Redbridge Expands Underground Hydrorock System to Reduce Flood Risk 2026

Key Points

• Redbridge Council has expanded the implementation of an underground “sponge” drainage system known as Hydrorock beneath key roadways to mitigate flood risk.
• Installations have been placed in High Road, Seven Kings; Claybury Broadway, Clayhall; and Tomswood Hill, Barkingside—locations selected due to their severe history of surface water flooding.
• The expanded installations form part of a wider £11 million, 10-year capital investment plan by Redbridge Council aimed at strengthening regional flood defences.
• Councillor Jo Blackman, Cabinet Member for Environment and Neighbourhoods, highlighted that the system provides a sustainable, practical solution as extreme weather events become more frequent.
• The newly fitted Hydrorock blocks can temporarily hold approximately 426,000 litres of stormwater (equivalent to 2,400 household baths), bringing the borough’s total rainwater storage capacity across all flood measures to over 2.2 million litres.
• Sections of the affected roads have been resurfaced with permeable paving to optimize water absorption directly into the underground system.
• Led by the council’s highways team, the broader flood management programme has also introduced six rain gardens across Clayhall, Woodford, and Hainault to mimic natural drainage.

Redbridge (East London Times) October 14, 2026 – Redbridge Council has expanded its deployment of an innovative underground subterranean “sponge” drainage system to mitigate surface water flooding and safeguard local homes and commercial properties. The advanced Hydrorock attenuation technology has been installed beneath major road networks across High Road in Seven Kings, Claybury Broadway in Clayhall, and Tomswood Hill in Barkingside, all of which have historically suffered from severe flood incidents during intense rainstorms. The initiative operates as a key component of the local authority’s £11 million, 10-year strategic investment plan designed to modernise public infrastructure and fortify flood defences borough-wide.

How Does the Hydrorock Technology Mitigate Local Flood Risks?

The Hydrorock system functions as a high-capacity underground sponge, absorbing surface water run-off during heavy rainstorms, storing it temporarily in sub-surface retention units, and releasing it at a controlled rate into the municipal drainage network. By regulating the flow of rainwater, the system prevents sudden surges from overwhelming the sewer infrastructure, which has historically been the primary catalyst for severe road flooding across the borough.

To support the structural performance of the underground blocks, key sections of the affected highways have been resurfaced with permeable paving. This porous surface allows surface water to filter directly through the road layer and into the subterranean Hydrorock system beneath. The latest scheme additions are capable of temporarily retaining approximately 426,000 litres of stormwater—an attenuation capacity equivalent to 2,400 standard household baths. Combined with existing flood mitigation structures across the borough, Redbridge Council can now retain and gradually release over 2.2 million litres of rainwater during storm events.

What Are Local Authority Leaders Saying About the Infrastructure Investment?

As reported by Robyn Bennett of the Ilford Recorder, Councillor Jo Blackman, Cabinet Member for Environment and Neighbourhoods at Redbridge Council, emphasised the authority’s commitment to climate resilience. Cllr Blackman stated:

“Hydrorock is just one of the ways we’re helping protect homes, businesses and communities from flooding. As extreme weather becomes more common, we’re investing in innovative and practical solutions that strengthen our flood defences, reduce local flood risk and help build a more resilient Redbridge for the future.”

The rollout of the subterranean sponge modules forms part of a broader, multi-faceted flood management strategy directed by Redbridge Council’s highways team. Alongside the underground engineering works, municipal teams completed the construction of six specialized rain gardens across Clayhall, Woodford, and Hainault earlier this year. These rain gardens utilize engineered soil beds and native vegetation to slow surface runoff, mimicking natural hydrological drainage processes to divert surface water from overburdened drainage networks. Additional engineering projects are set to be introduced under the local council’s long-term Flood Risk Management Strategy and Surface Water Management Plan.

What Is the Background of Flood Management in the London Borough of Redbridge?

The London Borough of Redbridge, situated in East London, has faced systemic surface water flood challenges driven by urban density, expansive impermeable road surfaces, and low-lying topography. The urgency for municipal intervention heightened following the severe flash floods of July 2021, which caused extensive property damage and commercial disruption across several urban centres in the borough. In response, Redbridge Council established its Local Flood Risk Management Strategy and Surface Water Management Plan, committing £11 million over a 10-year period to overhaul drainage infrastructure.

To address localized flood points where space beneath roadways is limited by existing underground utilities and tree roots, the council trialled sustainable drainage systems (SuDS) such as Hydrorock technology on High Road in Seven Kings. Unlike traditional plastic soakaway crates or massive subterranean concrete holding tanks, natural basalt stone wool blocks fit around underground utility networks without requiring extensive land acquisition or reducing valuable street parking. Coupled with rain gardens and permeable paving, these ecological engineering projects form a layered defence system designed to manage surface water runoff before it impacts local infrastructure.

How Will This Flood Defence Development Affect Local Residents and Businesses?

The expansion of the Hydrorock drainage scheme is expected to yield significant physical and economic protection for local residents, property owners, and business operators across Redbridge, particularly in high-risk zones like Seven Kings, Clayhall, Barkingside, Hainault, and Woodford.

• Business Continuity and Economic Security: Local traders and high-street business owners on High Road, Seven Kings, and Claybury Broadway will benefit from reduced risk of flash flooding during sudden cloudbursts. In prior years, localized surface flooding caused severe financial losses through structural damage, inventory destruction, temporary shop closures, and reduced footfall. The increased capacity to store 426,000 litres of stormwater reduces the likelihood of emergency closures and structural repairs.
• Property Protection and Insurance Stability: For residential homeowners in historically vulnerable locations, the reduced probability of sewer surcharging and surface water runoff entering ground-floor properties offers greater peace of mind. Over time, verified local flood alleviation measures may assist residents in maintaining lower property insurance premiums and protecting property values that were previously vulnerable to recurrent flooding events.
• Minimized Travel and Infrastructure Disruptions: Motorists, public transport operators, and pedestrians using major arteries such as Tomswood Hill and Seven Kings High Road will experience fewer road closures, hazardous standing water pools, and traffic delays during periods of heavy rainfall.
• Environmental Health and Community Resilience: By controlling stormwater surges, the system reduces the likelihood of contaminated sewer overflows discharging into local streets and nearby watercourses. Residents gain a cleaner, more resilient urban landscape supported by complementary natural drainage features like rain gardens, enhancing both public health safeguards and local biodiversity.