Giant new screws take a turn at keeping floodwaters at bay
TO most Islanders it may just appear to be an obscurely-shaped industrial building...
And to others it is one of Jersey’s most highly regarded unofficial skateboarding spots.
But under a number of sloping paving slabs beside the Dicq Shack lie two 32-foot-long rotating screws – essential for protecting a large swathe of land in the the east from flooding.
And after being in place for around 50 years, the two 5.5ft wide devices – capable of moving 735 litres of water every second – were replaced during a three-month long operation.
Georgina Durell, civil engineer for Geomarine, who have been contracted to carry out the works on behalf of the government, said that the screws were linked to Baudrette Brook, which stretched as far as St Clement’s Golf Course.
‘At low tide, the water from the brook goes out to sea through a channel which has a tidal valve at the end,’ she said.
‘On high tides [above nine metres] the valve on the channel closes and the brook can back up, depending on the rainfall.
‘This triggers the pumps [screws] to come on and, with the pressure, forces the valve open. They were invented by Archimedes in the third century [BC] and the technology has not changed – they are still one of the most effective ways of moving water.’
Many large, essential pieces of infrastructure around the Island, such as the desalination plant, back-up generators at La Collette and Queen’s Road and the storm gate at Elizabeth Marina are used relatively infrequently. However, the same cannot be said for the pumping station and at least one of the Archimedes screws had to remain in place for the duration of the project – and were activated a number of times during the works.
Other flood prevention systems around the Island include a 25-million-litre cavern some 25 metres underneath Snow Hill car park.
At times of heavy rain, surface run-off from across much of town runs into the cavern, where it can be stored before being pumped to Bellozanne for treatment.
This prevents thousands of litres of untreated water entering the sea.
And following a deluge in 2010, a large number of businesses around West’s Centre and Beresford Street were forced to close temporarily after their premises were completely flooded.
Following this, a £5.6 million 24-metre-deep shaft was constructed below the former Ann Court housing estate – on the corner of Charles Street and Providence Street – and a tunnel was bored, connecting sewers in the area to the cavern.
Similar shafts are also in place at the Weighbridge, Gas Place and Snow Hill.