Estimation of 1D-confluence model parameters in right-angled discordant beds’ confluences using 3D numerical model

Abstract

Parameters of 1D confluence models are originally defined for concordant beds’ (CB’s) confluences. This paper aims at estimating these parameters for discordant beds’ confluences using numerical simulation results of 3D flow. A 3D finite-volume based model SSIIM2 that was successfully validated in CB’s confluences is applied in this study, too. Confluences with the low, moderate and maximal observed bed elevation discordance ratio values are analysed for three characteristic hydrological scenarios: dominance of the tributary flow, equal contributions of the combining flows and dominance of the main-river flow. It is shown that: 1) the mean flow angle δ approaches junction angle α with the increase in bed elevation discordance, especially when tributary flow dominates, 2) the value of Hager’s correction coefficient σ is not constant and 3) the contribution of the tributary flow to the 1D momentum equation is under predicted when either parameter δ or σ is used for its estimation.