Highway surface water management: Designing for performance, compliance and long-term resilience

Surface water management is a defining challenge in modern highway design. As rainfall patterns intensify and drainage networks come under increasing strain, the ability of highways to manage water effectively is no longer a secondary consideration, it is fundamental to safety, durability and long-term performance.

For highway designers and Tier 1 contractors, the focus has shifted beyond simply removing water from the carriageway. The challenge is to deliver systems that are hydraulically efficient, compliant with national standards, practical to construct and resilient over time.

The growing challenge of surface water on highways

Highways are inherently vulnerable to surface water due to their impermeable nature and scale. During rainfall events, runoff is generated rapidly and must be intercepted and conveyed before it accumulates on the carriageway.

The consequences of inadequate drainage are immediate and wide-ranging. Surface water can compromise driver safety through standing water and spray, while prolonged exposure accelerates deterioration of pavement materials, contributing to rutting, deformation and reduced asset life. At a network level, this translates into increased maintenance demand, higher costs and potential disruption to traffic flow.

As climate patterns shift and storm events become both more intense and less predictable, traditional approaches to drainage design are being tested. This places greater emphasis on systems that can perform reliably not only under typical conditions, but also during peak and extreme events.

Designing in line with the Standards for Highways

The Design Manual for Roads and Bridges (DMRB) provides the governing framework for highway drainage design in the UK, establishing clear expectations for hydraulic performance, flood risk management and environmental protection.¹

For designers, working within this framework requires a detailed understanding of how water behaves across the highway environment. Road geometry, gradients, crossfalls and flow paths all play a critical role in determining how effectively water is removed from the surface. Equally, discharge points and downstream capacity must be carefully considered to avoid transferring risk elsewhere.²

Compliance with the standards is not simply about meeting minimum requirements. When applied effectively, the DMRB supports a more structured and consistent approach to design, helping to ensure that systems are robust, safe and capable of accommodating future pressures.

Importantly, the standards also reinforce the need to consider climate change, requiring drainage systems to account for increased rainfall intensity and long-term variability. This further underlines the need for adaptable, forward-thinking solutions.

Moving from components to integrated drainage systems

A key development in highway drainage is the move away from traditional, component-based systems towards more integrated approaches.

Historically, drainage solutions relied on a combination of gullies, carrier pipes and underground networks to collect and transport water. While effective, these systems can introduce complexity in both design and construction, with multiple interfaces that must be carefully coordinated.

Increasingly, designers are adopting solutions that combine interception and conveyance within a single system. This shift simplifies both layout and installation, while also improving hydraulic efficiency by reducing the distance water travels across the carriageway before being captured.

Integrated systems can also help reduce the number of components required on site, improving programme efficiency and lowering the potential for installation errors. For Tier 1 contractors working within tight timescales and constrained environments, this can be a significant advantage.

Simplicity as a driver of performance

As highway schemes become more complex, there is growing recognition that simplicity in design often leads to more reliable outcomes.

Drainage systems that are straightforward to specify and install are less prone to misinterpretation, easier to construct accurately and more likely to perform as intended over time. Reducing the number of connections and interfaces within a system can eliminate common points of failure, improving overall robustness.

This approach is particularly valuable in live highway environments, where construction windows may be limited and disruption must be minimised. Systems that can be installed quickly and efficiently help to support programme certainty without compromising on performance.
At the same time, simplicity must not come at the expense of hydraulic capacity. Modern drainage solutions must still be capable of handling increased runoff volumes, maintaining flow efficiency and minimising the risk of blockage. Features that promote self-cleansing and reduce sediment accumulation are therefore an important part of long-term performance.

Designing for long-term performance and maintenance

Effective highway drainage design extends beyond initial installation. Systems must be capable of maintaining performance over their full lifecycle, often in challenging conditions.

Traffic loading, environmental exposure and the continuous movement of debris can all affect system performance over time. Without appropriate consideration at the design stage, this can lead to reduced capacity, increased maintenance frequency and, ultimately, system failure.

Designers therefore need to consider how systems will be accessed, inspected and maintained. Solutions that simplify maintenance processes, such as providing clear access points or reducing the likelihood of blockage, can deliver significant long-term benefits for asset owners.

Durability is also critical. Materials and construction methods must be selected to withstand the demands of the highway environment, ensuring that systems remain structurally sound and hydraulically effective over extended periods.

Understanding the role of different drainage approaches

While integrated systems are becoming more prevalent, it remains important to understand the range of drainage approaches available and where they are most appropriate.

Traditional gully-based systems continue to be used widely, particularly where connection to existing underground drainage networks is required. Linear drainage channels offer an alternative where continuous collection along the carriageway edge is needed, providing effective interception over longer distances.

Combined kerb and drainage systems represent a more integrated solution, incorporating water capture directly into the kerb line. These systems can provide high-capacity drainage while reducing the need for additional surface channels or gully spacing, making them particularly suited to high-speed roads and heavily trafficked routes.

The choice between these approaches depends on a number of factors, including hydraulic requirements, road layout, maintenance considerations and construction constraints. For designers, selecting the most appropriate system is not simply a technical decision, but one that must also reflect the practical realities of delivery and long-term operation.

Integrating environmental and water quality considerations

Modern highway drainage design must also account for environmental performance. Runoff from roads can carry sediments, hydrocarbons and other pollutants, which can impact receiving watercourses if not properly managed.

As a result, drainage systems increasingly need to incorporate measures that support water quality as well as flow management. This may include features that slow down water, encourage settlement of particulates or provide some level of filtration before discharge.

These considerations align with broader sustainability objectives and regulatory expectations, reinforcing the need for drainage solutions that deliver both hydraulic and environmental performance.

Delivering resilient highway drainage

Ultimately, effective highway surface water management depends on a coordinated approach that brings together design intent, regulatory compliance and practical delivery.

Designers must develop solutions that are capable of managing current and future conditions, while Tier 1 contractors must ensure those solutions are delivered accurately on site. Both must work within the framework of the Standards for Highways, using them as a foundation for achieving consistent and reliable outcomes.

The increasing use of integrated drainage systems, combined with a focus on simplicity, durability and maintainability, reflects a broader shift in the industry towards solutions that are not only effective, but also efficient to deliver and operate.

Conclusion

As the demands on highway infrastructure continue to grow, so too does the importance of effective surface water management.

Sea change is already underway in how drainage systems are designed and delivered, with greater emphasis on integration, long-term performance and environmental responsibility. Understanding the range of available drainage approaches, and how they can be applied effectively, is a key part of this evolution.

For designers and Tier 1 contractors, the priority is clear: to deliver highway drainage solutions that are robust, compliant and capable of performing under increasingly challenging conditions. By combining strong design principles with practical, well-considered systems, the industry can ensure that highway networks remain safe, resilient and fit for the future.

References: 

1 - https://www.standardsforhighways.co.uk/dmrb/

2 - https://cis.ihs.com/CIS/document/337734 

Written By

Paul Curtis

Paul has been with Marshalls plc for 24 years, and for the last five, has served as Managing Director of Marshalls Civils & Drainage.

Read Paul's full profile here.