How to fight the urban flooding

Climate change is likely to bring more flooding to the UK in the coming years. Chris Digman reports on how a more sustainable approach to drainage will help prevent the potentially devastating economic and environmental impacts.

AS THE flooding experienced in the summer of 2007 demonstrated, the UK has a history in urban areas where the risk from flooding needs to be more effectively managed. On top of this, part of meeting the challenges posed by this history is the need to reduce the impacts on water quality from pollution and combined sewers, as well creating better places to live.

In addition to the obvious financial costs, flooding can have a huge social, economic and environmental impact - and with climate change it is expected that such impacts will only increase in the future.

These concerns have led the Construction Industry Research and Information Association (CIRIA) to commission MWH to develop guidance for its members on retrofitting surface water infrastructure in urban areas to manage flood risk and address concerns about water pollution (CIRIA Project RP922).

This will not just cover sustainable drainage systems (SUDS), but other forms of traditional and adaptive drainage techniques above and below ground, for example water re-use and green roofs, leading to piped systems and urban ponds, with discharge to the ground or to a receiving water body such as a river.

The guidance will be backed by a process to support practitioners make the right decision for what can and cannot be incorporated into the existing urban area.

Drainage design
In an attempt to address the current situation, providers of sewerage services alone in the UK are investing some £200M annually on sewer flooding management, with similar amounts also being invested by the Environment Agency (EA) and local authorities - but everyone recognises that more needs to be done.

There is growing acceptance that a more sustainable approach to drainage design is required, and that it is also feasible. Much of the work in this area has so far focused on sustainable drainage systems (SUDS) and designing for exceedance in drainage systems for new developments.

Within a context of providing better places to live, it is increasingly desirable for more sustainable surface water management options to be retrofitted to existing developments, rather than just being implemented in "new build" situations. This supports the delivery of multiple objectives of flood risk management, water quality improvement, and climate change adaptation and mitigation.

Retrofitting surface water management is a relatively new concept in the UK and the research and guidance work has, in the main, been limited to feasibility studies for specific catchments.

Our guidance will investigate the wide range of options for retrofitting surface water management infrastructure, and will help determine critical success factors. This will be set within a framework that can assist in delivering improvements to flood risk management, water quality and other benefits. Particular areas of benefit to the industry will be:
  • Helping engineers and planners design and manage drainage systems in a more holistic and sustainable manner
  • Enhancing knowledge gained from existing research and ensuring this is progressed into practical delivery and implementation
  • Helping those delivering and managing infrastructure to positively respond to the challenges of climate change adaptation and mitigation as well as delivering improved value to customers
The project aims to dispel some of the myths surrounding retrofitting surface water management and provide professionals, particularly within local authorities and the water and sewerage companies with the confidence to design and deliver innovative approaches to managing urban flood risk and water quality.

Carbon footprint
Climate change mitigation and adaptation through the retrofitting of surface water management will facilitate improved flood risk management and reduce energy consumption and carbon footprint during the construction and management of urban drainage systems. This could help providers of sewerage services to manage their carbon footprint and operational expenditure by reducing flows and intermittent discharges, and the subsequent need for pumping.

Paul Shaffer, CIRIA's manager for the project, is enthusiastic on the potential impact the guidance could have: "The industry has, until now, primarily focused on opportunities within new developments. This project will improve the way we manage water within the existing urban environment, engaging a variety of disciplines with the potential to deliver multiple benefits."

At MWH, we are pleased to be working with CIRIA at the forefront of this vital area, helping to develop potential strategies for flood management in our existing urban areas.

This is not just an issue for new build developments - the current urban infrastructure needs to be adapted to meet the challenges that are with us now, and those that seem sure to come.

Chris Digman is principal engineer at MWH. E: christopher.j.digman@mwhglobal.com

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