Flood routing simulation for dam failure time estimation

Yeon-Cheon dam was built in Han-Tan river in south Korea in May 1985. It was originally constructed for the purpose of small hydro power made by concrete and partly earth. And it was located cross the mid stream of Han-Tan river having hilly topographic characteristic. Therefore it has run-of-river type reservoir with very short detention time and small storage volume. Yeon-Cheon dam was destroyed in 1st Aug. 1999 due to extremely heavy rain, and the dam failure yielded the disaster downstream area form dam site. But there is no accurate information and records about failure time and duration because it happened in the early dawn, so the public arguments are growing up to now. This case study is to predict the dam failure time and simulation model is established as an un-coupled type which are runoff model, dam breach model and flood routing model. The uncoupled model for prediction dam failure time include HEC-HMS model for runoff rate at dam site, DAMBRK module of FLDWAV model for flow rate through dam failure part, and unsteady simulation model called of HEC-RAS model for flood routing in the downstream reach from dam. Simulation results show that peak runoff rate at dam is 10,324 m³/sec total runoff volume is 1,264million m³ and peak time is 05:00 1st Aug. 1999. Where total rainfall during 4 days is 861.9mm and peak runoff rate of 10,324 m³/sec is exceeding in the design return period of 200 years of Han-Tan river. Also the simulated peak discharge through dam including gate over flowed is 12,054.8 m³/sec and dam failure time is estimated at 02:45 until 03:10 1st Aug. Dam failure time can be determined by comparing the simulated results of observed water surface stage.