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Under sea job kicks off: Wastewater plant

Some projects are trickier than others – and one about to start has a bunch of elements that will make it interesting: pipe “strings”, boats, dive squads; wastewater and a very real reliance on good weather.

And then there is the fact that the work area will impact on a road, a small section of a limestone walk and cycleway, and a bridle path for a short time. All of this means that a great deal of planning has been completed before the physical works started this week.

The near $3 million project will see the replacement of the 300 metre diffuser attached to the end of the 2.5 kilometre pipe which carries Hastings treated wastewater out to sea. The diffuser ensures that not all the water leaves the pipe in the same place.

The old one has reached the end of its life – in fact it has lasted a great deal longer than originally expected, said Hastings District Council’s asset group manager Craig Thew.

It was installed in 1981, and is inspected every year. It had been due for replacement in 2006 but inspections showed it was standing up well to the underwater conditions so had lasted a great deal longer.

Installing the new one will be a tricky operation. Firstly almost one metre diameter pipes will be welded into two strings of 150m long. They will then be loaded onto rollers along Richmond Rd and inched over the stop banks to the water’s edge. From there the first string will be towed out to sea using four boats and then slowly submerged so it is in the right place to be attached to the outfall pipe. The second diffuser pipe will them be towed out to the end of the first, and submerged.

The submersion is an intricate operation of its own; needing to be done slowly, allowing gentle angles can be maintained so there is no risk of the pipe being damaged.

Once the new pipe is in place, the contractors have a two hour window in which the wastewater plant can be switched off to allow the changeover to the new diffuser. That will also not be easy, as there is little to no visibility for the divers in that area, because of very fine sediment that clouds the water. The dive teams will practice on dry land “to get the hang of it”, said Council’s wastewater manager David James.

The work will mean that Richmond Rd will need to be closed at times during the construction of the diffuser, and for about five days as the pipe is moved to the sea edge. That closure will also affect the cycleway along the top of the stop bank, and the bridle path on the seaward side of the stop bank. Alternative access ways and detours will be sign posted.

Council asks that people show patience during this time, as staff and contractors work to enable the management of wastewater with as little disruption as possible.

4 October 2017

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