Multiscale structure of meanders
Vermeulen, B. ; Hoitink, A.J.F. ; Zolezzi, G. ; Abad, J.D. ; Aalto, R. - \ 2016
Geophysical Research Letters 43 (2016)7. - ISSN 0094-8276 - p. 3288 - 3297.
bends - meanders - multiple loops - scale space tree - valley cuvature - wavelets
River meander planforms can be described based on wavelet analysis, but an objective method to identify the main characteristics of a meander planform over all spatial scales is yet to be found. Here we show how a set of simple metrics representing meander shape can be retrieved from a continuous wavelet transform of a planform geometry. We construct a synoptic multiple looping tree to establish the meander structure, revealing the embedding of dominant meander scales in larger-scale loops. The method can be applied beyond the case of rivers to unravel the meandering structure of lava flows, turbidity currents, tidal channels, rivulets, supraglacial streams, and extraterrestrial flows.
Redistribution of velocity and bed-shear stress in straight and curved open channels by means of a bubble screen: laboratory experiments
Blanckaert, K. ; Buschman, F.A. ; Schielen, R. ; Wijbenga, J.H.A. - \ 2008
Journal of Hydraulic Engineering 134 (2008)2. - ISSN 0733-9429 - p. 184 - 195.
waterbouwkunde - kanalen, klein - hydrodynamica - waterstroming - buigen - herverdeling - snelheid - turbulentie - laboratoriumproeven - hydraulic engineering - channels - hydrodynamics - water flow - bending - redistribution - velocity - turbulence - laboratory tests - submerged vanes - secondary flows - alternate bars - topography - bends - rivers
Open-channel beds show variations in the transverse direction due to the interaction between downstream flow, cross-stream flow, and bed topography, which may reduce the navigable width or endanger the foundations of structures. The reported preliminary laboratory study shows that a bubble screen can generate cross-stream circulation that redistributes velocities and hence, would modify the topography. In straight flow, the bubble-generated cross-stream circulation cell covers a spanwise extent of about four times the water depth and has maximum transverse velocities of about 0.2 ms¿1. In sharply curved flow, it is slightly weaker and narrower with a spanwise extent of about three times the flow depth. It shifts the counter-rotating curvature-induced cross-stream circulation cell in the inwards direction. Maximum bubble-generated cross-stream circulation velocities are of a similar order of magnitude to typical curvature-induced cross-stream circulation velocities in natural open-channel bends. The bubble screen technique is adjustable, reversible, and ecologically favorable. Detailed data on the 3D flow field in open-channel bends is provided, which can be useful for validation of numerical models