Creating Sponge Cities to Tackle Surface Water Flooding
Bentley TwinTalks - breakfast meeting – 25 March 2025
Interview with Lee Pitcher, MP for Doncaster East and the Isle of Axholme, and chair of the All-Party Parliamentary Group on Water
BACKGROUND
Before the U.K. general election in July 2024, Lee Pitcher had a successful career as a water engineering consultant, with decades of experience working for Yorkshire Water and, most recently, with Jacobs Engineering. Today, he is MP for Doncaster East and the Isle of Axholme, chair of the Water All Party Parliamentary Group, and a passionate and knowledgeable advocate for the water sector.
This passion for the water sector put him in a great position to support the launch of a new white paper on surface water flooding titled “Creating Sponge Cities to Tackle Surface Water Flooding” that was produced by Bentley, water consultancy Aqua Consultants, and British Water.
It is a critical topic. As the paper points out, urbanisation, outdated drainage systems, and climate change are compounding the growing problem of urban pluvial flooding, a problem that is increasingly impacting lives and communities across the U.K.
The discussion of the white paper focused on the development of so-called sponge cities as a key solution—embracing sustainable drainage systems (SuDS), green infrastructure solutions, and a range of new strategies to create cities designed to absorb, store, and manage water more effectively.
“Our systems are bursting at the seams. If you look back at the Victorian era and what they put in, they oversized and future-proofed, and that's held us in good stead. But we're at that position again where we need to do something radically different to cope.”
Lee Pitcher
Bentley TwinTalks - breakfast meeting – 25 March 2025
Interview with Lee Pitcher, MP for Doncaster East and the Isle of Axholme, and chair of the All-Party Parliamentary Group on Water
BACKGROUND
Before the U.K. general election in July 2024, Lee Pitcher had a successful career as a water engineering consultant, with decades of experience working for Yorkshire Water and, most recently, with Jacobs Engineering. Today, he is MP for Doncaster East and the Isle of Axholme, chair of the Water All Party Parliamentary Group, and a passionate and knowledgeable advocate for the water sector.
This passion for the water sector put him in a great position to support the launch of a new white paper on surface water flooding titled “Creating Sponge Cities to Tackle Surface Water Flooding” that was produced by Bentley, water consultancy Aqua Consultants, and British Water.
It is a critical topic. As the paper points out, urbanisation, outdated drainage systems, and climate change are compounding the growing problem of urban pluvial flooding, a problem that is increasingly impacting lives and communities across the U.K.
The discussion of the white paper focused on the development of so-called sponge cities as a key solution—embracing sustainable drainage systems (SuDS), green infrastructure solutions, and a range of new strategies to create cities designed to absorb, store, and manage water more effectively.
“Our systems are bursting at the seams. If you look back at the Victorian era and what they put in, they oversized and future-proofed, and that's held us in good stead. But we're at that position again where we need to do something radically different to cope.”
Lee Pitcher
IN PARTNERSHIP WITH
Sponge cities: An urgent solution to urban flooding
Urban flooding is an increasing concern across the world, as it is exacerbated by climate change, urbanisation, and outdated infrastructure. As cities expand and weather patterns become more unpredictable, traditional flood control measures—such as hard drains and sewers—are no longer sufficient to handle the intensity and frequency of heavy rainfall.
This new reality has led to development and promotion of the concept of sponge cities, an innovative approach to flood management that aims to absorb, store, and manage water efficiently, reducing flood risks while also providing sustainable water solutions.
The new white paper, which was produced Bentley Systems, water consultancy Aqua Consultants, and British Water, explores the concept of sponge cities, their potential to tackle urban flooding, and how this approach can become a widespread reality.
The need for this new, comprehensive, independent, and credible report on urban flooding and water management is crucial. Policy makers often lack the technical knowledge needed to devise effective solutions, relying instead on oversimplified soundbites or reactive measures.
Well-researched reports that offer concrete, actionable solutions serve not only to identify the problems, but also to propose practical responses, enabling governments, businesses, and communities to take decisive action against urban flooding.
