Variations in Sediment Yield and TransportationCharacteristicsin the ZengWen Reservoir (extended abstract MSD9)

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Variations in Sediment Yield and TransportationCharacteristicsin the ZengWen Reservoir (extended abstract MSD9)

作者：Yu-Shiu Chen, Chien-Yang Lin, Ping-Kun Lu, and Chun-Yi Wu; 公佈日期：109 年 04 月 27 日

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Typhoon Morakot brought long-duration and high-intensity rainfall to southern Taiwan in 2009. A cumulative rainfall of 3,005 millimeters in five days was observed at the upstream side of ZengWen River (Alishan Weather Station). About 91,080,000 m3 sediment was brought into ZengWen Reservoir. The landslide and bare areas in the ZengWen Reservoir watershed increased from 255 hectares to 1,467 hectares. Henceforth, sediment monitoring projects were launched by Southern Region Water Resources Office. Aerial photography and satellite imagery were used for tracking landslide and bare areas. LiDAR was applied to topographic variation analysis of slopes and river bed. Discharge and concentration were measured at DaPu Check Dam monitoring site, which is the entrance for the mainstream to ZengWen Reservoir.
This study has an eight-year duration (2011-2018). The main purpose of this study is using monitoring and simulations to determine variations in sediment yield and transportation characteristics.
This study found landslide and bare areas decreased to 213 hectares in 2018. There were 62 bare areas which were individually more than five hectares in 2009. Lately, there were only nine left in 2018. Mass sediment deposited on the river bed right after typhoon Morakot. Since then, the elevation of most sections of mainstream gradually decreased. Rating curves of discharge versus suspended load concentration were established annually according to the site monitoring data. The concentration was 35,809 ppm at discharge of 500 m3 /s in 2011. It decreased to 8,889 ppm in 2018, which is much closer to the concentration of 7,983 ppm in the past research in 2006. Sediment numerical simulations (Sediment Budget Model, SBM) were done to analyze sediment yield and transport characteristics. It represented similar henomenon as above observations. Furthermore, the proportions of deposits in the reservoir which came from the mainstream were obtained. Those were 65% in 2009, 72% in five years, and 80% in ten years; therefore, the mainstream has the most effect of sediment supply to the reservoir.

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