Sustainable Urban Drainage Systems

Hebden 401 permeable paving - A quick guide for SUDS

2011-01-31T02:06:00.000-08:00

Low Carbon Products permeable paver, the Hebden 401, is used to mitigate against flooding, providing a high strength, low cost surface for car parks, driveways etc. This product can be incorporated into SUDS strategies to help avoid surface water runoff and allow rainwater to enter the water table rather than the drainage system.

Here is a quick introduction to SUDS. For any further information on SUDS, or on the Hebden 401, please visit www.ecopaving.co.uk

Sustainable Urban Drainage Systems

(from Landscape Architects Pocket Book – isbn: 978-0-7506-8348-7)

What are SUDS?

Sustainable Urban Drainage Systems are an alternative approach to conventional drainage design that replicates natural drainage and deals with run-off where it occurs, thereby reducing environmental impact from surface water drainage. It is now increasingly a requirement by Local Authorities in authorising developments due to the increased risk of flooding in the UK

Benefits of using SUDS

reduction in pollution
reduction in risks of flooding
improvements to the environment
reduction in costs

SUDS techniques

The following methods of control can be used to manage surface water run-off and prevent pollution

filter strips and swales
filter drains and permeable surfaces
infiltration devices
basins and ponds

These systems of control should be positioned close to the source of run-off to provide maximum attenuation by reduction in flow and prevention of erosion and flooding. Each one can also provide varying degrees of treatment for surface water through the natural processes of sedimentation, filtration, absorption and biological degradation. The decision to use the following systems will be based on available land, nature of the site – rural or urban, use of the site and its long term management.

Filter drains and permeable surfaces

Filter drains and permeable surfaces are devices that allow storage of surface water in an area of permeable material below ground flowing via a permeable surface which can include:

un-trafficked grass or reinforced grass
gravel
cellular paving such as the Hebden 401
continuous surfaces with an inherent system of voids

How they work

The rainwater run-off drains through the surface to the permeable fill which then allows the storage, treatment and infiltration of water. Both the surface and the sub base material must allow the water to flow through to ensure this system will work. The volume of the water stored will depend on the plan area, depth of fill and the ratio of voids to fill. Water can be disposed of by infiltration, underdrain or pumping out.

Where used

Can be used for car parks, residential driveways, paths and patios. Not currently used for adoptable roads and footways.

Maintenance

Surfaces should be kept clear of silt and cleaned twice a year to keep voids clear and the system operational.

The Problem With Impermeable Surfaces

2009-12-21T02:39:00.000-08:00

Paved, impermeable surfaces cover millions of square miles of our planet. They are possibly the most ubiquitous structure created by man, in the main part to service our love affair with the car.

This massive man-made alteration to our environment has created a major, growing problem with flooding, as rainwater runs off the surface, not through it.

Surface water run-off puts a massive strain on our drainage infrastructure, and when torrential rain hits this system is often overloaded. The recent floods in the UK illustrate what happens when water cannot drain away. The Environment Agency calculated that two-thirds of the flooding experienced in the UK in 2007 was caused by surface water overwhelming the sewerage system. Water falling on impermeable surfaces did not drain into the ground, and when rivers broke their banks the combination of the two resulted in catastrophe.

Surface water run-off is also extremely polluting. Impermeable surfaces collect matter from the atmosphere, nitrogen oxides from car exhausts, rubber from tyres, phosphates from residential and agricultural fertilizers, amongst dozens of pollutants. With permeable surfaces much of this material would seep back into the ground where micro-organisms would begin a rapid breakdown process, but with impermeable surfaces it has nowhere to go, and the pollutants enter the water system. This has a major impact on marine environments, and in serious pollution blackspots only the toughest reptiles and amphibians can survive.

Environmentalists are also concerned about the effects the sheer velocity of surface water run-off has on an ecosystem; in effect, mini-tsunamis are created when rainfall is heavy that cause serious damage to stream ecosystems.

In addition, impermeable surfaces damage the ability of the groundwater system to recharge itself, resulting in a loss of base flow, seriously damaging streams and rivers fed by groundwater.
They also create the 'Heat Island Effect'. Impermeable surfaces are generally dark and absorb heat, therefore heating rainwater. This means, for example, a thunderstorm after hot weather creates hot water which then goes into the river system. Many aquatic organisms are vulnerable to even small increases in water temperature, and the results of heated water entering the eco-system are devastating. For example, increased temperature decreases water's ability to hold oxygen, choking life, as well as killing off fish eggs, and retarding growth in young creatures.

Therefore, impermeable surfaces are a little known, but very serious environmental menace. Government legislation has been introduced banning new impermeable surfaces without planning permission, e.g when creating a driveway. Water company's also levy a charge on businesses and individuals dubbed the 'Rain Tax' (for a blog on the subject, click here) as a government backed way to encourage conversion to permeable surfaces.

Porous Paving

Water permeable ground reinforcement blocks are increasingly becoming the product of choice for architects and landscapers when seeking to avoid the problems of surface water run-off, and are often cheaper than laying concrete or asphalt.

One such product is the Hebden 401. Filled with either gravel or seeded soil for a grass finish, the Hebden 401 allows water to drain through into the water table, thus avoiding the problems described above with surface water run-off. The fact that the product is 100% recycled plastic adds to its environmental credentials.

The use of this product is picking up momentum in a big way, as more and more people become aware of the benefits, both financial and ecological, of the Hebden 401. It is perfect for car parks, driveways and paths as it can withstand up to 250 tonnes per m2, thus creating excellent hard standing without the drawbacks associated with traditional impermeable surfaces.

Flooding is always going to happen, but we as a society need to do everything possible to lessen the impact. Building away from flood plains, upgrading the sewerage system, and replacing impermeable surfaces with products like the Hebden 401 can all help reduce some of the suffering cause by flooding.

About SuDS

2009-04-20T03:25:00.000-07:00

Sustainable Drainage Systems (SuDS), sometimes known as Sustainable Urban Drainage Systems (SUDS), are designed to reduce the potential impact of new and existing developments with respect to surface water drainage discharges.

The idea behind SuDS is to try replicate natural systems that use cost effective solutions, like the Hebden 401, with low environmental impact to drain away dirty and surface water run-off through collection, storage, and cleaning before allowing it to be released slowly back into the environment, such as into water courses. This is to counter the effects of conventional drainage systems that often allow for flooding, pollution of the environment - with the resultant harm to wildlife - and contamination of groundwater sources used to provide drinking water.

The paradigm of SuDS solutions should be that of a system that is easy to manage, requiring little or no energy input (except from environmental sources such as sunlight, etc.), resilient to use, and being environmentally as well as aesthetically attractive. Examples of this type of system are reed beds and other wetland habitats that collect, store, and filter dirty water along with providing a habitat for wildlife.

Originally the term SuDS described the UK approach to sustainable urban drainage systems. These developments may not necessarily be in "urban" areas, and thus the "urban" part of SuDS is now usually dropped to reduce confusion. Other countries have similar approaches in place using a different terminology such as Best Management Practice (BMP) and Low Impact Development in the United States.

SuDS use the following techniques:

source control
permeable paving, like the Hebden 401
storm water detention
storm water infiltration
evapo-transpiration (e.g. from a Green roof)

Unlike traditional urban stormwater drainage systems, SuDS can also help to protect and enhance ground water quality.

Sustainable Urban Drainage Systems

2009-01-18T01:35:00.001-08:00

Welcome to the Sustainable Urban Drainage Systems blog.