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Three-dimensional flow structure and bed morphology in large elongate meander loops with different outer bank roughness characteristics
- Konsoer, Kory M., Rhoads, Bruce L., Best, James L., Langendoen, Eddy J., Abad, Jorge D., Parsons, Dan R., Garcia, Marcelo H.
- Water Resources Research 2016 v.52 no.12 pp. 9621-9641
- bedrock, coarse woody debris, geometry, momentum, riparian areas, roughness, spatial variation, stream channels, topography, velocity, water flow
- Few studies have examined the three-dimensional ﬂow structure and bed morphology within elongate loops of large meandering channels. The present study focuses on the spatial patterns of three-dimensional ﬂow structure and bed morphology within two elongate meander loops and examines how differences in outer bank roughness inﬂuence near-bank ﬂow characteristics. Three-dimensional velocities were measured during two different events-a near-bankfull ﬂow and an overbank event. Detailed data on channel bathymetry and bed form geometry were obtained during a near-bankfull event. Flow structure within the loops is characterized by strong topographic steering by the point bar, by the development of helical motion associated with ﬂow curvature, and by acceleration of ﬂow where bedrock is exposed along the outer bank. Near-bank velocities during the overbank event are less than those for the near-bankfull ﬂow, highlighting the strong inﬂuence of the point bar on redistribution of mass and momentum of the ﬂow at subbankfull stages. Multiple outer bank pools are evident within the elongate meander loop with low outer bank roughness, but are not present in the loop with high outer bank roughness, which may reﬂect the inﬂuence of abundant large woody debris on near-bank velocity characteristics. The positions of pools within both loops can be linked to spatial variations in planform curvature. The ﬁndings indicate that ﬂow structure and bed morphology in these large elongate loops is similar to that in small elongate loops, but differs somewhat from ﬂow structure and bed morphology reported for experimental elongate loops.