The Hull floods of 2007: implications for the governance and management of urban drainage systems

On 25 June, the City of Hull suffered from extensive pluvial flooding, causing damage to over 8600 homes and 1300 businesses. Over 100 mm of rain fell over a 24-h period, rapidly overwhelming the city's drainage system. Hull is especially vulnerable to flooding as it is largely below sea level and relies on a pumped drainage system with no natural ways of drainage. The causes of the flooding can be locally attributed to blocked roadside gulleys but in the main were due to issues with the conveyance of drained water in sewers and the performance of the three pumping stations. In particular, an extensive redesign of the system in 2001 increased flood storage and reduced the pumping capacity. In 2004, remodelling of the 2001 system indicated that it may be underpredicting flood volumes by 100% and decommissioned pumping stations were re-activated to rectify matters. Subsequent modelling showed that the performance of the drainage system in 2007 was slightly worse than its 2001 configuration. The floods also revealed a series of key weaknesses in how urban drainage systems are managed. There is no system of warning from surface water flooding in the United Kingdom, despite there being an extensive warning system for coastal and fluvial flooding. Urban drainage is largely designed to accommodate 1 in 30-year events, but this level is not appropriate in all areas, especially low-lying regions with little or no natural drainage such as Hull. Finally, the structure of the UK water industry postprivatisation, with Local Authority, the Environment Agency and the Water Utility all having control over separate parts of the system, left no single agency with lead control or responsibility for urban surface water flooding.