Stretching about 6,500 metres in a westerly arc from Silver Beach at Kurnell to Lady Robinson’s Beach at Kyeemagh, the twin and single steel pipelines will impact approximately one per cent of the overall area of Botany Bay. Along the whole route, however, less than half of one per cent of existing seagrass along the southern shore (0.45 per cent) and Botany Bay (0.42 per cent) will be removed as a result of pipeline construction.
Trenching through these seagrass beds would have required a seagrass management plan to be implemented during and after construction, and a compensatory seagrass package involving steps like transplantation. Instead, Sydney Water has chosen to microtunnel the pipeline from its Silver Beach construction area under Botany Bay for a distance of about 800 metres in order to protect the seagrass.
The Water Delivery Alliance will join the single 1,800 mm diameter pipeline from Silver Beach to the twin 1,400 mm diameter pipeline about 800 metres from the shoreline, and (as always) protection of the environment will be a key consideration. Pit construction is nearing completion at the Silver Beach site. This pit is supported by secant piling, has internal jet grouting and is around 10 metres deep. Land-based sections of the pipeline will be constructed first. Material that has been dug up from the pit is being used on site, where possible, in order to minimise truck movements. Continual water quality monitoring is carried out around the Silver Beach construction area. Recent monitoring of the site has indicated good water quality conditions, with similar results both inside and outside the silt curtain.
A TBM is also an essential tool to minimise disruption onshore. The bore passes beneath Tasman and Dampier Streets, Kurnell for the water delivery pipeline. The model shown is a Herrenknecht earth pressure balance and AVN machine, weighing approximately 100 tonnes.