ABSTRACT
Typhoon Morakot which invaded Taiwan in August 2009 and brought 2249 mm of rain with maximum intensity of 157 mm/h in three days. Landslide from headwater watershed caused severe sedimentation problem in Lai-Sher Stream and Nei-Sher tributary. Maximum depth of sediment deposited reached 37.8 m from Mileage 6K to 7K and 17.3 m in the study reach. Subsequent LiDAR and field survey indicated that Lai-Sher Stream has been continuously downcutting that made implementation of countermeasures difficult. Therefore, a 1:300 scaled mobile-bed hydraulic model was built to test the feasibility of several countermeasure scenarios. Laser profiler was used to scan the channel bed elevations prior to and after experiments. UAV was deployed to document the channel and flow behaviors as well as to conduct PIV measurement. Combination of countermeasures, which included channel dredging, caisson foundation, and spur dikes finally passed all the task objectives satisfactorily at 50-yr return period flow.
