Floodplain Connectivity and implications for flooding and floodplain function

Regime theory suggests that floodplains should be inundated on average once every two years to maintain form and function of both the river and the floodplain. Natural disconnection along non-alluvial reaches and where the river has moved to flow against terrace edges is to be expected, however, disconnectivity caused by river management is now affecting increasing lengths of watercourses. This study utilises aerial Lidar data to determine the relative height difference between the watercourse and adjacent valley bottoms to assess the degree of disconnectivity along main river systems across Cumbria in the UK. The results reveal that many rivers are now poorly connected to their floodplains which are now largely non-functional. Floodplain geomorphic units, although often present, are currently inactive and water table levels are reduced resulting in a loss of wetland in favour of ruderal species tolerant of drier conditions. The causes of such widespread disconnectivity may be attributed to historic dredging and straightening of these rivers and revetment and riparian tree planting has further exacerbated the problem restricting lateral activity and the subsequent development of new areas of connected floodplain. The high degree of disconnection has implications for future river management and river restoration and these are discussed.