Visitors to Orakei’s popular Waiatarua Reserve were witness to some pretty impressive works recently when a sediment removal project required unique machinery.
Sediment build-up in waterways and stormwater ponds is a constant battle in Auckland with sediment needing to be removed from the forebays, stormwater channels and ponds so that they continue to operate as intended.
In Waiatarua Reserve, located in the Ōrākei Local Board area, coarse sediment traps were installed at two locations, designed to capture sediment run-off before it reaches the main body of the wetland. According to the management plan, sediment removal at these locations could take place every 2-4 years.
In May 2020, Ōrākei Local Board approved a landowner application from Healthy Waters to access Waiatarua Reserve to clean out the sediment traps, contractors removed a total of 160 cubic metres from the traps using a specialist amphibious dredge.
“Sediment removal can be a challenging and costly operation, so we certainly don’t undertake such work unnecessarily," explains John Adams Healthy Waters Specialist.
“Cleaning out of sediment traps helps the stormwater treatment device function properly and reduces the flooding potential in community reserves.
“An amphibious dredge called a 'Truxor' was bought in. It works by sitting in the waterway, loosening sediment by using a screwdriver-type attachment before pumping it out to holding containers - in this case the containers were located in the carpark. The sediment was then treated to separate it from water.”
John goes on to explain that the whole operation is tidy, quiet, and efficient and had a very minimal impact on park users. “Using this new type of machinery is much less intrusive both on the public and the environment compared to typical methods which use long-reach excavators.
“This was truly an environmentally focused project," explains Scott Milne, Chair of Ōrākei Local Board.
“Not only was a process chosen for the low impact on the surrounding area and the channels themselves, but native fish and eels were taken into consideration and prior to works commencing, were collected and relocated further downstream to prevent injury during the cleaning process.”
Due to the significant amount of sediment removed, it is clear that further works to remove sediment from the entire channel of Waiatarua Reserve wetland may be required.
However, due to the size and ecological significance of this wetland, this would require resource consent and significant budget and staff resource. A survey of the area is planned for 2021 which will help clarify the extent of the issue.
“Though it is unlikely we will be able to undertake this work immediately, it is safe to say that this treasured reserve and the work needed to protect it is high on Ōrākei Local Board's priority list. I hope to see further remedial works being undertaken soon” explained Milne.