Following concern over the water levels at Carshalton Ponds, this update explains what we are doing and who we are working with to help restore the water levels.
SES Water aims to continue providing a reliable and sufficient supply of safe, high quality drinking water. To ensure their customers in the Carshalton and Sutton areas are kept supplied with water, they have a licence with the Environment Agency to extract water from the North Downs chalk aquifer. The chalk geology of the North Downs is also a primary source of the River Wandle. Part of their licence agreement with the Environment Agency is that they ensure there is enough water in the River Wandle to sustain the many species of insects, birds and fish in the river which need flowing water.
When the aquifer is low and the springs are not flowing, they turn on an artificial recirculation system which pumps water from the Wandle – just north of Goat Bridge – up to Carshalton Ponds, which then replenishes the Carshalton arm of the river. Without this system, the Carshalton arm of the Wandle would be dry for much of the year.
The last six months of 2016 were very dry with only two-thirds of the long term average rainfall being received. This means the groundwater levels are currently low for this time of year which has been a major cause of the Carshalton ponds becoming drier in recent weeks. There are also some cracks in the edges and bottom of the ponds, which means that when SES Water pumps water into the ponds, it seeps back into the ground before it can get out of the lower pond and flow down the Wandle. This would cause SES Water to fail their licence requirement in keeping the Wandle flowing. So instead, they have been pumping most of the water straight into the river below the cascade in Grove Park, with a small flow to the ponds to top them up.
SES Water, the Environment Agency and Sutton Council are now working together to plan and deliver restorative works to the ponds whilst levels are low to ensure the ponds can continue to form part of the system to feed the Wandle. These works will be completed as soon as possible to ensure the Carshalton ponds return to their usual state.