A case of severe channel-morphology change due to human influences in the Touqian River, Taiwan

One reach that locates in the midstream of the Touqian River in northern Taiwan was subjected to various human disturbances; the channel morphology in the reach changed severely as a result. This case study looks into the role of human disturbance on channel evolution by exploring the chronological change in channel morphology due to human influences in the studied reach. The major human influences in this reach include gravel mining, bridge construction and its protection works, and weir construction. Channel morphology downstream the bridge was transformed from an alluvial channel to a bedrock channel since the installation of a massive protection work. Later on, the bridge and its protection work were broken in recent years. After their failure, the reach started to take re-deposition and has returned to an alluvial channel. Chronological data including aerial photographs, cross-section surveys and hydrological data were compiled and analyzed. Also, field geology was conducted to characterize the distribution of bedrock outcrop and the erosion processes in the studied reach. According to the study results, the maximum depth of bedrock incision exceeds 15 meters. Main influences can be attributed to various human activities and the low resistance of young sedimentary rocks to erosion. The case study, as a fine example, demonstrates the processes of channel-morphology change due to human disturbances.