A conservation group is preparing to unveil an 18th century garden folly.

Friends of Carshalton Water Tower have restored the sham bridge – which is designed to act as a dam, but has the facade of a bridge – after two years of fundraising.

Jean Knight, 72, honorary deputy chairwoman of the Friends of Carshalton Water Tower, said the mock bridge was built sometime in the 1750s and restoration was mainly to its three arches.

She said: “A folly is an attraction you would have put in your garden to make it look interesting. The 18th century didn’t have so many flower beds.

“They tended to have a landscape in which they would put a little gazebo or a little ruined castle or part of a little abbey.

“This sham bridge was built at the end of the lake bed. The water never ran through it at any point.”

The water tower is a unique Grade II listed early 18th century garden building and provided water for 17th century Carshalton House and the fountains in it gardens.

It was built between 1716 and 1721 for Sir John Fellowes, the sub-governor of the South Sea Company.

The tower itself rises from the middle of a suite of ground floor rooms and is decorated with a curved parapet and blind arcading below it, with stone pinnacles and urns topping the angle buttresses.

The tower once held a large lead water tank, which was filled with water pumped up from the engine room below.

The engine room once held an engine pumping spring water up from a well under the floor, but was replaced in the 19th century by a cast iron waterwheel.

The bridge will be unveiled by Michael Symes, a garden historian, writer, lecture and trustee on Saturday at 3pm.

Mr Mark Girouard, architectural historian lecturer and writer, will also attend as will MP for Carshalton and Wallington Tom Brake.

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