Morphodynamics of active meandering rivers reviewed in a hierarchy of spatial and temporal scales

Meandering planforms are common on rivers but active, rapidly changing meandering channels are particularly instructive in indicating meander processes and dynamics and can extend our understanding of fluvial behaviour more generally. Questions arise in relation to the relative effects of flow events, phases and sequences of conditions, on the extent of autogenesis in changes, and the spatial propagation of change. In this review, the direct field and real-world evidence of the morphodynamics is examined through a hierarchy of spatial and temporal scales. Within bends, the channel interaction with bars is a major component of the morphodynamics. High variability in rates and patterns between events and years is evident, but a systematic sequence of mid-channel bar development emerges. Relations to discharge parameters are complex. At bend scale, clear autogenic sequences of bend evolution from simple loops to compound forms then cut-offs are apparent, in spite of short timescale episodicity and variability, and modulation by bank inhomogeneities. Two major morphodynamic issues are discussed, that of migration rate-curvature relations and of push-pull of bends. Cut-offs are important in active bend morphodynamics and an immediate phase of widening and multiple bars within the cut-off zone commonly occurs but then the channel stabilises. Conditions for clustering of cut-offs are discussed. Analysis at reach scale of multiple bends tends to produce much more systematic morphodynamics relations but may be obscuring the spatial and temporal variability. Evidence is equivocal on the extent and rates of spatial propagation of changes, some indicating change tends to be localised but other showing systematic interaction between bends. Much adjustment is by local feedbacks. The high rates and variability of the morphodynamics of active meandering rivers have implications and challenges for management. A strategy of allowing for the mobility is advocated. That requires understanding of the morphodynamics.

Automated summary

Meandering rivers have constantly changing planforms, which can provide guidance on river behavior. The interaction between channels and bars is a major component of morphodynamics at bends. Cut-offs are important in active bend morphodynamics, but then the channel stabilizes. The high rates and variability of morphodynamics in rivers pose challenges for management.