| Summary: | 博士 === 國立彰化師範大學 === 地理學系 === 103 === The research area of this study is the Central Tablelands in Taiwan, which includes Houli, Tadu and Pakua Tablelands. It stretches over Taiwan’s youngest fold-and-thrust belt and features lithological homogeneity and time scale consistency, indicating that geomorphic evolution across the area is primarily controlled by structure. Studying river capture and landscape evolution in this area helps understand how active tectonics affect drainage evolution. Through interpretation of aerial photographs and field studies, patterns such as river capture and stream migration have been observed in the drainage systems in Houli, Tadu and Pakua Tablelands of the area. Pakua Tableland particularly has up to 65 beheaded valleys and 46 river captured catchments, topping the rest in the area. River captures by way of abstraction and headward erosion of beheading are actively taking place in the area. It is a common phenomenon that a beheaded river and a capturing river coexist in the same catchment. Based on the tectonic evidence of river captures in the Central Tablelands, including heights of beheaded rivers and wind gap terraces and watercourse states of diverted rivers, the degree to which these river captures have evolved can be inferred. There are two types of evolution. (1) In the early stage of a river capture, only the watershed in the course of a high-level river is cut open, resulting in partial river diversion. (2) In the maturity stage of a river capture, a beheaded river, a wind gap terrace and a diverted river have clearly formed, indicating that the river capture has entered its maturity stage.
The Wattsyao stream, Jhukengbei and Nanshihpo Ditches are located on the Tachia, Qingshui and Changhua faults, respectively, and are topographic features formed by erosion and faulty activity jointly. This study, using methods such as interpretation of aerial photographs, field studies, topographic measurement, and tectonic geomorphology indices, reveals river capture mechanisms in the Jhukengbei and Nanshihpo Ditches and their implications for tectonic geomorphology. Findings of this study show that the drainage basins of the Wattsyao stream, Jhukengbei and Nanshihpo Ditches are influenced by east-southeastern stress and have developed asymmetrically, and active tectonics continue to extend northward or northwestward, causing river captures.
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