The data consists of separate packages of data for each large raised reservoir showing the flood extents for two scenarios; a “dry-day” and “wet-day”.
The dry day scenario shows the flood extent in the event that the reservoir were to fail and release the water held on a “dry day” when local rivers are at normal levels.
This wet day scenario shows the flood extent in the event that the reservoir were to fail and release the water held on a “wet day” when local rivers had already overflowed their banks.
Each scenario represents a prediction of a credible worst case scenario, however it’s unlikely that any actual flood would be this large. The data gives no indication of the likelihood or probability of reservoir flooding.
Flood extents are not included for smaller reservoirs or for reservoirs commissioned after the reservoir modelling programme began in October 2016. Attribution statement: © Environment Agency copyright and/or database right 2025. All rights reserved.
