From the Wikipedia page [1] The Falconbrook is a subterranean river that flows under Balham and Battersea where it enters the River Thames. school), and the significant valley under Northcote Road in Battersea. The source of the Falconbrook is in Streatham Hill, above Tooting Bec Common, South West London. The springs are in the foundations of the parade of shops on Streatham High Road between the top of Drewstead Road and Broadlands Avenue. During the building of the shops, extra access space was built below the basement floors to accommodate the springs when in full spate. The river flows underneath Drewstead Road, where it may be heard under a manhole above the junction with Woodfield Avenue, before going to the Common.