The significance of mid-channel bars in an active meandering river



Mid-channel bars are common on many active meandering gravel-bed rivers, but specific information on timescales of development and on the occurrence of bars is lacking. Data from the River Dane in Cheshire, NW England, are presented here which indicate that a sequence of formation from accumulations of coarse gravel on the centre of riffles through to attachment of bars to floodplains is common and takes a period of 5–15 years. The sedimentological and vegetation changes through the sequence are described and the ro̊1e of flow events is discussed. About 10% of bends in this meandering reach contain mid-channel bars at any time. Bars develop in steeper sections of the channel and downstream of sharp corners and rapidly eroding apices. Many of the bars are caused by excessive erosion of the banks which overwidens the channel. In the longer-term the bars become incorporated in the developing meanders.