The Pressure is Rising
Or at least it will be soon, when Geomarine have successfully finished replacing the Archimedes screws deep inside the belly of the Baudrette Brook pumping station that sits anonymously atop the Dicq slipway by Havre des Pas. Adjacent to the public loos, you probably haven't noticed it before (I certainly hadn't), the only giveaway that there's more going down than, well, I'll leave that to your imagination, is the chimney protruding from the building into the skyline.
The chimney itself, now a listed structure, is a relic from the facility in its original incarnation, where a coal-fired steam turbine was used to turn the screws (pictured page right) before the site was converted to use electric motors – but this year marks the first time since the 1960s that the screws themselves have been replaced. So what exactly are they, and what purpose do they serve?
The Baudrette Brook runs just behind the site, collecting surface water from as far as the golf course in St Clement, and this water flows directly out to sea at times of low tide. When the tide is up, however, the water pressure isn't sufficient to allow the brook's water to counteract the pressure from the seawater acting upon the gate at the end of the outflow pipe that runs underneath the Dicq slip, because it's submerged. To find a solution to this relatively infrequent but far from trivial issue, which required solving to prevent floodwater engulfing the properties in the area, the engineers who originally devised the plant decades upon decades ago turned to technology from even further in the past. Technology from around the year 240BC, in fact.
Believed to have been invented to remove water from the bilge of the ship Syracrusia, named after his home town and the largest vessel ever to have set sail at the time, the design of the gigantic metal 'screws' pictured here was the brainchild of Archimedes, a Greek mathematician, physicist, engineer, inventor and astronomer. These days I’m sure his Instagram account would also list social influencer, and I've no doubt he dabbled in other pastimes, but those are said to be his main focuses. Thousands of years later, his invention is still being put to use for its effectiveness and reliability.
When the water level in the brook reaches a high enough level, a float switch activates the control system and in turn one screw begins to turn. This lifts water to a higher level, causing a greater head of water behind the outflow gate and therefore higher water pressure – high enough to counter the force of the sea holding the gate back and allowing the surface water from the brook to flow into the sea, rather than flooding the land between. When the heavens are fully open, another float switch commands both of the 10.5 metre-long screws to turn simultaneously, allowing them to move a staggering 735 litres of water five metres vertically every second. Yes, every second. That might sound like overkill, considering the facility generally operates in brief stints of between ten and thirty minutes at a time, but that's exactly what it takes to mitigate the risk of flooding when mother nature is causing the water to flow from both above and below the outlet simultaneously.
Unlike the original, corroded and eroded screws that they've replaced, the new screws have been engineered to grease themselves and should remain serviceable for another 100 years, according to the specialist UK contractor who chimed in during my visit. This means that once the concrete has set, the ceiling is reinstalled and the brand new sluice gate opened, the site will go about its business with very little need for physical maintenance for a good while yet – especially as the control panel has been updated to provide live data wirelessly to those who need to know what's going on.
This project is part of a coastline protection initiative in response to rising sea-levels, and has also served to consolidate the control systems of other pumping stations in the area to increase efficiency. I'm told that good old Archimedes' screws have been put to work across the island, but these are by far the largest ones. It just goes to show, that for all of humanity's technological advancement, especially in the last 100 years, sometimes the most effective solution can be found within the pages of the history books. Although said history books have probably been digitised by now, in the interest of efficiency.
As featured in issue 164 of Gallery magazine published 1st July 2019. www.gallery.je
Words and images written, shot and edited by Russ Atkinson (not to be reproduced without permission).