When heavy rains hit urban areas, traditional drainage systems can become overwhelmed within minutes, turning streets into rivers and overwhelming sewage systems. As cities continue to expand and climate change intensifies weather patterns, this problem is only getting worse. Street trees, however, present a proven natural solution to these urban stormwater management challenges.
The Problem with Traditional Drainage
Traditional surface water drainage systems have been designed with one primary goal: to move rainwater away from where it falls as quickly as possible. This rapid conveyance approach typically directs water into soakaways or nearby watercourses, but that methodology can comes with significant drawbacks.
This ‘quick removal’ strategy increases the risk of localised flooding, pollution and damage to aquatic ecosystems. Runoff from urban surfaces often contains pollutants such as oils, heavy metals, pesticides and other contaminants from roadways and built environments. The increasing levels of urbanisation have only highlighted these limitations, making it clear that conventional surface water drainage systems alone are no longer adequate for modern cities.
What Are SuDS?
Recognising these limitations has sparked a fundamental shift in how we approach urban water management. Sustainable Drainage Systems (SuDS) are being widely implemented across the UK as a comprehensive solution to these challenges. SuDS aim to replicate natural drainage processes by slowing the flow of water, improving water quality, enhancing biodiversity and reducing the risk of flooding. A key principle of SuDS is the reduction of the negative impacts of urban stormwater runoff, including surface flooding and water pollution. Rather than fighting against natural processes, SuDS work with them to create more resilient urban environments.

Policy Support for SuDS
This approach now has strong policy backing. UK planning policy and local authority guidance increasingly require developers to incorporate SuDS into both outline and detailed planning applications. Sustainable drainage is now embedded in best practice frameworks, from initial site appraisals through to completion and long-term management.
The introduction of new national SuDS standards further reinforces this approach, providing a consistent framework for the design, construction, and maintenance of sustainable drainage across England. Incorporation into Environmental Impact Assessments (EIAs) and Building Regulations underscores its growing importance.
Why Trees Are Perfect for Urban Water Management
Urban street trees are increasingly recognised as vital components in managing stormwater within urban environments. Much like trees in natural woodland settings, urban trees intercept rainfall via their canopies, direct water to the ground via trunk flow and absorb moisture through their roots, making them a valuable sustainability asset in towns and cities.
Street trees play a crucial role in SuDS by reducing the volume and rate of runoff from urban catchments. Unlike other green interventions such as vegetated swales or large biofiltration areas, trees can be more space-efficient, an important consideration in dense urban settings.
Research has also shown that urban trees can significantly reduce nitrogen and other pollutant loads in rainwater runoff. While trees have long been a part of the urban landscape for aesthetic and ecological reasons, their function in urban water management is now gaining broader recognition among planners and urban designers.
Modern Tree Pit Design
As awareness grows, integrating street trees into drainage strategies is becoming more commonplace. Modern approaches to tree pit design, particularly in hardscaped areas, are helping to reduce maintenance costs and improve tree health and longevity. These engineered solutions also enhance stormwater management by enabling greater soil volume, better aeration, and increased water infiltration.
One proven approach is the use of engineered tree pits, which improve access to high-quality soil and encourage deep root growth while managing surface water runoff. Integrated systems like the ArborSystem, widely used across the UK, provide comprehensive solutions to meet both arboricultural and SuDS performance requirements.
For example, the ArborFlow SuDS tree pit system combines sustainable drainage with high-quality urban tree planting. This system effectively slows the flow of stormwater and reduces runoff volume, helping meet local authority discharge requirements. It also contributes to pollutant reduction by filtering surface water through engineered soil media designed to capture and retain contaminants such as hydrocarbons, heavy metals, and suspended solids. The design allows water to either infiltrate surrounding soils, enhancing tree health, or be directed to a flow-control chamber for regulated outflow. This dual functionality maximises both environmental and infrastructure benefits.

The Future of Urban Water Management
By recognising the multifunctional value of street trees and incorporating them into sustainable drainage strategies, urban spaces can become more resilient, attractive, and ecologically sound. As cities face increasing pressure from climate change and urban growth, these nature-based solutions offer a practical path forward.
The integration of street trees into SuDS represents a fundamental reimagining of how our cities can work with nature rather than against it. With strong policy support and proven technologies now available, the widespread adoption of tree-based sustainable drainage systems becomes essential for creating sustainable urban futures.