The Wandle Trust is embarking on an exciting new project to research and understand the source of the river and how it has moved over time.
The River Wandle, Beddington Park in early spring
What is the source of the Wandle?
The source of the River Wandle is found where two rocks – chalk and clay – meet. This occurs in our local area along an east to west to line starting in Croydon, going through Wallington and Carshalton to Esher.
A simplified geological map of North East Surrey
Chalk makes up the North Downs, shown in light blue on our simplified map. Chalk has the capacity to allow water to flow through it so when rain falls it soaks into the rock as if it’s a sponge. As a result the water builds up within the chalk to create huge underground reservoirs called aquifers.
Overlaying the chalk is clay – shown in dark blue on our simplified map. Unlike chalk, clay does not allow water to flow through it. As a result rainfall flows across the surface of the clay rather than flowing down in to it.
Our east-west line marks where the chalk and the clay meet. Along this line any water held in the chalk aquifer is forced to come to the surface, creating the spring sources we know and love on the Wandle.
How does the source of a river move?
The sources of the River Wandle has changed its position over time.
One theory suggests that the River Wandle once started near the village of Merstham in Surrey (south of the M25!) but was ‘captured’ by the River Mole. This is going back to the time when the climate was a lot colder than it is today – back in the Ice Age when mammoths were strolling around your back garden.
We do know from the shape of the North Downs – (the hills that now separate Merstham from Carshalton and Croydon) – that they have been shaped by water action. Look at the ‘dry valleys’ around Woodmansterne, Coulsdon and Caterham.
Happy Valley near Farthing Downs, Coulsdon showing a typical ‘dry valley’ on the North Downs
Back in the Ice Age the climate was very different to what we have today…
Imagine where we live today looking more like the Alaskan tundra – sub-zero temperatures, freezing cold arctic winds and most importantly frozen ground. The chalk, which today allows water to flow through it, was then permanently frozen (called permafrost). When snow and ice melted in the summer, the rocks and soil could not allow the water to flow down through them. The water flowed across the land surface instead, and eroded the ‘dry valleys’ we can still see today.
But the story doesn’t end there – because we’re all still having an effect on the position of the Wandle’s spring line.
People use water. Where does our water come from? From those underground aquifers of water caught inside the chalk.
As there are now more and more people using more and more water, it is being taken out of those underground reserves. What happens next? Instead of water bubbling out all along our west-east line in many places the springs have simply dried up as water is ‘over abstracted’ from the underground aquifer.
People have also built houses, roads and factories. As a result our east-west line has disappeared under concrete – the river is now flowing underground under all this stuff.
Go to Wandle Park in Croydon and you can see efforts to bring the River Wandle back to the surface where it was previously culverted under the park.
An Autumn Scene – The River Wandle in Wandle Park, Croydon
So we know that the source of the River Wandle has changed over time, and is still continuing to change – some of these changes are natural (ice age, permafrost, mammoths) whilst others are not (abstraction and concrete).
Will it change in the future? Who knows? Very likely, some would say – our population of people is likely to increase, so we’re going to need more houses and roads and need more water. We think too that the climate is changing – what impact will this bring to the source of our local river?
Who remembers the floods in Purley back in 2014? Is this a sign of the future?
Discovering the Source of the Wandle – The Project
The Wandle Trust will work with local volunteers to research the source of the River Wandle and how it has changed over time – this will include using archived material, geological maps, photographic evidence and oral histories. The project will use resources in libraries and other local sources.
How can you help?
Contact Project Officer David Gill to show your interest. Let him know your particular areas of interest and any areas of relevant skills and knowledge you might possess.
David can be contacted at firstname.lastname@example.org or you can call his mobile on 07468 529 312.
Do keep looking for updates on our Wandle website (www.wandletrust.org) and Twitter: #DiscovertheSource
The project is funded through the Living Wandle Landscape Partnership, a Heritage Lottery Funded scheme aims to bring people closer to their local river.