Author(s): Fong-Zuo Lee; Jihn-Sung Lai; Student Cheng-Chia Huang; Yih-Chi Tan; Hui-Ming Hsieh; Zhi-Xian Yang
Linked Author(s):
Keywords: Sediment flushing efficiency; Netstarts; Long-term flood event
Abstract: Earthquake-triggered landslides in mountainous areas could supply large amount of sediment to river basin. Sediment produced in upper basins may not immediately deliver to lower basin owing to river aggradations. However, still great part of sediment can be transported and deposited in downstream river particularly during extreme rainfall events, which could generate turbidity current into a reservoir. Typhoon Aere of 2004 year attacked northern Taiwan. Flood-induced high sediment concentration of 242,000 Nephelometric Turbidity Unit (NTU) was measured in the Shihmen reservoir. After venting tunnel was implemented in 2013, morphological impact of river below the Shihmen dam was investigated in present study. Shimen Reservoir is one of the most important reservoirs in northern Taiwan. Due to sedimentation problem, Water Resource Agency updated the existed facilities, the deposition-prevented tunnel will also finish in the future. However, the river bed deposition will increase in downstream river when the sediment flushing efficiency lifted up. In order to understand the long-term river bed deformation, the one dimension model, NETSTARTS, was adopted in this research to simulate suspended sediment transport and river bed variation for the investigation of morphological changes in downstream river reach. The results show, bed elevation changes resulted from desiltation operation may affect the important issues in this study area, especially in the entrance of Erchung Floodway and the ferry routes. Different cases were used in this research, include of one flood event (Typhoon Aere, 2004) and long-term flood event (Imposing same hydrological conditions of Typhoon Aere for ten times). In conclusions, the effect of one flood event is not evident. In the other words, the effect would be obvious in long–term event. If sediment desiltation operation is implemented, the bed elevation changing from the Shihmen reservoir to the Tanshui river mouth would present deposition pattern. The highest deposition magnitude reaches 4 m between accumulated distances 25000 m to 32000 m, which may provide useful information for river management.
Year: 2016