Journal of Geophysical Research (Earth Surface), submitted 10/05.

Tropical cyclone triggering of sediment discharge in Taiwan

Joseph Galewsky
Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM.

Colin P. Stark
Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY.

S. Dadson
Centre for Ecology and Hydrology, Wallingford, UK.

Chun-Chieh Wu
Department of Atmospheric Sciences, National Taiwan University, Taipei, Taiwan.

Adam H. Sobel
Department of Applied Physics and Applied Mathematics and Department of Earth and Environmental Sciences, Columbia University, New York, NY.

M. Horng
Water Resources Agency, Ministry of Economic Affairs, Taipei, Taiwan.


Tropical cyclone rainfall influences sediment production and transport in Taiwan in ways that are not reflected in the annual mean rainfall. The interaction of the cyclonic atmospheric circulation with topography can produce complex patterns of heavy precipitation that are critically dependent on the track of the tropical cyclone. Here we use suspended sediment and river discharge data along with numerical simulations of tropical cyclone dynamics to quantify the meteorological and geomorphic impact of Typhoon Toraji, which struck Taiwan in July 2001, the first major tropical cyclone to affect the island after the 1999 Chichi earthquake. Two meteorological processes drove the observed sediment discharge that was associated with the tropical cyclone. Eyewall processes, largely decoupled from topography, brought extremely heavy rainfall (>100 $\,$mm$\;$h$^{-1}$) to the landfall zone in east Taiwan for a short period (about 2 hours), triggering the highest sediment concentration ever recorded on the Hualien River. The southwestern Central Range received about 10 hours of less intense rainfall (between 10 and 50 $\,$mm$\;$h$^{-1}$) that was orographically controlled and triggered the second highest sediment concentration recorded on the Kaoping River and flushed coseismic debris generated during the Chichi earthquake from storage into the Choshui River system. These results illustrate how tropical cyclone rainfall and its geomorphic consequences are a joint function of the tropical cyclone track and the topography of the underlying mountain belt.