect homes from 1-100-year storm events, and mitigate risk to life in larger events. As with all flood mitigation, protection from extreme events cannot be guaranteed.