The paper studies a combined effect of bed steps (BS) in both converging channels on the 3D flow in a confluence with alpha = 90 degrees. Nine combinations of bed elevation discordance ratio values in the two channels are analysed. It is shown that: 1) a portion of the tributary flow is redirected upstream and that the vertical flow deflection in the lower half of water column is significantly reduced when the BS in the main river is higher than that in the tributary, 2) the shape of the recirculation zone (RZ) and the delay in its development are strongly governed by the presence of the BS in the tributary, whereas the BS in the main river only affects the size of the RZ and the dynamics of its distortion and 3) both river banks are endangered by erosion in confluences with BSs in both converging channels. (C) 2016 The Authors. Published by Elsevier Ltd.