In the second bend with the outer-bank embayment, the entire horizontal recirculation zone in the outer bend disappeared due to the topographic forcing of the flow into this zone. Just downstream of the bar there was a weak recirculation zone near the inner bank, whilst the outer bank from the apex onwards showed strong vertical flow structure. The mobile bed responded dramatically to the sharp bend flow structure, with deep outer-bend pools and high bars approaching the water surface at the inner bank which almost completely removed the flow-separation-recirculation zone in the first constant-width bend. Possibly there is a relation with the degree of curvature. Results did not indicate any dependence of flow separation on the Froude number, which contradicts previous observations in natural river bends. We measured the detailed flow structure in sharp bends with i) constant width, and ii) an outer-bank embayment, in the Total Environment Simulator flume facility at the University of Hull across a range of flow conditions and over both fixed and mobile beds. MEANDER BENDS SERIESWe will present the results from a series of experiments of flows within sharp meander bends. While many smaller or confined meandering rivers have bends that are sharp enough for flow separation and recirculation, the problem has been little studied in the meandering literature. Downstream of such abrupt changes, zones of flow recirculation often exist. It is well known that abrupt changes in flow direction can lead to flow separation from boundaries. In many small and some large rivers, extremely sharp meanders frequently occur, sometimes with large embayments in the outer bank region. River meanders exhibit a wide variation of bend radii relative to channel width.
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