Sustainable Drainage Systems

Sarah Dyke Excerpts

Thursday 5th February 2026 Westminster Hall

[Sarah Dyke (Glastonbury and Somerton) (LD)]

It is a pleasure to serve with you in the Chair, Mrs Barker. I congratulate my hon. Friend the Member for Newton Abbot (Martin Wrigley) on securing this debate and on his excellent and knowledgeable speech. I also point to the important intervention made by my hon. Friend the Member for Honiton and Sidmouth (Richard Foord) about developers using up-to-date datasets.

In Somerset, management of water is essential. My constituency is frequently impacted by extreme weather—flooding in the winter and droughts in the summer. The low-lying land of the Somerset levels and local river catchments can become overwhelmed quickly when heavy and prolonged rain sets in, or when hit by a flash flood, as we were in May 2023.

The Somerset Rivers Authority was established in 2015 as a partnership of local stakeholders, and it is now knowledgeably chaired by the Liberal Democrat councillor, Mike Stanton. Its overarching purpose is to reduce the risks and impacts of flooding across Somerset. The SRA was formed after devastating floods in 2013-14, which was the wettest winter for over 250 years. Around 150 sq km of the Somerset levels was submerged for weeks, 165 homes were flooded, 7,000 businesses affected and 81 roads closed across the area. The cost to Somerset was in the region of £147.5 million.

Once again this winter my constituents are dealing with the devastating impact of flooding. Last week, Storm Chandra saw 50 mm of intense rainfall across large parts of Somerset in a really short period. It exacerbated the already saturated ground; as a result Somerset council declared a major incident last Tuesday, as 50 homes across the county fell victim to floodwater.

I pay tribute to everyone who has been part of the emergency effort to support communities across Somerset. Their commitment to help in times of need is much appreciated, whether we are talking about staff members from Somerset council, the SRA, the Environment Agency, the emergency services or other partners; members of affected communities who have opened their homes to displaced residents or those at risk of displacement; people who have been out with sandbags in 4x4s; those who made hot drinks for people who were cold and wet; or, as in my case last Saturday, people sweeping up car parks as floodwaters receded.

Sadly, the incident is not a one-off. Given the Environment Agency warning that river levels are expected to remain high for several weeks, unsettled weather forecasts for some time ahead and the imminence of high spring tides, the risk of further flooding in Somerset remains. With increasingly unpredictable, intense and changing patterns of rainfall, it is essential that local communities are now given the resources they need to prepare long-term, bespoke, extreme weather resilience plans.

Residents must feel confident that their homes will be safe from severe damage by floodwater, and they must be better prepared to cope with flooding when it happens. Sustainable drainage systems have an important role to play, but proper measures must be in place to bring sustainable drainage provisions into force and the systems must be properly maintained. As my hon. Friend the Member for Newton Abbot argued, the Government should implement schedule 3 of the Flood and Water Management Act 2010 to require sustainable drainage systems in all new developments.

Well-designed sustainable drainage systems contribute to climate change resilience, provide habitats for nature, boost biodiversity and build flood preparedness. But the current lack of clarity has contributed to widespread problems on new estates, particularly where SuDS fall under the control of private estate management companies. Homeowners are often left paying for poorly maintained systems with no public accountability. In some cases SuDS are simply left unmanaged and it is no surprise when, inevitably, they fail. If the Government are committed to building the homes that people need, they must ensure that new developments provide suitable flood mitigation measures, including SuDS, that properly manage excess rainfall.

Since 2020, Somerset council has carried out over 100 formal inspections of SuDS on housing developments. While most are found to be inadequate, maintenance issues are often highlighted. In Somerton, there are examples of where that has not happened. During the 2013-14 floods, Somerton was badly hit and flooded between Farm Drive and the recreation field. Defects were found in the drainage provided by the developers, while the attenuation pond that had not been maintained appropriately overtopped. Retention tanks were later installed, but they were paid for by the taxpayer and not the developer, as they should have been.

Last week, the same area experienced heavy flooding yet again. Sue and Amber, live locally in Somerton, told me they had lost three days’ worth of income due to the recent floods, because they simply could not get through the flood water. They are concerned about a planning proposal on Ricksey Lane that could make the situation much, much worse. They are not alone: many people fear that the development will create increased surface run-off, leading to flooding downstream.

Those anxieties are sadly not restricted to Somerton. Residents in Street fear that the developer of a planned additional 280 homes has not taken the precautions necessary to prevent the potentially catastrophic flooding of their properties. Residents told me that their key concerns are about the proposed surface water drainage for the site, because the developer plans to discharge water into two attenuation ponds. That, along with the volume of the Portway stream, will then flow into an existing northern watercourse; however, they believe the watercourse will not be properly maintained as it falls outside the developer’s remit.

Current national guidelines are designed to prevent new developments from worsening flooding downstream, but the existing drainage guidance is based on assumptions that do not always hold true in Somerset. In very flat areas like the Somerset levels and moors, water can linger for days, weeks or even months, rather than flowing quickly away. Across different sub-catchments, many factors such as soil type, infrastructure and rainfall patterns interact in complex ways that current standards simply do not address fully. That is why Somerset council is asking the Somerset Rivers Authority to fund an ambitious study of how water really behaves across Somerset’s catchment. The aim is to build a better evidence base, so that planners can update guidance, developers can design smarter drainage systems, and communities face less flood risk.

I hope the study can influence the national conversation, but without action from the Government setting mandatory standards for developers, residents’ anxieties will continue to grow. Disappointingly, the Government are consulting on deleting the rule that prevents planning permission from being granted where the Environment Agency objects due to flood risk. The Liberal Democrats are clear that that must not happen and that the absolute need for new homes must be weighed against very real flood risk. The water management sector is already frustrated that the Government have yet to commit to implementing mandatory SuDS, and the recent Cunliffe review identified inconsistencies in their use as one of the four main issues with the current waste water and drainage regime. The updated standards published last June were a welcome step in the right direction, but they are not a substitute for legislation.

The Liberal Democrats believe that a clear, enforceable national SuDS framework is required that standardises design, guarantees long-term adoption and maintenance, and ensures that someone is genuinely responsible when systems fail. Anything less will continue to leave residents exposed to flooding, unexpected charging and environmental harm. That is why we tabled an amendment to the Water (Special Measures) Bill that would have required water companies to provide, when consulted, honest and accurate assessments of their infrastructure’s capacity to meet the needs of proposed developments, and it was disappointing that the Government and the Conservatives did not support it. I hope the Government will review that proposal, as it is essential to ensure that water system capacity is better accounted for in future developments. Will the Minister provide an update on that?

The Welsh Government have implemented schedule 3 to the Flood and Water Management Act 2010, and their post-implementation review has revealed the value and benefit of the legislation. Although improvements may still be required, it is a necessary first step, and we must follow that example. The Minister has previously confirmed that the Government are considering what action to take but are still deciding whether they will improve the planning-led system or commence schedule 3. I urge her to listen to the Liberal Democrats’ calls. She is very welcome to take forward our ideas, because the current regime has not done enough to make at-risk communities more resilient to flooding, which leaves residents frightened, anxious and desperately worried every time dark clouds roll in.

In Somerset, we know what it is like to live at the forefront of climate change. The county will always be at risk of flooding, but with the right planning, investment and collaborative working, the risk and impact of flooding can be mitigated so that people feel safer in their homes. I once again extend to the Minister, and other right hon. and hon. Members, an invitation to visit my constituency and witness the terrible impact of flooding on communities. It is important to see that while the water levels remain high. I am certain that that would focus minds and give impetus, if any is needed, to the urgent implementation of schedule 3.