New York’s sewer upgrade plan offers a comparative case for London’s flood resilience

New York City’s Department of Environmental Protection is working on a new strategy to upgrade the city’s sewer system after successive flash floods overwhelmed the network. Speaking to PIX 11, a spokesperson said the agency is combining sewer upgrades with “underground stormwater storage, rain gardens, and bluebelts that capture and hold rainwater before it enters the sewer system.”

The announcement follows two recent storms that flooded parts of Brooklyn, Queens and Manhattan, closing the Long Island Expressway and damaging homes. New York’s sewer system is designed to handle 1.5 to 1.75 inches of rain per hour; short, intense downpours now regularly exceed that threshold.

For London, the story is strikingly similar. The capital’s Victorian sewer network, built by Joseph Bazalgette in the 1860s, was designed for a population half today’s size and for far less intense rainfall. Combined sewer overflows (CSOs) discharge untreated sewage into the Thames roughly 40 times a year, according to Thames Water’s own data. The £4.5 billion Thames Tideway Tunnel, due for completion in 2025, is designed to capture and store 1.6 million cubic metres of sewage and stormwater, but it addresses only the central London CSO problem. Surface water flooding – which affects tens of thousands of properties – is handled by a patchwork of sustainable drainage systems (SUDS) and local authority schemes.

Key facts

The parallel is not exact. New York’s system is a combined sewer (stormwater and sewage in one pipe), while London’s is mostly combined but with separate sewerage in some newer suburbs. Both cities, however, face the same structural problem: a century‑old network sized for a climate that no longer exists.

What the NYC plan means for London readers

The New York approach is notable for its emphasis on multi‑benefit infrastructure. Bluebelts – stream corridors that are restored and used to convey runoff – are similar to London’s “blue‑green” network, which includes the River Wandle, the Regent’s Canal and the restoration of the River Quaggy. Rain gardens, which are shallow planted basins that soak up runoff, are being piloted in several London boroughs, including Camden and Islington, but rollout remains slow.

The key difference is scale and funding. New York’s DEP is a single agency with a dedicated capital programme. London’s drainage is split between Thames Water (sewerage), the Environment Agency (flood risk), the GLA (strategic planning) and 32 boroughs (local drainage). Coordination is improving through the London Drainage Programme, but the fragmented governance means that large‑scale SUDS deployment is often held up by ownership, maintenance and funding disputes.

The NYC floods also highlight a growing risk that London planners must account for: back‑to‑back storms that leave no time for the system to drain. The London Climate Change Partnership projects that summer rainfall intensity could increase by 30% by 2050. The 2021 floods in London, which submerged parts of the M25 and flooded homes in Chiswick and South Kensington, were caused by a single storm that dumped a month’s rain in a few hours.

What remains unclear

The source for this story is a single press article. No official NYC DEP plan documents or consultation papers have been published yet. The details about underground storage volumes, timelines and costs are not yet available. For London, the Thames Tideway Tunnel is already under construction, but its impact on surface water flooding is limited to the central CSO system. The GLA’s Green Infrastructure and Water Management Strategy, published in 2024, sets out a vision for a “sponge city” approach, but implementation relies on borough planning decisions and developer contributions.

The NYC announcement serves as a useful comparative case for London’s own drainage planning. The combination of grey infrastructure (sewer upgrades) and green infrastructure (rain gardens, bluebelts) is the same blend that London’s drainage engineers are promoting. The open question is whether London’s fragmented institutional landscape can deliver that blend at the speed and scale required.

Source: Planetizen News, “NYC plans sewer upgrades after back-to-back floods,” 24 July 2026. https://www.planetizen.com/news/2026/07/138063-nyc-plans-sewer-upgrades-after-back-back-floods