Natural rivers are often compound channels constituted by main channel and flood plain, the flow conditions are very complicated during the flood. The characteristics of Taiwan’s rivers include steep slope and fast flow, channel migration and bed erosion often happen at the lower-middle reaches. Under the global climate migration, the variation of rainfall intensity, rainfall duration, rainfall distribution and flow discharge induce extending the period of low water level or increasing the main channel flow. Therefore reconsidering assessment stability of channel and standard of protection embankment is necessary. Many of rivers on the Western Taiwan have the problems of channel migration, in the different types of river, the flow of meandering river through curve is affected by centripetal force, super-elevation, higher water surface of concave and lower water surface of convex, channel morphology affected by discharge.
This study adopts the assessment of future rainfall in Bajhang River made by NCDR, and uses SOBEK rainfall-runoff model to estimate the discharge. The results show under climate migration the return period between100 year and 200year exceed the amount of flood plan in the lower-middle reaches of Bajhang River, from Bajhang River Bridge to Housheng Bridge. Then analysis the stability of compound channel and the process of channel migration by using CCHE1D and CCHE2D sediment models simulating each cases of different return periods and long period case.