Environment Agency definitions:
A floodplain is the area that would naturally be affected by flooding if a river rises above its banks, or high tides and stormy seas cause flooding in coastal areas.
There are two different kinds of area shown on the Flood Map. They can be described as follows:
Dark blue shows the area that could be affected by flooding, either from rivers or the sea, if there were no flood defences. This area could be flooded:
from the sea by a flood that has a 0.5 per cent (1 in 200) or greater chance of happening each year;
or from a river by a flood that has a 1 per cent (1 in 100) or greater chance of happening each year.
(For planning and development purposes, this is the same as Flood Zone 3, in England only.)
Light blue shows the additional extent of an extreme flood from rivers or the sea. These outlying areas are likely to be affected by a major flood, with up to a 0.1 per cent (1 in 1000) chance of occurring each year. (For planning and development purposes, this is the same as Flood Zone 2, in England only.)
These two colours show the extent of the natural floodplain if there were no flood defences or certain other man-made structures and channel improvements.
A purple line shows all flood defences built in the last five years to protect against river floods with a 1 per cent (1 in 100) chance of happening each year, or floods from the sea with a 0.5 per cent (1 in 200) chance of happening each year, together with some, but not all, older defences and defences which protect against smaller floods. Flood defences that are not yet shown, and the areas that benefit from them, will be gradually added.
Hatched areas benefit from the flood defences shown, in the event of a river flood with a 1 per cent (1 in 100) chance of happening each year, or a flood from the sea with a 0.5 per cent (1 in 200) chance of happening each year. If the defences were not there, these areas would be flooded.
Flood defences do not completely remove the chance of flooding, however, and can be over-topped or fail in extreme weather conditions.
For information on flood defences which are not yet shown on the map, contact your local Environment Agency office.