Due to numerous landslides caused by Typhoon Morakot in 2009, much loose sediment was deposited in the upper reach of the tributary of Laonong River. Loose material was transported into the main stream during the heavy rainfall of the typhoon and formed a tributary-dammed lake. If the dam were to fail, this would pose a significant threat to downstream villages. In this research, we present a diffusion equation–based one-dimensional semianalytical
model of a tributary-dammed lake breach. To estimate the most dangerous scenario, the model incorporates the intense
discharge caused by torrential precipitation during typhoons. To assess the security of downstream villages, the floods are routed by a one-dimensional kinematic wave solution for a nonuniform valley. The solution can simulate areas impacted by flooding with much reduced computational cost and topographical data requirements. Finally, the research applies combined methods to the tributary-dammed lake at the confluence of the Putunpunas tributary river with the Laonong River. The maximum flood elevation of the dam was estimated for breach floods under different scenarios.
Key Words: tributary-dammed lake, breaching model, kinematic wave model