HR: 0830h
AN: T21C-0465    [PDF]
TI: Control of Bedload Sediment Supply Upon Bedrock Incision and River Longitudinal Profile in the Eastern Central Range, Taiwan
AU: * Hsieh, M
EM: hsiehml@pchome.com.tw
AF: National Taiwan University, No. 1, Sec. 4, Roosevelt Rd., Taipei, 106 Taiwan
AU: Liew, P
EM: liewpm@ccms.ntu.edu.tw
AF: National Taiwan University, No. 1, Sec. 4, Roosevelt Rd., Taipei, 106 Taiwan
AU: Chen, Y
EM: ygchen@ccms.ntu.edu.tw
AF: National Taiwan University, No. 1, Sec. 4, Roosevelt Rd., Taipei, 106 Taiwan
AB: Rivers (drainage areas: 130-620 km2) draining the eastern slope of the Central Range, Taiwan, show distinct erosion/sedimentation histories during the Holocene: some develop fill terraces with abandoned alluvial fans at the river mouths while others do not. We conducted area-slope analyses for these rivers by using 1: 25,000 topographic maps (contour interval 10 m). We found that although underlain by similar types of bedrock, the rivers developing fill terraces all exhibit higher values ($>$ 0.4) of profile concavity, and are generally wider and consist of fewer/lower knickpoints in their downstream parts. This feature is difficult to be explained by differential rock uplift. Rather, the stronger concavity of river profiles could reflect greater supply of bedload sediments that enhance incision in the lower parts of the rivers. In this case, the aggradation of the terrace fills appears to be a short-term phenomenon. Maximal incision occurred when the supply of bedload sediments after the aggradation decreased to a degree, at which the dual roles of bedload sediments acting as abrading tools while insulating underlying bedrock were suitably balanced. We also focused on the Liwu River, where the late Holocene bedrock incision rates are estimated over few centimeters per year. Only the river­Ýs largest tributary develops fill terraces connecting to those in the trunk stream. This tributary is more concave than the trunk stream, such that much of the river is lower than the corresponding trunk stream that has the same lengths from the river mouth. Counting lithological types of gravels further indicates that most of the bedload sediments in the trunk stream are currently supplied from this tributary.
DE: 1625 Geomorphology and weathering (1824, 1886)
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 1899 General or miscellaneous
DE: 8102 Continental contractional orogenic belts
SC: Tectonophysics [T]
MN: 2003 Fall Meeting