Channel confluence is one of the important features of each river system and some hydraulic structures. The features that can dominantly control flow characteristics in a confluence are confluence angle, discharge, width ratios, and Froude number of flow. Several research studies have been conducted however a comprehensive three-dimensional (3-D) numerical study of flow characteristics in a confluence has not yet been reported. In the present study, SSIIM2.0, a 3-D numerical model, is validated and applied to investigate secondary currents, velocity distribution, flow separation, and water surface elevation in different conditions. The results of the present study illustrate that flow structure and water surface variations in a confluence are highly influenced by confluence angle, discharge, and width ratios as well as Froude number because of their effect on flow deflection, separation, and secondary currents. The graphs from the present study can be used to analyze water surface variation, velocity field, and flow separation dimensions in difference conditions for engineering designs.

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Internal erosion in composite stream banks can have negative effects on agricultural lands due to seepage, which can be affected by soil properties. We document the effects of physical and chemical properties of bank materials on the dimensions of cavities caused by internal erosion along the middle reach of the Atrak River. The goals were to (1) identify physico-chemical soil factors, (2) select significant factors affecting cavity dimensions, and (3) identify soil properties that could be used as indicators for future soil quality conservation programmes. Soil samples from nine locations with, on average, 25 cavities per 100 m, along a 50-km reach of the river were analysed. Using discriminant and factor analyses, five principal soil factors were identified, among which soil dispersion and Ca 2+ content most influenced cavity dimensions. The sodium adsorption ratio and total dissolved salts for the non-cohesive layer were found to be the most important quality-related properties.

The radial flow of air between two closely spaced parallel disks is studied experimentally and the behaviour of the flow, especially the turbulence decay mechanism, is examined. At high Reynolds numbers the flow resembles fully developed turbulent two-dimensional channel flow. A quasi-laminar boundary layer is found to gradually replace the viscous sublayer as the Reynolds number decreases. At low Reynolds numbers, the turbulence decays and the flow gradually approaches a laminar-type profile. The decay process is shown to be very slow and indications of a weak turbulence-generating mechanism is observed even at very low Reynolds numbers. Relaminarization, rather than being an abrupt change in the state of the flow, is an eventual outcome of the turbulence decay process.