Our Auckland team has been busy completing stormwater pond renewals before the winter season. Stormwater treatment ponds are designed to retain and treat stormwater runoff from a nearby road or catchment area, before it discharges into receiving waterways. They need regular cleaning in order to make them effective and efficient in their performance.
The two ponds we’ve worked on recently were in Oteha Valley and Hobsonville, each with its own challenges.
For this job, we created a disposal area on-site as well as installing a silt fence to mitigate any run-off from vegetation and sediment removed from the pond. Most of the vegetation and sediment was removed using a long-reach digger, taking care to not compromise the clay base of the pond, before being loaded into a skip for transition to the disposal area.
Instead of digging by hand, we used hydro-excavation to clear the thick roots that had worked their way into the bund.
Some of the energy-dissipation rocks off the mouth of the wingwall needed reworking. We removed all rocks, gently reshaped the clay base, installed new geo cloth and re-installed the rocks along with additional gabion to leave a result twice as large as the pre-existing setup.
We also remedied the embankment digger access points, laying new top soil and coconut coir mat to preserve these areas ahead of the new planting program to be undertaken at a later date.
Safe to say with the installation of the mat and a bit of water in the forebay and main pond, the team are very happy and proud of their work.
Oteha Valley pond
Day one saw us dewatering the pond, preparing access by trimming vegetation, shaping track corners and laying hard material and track mats where necessary to allow access for large vehicles.
This job saw us removing sediment and vegetation in both the forebay and main pond. We used hydro-excavation to break up and remove accumulated aggregates and clay at the inlet wingwalls along with vacuum trucks to remove sediment from the forebay mid-point. Altogether, we removed approx. 70m³ of sludge from the forebay, which made a huge difference to the look of the area — if you were to stick a deck chair on the sandstone at the inlet end, it would be a very idyllic chill zone!
With the main pond, the largest and most significant challenge for the team was the 400mm-600mm of soft grey clay beneath the 300mm-400mm black sediment and matted weed. As you can see by the photos, it was taxing for our team to move themselves through it so hats off to them for their efforts here! In fact, the morale and sense of achievement amongst Iulai and Patrick’s team on this challenging renewal was absolutely incredible and we are proud to have such a great group of operators in our mix.