“Reports like this, first and foremost, have credibility; produced and created based on experience, knowledge, and intelligence from people that have worked in the industry. That's massively important. It gives us a real insight into the true issues out there, but also the solutions.”
Lee Pitcher
What is a sponge city?
A sponge city is an urban area designed with the aim of managing stormwater efficiently, reducing flood risks, and supporting water conservation. It is an approach that recognises the value of water as an asset, not just as a challenge to be managed. Key to the concept is the idea that cities should “absorb” water like a sponge, managing both floodwater and the storage of water for future use.
Sponge cities aim to integrate natural systems with urban environments, enhancing water retention, absorption, and flow. Some of the core principles of a sponge city include:
- Understanding the flow of water within a city, from rainfall to rivers, ditches, and dikes.
- Implementing interventions that allow the city to absorb, harvest, and redirect water efficiently.
- Designing cities that can retain water for future use while minimizing the risk of flooding.
In practice, this can include the use of permeable surfaces, green roofs, rainwater harvesting systems, and natural water bodies, such as wetlands and ponds. The goal is to create an urban ecosystem that mimics natural water cycles, ensuring that the city can manage excess water during storms without overwhelming drainage systems.
“You take a whole city landscape, look at the water that's in that city, or could fall on it, and then assess the interventions you can make to absorb, harvest, and help guide that water into a safe space. That means it's collected up like a sponge—it doesn't cause flooding, but ensures there is water around when you do need it."
Lee Pitcher
White paper recommendations
The new white paper made five key recommendations to promote the adoption of sponge cities, emphasising the urgency of action. These recommendations include:
- Pace and scale: The Environment Agency is urged to collaborate with OFWAT and the Local Government Association to enable water companies to drive catchment-based flood solutions, accelerating implementation through better funding access and multiagency cooperation.
- Water Management Act: The delayed implementation of Schedule 3 of the Flood and Water Management Act 2010 is hindering sustainable drainage adoption. This paper calls for an immediate public consultation to establish a framework for drainage system approval, ensuring alignment with biodiversity net gain requirements and helping developers integrate sustainable solutions to mitigate surface water flooding.
- SuDs manual: The CIRIA SuDS manual, last revised in 2015, requires updating to incorporate new insights on scalable, modular sustainable drainage systems. This paper supports an update to enhance best practices, ensuring water companies, flood authorities, and contractors can deploy cost-effective SuDS solutions more efficiently.
- Outreach: With increasing urban paving exacerbating flooding, this paper recommends that planning authorities and water companies collaborate with schools, community groups, and homeowners to promote green infrastructure. Encouraging less paved and more permeable surfaces in urban environments will help manage surface water effectively.
- The importance of integration: Integrated water management is essential to address evolving flood risks. This paper highlights the role of data, digitisation, and climate modelling in developing resilient, adaptable solutions. By testing and refining strategies in digital environments, planners can create sustainable, long-term flood management systems that enhance urban resilience.
Overall, the report advocates for practical, on-the-ground solutions that can be implemented in the short term. This action includes creating more green spaces and integrating SuDS into urban planning.
Public involvement and community buy-in was highlighted as being crucial since flood resilience is not just about engineering solutions—communities must be involved so that the people living in flood-prone areas understand the risks and are prepared to respond effectively.
“Local communities are best placed to understand and support flood mitigation efforts. There’s no one that knows their area, their community, how it works, what makes people tick, more than the person that lives there."
Lee Pitcher
Challenges in urban drainage infrastructure
Many existing urban drainage systems were designed years, or even decades ago, and are no longer capable of managing the increasing volume of water generated by extreme weather events.
The growing frequency and intensity of rainfall due to climate change have made it clear that conventional drainage systems—primarily designed to handle smaller, less frequent storms—are ill-suited for today’s climate reality.
Other factors that contribute to strains on urban drainage include:
- Population growth and urban expansion: As cities continue to expand, there is an increasing demand for water management solutions.
- Aging infrastructure: Much of the drainage infrastructure was designed in an era with different rainfall patterns and urban layouts, making it inadequate for modern needs.
