Sustainable Urban Drainage Systems

Published by Guy Woodward @ calfordseaden for calfordseaden LLP in Environment and also in Central Government, Housing

Sustainable Urban Drainage Systems, or SUDS for short, has become something of a buzz phrase in the construction industry over the past four or five years. Richard Newman of calfordseaden explains more.

But what is it all about, and why has it become so important for clients, developers and their professional teams to understand and embrace?

Whatever the root cause, we are experiencing noticeable change in our weather patterns in the UK. When it rains, we often experience higher intensities of precipitation and for greater duration than hitherto. In these circumstances, our surface water drainage networks, which have generally stood us in good stead, can frequently become overloaded and significant flooding may result, to which the residents of Sheffield and Hull can bear witness.

As the incident rate for storms of this type increases, the risk of flooding becomes even more significant. Ironically, despite these bigger storms, the longer hot dry summers predicted also mean that we could become short of drinking water, particularly in the southeast of England. Clearly these major issues need to be addressed.

At a strategic level, civil engineers are working with government to devise flood management strategies and to examine ways to capture the rainfall that we are blessed with, so that it may be directed or stored for our benefit. Sustainable Urban Drainage Systems (SUDS) is a very effective approach to addressing these issues at a local level. The basic principle is to replicate, as closely as possible, the natural drainage from the site before development.

Sustainable Urban Drainage Systems, or SUDS for short, has become something of a buzz phrase in the construction industry over the past four or five years. Richard Newman explains

"The objectives are to minimise the impact from the development on the quantity and quality of runoff and to maximise amenity and bio-diversity opportunities. In practical terms, this means that conventional piped drainage solutions are being modified or substituted by alternatively engineered solutions. These vary in type depending on the existing ground conditions, history of development, etc".

Where the ground is permeable, it is possible to construct roads using permeable pavements, which allow rainwater to collect in a drainage blanket and slowly percolate into the ground. In appropriate conditions it is also possible to collect the discharge from roof drainage and drain this into the same blanket. This has the advantage of dealing with the drainage on site, avoids taking water into the surrounding pipe network, and recharges the underlying aquifer directly.

Enlightened local authorities are now adopting roads of this type. A major principle behind most SUDS schemes is the reduction or attenuation of flows. Thus where direct infiltration is impractical or not permitted, other SUDS tools in the civil engineer's armoury can be employed. These generally involve some form of storage, either above or below ground, depending on the land available and the degree of bio-diversity intended. and include:

• Simple water butts, where water can be stored for irrigation purposes;
• Swales, which are basically wide open channels used to hold water (or allow some direct infiltration) prior discharge to a watercourse;
• Buried tank type structures;
• Roof storage: green roofs can provide some attenuation;
• Infiltration Basins: basically an open soak-away;
• Retention and Detention Basins: essentially variations on the swale, for holding water and allowing some permeation;
• Paved surface flooding: using car parks to store flood water;
• Wetlands and Reed-beds: a system of shallow pools that hold water and remove pollutants whilst enhancing the overall bio-diversity of the neighbourhood.

Currently calfordseaden's civil and structural engineering group are undertaking the design of a number of schemes where the above principles are being utilised. In Oxfordshire, we are undertaking the design of a new housing estate where the roads are of permeable block paving. The roof drainage is also collected and discharges through silt traps into the same drainage blanket. The design has been approved by the local authority and has been accepted for Adoption. There can be little doubt that these design principles will become the norm in the years to come, and calfordseaden are well placed to advise clients on the most appropriate solution for their particular development.
 

For more information contact Richard Newman (T: 01689 888222 / E: rnewman@calfordseaden.co.uk)
www.calfordseaden.co.uk