Application of SSIIM1 Model to Investigate The Effect of The Open-Channel Junction Angle on The Flow Characteristics

River channel confluences form one of the most important morphological elements in river systems. The entry of a lateral inflow into the main channel generates substantial changes to the flow velocities and turbulence, and result in characteristic patterns of scouring and deposition. Junction angle has highlight effect on flow pattern in open channel junction. In this research the capability of SSIIM1 model to simulate the 3D flow at channel junction and the effect of junction angle on its pattern have been investigated. Using the experimental data of a 90° junction flow collected by Weber et al. (2001) in Iowa University the model was calibrated and validated. Good agreement is obtained between simulated velocity profile and water surface mapping by the SSIIM1 model and the experimental measurements so that the maximum error to predicted water surface and velocity value was about 3% and 10% respectively. The model is then applied to investigate the effect of three junction angles (45, 90 and 135°) on the flow characteristics such as: Bed shear stress, separation zone dimension, and secondary flow pattern and water surface and velocity profiles. The result showed increasing junction angle leads to higher separation zone dimension. For 45o junction angle a clear separation zone has not appeared. Shape index of separation zone (wide to length ratio) were calculated as 5.8 and 7.45 for 90o and 135o junction angle, respectively. The ratio of upstream depth to downstream depth of junction is 1.05, 1.06 and 1.09 for 45°, 90°, and 135°, respectively. Also the result indicated that increasing the junction angle from 45°to 135° bed shear stress increases about 80.2%.