Abstract
Midchannel islands (MCIs) are influential instream geomorphic units
generally emerge in lowland rivers. Despite their significant
ecomorphological services in the river ecosystem, the flow structures
around these self-forming riparian landforms are not fully understood
yet. Understanding the flow pattern around these formations enables
practitioners to produce cost-effective, sustainable, and eco-friendly
river management projects/strategies. From this motivation, the
secondary flow pattern around MCIs was analyzed employing RANS based
numerical model. Flow around the simplified bodies were simulated to
give a more precise analysis regarding flow-island interactions. Once
the numerical validation process was completed for the cylinder using an
experimental dataset, the validated model was implemented for islands
(streamlined island, vertically sloped island (VSI), and realistically
sloped island (RSI)). The simulations revealed these findings: 1) The
RSI acted like a streamlined object and produced weaker lee-wake
vortices with a longer recovery distance. 2) The RSI gained a better
streamlined form near the bed than near the water surface due to
enhanced elongation. 3) This situation generated highly variable
coherent flow structures along the depth behind the MCI. 4) Due to the
three-dimensionality of the RSI, the generated large-scale vortices
propagated asymmetrically towards sides of the channel rather than
remaining around the centerline.