Flood Routing Modeling to calculate Levee-Break and Overbank Flows in Danshuei River system due to Mega Even

• Main Authors: Chung-Ying Wu, 吳仲英
• Other Authors: Wen-Cheng Liu
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/08300100093191193011

碩士 === 國立聯合大學 === 土木與防災工程學系碩士班 === 96 === Due to the global change, amount of precipitation increase year by year. In summer and fall seasons, the typhoons, or tropical cyclones, with the torrential rainfall occur frequently because of the attributes of the subtropical climate in Taiwan. It will result in levee-break and/or overtopping the banks at the narrow neck locations in the river system and produce the inundation. The study domain includes main and tributaries in the Danshuei River system in northern Taiwan that covers Tahan Stream, Hsintien Stream, Jiang-Mei Stream, Erchung floodway, and Keelung River. The hydrological, geometric, and hydrodynamics data have been collected and analyzed to supply for the model simulation. The storm surge hydrograph has been designed served as downstream boundary condition at the Danshuei River mouth. Based on flood routing model, the levee-break and overtopping functions was developed and incorporated into the one-dimensional unsteady flood routing model that consists of continuity and momentum equations to predict the levee-break and/or overbank discharges. In order to test the model availability, Typhoon Talim (2005) was severed as study case and assumed the levee-break in the tributary of Tahan Stream. The sensitivity analyses were conducted with different scenarios such as levee-break width, duration, and final water level. To validate suitable modification of the model, the Typhoon Nari (2001) was used to calculate the overbank discharge in the Danshuei River system. The modeling results reveal that Typhoon Nari seriously resulted in overtopping the banks at the upper reaches of Keelung River. The simulated results of these two cases indicate that the developed model for calculating levee-break and overbank discharges is available. Five typhoon events were selected for model calibration and verification to ascertain the Manning friction coefficient (n) in the river system. Typhoons Area and Nock-ten were severed as model calibration, while Typhoons Matsa, Talim and Longwang were acted as model verification. Statistical errors between modeling results and field measured data of water stages were used to quantify the model capability. The simulated results of water stages are in qualitative agreement with the measured data at various gauge stations. The model utilities were performed for modeling the levee-break and overbank flows resulted from mega events in the Danshuei River system. The validated model is then used to simulate five different situations of extreme rainstorms when the upstream catchment occur the mega events and the downstream boundary at the river mouth happens the storm surge concurrently. Through the scenarios runs, overbank discharges at the narrow neck are evaluated. If the mega events happen, the levee-break location at the Taipei Bridge is used to calculate the levee-break discharge.