On the effect of the bed morphology on the river confluence hydrodynamics

Abstract

A river confluence is known for the strong three-dimensional flow effects. The confluence hydrodynamics is significantly influenced by the river bed morphology. Two morphological features are typical for river confluences: a discordance of the two river bed elevations at the entrance to the confluence and presence of a scour hole in the post-confluence channel. The objective of this paper is to examine the influence of these morphological features on the flow structure by using a three-dimensional numerical model. The confluence of the Sava and Danube Rivers (in the city of Belgrade) offers excellent possibilities for this investigation, as both bed elevation discordance and scour hole are present. The results of numerical simulations for this case are compared to the results obtained for the three hypothetical bed configurations of the same confluence: a) concordant bed elevations and the scour hole, b) concordant bed elevations and no scour hole, and c) discordant bed elevations and no scour hole. An attempt is made to generalise the results of numerical simulations. Results are discussed in terms of the secondary flow pattern and the distribution of the turbulent kinetic energy.