Loss of sediment transfer to the floodplain

A reduction in the amount of fluvially-transported sediment that is deposited on the floodplain surface during overbank flows. This can be attributable to modifications which disconnect the river from the floodplain (e.g. embankments and revetments); alterations to the flow regime which reduce the frequency and / or duration of overbank flows and increase in-channel capacity allowing smaller return events to be contained within the channel. A reduction in the volume of sediment that is trnasferred from a river to its floodplain can cause a variety of geomorphological and ecological responses. The loss of channel-floodplain connectivity reduces the floodplain attenuation of sediments and as a result increases sediment loadings within the channel, which may increase turbidity in-channel sedimentation further downstream. Increases in in-channel sediment loadings can be detrimental to aquatic habitats by smothering coarse substrates and reducing light penetration through the water column. In addition, the reduction in sediment transfer to the floodplain can adversely impact upon riparian and floodplain habitats by reducing the supply of sediment-associated nutrients.

Flood embankments on the River Derwent in North Yorkshire, which reduce channel-floodplain connectivity