how Carshalton Park offers an overflow – Inside Croydon

Flowing with wildlife: what for years was a mostly dry, grassy ditch in Carshalton Park has now become a haven for wildlife

Where is all the rainwater going from one of the wettest years on record? Well, in the catchment area of ​​the River Wandle, as ANDREW FORD, left, discovered, it has taken up quite a bit of Carshalton Park.

After exceptionally heavy rainfall over the last year or so, the normally dry stream bed at Carshalton Park is filled with water.

The stream will have originally been a ‘Winterbourne’ which filled with water in winter and dried up in summer and formed one of the sources of the River Wandle.

Winterbourne: the canal at Carshalton Park has become a vital overflow since the local floods of 2014

In the 18th century, it was dug as an ornamental canal for a large house or mansion that was planned for the park.

It is usually seen as a shallow grass channel. But this spring, and often during the last two winters, when the rains were heavier than before, it was full, looking like a flowing stream or river.

This reflects the geology of the Carshalton area, which lies at the junction of the North Downs Chalk and the London Clay of the Thames Basin. Rainwater seeps through the chalk, but when it hits the clay, it comes out as springs, streams and bournes.

The series of historic villages, now suburbs such as Beddington, Wallington, Carshalton and Sutton, owe their existence to these springs, which provided very pure water due to the long journey through the chalk.

In more recent times, due to excessive water extraction by water companies, many of these springs have dried up, or only appear once every few years. The Carshalton Stream was last in water in 2021, and before that it was seven years since it was last used as an emergency water storage when nearby areas such as Purley and Kenley suffered flooding from the cause of their overflow.

Grot: Carshalton’s is believed to be one of the earliest in this country

The Environment Agency monitors groundwater levels and has had a ‘localized flood’ warning for the Caterham and Coulsdon Bournes area and the Wandle River valley for most of this year so far. Only in the last week, according to EA, the groundwater level started to decrease.

The source of the Carshalton Park stream is in ‘The Grotto’, an interesting structure which is on the southern edge of the park. It is shaped like a horseshoe built of brick, with iron grates for the water to flow through, and behind them, channels lead into the chalk for about 20 meters to collect the water.

In the past, the Grotto was highly decorated with plaques, shells and statues, parts of which remain today. Carshalton’s is one of the oldest ornamental grottoes in the country.

All of these were built for the Scawen family, who were wealthy in the area in the 17th and 18th centuries.

Free flow: following works on Carshalton Ponds and very heavy rainfall, water features in Carshalton Park have helped to reduce flood risks

They intended to build a palace on their land, but in 1720 they lost all their money in the South Sea Bubble, one of the earliest capitalist crises, perhaps the first stock market crash.

The mansion was never built except for the Orangery just south of Carshalton High Street, the Grotto and the landscaped stream we see today.

The Scawens also planted the impressively huge chestnut trees dotted along the western edge of the park, which are now just over 300 years old. The largest of them are over 20 feet in circumference.

When they unwittingly created our humble, modern park, the Scawens could have had no idea that some of their facilities would one day provide vital infrastructure to deal with the extreme weather conditions of our changing climate.

Read more: Purley and Coulsdon could be set for a new Bourne adventure
Read more: Underground: Purley Underpass used as a flood spillway

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