ABSTRACT: A distributed watershed model combining kinematic wave routing, 1-D dynamic channel-flow routing, and 2-D diffusive overland-flow routing has been developed to simulate flooding and inundation levels of large watersheds. The study watershed was linked to a GIS database and was divided into an upstream mountainous area and a downstream alluvial plain. A kinematic wave routing was adopted at the mountainous area to compute the discharge flowing into the alluvial plain. A 1-D dynamic channel routing solving the St. Venant equations by the Preissmann method was performed for the main channel of the alluvial plain, whereas a 2-D overland-flow routing solving the diffusion wave equation with the Alternating Direction Explicit scheme was used for floodplains. The above two routings were connected by weir-link discharge formula. The parameters in the model were calibrated and independently verified by single-event storms. An example application of flooding/inundation analysis was conducted for the Taichung station and the Woozi depot (Taiwan High Speed Rail). Suggested inundation-proofing measures - including raising ground surface elevation of the station and depot and building a waterproofing exterior wall and their combination - were investigated. It was concluded that building the waterproofing exterior wall had a strong tendency to decrease peak inundation depth.