Author Topic: The Gorrell Tank Whitstable  (Read 3185 times)

Offline stuartwaters

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The Gorrell Tank Whitstable
« Reply #1 on: August 05, 2023, 09:34:19 PM »
Those who have visited Whitstable will be aware of the large car park by the harbour known as the "Gorrell Tank". You may also be aware of the fact that the ar park is built on top of a large tank and that the tank is managed by Southern Water. People may not be aware of the fact that the tank is suffering with significant structural problems. It would be easy to point the finger of blame for this at Southern Water, given the negative publicity the Company has attracted recently and the delapidated state of the Pump House at one end of the tank. Much of that negative publicity has been self-inflicted, but it's not entirely fair to blame Southern Water for the problems at the Gorrell Tank. Those problems have been ongoing for a great many years and the purpose of this article is to explain how the area has suffered with a litany of problems going back for almost 200 years.

The Gorrell Stream rises near Duncan Down, on the outskirts of modern-day Whitstable, and flows to the harbour. In a map dated 1757, it is shown as flowing through a marsh known as the White Marsh, meeting the sea in a place known as "The Outletts" to the east of the modern harbour.

In the late 18th Century, the White Marsh was drained for farmland, river defences were built and the Gorrell Stream itself was straightened to try to control tidal flooding.

In the 1830s, the harbour we know today was built, but almost as soon as it was completed and opened to shipping, it began to suffer with silting.

In the 1840s, a solution was devised and a large reservoir was built behind the harbour which was fed by the Gorrell Stream and by the high tide. The purpose of this was to release the water at low tide so that the flow from the reservoir would scour the harbour and wash the silt back into the sea. Penstock valves were built, which would be opened at low water allowing the tide to fill the reservoir and then closed. They would be opened at low water, allowing the water in the reservoir to escape.

The problems began when the town of Whitstable began to expand and the newly-built properties began to discharge their sewage into the Gorrell Stream. Eventually, the Gorrell Stream and the reservior, known by now as The Backwater became a stinking putrid mess. The problems grew worse when the farmland created by draining the White Marsh was built over. When periods of heavy rain coincided with high tides, the reservoir overflowed and flooded the entire area.

In the early 20th Century, the Gorrell Stream was enclosed by a culvert, but the problem with the unsanitary reservoir remained. When heavy rain fell, instead of soaking into the farmland, it was now running off roofs, footpaths and roads, overloading the Gorrell Stream and further flooding the area behind the harbour. A new solution was needed.

In the late 1960s into the 1970s the Backwater was itself rebuilt and was converted into the large tank we know today, with a large pumping station at one end to take the excess water away and pump it to the Sewage Works at Swalecliffe.

In the mid 2010s, Southern Water, now responsible for the management of the Tank, engaged with contracctors to have 40 years worth of silt and debris removed from the tank and this was where the structural problems with it were found. The contractors found that numerous columns supporting the car park on top of the tank had blown and were damaged by corrosion in the steel reinforcing inside the concrete.

What is happening at the time of writing is that contractors are performing a detailed survey of the state of the whole tank. Concrete dust samples are being taken from all the columns and this will be sent off to a lab so that the salt content of the sand forming the concrete can be determined. There is a suspicion that the concrete was mixed using unwashed, dredged sand, taken from sandbanks in the Thames Estuary and that the salt in the sand had attacked the steel reinforcing causing corrosion. This corrosion has blown out the concrete. Samples are also being taken from the concrete roof and cracks are being explored to see how deep they are. Samples also need to be taken from the floor slab but that can't be done until the tank is cleaned out again. That process will begin soon and once all the results are in, Southern Water can then decide what to do. By way of a precaution, all the columns inside the tank have been reinforced by substantial scaffolding.

This excellent website gives a history of the area:

https://kentishstour.org.uk/wp-content/uploads/2022/01/gorrell-stream-panel-final-draft2.pdf

This page on the Kent Messenger gives details of when the damage to the Gorrell Tank was discovered:

https://www.kentonline.co.uk/whitstable/news/strange-items-found-under-whitstable-19364/

"I did not say the French would not come, I said they will not come by sea" - Admiral Sir John Jervis, 1st Earl St Vincent.