Sustainable Drainage Systems (SuDS) and key SuDS techniques have been a planning requirement for several years now. But the current focus on climate change makes them more important than ever, as Chris Hodson of Interpave, explains
With climate change, we are experiencing more frequent and heavy rainstorms, resulting in flooding from rainwater runoff. This is made worse by ‘sealing up’ our towns and cities, which stops rainfall soaking into the ground. Our old drainage systems simply cannot cope, causing downstream flooding. In addition, roads, car parks and drives collect pollution – from car exhausts and oil leaks, as well as from wearing brakes and tyres – including electric cars. These are washed into drains with rainwater, damaging our rivers and streams.
THE TROUBLE WITH SEALING-UP
Water table levels drop causing water shortages, streams and ponds to dry up, and trees to be deprived of water. This can also affect the foundations of your home, particularly on clay soils as they dry out and shrink. These problems are made worse when gardens are sealed-up and water runs straight into roads and sewers. Although one small area of sealed paving in isolation may not cause major flooding – the cumulative impact of many homes in a city can. Simply allowing rainwater to run straight off roofs and paving into drains is no longer an option.
For many years, it has been recognised that SuDS are essential in curbing flooding and pollution from rainwater runoff. SuDS manage rainwater by slowing it down and cleaning it up – copying, as closely as possible, the natural drainage from the land before any building work or paving takes place. SuDS manage rainwater near the surface and as close to its source as possible, slowing the flow and providing additional benefits including clean water for wildlife, irrigation or other uses. Typical SuDS include ‘green’ roofs and other planted features like rain gardens.
MULTIFUNCTIONAL SUDS
With decades of predictable performance, concrete block permeable paving has shown itself to be a particularly reliable and multifunctional SuDS technique, offering attractive hard surfaces for people and traffic, combined with effective rainwater drainage. There is a growing choice of concrete products available on the market, designed specifically for permeable paving. Essentially, they have the same impressive performance as other precast concrete paving products, being slip resistant, durable, strong and sustainable. And today there are more shapes, styles, finishes and colours than ever to give real freedom of choice.
The difference with concrete block permeable paving is enlarged joints, filled with a permeable grit aggregate, and materials below the blocks specifically selected to accommodate water, all without clogging. Concrete block permeable paving is unlike – and not to be confused with – permeable materials, like resin-bound aggregates, which behave differently. Concrete block permeable paving can be laid level and still avoid puddles, or adapt to slopes, all without the need for drainage gullies. It also provides a safe surface for everyone, unlike gravel and other loose material.
SUDS RULES
For new developments, SuDS and techniques like permeable paving will generally be required as part of the planning process, although details will depend on which part of the country. Local policies affecting planning applications will generally demand SuDS. For example, the London Plan says that: “Development proposals for impermeable paving should be refused where appropriate, including on small surfaces such as front gardens and driveways.”
For existing homes, installing drives or other paving anywhere in your garden used to be considered ‘permitted development’ – in other words an automatic planning permission. But changes a few years ago took away these rights from much new or even replacement paving, unless it’s ‘permeable paving’ or drains onto a permeable garden area or soakaway within the property. The aim of the requirements is to hold back water on the property during heavy storms to avoid downstream flooding and treat it to trap pollution.
Alternatively, you will need to apply for planning permission, involving an application, drawings and a fee. With policies in favour of SuDS, an application should be rejected. And if you go ahead, this could result in local authority enforcement action or legal problems when the house is sold.
STRAIGHTFORWARD GUIDANCE
Inerpave’s ‘Paving for Rain’ guide offers straightforward advice using either concrete block permeable paving or rain gardens, where conventional paving simply drains to a landscaped depression, maybe with plants. In both systems, water is held back on your property during heavy storms to avoid flooding and filtered to remove or trap pollution. What happens next depends on the ability of the ground to absorb water and whether you want to make use of the rainwater, for example for irrigation.
PAVING AND TREES IN HARMONY
Climate change has highlighted the importance of trees and other plantings for carbon storage, urban cooling, shading, biodiversity and wellbeing. But irrigation is important – particularly in summer – and permeable paving can provide a gradual supply of clean water. Although urban trees and paving have traditionally been seen as in conflict, this is not the case with concrete block permeable paving which works in harmony with trees, allowing air, as well as water, to reach tree roots, so that they grow downwards and don’t damage the paving over time.
Chris Hodson is consultant to the trade association Interpave