Block vote

Drainage legislation coming into force early next year might be sending some developers into a tailspin Schedule 3 of the Flood and Water Management Act is due to be implemented in England in early 2024, meaning that all new developments will need to include Sustainable Drainage (or SuDS) features as part of their water management masterplan The intention of this legislation is to ensure that new developments don’t increase local flood risk by generating higher volumes of surface water runoff

SuDS, in principle at least, are delightfully uncomplicated The concept is to collect and manage water on the surface (or as near to the surface as possible), slowing its flow and limiting the volume that heads into receiving water courses.

In an ideal situation, over time, stored water can soak down into the ground at source without ever needing to meet a sewer or stormwater drain – but even when that’s not possible, these features sufficiently slow the flow of water downstream which means that the receiving water course isn’t overburdened and flood risk is drastically reduced In addition, water that flows through these features is cleansed, improving the quality of runoff that will have collected a variety of pollutants on its route downstream

But clearly, not all developments have the space to hand over to SuDS features

Land is expensive, so how can you satisfy SuDS legislation without giving up valuable space?

Permeable paving is the ideal solution It provides a durable, hardwearing, loadbearing surface that’s ideal for access roads, car parks and driveways, but due to its clever design, it also collects and stores rainwater at source – so shrewd designers can marry hardstanding and excellent SuDS performance in one simple system

The system comprises of concrete block paving which features special spacer nibs around the edge of each block Although the concrete itself isn’t permeable (the blocks are made from the same material as any other concrete block paving) the joints around the edge of the block keep the individual units a few millimetres away from each other, creating a uniform gap at every joint that allows surface water to flow cleanly though

The blocks are laid on a specially prepared sub-base composed of different grades of angular crushed rock which provides both excellent storage for the water that flows into it, and also excellent structural performance Once stored in the sub-base, water either soaks naturally into the ground at source or (where infiltration isn’t possible) is channelled away at a controlled rate to a receiving water course

This means that all of the rain that falls onto a permeable surface can be intercepted and stored where it falls

Often, roof runoff is also directed into the sub-base of a permeable pavement too, via downpipes. This means that a permeable paving system effectively becomes a large-volume, structurally robust storage tank beneath a completely porous trafficable surface.

While it’s true that a permeable pavement system doesn’t satisfy all four pillars of SuDS, it’s an excellent solution for dealing with high volumes of runoff –although even the most optimistic manufacturer would struggle to claim that it provides biodiversity or amenity benefits.

However, studies have proved that water that flows through a permeable pavement undergoes significant cleansing (by a combination of mechanical filtration and biological activity) – so enlightened designers recognise that the controlled flow of clean water leaving a permeable sub-base can be used to successfully irrigate a soft planted area of landscaping. Thus, even when infiltration systems aren’t possible, permeable paving becomes a pragmatic and sensible element of a holistic water management system.

So while permeable paving isn’t a water management panacea, it’s one of the most pragmatic, simple and costeffective solutions to help developers satisfy incoming SuDS requirements.