Alan Titchall catches up with Crowley Excavators to talk about their work on a major BOP wetlands project.
I MEET CRAIG and his son Brandon Crowley at the National Excavator Operator Competition back in March. Brandon was competing at the nationals after winning the Bay of Plenty regional competition, narrowly beating his father.
With his father’s support, Brandon won the Contractor magazine One-day Cup at the nationals.
At the time Crowley Excavators was about to start work on the Papahikahawai Island project commissioned by the Bay of Plenty Regional Council.
The project will improve natural water flows through the Papahikahawai Creek into a sea estuary, and create new areas of wetland in the Lower Kaituna Wildlife Management Reserve.
This project is also a preparatory step toward part of a larger one involving the Kaituna River Re-diversion and Maketu Estuary Enhancement Project, which involves the re-diversion of 20 percent of the Kaituna River flow back into the estuary at Maketu.
The total project is a priority for the Bay of Plenty Regional Council and involves putting right some of the things that have led to the estuary becoming degraded since 1956, when the Kaituna River was diverted out to sea at Te Tumu.
This original work deprived the estuary of nearly three million cubic metres of fresh water per tidal cycle, and led to it half filling with sand. The original diversion also increased the salinity of estuarine water that, in turn, led to wetland disappearance. These things, combined with stopbanks and causeways encroaching into the estuary, have significantly decreased its ecological and cultural value.
The wetlands were once valued for growing flax and collecting seafood. Local Maori landowners are involved in the restoration and have removed grazing stock from wetland islands to reduce erosion and nutrient run-off into the estuary.
A causeway built in 1963 has also been replaced with a bridge so that the tide can work like it used to and flush 13 hectares of estuary.
Bay of Plenty Regional Council is coordinating and funding the work and its Kaituna Catchments manager Pim de Monchy says construction work for the re-diversion is scheduled to start this spring.
“In the meantime, as well as removing the causeway between the island and Maketu Spit, we’re replacing the stop banks along Papahikahawai’s southern shore with a more natural contour and replanting it over the next couple of months.
“That means the wetlands can establish more quickly once the re-diversion is in place.
“The sand for re-contouring is coming from the nearby Lower Kaituna Wildlife Management Reserve where it’s being removed from a pasture area to create yet more wetlands there.
“So it’s a win for waterways and wildlife all round.”
Baseline monitoring in the upper estuary reinforced the need to improve water quality and wildlife habitat there, he adds.
“During recent fish surveys we found only eels and mosquito fish. Other fish species that we would expect to see weren’t there, probably because the water has very low oxygen levels.
“It’s great to know there’s already good numbers of eels there and we expect them to thrive with improved flushing in the upper estuary. We also hope to see other species such as inanga, mullet, flounder and kahawai recolonise the area.”
Work so far
Altogether, three preparatory projects have been underway since March ahead of the main re-diversion construction works scheduled to start in September.
Crowley Excavators has been engaged to create new wetland within the Lower Kaituna Wildlife Management Reserve, and in the process extract about 7000 cubic metres of sand for use on the estuarine margin.
The contractor’s work involved creating a haul road for tractor and trailer units across very deep and wet peat close to the Tauranga Eastern Link to access the new wetland area. Crowley then scraped off the topsoil from a one hectare grassed area and ‘bund’ it off from the surrounding wetland, before excavating around one metre depth of medium sand from the area and loading it before water fills in the excavated area.
There were several challenges in the work, including gaining access across very weak and wet peaty ground, high ground water levels, the possibility of discovering archaeological or cultural finds of significance, and the push to get work done ahead of the duck shooting season, which started in May.
With the duck shooting season just finished, Crowley has returned to the area to re-contour the extraction site with some of the remaining sand and topsoil to optimise its ecological, cultural and recreational value as wetland, and link it hydraulically to the rest of the reserve’s wetlands.
The other two preparatory projects include the construction of a wooden bridge suitable for pedestrians and light utility vehicles, and the re-contouring and planting of coastal margins on Papahikahawai Island, which borders the Maketu Estuary, to form a more natural transition between the estuary and some wetland areas that are being retired from grazing by the landowners.
We will update this project later in the year.