Flowing with wildlife: what for years was a mostly dry, grassy trench in Carshalton Park has now become a haven for wildlife
Where does all that rainwater go from one of the wettest years on record? Well, in the catchment area of the River Wandle, as ANDREW FORD, left, has discovered, it has been taking up quite a bit of Carshalton Park
After the exceptional heavy rainfalls of the last year or so, the stream bed in Carshalton Park, normally dry, is filled with water.
The stream will originally have been a “winterbourne” which would fill with water in winter and dry out in summer, and formed one of the sources of the River Wandle.
Winterbourne: the channel in Carshalton Park has become a vital overflow since the local flooding in 2014
In the 18th Century, it was dug out as an ornamental canal for a large house or mansion that was planned for the park.
Usually it is seen as a shallow grassy channel. But this spring, and often during the past couple of winters when the rains have been heavier than previously, it has been full, looking like a flowing stream or river.
This reflects the geology of the Carshalton area, which sits on the join between the chalk of the North Downs and the London clay of the Thames basin. Rainwater percolates down through the chalk, but when it hits the clay, it emerges as springs, streams and bournes.
The series of historic villages, now suburbs like Beddington, Wallington, Carshalton and Sutton, owe their existence to these springs, which provided very pure water due to its long journey through the chalk.
In more recent times, due to excessive extraction of water by the water companies, many of these springs have dried up, or else only appear every few years. The Carshalton stream was last in water in 2021, and before that it was seven years since it last occurred, when it was utilised as emergency water storage when nearby areas, like Purley and Kenley, were suffering flooding from their overflowing bournes.
The Grotto: Carshalton’s is thought to be one of the earliest in this country
The Environment Agency monitors water table levels and has had a “localised flooding” warning for the area of the Caterham and Coulsdon bournes and the River Wandle valley for most of this year so far. Only in the past week, according to the EA, have water table levels begun to drop.
The source of the Carshalton Park stream lies in “The Grotto”, an interesting structure that lies at the southern edge of the park. It is formed as a brick-built horseshoe with iron grills for the water to flow out from, and behind them, culverts lead into the chalk for around 20 metres to collect the water.
In the past, the Grotto was highly decorated with tiles, shells and statues, parts of which remain today. Carshalton’s is one of the earliest ornamental grottoes in the country.
All this was built for the Scawen family, who were rich gentry in the area in the 17th and 18th centuries.
Free flowing: after works at Carshalton Ponds and the very heavy rainfalls, Carshalton Park’s water features have helped reduce the risks of flooding
They intended to build a palace on their land, but in 1720 they lost all their money in the South Sea Bubble, one the earliest capitalist crises, perhaps the first stock market crash.
The mansion was never built, except for The Orangery which sits just south of Carshalton High Street, the Grotto and the landscaped stream we see today.
The Scawens also planted the impressively huge sweet chestnut trees dotted along the western edge of the park, which are now just over 300 years old. The largest of them have a circumference of more than 20 feet.
When unwittingly creating our humble, modern-day park, the Scawens could have had little notion that some of their installations would one day provide vital infrastructure for coping with the extremes of weather in our changing climate.
Read more: Purley and Coulsdon might be set for new Bourne adventure
Read more: Going Underground: Purley underpass used as flood overflow
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An absolutely joyous read, thank you very much. I’ll take great joy in spouting new facts to my wife the next time I point at the new streams.