Flooding from main rivers is caused by heavy rainfall upstream, and can also be caused by flood surges up rivers from the sea – caused by high tides, low pressure and strong winds.
River flooding is often able to be identified well in advance, and Flood Alerts are able to be used to warn those living in flood risk areas in addition to any press reporting, and river flood defences can be raised.
River flooding is often typified by long durations and relatively high velocities. We have a relatively good level of data to understand areas susceptible to river flooding, with studies of catchment areas, river profiles and flood plains helping the provision of effective river flood defences. Some river flood defence schemes utilise land upstream to store floodwater to regulate the flow through constrictions – typically through towns and cities.
The main options for river defences are:
Permanent solid flood walls and banks: These have the benefit of being permanently installed, with minimal operation and maintenance cost. However, the visual amenity of rivers within an urban setting mean that these flood defence solutions can be obtrusive, especially if above 1 metre in height.
Demountable river barriers: These river defence barriers normally comprise removable posts and beams that can be fitted along the side of a river in advance of a flood. There is no visual intrusion when not installed, but they do require a logistical operation to install and remove each time.
Glass Floodwalls: These have the benefit of offering permanent flood defence, whilst minimising the visual impact. Glass floodwalls can be incorporated with a solid wall to give greater heights of river flood protection, as well as with flood gates or demountable river defences. The Environment Agency’s recent 'Wells-Next-the-Sea' project illustrates the benefits of a glass floodwall over permanent and demountable defences.