We’re gonna need a bigger pump!

Landmark Trees just helped clients successfully discharge conditions on a difficult planning consent for a large basement extension in St John’s Wood. Trees and development are never a simple pairing where space is at a premium, and this proposal was more than complicated by the possibility of the River Tyburn turning up in the applicant’s basement. The infamous Tyburn is one of London’s various lost historic rivers, which winds its way from source on Hampstead Heath, through Regents Park, past the old gallows site, onto Westminster, and Vauxhall Bridge beyond, “weaving black melancholy as a net,” according to the poet, Blake. That melancholy perhaps explains the relative profusion of weeping willows in an otherwise landlocked enclave.

How exactly do you put a basement across a river though, especially when there are more flood-sensitive tree species directly upstream? The problem only came to light when digging a trial trench to ascertain the presence or not of roots on site from a neighbour’s rather fine, overhanging copper beech. The deep trench kept filling up with water before the local authority Tree Officer could inspect it. For Blake, all this world’s woe stemmed from a poison tree, first nourished in the Tyburn water. One might have forgiven the applicant for sharing the poet’s sentiment. In reality, it was fairly unlikely a shallow beech would be rooting under such mournful conditions or to such profound depths, though we certainly didn’t want to aggravate the situation.

Trouble was, with space at a premium, how do you install additional / extreme drainage without cutting back on basement or Root Protection Area? Even installing over the slab threatened to reduce the landscape soil provision. In the end, we consulted with a hydrologist (not a poet) to trace the path of least resistance between soil and tree roots with extensive site investigations, using an airspade (and very large pump!), and so reassuring the local authority mitigation could be delivered without impact on tree health. We even designed a bespoke crash-deck to sit beneath the canopy and protect the branches from the above ground installation. As always, the success of the proposals will depend upon site monitoring and supervision, which has been factored into the conditions. We look forward to seeing the scheme develop successfully and the Tyburn sent on its way again.