Properties which are at risk of internal flooding due to overloaded public sewers are recorded by South West Water and disclosed in CON29DW reports.

A property which is likely to flood during a storm event of either 2 in 10 or 1 on 10 year magnitude may be considered to be added to the at risk register. That means a natural storm event with a 1 in 10 or 2 in ten recurrence is likely to cause internal flooding to the buildings of the property, because the public sewers cannot cope with the volume of sewerage and rainwater trying to flow through them.

All of these properties are reported to the water regulator, Ofwat, on an annual basis

A sewer is ‘overloaded’ when the flow from a storm is unable to pass through it due to a permanent problem i.e.: flat gradient or small diameter. Flooding as a result of temporary problems such as blockages, siltation, collapses etc. are excluded.

Although South West Water make every effort to remove this risk of flooding, changes in climate trends and increasingly dense residential and industrial development combine to add further chance of this risk becoming apparent.

The measures taken by South West Water to alleviate this risk vary from site to site. Upsizing of sewers, where practicable, or regarding the slope to ensure more efficient run through are also possible methods of change, however there are occasions where access or natural or other factors mean that we are unable to get to or work on the sewer in question. Remediation of these cases can often be expensive and take a long time to bring about.

There are properties which suffer from internal sewage flooding but which may be caused by problems other than sewer capacity, (blockages, collapses etc.) and there may be properties which flood as a result of overloaded private sewers. These would not appear on the register of ‘at risk’ properties held by South West Water. Properties may be at risk of flooding, but have not been included on the ‘at risk’ register where flooding incidents have not been reported to South West Water.

Similarly, properties which are or have been flooded by a storm event greater than 1 in ten years (one in 20, 40 or 50 for example) are also excluded from the At Risk register.

For further help and advice on the impact of sewer flooding, please contact South West Water’s helpline on 0344 346 2020.