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The Scientific World Journal
Volume 2014, Article ID 580936, 12 pages
http://dx.doi.org/10.1155/2014/580936
Research Article

The Variation of Riverbed Material due to Tropical Storms in Shi-Wen River, Taiwan

Department of Civil Engineering, National Pingtung University of Science and Technology, Pingtung 91201, Taiwan

Received 28 October 2013; Accepted 12 December 2013; Published 12 January 2014

Academic Editors: G. Cai, R. Feng, and H. Moayedi

Copyright © 2014 Chin-Ping Lin et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Taiwan, because of its location, is a flood prone region and is characterised by typhoons which brings about two-thirds to three quarters of the annual rainfall amount. Consequently, enormous flows result in rivers and entrain some fractions of the grains that constitute the riverbed. Hence, the purpose of the study is to quantify the impacts of these enormous flows on the distribution of grain size in riverbeds. The characteristics of riverbed material prior to and after the typhoon season are compared in Shi-Wen River located at southern Taiwan. These include grain size variation, bimodality, and roughness coefficient. A decrease (65%) and increase (50%) in geometric mean size of grains were observed for subsurface and surface bed material, respectively. Geometric standard deviation decreased in all sites after typhoon. Subsurface material was bimodal prior to typhoons and polymodal after. For surface material, modal class is in the gravel class, while after typhoons it shifts towards cobble class. The reduction in geometric mean resulted to a decrease in roughness coefficient by up to 30%. Finally, the relationship of Shields and Froude numbers are studied and a change in the bed form to antidunes and transition form is observed, respectively.