To ask the Secretary of State for Environment, Food and Rural Affairs what capacity of excess rainfall the storm water and sewerage system of each major urban area in England can bear; and if he will make a statement.
My Department does not hold this information. Water and sewerage companies are responsible for assessing the capacity of public sewers in order to ensure the effectual drainage of their area.
Typically, the public sewerage system overall is designed to withstand a one-in-30-year storm event and waste water treatment works are designed to deal with six times dry weather flows without discharging excess water to a watercourse.
It has been estimated that up to 50 per cent. of the sewerage network may be in private hands (for example, householders) and information on capacity for this section of the network is not available. Earlier this year, the Government announced that existing private sewers and lateral drains that drain to public sewers would be transferred into the ownership of water and sewerage companies. This will significantly improve the integrated management of the sewerage network as a whole.
As well as private sewers, there is also an extensive network of surface water drainage associated with highways which is the responsibility of highways authorities. This frequently discharges and interacts with the public sewerage network.
DEFRA is also funding 15 pilot projects to test alternative approaches to the integrated management of urban drainage across the different organisations with responsibilities in this area.
The Office of the Water Services compiles figures on the numbers of properties at varying risk of flooding from overloaded public sewers. The price limits for 2005-10 allowed a programme of nearly £1 billion to safeguard homes against the risk of sewer flooding. By then, the proportion of properties at risk would reduce to 0.01 per cent. of households.