Redbridge Council rolls out innovative Hydrorock flood defence technology following successful trial
Published: 16 September 2025
After the successful use of Hydrorock in Seven Kings, Redbridge Council has rolled out the advanced flood defence technology to further locations to reduce flood risks in the borough
The Hydrorock system was first trialled in Seven Kings High Road last year, with positive results. Since its installation there has been no flooding at the site despite heavy downpours.
Its success has led to further roll out of the Hydrorock system at Hermon Hill and Wellesley Road in Wanstead Village – locations identified as potential flood risks due to previous episodes of flooding, including for those living in local basement flats.
Acting like a sponge block, the Hydrorock blocks were placed under the road that connects to the gullies to rapidly absorb and hold water from heavy rainfall, which is then gradually and slowly released into the sewer system. This prevents the sewer system from becoming overwhelmed from sudden surges of water from heavy rainfall - one of the main causes of road flooding.
In addition to the underground flood defence works, sections of the road were also re-surfaced with permeable paving to further help absorb rainwater off the road and into the underground Hydrorock blocks.
Redbridge Council is also liaising with Thames Water regarding the progress of their works to fix a defective sewer in Hermon Hill to further reduce flood risks to homes and businesses in the area, who were previously impacted by flooding. This is a critical element to reducing flood risk in the area as Council drains connect to Thames Water sewers, so if the sewer is defective water could surcharge back out onto roads and properties because it has nowhere else to go.
Flooding remains one of the most disruptive and distressing experiences that any resident, school, or business can face. It can cause extensive damage to homes and public buildings, disrupts lives, and has lasting emotional and financial impact.
With flash floods and intense storms occurring more frequently because of climate change, the borough has ramped up investment in flood defence schemes to help protect local homes and businesses against flooding.
The installation of Hydrorock is part of a more extensive programme of flood alleviation works, led by Redbridge Council’s Highways Team, which has already seen a wide and varying range of flood defence measures installed across the borough.
These include sustainable drainage schemes (SuDS) such as raingardens and adapted planters, which mimick natural drainage processes to slow the flow of surface water entering sewers and drains.
In a further milestone success towards boosting the borough’s resilience to flooding, the Council recently announced that more than 1.6 million litres of rainwater can now be held at one time and diverted away from the local sewer system through the combination of flood alleviation measures that have been installed across the borough.
Put into perspective, 1.6 million litres equate to around 64,000 five-minute showers, or 8,889 council wheelie bins filled with water. This is rainwater that, without intervention, might otherwise have pooled on roads, backed up the Thames Water sewer networks, and flooded people’s homes and businesses.
Cabinet Member for Environment and Sustainability Cllr Jo Blackman said: “Hydrorock is one of a number of measures we’re putting in place to help keep local homes, businesses, and communities safe from flooding. With climate change making extreme weather more likely, Redbridge Council is taking a proactive, practical approach to keep our communities safe, and is committed to continued investment in sustainable drainage systems and innovative technology to boost the borough’s flood defences. The priority is to protect local communities from flooding and build a more flood resilient borough for the future.”
The Environment Agency also recently visited the borough, and was keen to see how Redbridge Council was applying new flood defence technology and other flood prevention initiatives.
After seeing the use of rain gardens and Hydrorock in Wanstead Mandy Sullivan, a local Flood and Coastal Risk Management Advisor at the Environment Agency said: “It was good to see these new flood prevention measures in place. It is clear to see that the London Borough of Redbridge are doing some great work to reduce flood risk.”
Other new flood alleviation schemes are also set to go ahead. It will see further flood risk reduction works in several areas that have previously been prone to flooding, with a focus on Monkhams Lane area, as well as further works in the Clayhall area and to better protect schools that are at risk of flooding in the borough - subject to grant funding approval.
Over the next ten years the Council will be investing just over £11m into schemes that help reduce local flood risks in the borough in addition to £2.5m spent since 2022.
For information on staying flood aware, go to the council’s flooding web page on: https://www.redbridge.gov.uk/flooding
