Future FRM>Water, water, everywhere - The widespread flooding of summer 2007 demonstrated the severe financial and social consequences of surface water flooding in urban areas with the combined damage estimated at £3 billion. This issue is predicted to worsen with climate change and is made all the more obvious by the number and severity of floods that have occurred since. The Environment Agency, as part of its review of the floods, estimated that two-thirds of the 57,000 homes affected in 2007 were flooded from surface water runoff overloading drainage systems. In this context, surface water flooding describes flooding from sewers, drains, small water courses and ditches that occurs during heavy rainfall in urban areas. In his review of the 2007 floods, Sir Michael Pitt made recommendations for local authorities to take the lead on coordinating the management of local flood risk and for Surface Water Management Plans (SWMPs) to form the basis for accomplishing this. These recommendations were accepted by the Government and have been incorporated into the draft Flood and Water Management Bill currently before Parliament. A Surface Water Management Plan is a framework through which key partners, with responsibility for surface water and drainage in their area, work together to understand the causes of flooding and agree the most cost effective way of managing the risk. This partnership typically involves different tiers of local government with key inputs from the Environment Agency and water companies with leadership from the county or unitary authority. Other partners may include local community groups and conservation groups. |
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Considerable work has already been carried out by Defra, local authorities and flood risk consultants to develop the methodology for SWMPs. In 2007/08 Defra funded 15 Integrated Urban Drainage (IUD) pilot studies under its Making Space for Water programme. The objectives of this programme were to understand the causes of urban flooding and the best ways of managing drainage, examine the effectiveness of partnership working between various drainage organisations and test the effectiveness of new approaches to urban flood risk management.
Entec was heavily involved in two of the pilots - Camborne, Pool and Redruth (CPR) in Cornwall and Telford and Wrekin in the West Midlands. These two pilots were unusual in that draft SWMPs were produced for both areas and in both cases were incorporated into local planning guidance. Output from the studies included identification of overland flow routes for excess flow based on a strategic overview of sub-catchment drainage and guidance for developers on drainage requirements for particular areas. As a result of the pilot IUD programme the need for SWMPs was recognised and new draft guidance was prepared for Defra based on the outputs from the programme. Recommendations from the CPR and Telford pilots provided important input to the guidance, particularly in relation to the advantages of providing strategic drainage systems within regeneration areas.
In December 2008 six local authorities with particularly severe surface water flooding issues were given funding to trial the draft guidance and prepare first edition SWMPs. In August 2009 the Government subsequently provided £15 million of funding to help local authorities’ co-ordinate and lead local flood management work. From this, 77 local authorities have been awarded grants by Defra to develop SWMPs in highest risk areas. A further £5m is now available for smaller projects in response to grant applications.
Surface water management plans are the key to finding sustainable, local solutions to drainage management. Their success relies on partnership working, the establishment of steering groups and good communication, with each partner seeing the benefits of the overall approach to ensure buy-in and cooperation. Data sharing between stakeholders is also essential to provide a clear picture of the current situation and for forward planning and establishing data protocols.
SWMPs offer the opportunity to provide a strategic solution to a drainage problem where all partners understand the risks and can contribute to a joint solution to the drainage management issues in their area. This can include establishing strategic Sustainable Drainage Systems (SuDS) rather than relying on site-by-site piecemeal solutions.
To find out more about SWMPs contact Nick Jarritt, Steve Anderton or Bill Finlinson on 0800 371733.
Case Study - Camborne, Pool and Redruth
Entec was appointed by Telford & Wrekin Council to assist in delivering a pilot IUD study for Defra, one of 15 funded by Defra around the country. The principal objective of the pilot was to prepare Surface Water Management Plans for new development zones within Telford to support new Supplementary Planning guidance. One of the aims of the study was to provide strategic drainage information based on sub-catchments to inform planning of future development and assist developers. |
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Entec developed innovative techniques to enable rapid production of flood risk data that would assist planners and developers in the initial stages of site design. In particular the study considered overland flows, when the conveyance capacity of the urban drainage system is exceeded and excess flow is conveyed on the ground by surface flood pathways. Initially a broad-scale borough-wide analysis was conducted using 2D TuFlow pluvial modelling whereby a design rainfall event was simulated over the Borough and the resulting runoff flowed according to the underlying digital terrain model. This gave strategic information on indicative flow pathways and areas of ponding during extreme events. A key development site in the town centre formed the focus of more detailed studies in which the input and output data were verified on the ground and inflows to the model were modified in the form of FEH flow hydrographs. Additional detail was provided by modelling the piped surface water drainage networks. This formed the basis of designing strategic overland routes to convey excess flow from and through the site to established storage features. The project involved working in close co-operation with both the Council’s drainage engineers and planners as well as consulting with the stakeholder group which included the Environment Agency and Severn Trent Water. Results from the modelling fed into a report to Defra on the lessons learned and benefits realised by employing a new integrated urban drainage approach. |
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