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Should All New Developments Include Sustainable Drainage?

Existing drains network may not be able to cope with new builds

More of the country is being built over as cities and towns expand and open areas are covered with new builds, a situation set to increase as construction intensifies to meet the UK’s housing shortfall.

Housing charity Shelter say some 250,000 new houses will be required each year to meet rising demand, so with more buildings and their surrounding infrastructure such as pathways, hard standing and access roads being connected to the drains huge demands will be placed on an already over stretched drainage system.

The existing drainage problem

Along with the extra demand created by large numbers of new homes taking up drainage capacity, is the issue of flooding caused by surface water run off.

More hard surfaces being built over ‘bare’ land such as roofing, paths, hard standing and roads means more water has to enter the existing drains as opposed to working its way naturally into the ground through absorption. During periods of heavy rainfall over short time frames – predicted to occur more frequently due to climate change – the drains sometimes cannot cope with such an influx of surface water so it runs off and flooding can result.

Incidences of blocked drains are increasing as the drainage system becomes more overloaded according to many drainage contractors.

The UK has suffered many flooding episodes in recent years with a particularly heavy bout striking Cumbria and the surrounding area during the winter of 2015. The Environment Agency and Cumbria County Council found that drains had reached capacity and overflowed as a result – a situation worsened by rivers bursting their banks and overwhelming existing flood defences.

Is flooding a long term problem?

Yes definitely. Environmental engineering consultancy company JBA Consulting warn that some 2 million people are at risk through surface water flooding; a figure that could rise by another 1.2 million by 2050. The majority of flood insurance claims are due to surface water, and flooding has been identified by the UK Climate Change Risk Assessment for 2017 as one of the top three risks posed by climate change.

What is sustainable drainage (SuDS)?

SuDS work by ‘managing’ surface water through controlling flow speed, direction and channeling it towards reservoirs and trenches so some can be absorbed naturally into the ground or evaporate naturally.

Some of the ways this is achieved:

  • Control – decreases the amounts of water likely to flow straight into drains and rivers. Water is intercepted and re-used – perhaps for irrigation – or stored, or absorbed into garden areas strategically placed in and around developments where it can be removed through evaporation
  • Pre-treatment – construction and careful siting of ditches (or swales) and trenches where the water is discharged ‘under control’ into watercourses
  • Retention – storing water before being carefully moving it to watercourses; ponds, basins and wetlands
  • Absorption – soakaways and infiltration trenches help water soak naturally into the ground

A clear case for SuDS

It would appear that SuDS has a critical role to play; existing flood risks clearly need addressing judging by the amount of flooding the UK has experienced in recent years. On top of this, the increase in housing and therefore hard surfaces means SuDS or at least some type of flood defence has to be part and parcel of new construction developments.

The government would appear to agree; a bill requiring new housing to incorporate SuDS as opposed to simply being connected to the existing drainage systems was put forward by MPs earlier this year. The bill was rejected by the House of Commons but later accepted by the House of Lords; while a degree of Parliamentary ‘ping pong’ between the Lords and Commons went on as the bill was amended, it looks like becoming law.

SuDS would seem to be a key component of managing flood risks in the light of more construction taking place in the years to come.

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Larry Walker

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