A sustainable drainage system is an alternative drainage solution compared to the usual method of water being directly channelled into sewers and then into nearby watercourses. Using a combination of methods to effectively slow the time it takes for water to dissipate, the sustainable drainage system (SuDS) aims to achieve three objectives:
- Improve water quality
- Reduce surface water flooding
- Enhance the environment
The SuDS basically achieves this drainage method by reducing water flow rates, increasing water storage capacity and reducing pollution.
Why are SuDS required?
One issue with usual drainage methods is the amount of water that runs into the sewers and sometimes overloads them. A combination of increased hard surfaces as more land is built over and climate change tending to produce periods of heavy rainfall over short periods can create a water flow problem.
Too much water enters the sewers and causes overload. A prime example of this issue is in London where the overflow system – previously designed to be called upon a handful of times a year – is nowadays pressed into action several times a month.
As a result raw sewage is being discharged into the Thames, and to remedy this the giant Thames Tideway Tunnel has been conceived to carry the excess water beneath the river to treatment works. In concert with this some SuDS projects in central London are being planned.
Similarly, where more and more development has taken place or is under construction further hard surfaces will result. These make it harder for water to drain naturally into softer ground and into underground and surface water retention structures such as ponds and lakes.
Instead it runs off the hard surfaces and into sewers already stretched to capacity. Flooding can result or there are overflow and pollution issues as discussed in the London example above. Few people realise that London is literally built on a complex network of undergrond rivers and sewers which take away millions of gallons of water every day.
How do SuDS work?
Using a combination of techniques, SuDS not only prevent too much water entering sewers and then water courses too soon but improve environmental conditions by reducing pollution.
Some of the methods:
Roof gardens and others carefully positioned retain some of the water and make use of it for irrigation. It naturally evaporates back into the atmosphere so avoids placing further demands on sewers.
Instead of a hard impermeable surface such as a concrete pathway or courtyard, permeable surfaces are sometimes used in property developments so water can make its way down into the ground naturally as opposed to a fast run off into the sewers.
Underground reservoirs catch and retain the water that has naturally drained into the ground or has been dispersed in staged movements rather than fast run offs.
Ponds, basins and wetlands may be used to retain water.
Filter strips and trenches
To filter the water before it trickles down for storage.
Fraser Ruthven, Head of Marketing and Growth at a leading drainage company covering the London and Essex area remarked: “we see a lot of evidence of over-worked drainage systems. There’s no doubt long term drainage demands have to be considered with the amount of new development work already under way.”
The government feels the answer lies in developing garden cities – not exactly a new innovation as Welwyn Garden City in Hertfordshire dates back to the 1920’s – to manage necessary but problematic new developments. For example, a major new development at Ebbsfleet Garden City is being planned with SuDS very much integral to handling the implications of building on previously open land that would naturally absorb much of the rainfall.
An integrated approach
These garden cities involve a whole integrated approach to managing drainage and environmental concerns with a new development. Careful planning of open spaces, garden areas and the layout of surfaces – both permeable and impermeable – and water routing methods are all key considerations.
SuDS are an essential part of the greater plan to provide a flood free future for all of our towns and cities. With increased rainfall predicted, urban planners must put drainage at the top of the agenda.
Fraser Ruthven is the Marketing Associate for London Drainage Facilities, one of London’s leading drainage companies. London Drainage provides a wide range of drainage diagnostic and repair services in and around London.