Thursday, 5 August 2010

Dunoon Waste Water Improvements

Previously shown in June were a couple of images of the little tug SAMSON and a length of prefabricated outfall pipe being towed from Sandbank to the new waste water treatment works under construction a mile south of Dunoon. This selection shows another of the pipes being put into position at the Milton Burn Pumping Station between Kirn and Dunoon. This outfall pipe is larger than others and will also act as a storm overflow pipe in periods of heavy rainfall. Screens will be fitted to minimise the environmental impact of storm overflow discharges to the East Bay.

A trench has been dug on the seabed by the long-reach excavator working from the jack-up platform, moved further out from the shore as required. The next length of pipe, meantime, had been prefabricated at Sandbank and brought round by SAMSON. Complete with pre-cast concrete blocks, the pipe weighs around 400 tonnes and is sealed at each end with blanking plates, allowing it to float.

With the pipe in position, the air contained within the pipe was allowed to escape from the landward end, while valves on the seaward end were opened which then allowed seawater to flood into the pipe. As can be seen, the far away end of the pipe then began to sink slowly to the seabed.

As the pipe settled into the trench, the little tug/workboat THE NOO made sure that it was aligned correctly. Once on the bottom, the pipe is to be covered with concrete mats and the spoil that was dug out will cover that too. Details of the project can be read here.