Reservoir flooding is extremely unlikely but has the potential to cause catastrophic damage to towns and cities, such as Derby, that lie downstream of reservoirs. Reservoir flooding could occur if the structures holding back water in the reservoir fail. Fortunately, due to the strict regulations of reservoir maintenance, reservoir flooding is the least likely source of flooding.
Whilst the Environment Agency enforces the Reservoirs Act 1975 in England, the safety of reservoirs is the responsibility of the reservoir's owner or operator. The responsibility of a reservoir’s owner includes regular maintenance of reservoir structures and arranging for regular inspection by qualified engineers to ensure that reservoirs are safe.
To assess the risk of reservoir flooding to your area, you can view the Environment Agency’s Risk of Flooding from Reservoirs datasets. It is worth noting however that these maps represent a worst case scenario, especially bearing in mind the very low likelihood of reservoir flooding.
The Environment Agency's Risk of Flooding from Reservoirs maps should not raise concern, but should make you think about what you might do if an emergency did happen and your home or workplace was at risk.