Because of steep slopes, rapid flow, and large amounts of sediment, rivers in Taiwan are mainly braided rivers, which comprise several bars and exhibit bifurcated flow. Channel shifting behavior and bar migration in natural conditions create difficulties for river engineering work. In this study, the Nays2DH model is used to simulate the braiding processes and the morphological changes downstream of the Shih-Kang Dam in Da-jia River from 2012 to 2013. Furthermore, the characteristics of riverbed erosion, channel stability in its longitudinal and transverse directions,and the impact of river structures on its morphology were analyzed. The numerical simulation results revealed common braiding processes and statistical topographic characteristics, as exhibited by natural rivers. The scour pools mostly occurred at the apex of the river bend and downstream from bars (confluence) in braided rivers, which means that bar migration is the main factor altering the scour position. Under the assumption of sediment transportation in equilibrium at the upstream inflow, the width of the channel determines whether the river undergoes longitudinal erosion or transverse changes. The results of this research serve as a reference for future research on river morphology evolution, river engineering, and river spatial planning.
Key word: Braided River, Numerical model, Nays2DH, Da-jia River, River structure