- Increased impermeable surfaces: The growth of impermeable surfaces—such as roads, buildings, and pavement—reduces the natural capacity of urban areas to absorb rainwater, leading to increased surface water flooding.
The use of data is critical to improving water management strategies. Despite the vast amount of global, regional, and local water data available, much of it remains trapped in silos, limiting its utility. The ability to access and integrate this data can significantly enhance urban water resilience.
Private finance and insurance industries are increasingly involved in water resilience planning. With advanced data analytics and digital twins, insurers and investors can better assess risks and make informed decisions. Well-managed water infrastructure reduces financial risks and enhances urban resilience, benefiting both businesses and residents.
“With the greater modelling of cities, more data is now available. But we've been collecting so much data for so long, we don't actually know what we've got. So, we need to take a clearer view of what we have and actually use that data to create far better environments for us to live in.”
Mark Coates, vice president of infrastructure policy advancement, Bentley
Funding and local authority constraints
The importance of devolved powers cannot be overlooked. Local decision-making and the ability to direct funding and resources are key to addressing flood risks effectively.
However, while the U.K. government has allocated funding for flood resilience measures, local authorities face significant financial constraints and increasing pressures, in terms of the need to invest in infrastructure maintenance and renewal, compounded by spiralling social service demands.
Implementing flood resilience measures, especially at a large scale, often requires substantial investment. Given that many cities are already grappling with tight budgets, finding the necessary funds to implement comprehensive solutions can be challenging.
While there is no question that investment in national scale flood resilience projects is vital, large-scale infrastructure projects may not always be feasible. As a result, solutions often need to be customised to local conditions and implemented at the street or even domestic level.
“The solutions that we're talking about, they're not necessarily building massive tanks or big lakes. This is about doing stuff at a street level, at domestic level; and I think the funds are there. We just need to use them efficiently.”
Lee Pitcher
Planning for future resilience
With the U.K.’s ambitious target of building 1.5 million new homes, integrating flood resilience into urban planning is critical. The discussion distinguished between two main strategies:
- New developments: When building new homes and infrastructure, it is easier to integrate flood resilience measures from the start, such as using permeable paving, installing rainwater harvesting systems, and designing landscaping that directs water away from buildings.
- Retrofit solutions: For existing properties, retrofitting flood resilience measures such as flood barriers, sump pumps, and waterproof materials can help minimize damage during floods and speed up recovery.
While it is probably easier to plan for flood resilience in new construction, it is also clear that, for existing properties, there are a range of solutions available to support future resilience.
Future planning strategies cannot underestimate the social and mental health impact of flooding beyond the physical damage caused. The trauma of losing homes and possessions can take a lasting toll on communities, particularly those that are less prepared.
Evidence suggests that when communities engage in flood preparedness, such as developing household flood plans, they are better able to cope with the stress of flooding and recover more quickly. This strategy should start at schools and make young people aware of the potential dangers and impacts of living in a flood prone region.
"I find it astonishing that in areas of high flood risk, children aren’t being taught to create flood plans for their homes—having a plan means you respond quicker and bounce back faster."
Lee Pitcher
A systemic approach to water management
The white paper highlights that addressing urban flooding and water management is not just an engineering challenge, but also a societal problem to be met.
Water resilience has significant implications for public health, the economy, and social wellbeing. Therefore, to achieve effective flood resilience, multilevel engagement from government, local authorities, businesses, and the public is essential.
Key steps for improving flood resilience include:
- Smarter use of available funding: Efficient allocation of resources ensures that funds are used effectively at the local level.
- Strategic urban planning: Flood resilience should be integrated into all new urban developments and retrofits of existing properties.
- Harnessing technology: Advanced modelling, digital twins, and AI can help predict flood risks and optimize mitigation measures.
Ultimately, creating flood-resilient cities requires both technical and social solutions alongside systemic policy changes that prioritize long-term sustainability over short-term fixes.
The concept of sponge cities offers a way forward by making cities more adaptive to water, ensuring that they can absorb, store, and manage water efficiently in the face of climate change and urbanization. By embracing these solutions, cities can not only reduce the risk of flooding, but also create more liveable, sustainable urban environments.
