8.3 SuDS Management train

At the heart of the SuDS philosophy is the ‘management train’ approach. A sustainable drainage system should be thought of as a series of sequential components, rather than a single standalone solution. Different components will have different, although sometimes overlapping, functions that together deliver the required performance in terms of water quantity and quality, as well as the amenity and biodiversity benefits.

Component choice will be determined by a site’s characteristics and layout.

The use of multiple components will maximise the potential to intercept and treat runoff as well as opportunities for good design. This contrasts with a conventional drainage system that would rely on single ‘end of pipe’ solutions such as large tanks or even ponds to provide storage and pollution control.

The principles of the management train are set out below:

• Prevention: Designing to reduce the impermeable area that needs positive drainage, and good management to ensure that pollutants don’t enter the drainage system in the first place.
• Source control: The first, and most important, components in the SuDS management train. These should be located at the source of the runoff and be designed to provide initial rainfall interception and pollution control as well as storage. Examples include rain gardens, green roofs, harvesting, permeable paving and filter strips. Providing runoff control and storage at this stage will reduce the scale and cost of downstream components. In some schemes, such as SuDS retrofit, it may only be feasible to provide source control measures.
• Conveyance: Components that convey flows downstream to storage systems. This includes swales, channels and rills. Conventional piped systems should be avoided if feasible and should be kept short and direct if required. In contrast to conventional drainage, SuDS conveyance components are designed to be slow and leaky. This helps intercept rainfall, through infiltration or uptake by plants, and remove pollutants. Conveyance features can also provide volume control, for example using check dams in swales.
• Site Control: Components that provide the remaining storage volume, and infiltration capacity, for a site. Such components include balancing ponds, storage tanks, detention basins, infiltration features, etc. These components would then discharge water to a watercourse, sewer or groundwater.
• Regional Control: Some storage volume may need to be provided in larger scale regional systems that serve multiple sites. However, where such systems are feasible, the focus should remain on controlling as much runoff at source as possible.

Figure 8-3: SuDS Management Train (Credit - Susdrain)