Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd.Ī meandering river forms an elaborate floodplain topography through meander initiation, expansion and cutoff (Hickin and Nanson, 1975 Hooke, 2004). This insight extends to many more fluvial, estuarine and coastal systems in morphological models and experiments, which require sustained dynamic perturbations to form complex patterns and develop natural dynamics. Our modelling of self‐formed meander patterns is evidence that scroll‐bar‐dominated and chute‐cutoff‐dominated meanders develop from downstream convecting instabilities. This explains why, in previous experimental studies, dynamic meandering was only accomplished with a sustained upstream perturbation in flumes that were short relative to the meander wavelength. The sinuosity, braiding index and meander period, which emerge from the inherent biomorphological feedback loops, are unrelated to the inflow perturbation period, although the spin‐up to dynamic equilibrium takes a longer time and distance for weak and absent inflow perturbations. This generates an intricate channel belt topography with point bar complexes truncated by chutes, oxbow lakes, and scroll‐bar‐related vegetation age patterns.
#Formation of a meander series
Following the cutoff cascade after initial meander formation from a straight channel, all runs with sufficient vegetation show series of growing meanders terminated by chute cutoffs. We tested the effect of a transversely migrating inflow boundary by varying the perturbation period between runs over an order of magnitude around typical modelled meander periods. We extended the morphodynamic model Nays2D with growth and mortality rules of vegetation to allow for meandering. Here, we numerically study the effect of the inflow perturbation period on the development and meander dynamics of a chute‐cutoff‐dominated river, which requires two‐dimensional modelling with vegetation forming floodplain on bars.
However, it remains unknown whether the period of the inflow perturbation affects self‐formed meander dynamics. Past experiments, one‐dimensional modelling and linear theory have demonstrated that the initiation and persistence of dynamic meandering require a periodic transverse motion of the inflow. Thus, the meanders have a distinct asymmetrical profile.A sustained dynamic inflow perturbation and bar–floodplain conversion are considered crucial to dynamic meandering. This is due to helicoidal flow which transports sediment eroded from the concave bank downstream to the next convex bank. The erosion of the outside bank of the meaner is accompanied by deposition on the convex bank (the inside of the meander), forming a sandy or gravelly area called a point bar or slip off slope. Energy increases within a pool area due to less friction and is then lost as the water flows over the shallower riffle where friction is greater.įlow over pools and riffles become uneven and results in the maximum flow being towards one side downstream, producing erosion of the material of the concave bank, forming a river cliff. The spacing between pools and riffles is usually very regular, being five to six times that of the bed width. A sequence of deep sections (pools) and shallow sections (riffles) develops at equal intervals along a stretch of the river. This causes erosion in some areas of the banks where velocity is high and deposition in other places where velocity is reduced.
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