Multiple drainage and environmental outcomes from new floodgate project

Waikato Regional Council’s three-year asset rationalisation project near the Piako River mouth has been completed, with positive outcomes for flood protection, land drainage and the environment.

The council has decommissioned three floodgates, which were part of the lower reaches of the Piako River flood management scheme and nearing their end of life, and replaced them with one to reduce asset operation and maintenance costs and ensure level of service over the 100-year lifespan of the new asset.

To undertake the required upgrade, it received $2.638 million from the COVID-19 Response and Recovery Fund, which is administered by Kānoa – Regional Economic Development and Investment; $250,000 from the New Zealand Lottery Commission’s Environment and Heritage Fund; and $35,000 from Hauraki District Council.

Integrated Catchment Management director Greg Ryan says a number of positive drainage and environmental outcomes were achieved through innovative engineering, including being able to clear floodwaters from the land faster, reduced sediment loads to the Piako River, deep water refuges for aquatic wildlife, safe fish passage for tuna/eels and a new 10-hectare wetland habitat for resident and migratory shorebirds.

The Piako River scheme was built in the 1960s and 1970s to provide protection to 159,000 hectares of low-lying – including below sea level – productive farmland.

“As we start to replace this aged infrastructure, we’re looking to achieve better outcomes all round,” says Ryan.

“That means making sure our service level for flood protection can continue to be met with climate change, that we can keep our maintenance and operational costs down by combining several old assets into one, and that we’re doing it in a way that also improves the health and wellbeing of freshwater ecosystems and habitats.” 

A new high capacity drainage network and floodgate inlet storage pond storage pond, which is designed to capture more than 90 per cent of the sediment from the water, means the catchment can now be drained within 24 hours – with the old structures, that took three days.

Should a pump station be required at this site in the future, the pond also provides enough start-up water volume for a pumping operation.

The floodgate allows fish passage, as does a tidal control structure that lets the newly created saltwater wetland habitat to become inundated with the high tide tide. 

The wetland habitat has islands to provide shorebirds with safe places to roost, which is particularly important for the migratory species –  such as godwits – that are declining due to land reclamation and habitat loss along their flyways.

The wetland habitat can be viewed by cyclists using the Hauraki Rail Trail between Kaiaua and Thames. A bird hide with information panels about shorebirds and the project has been installed next to the trail that goes along one of the new stopbanks. 

Michelle Paki, acting General Manager – Regions of Kānoa – RD, says the upgrades show what can be achieved when investing in infrastructure for resilience and growth.

“The establishment of the wetland habitat alongside upgrades to infrastructure is a marriage of climate resilience and environmental protection.

“To see this project come to fruition is a huge achievement. This is a great example of how regions working in partnership with central government can accelerate infrastructure projects, enabling them to get underway sooner. By implementing such significant infrastructure, Waikato Regional Council has ensured security for local communities and the surrounding environment. The positive impact of this project will be evident well into the future.” 

Waikato Regional Council Chair Pamela Storey says the project would not have been possible without the support of the many stakeholders involved.

“It has been a true partnership, from the funding from Kanoa, the New Zealand Lottery Commission and Hauraki District Council to the planning of the wetland habitat with Pūkorokoro Miranda Shorebird Centre, iwi and landowners. 

“This project is a true demonstration of the multiple outcomes that can be achieved by working together.” 

Stakeholders check out the newly completed project. This image shows the floodgate outlet (foreground) and habitat area (background).

The project decommissioned three floodgates and replaced them with one.

The wetland habitat, which becomes inundated during high tide, has islands to provide shorebirds with safe places to roost.