Leadenhall Street Transformation

Leadenhall Street is one of the City of London’s most heavily trafficked east-west corridors. In its existing state it drained entirely unrestricted and untreated to the combined sewer, with zero percent of runoff benefiting from any blue-green infrastructure. A proposed public realm transformation offered the opportunity to change that fundamentally. EGY carried out a streets-wide assessment of blue-green infrastructure opportunities along the full 450-metre corridor, commissioned by the City’s Transport and Public Realm team ahead of detailed design.

The starting point was evidence. EGY coordinated a programme of ground investigations along the full 450-metre length of the corridor, testing subsoil infiltration rates at intervals throughout. The results were overwhelmingly positive; we found the ground has significant capacity to support infiltration. This intern unlocked the potential to re-direct how surface water was disposed of for an entire catchment.

Building on that evidence, EGY developed a blue-green infrastructure opportunities proposal centred on rain gardens and SuDS tree pits. If enacted, the scheme could intercept up to 3.5 million litres annually, removing it from the combined sewer system entirely. That is water currently overloading Victorian infrastructure and contributing to combined sewer overflow discharges downstream during rainfall events.

What the analysis showed

The corridor had more viable SuDS locations than initial desk studies suggested. Infiltration rates varied considerably along the route. The analysis also confirmed that the landscape, once established, would be entirely self-sustaining in terms of irrigation demand. No ongoing irrigation means no operational cost and a lower embodied carbon outcome for the scheme. EGY quantified the co-benefits, establishing that canopy cover and evapotranspiration would provide ground-level cooling of 1–4°C, vegetation acting as a barrier to intercept traffic pollution and reduce particulate matter, and carbon sequestration accumulating as the landscape matures. These figures make the business case for investing properly in nature-based infrastructure rather than accepting the minimum.

The assessment was delivered to the City of London Corporation to inform the evolving scheme design. Every figure is grounded in the specific subsoil conditions, catchment area, and planting palette proposed for this street – not aspirational, but evidenced. The result is a compelling case that positions Leadenhall not just as a resurfaced road but as a future-proofed green urban corridor.