RIVER SURVEY - LOWER TUKITUKI CORRIDOR

SUMMARY

In 2024, the Lower Tukituki Corridor sub-catchment used a TLC Demonstration Grant to undertake their own river survey.

The Survey Company was engaged to conduct a detailed study of the river using modern imaging and empirical data to inform better river management and infrastructure protection.

The project, covering the river from just upstream of the convergence (including Walker Road) to a kilometer downstream of the Patangata Bridge, produced high-resolution LiDAR and visual datasets, allowing comparison with 2020 data, identification of key risk areas, and a robust baseline to guide future decision-making on flood capacity, gravel extraction, and river profile changes.

TUKITUKI RIVER LIDAR SURVEY

The 2024 report by The Survey Company highlights significant changes to the river following Cyclone Gabrielle, including areas of deep scour, bank erosion and gravel build-up. It also demonstrates how this information can help improve understanding of river behaviour, support infrastructure protection, and inform future discussions around river management and gravel extraction.

The report includes maps, aerial imagery and cross-sections from key locations along the river, as well as recommendations for ongoing monitoring.

DOWNLOAD REPORT

FINDINGS

LiDAR was used to identify areas where there is erosion or accretion. The image on the below illustrates a cross section with the blue line showing earlier shingle levels.

Overall The Survey Company found that between 2021 and 2023 more material was deposited in the river than was removed. But between 2023 and 2024 the river lost about 800,000 cubic meters of material. Keeping track of these changes can help understand how the river is behaving and provide information for decision makers to help manage risks to infrastructure and the environment.

THE REPORT RAISED A FEW QUESTIONS

Is this a broken river groyne at the Walker Road stop bank?

Groynes in rivers can help in protect the riverbank by restricting the flow of water near the bank.

According HBRC the groynes are designed to rotate and flex. While it looks extreme, once the gravel has built up around the groyne, it should eventually be covered with silt and with some native planting the whole area will be enhanced for flora and fauna, it just takes time to reclaim the edge that was lost during Cyclone Gabrielle.

Why have pines been planted between the stop bank and river?

Response from HBRC: In short it was decided after exploring some options that the area would be put into plantation forest and enhancement planting.

Reasons and justification for the plantings, after exploring options for the area included:

1. Plantation forest offered a landuse for the site that will provide erosion control, weed suppression, financial returns through carbon and log sales, and diversifies vegetation for people accessing the areas for walking and other forms of recreation.

2. Establish the majority of the site (14ha) in radiata pine due to it’s proven ability to establish in dry sites and suppress weeds.

3. Establish a smaller area (4ha) in Eucalyptus bosistoana. This is in conjunction with NZ Dryland forests as a research trial site. Although it is more expensive to establish, will not suppress weeds as well as radiata pine, and the level of financial return is unproven, providing some diversity would make a valuable contribution to wider HBRC afforestation initiatives.

The area was developed into a plantation forest after having recently received land/tree clearing and being retired from grazing.

Considerations included that the planting/area would:

1. Have no effect on flood capacity.
4. Retain gravel extraction stockpiling area.
5. Retain access for motorbikes

WITH THANKS

The Lower Tukituki Corridor Catchment Group
The Survey Company
Hawke's Bay Regional Council

FURTHER INFORMATION & CONTACT

To find out more about the Lower Tukituki Corridor sub-catchment, head to the Tukituki Corridor sub-catchment page on this site.

To get in touch, please contact TLC Catchment Coordinator Pixie Seligman:

Email: tukicoordinator@gmail.com

Phone: 027 721 2423