What does the dry day map tell me?
The reasonable worst case flooding that would result from an uncontrolled escape of water from a reservoir if the reservoir is full and when the river downstream is at a normal level.
What does the wet day map tell me?
The reasonable worst case flooding that would result from an uncontrolled release of water if the reservoir is full reservoir and the downstream river is in extreme flood.
Why do some reservoirs not have wet-day extents?
A wet-day scenario has not been run for all reservoirs. A wet-day scenario includes in the model representation of a river that is already flooded by an extreme flood downstream of the reservoir. If there is not a river downstream of the reservoir or the reservoir flood would be too small to have a significant extra effect a wet-day scenario has not been modelled.