9,800 properties in Belfast are at ‘significant’ risk of flooding from rivers and 6,000 of which are also at risk of flooding by the sea.

The floodplain of Northern Ireland is designed to protect the surrounding areas from 1 in 100 year floods. This is the light blue colour on the diagram and illustrates the large portion of the city which lies within the floodplain. To prevent future flood damage, the mitigation techniques in place are mainly soft engineering, in the way of avoiding any further developments in the floodplain or coast that do not reduce the risk of flooding or harm the environment. In terms of attack, defend, retreat the plan for Belfast is heading towards retreat and defend. The council will retreat from building in the floodplain in hopes of reducing flood risk. In addition to this the finished floor level of new developments should be set to protect the owner in the event of a flood and to reduce damages. There are 4 causes of floods; Rivers, Coastal, Surface run-off and water impoundment (Reservoirs). Surface runoff is the one that can cause the most unpredictable damage in the form of flash floods. This is common in Belfast due to the poor drainage systems, built in the Victorian period and unsuitable for the growing city. Many of the rivers and tributaries have become culverted or modified in some way.; this and the urban environment has reduced ground filtration causing floods and water pollution problems. The Wastewater treatment works serving Belfast is above its theoretical design capacity, which will cause problems in the near future. Sustainable integrated drainage is stressed as an important part of new developments and adapting old to aid this problem.

The low lying areas of the coast is mostly protected, by accident, due to the docks and channels created when the harbour expanded. This has meant there are no formal sea defences, although the dock will not be effective against extreme events or sea level rise.