| Summary: | 碩士 === 國立聯合大學 === 土木與防災工程學系碩士班 === 100 === Taiwan is located at the intersection of the Euro-Asian continent and the Pacific Ocean, and it suffers from typhoons during both summer and fall. The annual rainfall is substantial, averaging 2,500 mm, of which almost 80% falls during the period May to October as a result of the Mei-yu fronts and associated typhoons. Rivers in Taiwan are short and exhibit steep gradients. Many are meandering, which tends to encourage midstream/downstream flooding when heavy rainstorms arrive in a basin. As a result, flooding causes serious economic and social impacts every year in Taiwan. The rainfall patterns will significantly change due to the climate change, probably resulting in the increases of precipitation and runoff during the wet season. Whether the increasing runoff results in overtopping and flood inundation as well as the adaptive responses, it should be extensively studied. In this study, the FLO-2D model is implemented and applied to investigate flooding extent and depth in the Cishan Creek basin under 100-year and 200-year return periods pre and after climate change conditions.
The events of typhoon Kalmaegi, typhoon Sinlaku, and typhoon Morakot were adopted to validate the FLO-2D model. This model reproduced the observed discharge data at Nanfeng Bridge of Cishan Creek. The model also actually catches the observed inundation extents which were collected from the National Science and Technology Center for Disaster Reduction and Water Resources Agency. The validated model was applied to project the flooding inundation under the 100-year and 200-year return periods pre climate change. The results show that the left bank of the Cishan Creek is subject to serious inundation.
The model was also used to simulate the flooding inundation under different return periods and climate change (i.e. A1B, A2, and B1 scenarios). The modeling results reveal that the flood inundation occurs at the Cishan District, Meinong District, and Linang District. The overtopping locations are situated between No.1 to No.21 of left bank in the Cishan Creek, because the embankment elevation is less than water level. Three potential strategies including the river dredging, establishment of artificial lake, and embankment uprising are proposed to decrease the flooding extent and depth in the Cishan Creek basin. The simulated results indicate that the inundation area reduce 233ha by establishment of artificial lake, 118ha by river dredging, and 160ha by embankment uprising. If all of three improving strategies are adopted, the reduction of inundation area would be 379ha.
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