Author(s): Chung-Yu Sun; Shaohua Marko Hsu
Linked Author(s): Chong-Yu Sun, Shaohua Marko Hsu
Keywords: Floodplain River Braided Index Riverbed Evolution Process Flume Experiment
Abstract: Taiwan is located at the convergence of tectonic plates, leading to frequent orogenic activities. This results in distinct geomorphic features on the main island of Taiwan, such as towering mountains, fragile geological structures, severe upstream riverbed erosion, and high sediment loads in rivers. Due to these characteristics, upstream rivers in Taiwan frequently carry large amounts of sediment downstream, causing the middle and lower reaches of rivers to shift between straight, meandering, and braided patterns. Another prominent feature of Taiwan’s middle and lower river reaches is the presence of floodplains. Due to Taiwan’s limited land area and high population density, every piece of land is highly valuable. Urban land is mostly used for construction or human activities, leaving little room for farming or building parking lots. As a result, floodplains along riverbanks are often used for crop cultivation or parking facilities. To ensure sufficient usable floodplain areas, protective measures must be implemented. For example, placing wave-dissipating blocks can prevent erosion caused by river meandering, which could otherwise reduce crop yields. These actions also directly restrict the natural meandering of the main channel, preventing it from evolving according to its original flow path. Given these phenomena, understanding the impact of channel width on river meandering is crucial. This study employs indoor flume experiments to investigate the effect of channel width on floodplain cultivation. By altering the channel width, the evolution of the flow path within the riverbed is observed, with particular focus on factors such as main channel meandering, slope, sediment transport rates, and the braided index. The results show that under the same slope, flow rate, grain size, and without sediment input from upstream, the main deep channel upstream deepens regardless of channel width. In the middle and lower reaches, the river evolves into meandering and braided patterns, eroding the floodplains on both sides. The duration of deep channel meandering evolution indicates that wider channels reach the endpoint of channel evolution more quickly than narrower channels. Furthermore, sediment transport rates in wider channels decrease more rapidly than in narrower channels, suggesting that narrower channels have a longer developmental history. However, the average active Braided Index (BIA) development is similar for both wide and narrow channels.
Year: 2025