PPS 15: Planning and Flood Risk
Annex A: Flooding from Artificial Drainage Systems
A8 If the scale of a rainfall or storm event exceeds the capacity of ditches, drains, culverts and sewers to convey the water out of an area flooding may result. Such flooding can happen during events below the design capacity of the system when capacity is temporarily reduced due to a blockage. Flood events of this type while typically localised can be particularly unpleasant as the flood waters can be contaminated with sewage and can enter properties through the foul drainage system.