From 1996 through 2007, several heavy typhoons and earthquakes precipitated landslide hazards in
southeast Taiwan. In the present study, we analyze the impact of topography, lithology, rainfall and
earthquakes on landsliding and sediment transport by quantifying the landslide ratio (ratio of landslide area
to catchment area) and the sediment discharge for the Sinwulu and Luye upstream catchments of the Peinan
River. The steep topography in these two catchments causes a large proportion of landslide ratios on slopes to
exceeding 50°, a condition which accelerates the delivery of landslide debris to the downslope channel. The
landslide ratios of 0.84%–2.30% are obviously related to the rock strength and discontinuity density of the
terrain, but we find the magnitude of landsliding and sediment discharge to vary with the occurrence of
earthquakes. Typhoon-induced rainstorms generate the bulk of sediment discharge in the study catchments,
though the landslide debris is transported by the huge amounts of runoff produced by rainstorms. A
contributing factor is the recent occurrence of severe earthquakes which weakened the geomaterial, leading
in turn to further increases of fluvial sediment during subsequent typhoons. Additionally, the finding that
eventual reduction of unit sediment concentration after high magnitude earthquake events reveals that the
downslope transport of landslide debris associated with earthquake activity and subsequent typhoon events
precipitates a relatively short term, 1–3 year, increase of erosion rates in these two study areas in
southeastern Taiwan.
From 1996 through 2007, several heavy typhoons and earthquakes precipitated landslide hazards insoutheast Taiwan. In the present study, we analyze the impact of topography, lithology, rainfall andearthquakes on landsliding and sediment transport by quantifying the landslide ratio (ratio of landslide areato catchment area) and the sediment discharge for the Sinwulu and Luye upstream catchments of the PeinanRiver. The steep topography in these two catchments causes a large proportion of landslide ratios on slopes toexceeding 50°, a condition which accelerates the delivery of landslide debris to the downslope channel. Thelandslide ratios of 0.84%–2.30% are obviously related to the rock strength and discontinuity density of theterrain, but we find the magnitude of landsliding and sediment discharge to vary with the occurrence ofearthquakes. Typhoon-induced rainstorms generate the bulk of sediment discharge in the study catchments,though the landslide debris is transported by the huge amounts of runoff produced by rainstorms. Acontributing factor is the recent occurrence of severe earthquakes which weakened the geomaterial, leadingin turn to further increases of fluvial sediment during subsequent typhoons. Additionally, the finding thateventual reduction of unit sediment concentration after high magnitude earthquake events reveals that thedownslope transport of landslide debris associated with earthquake activity and subsequent typhoon eventsprecipitates a relatively short term, 1–3 year, increase of erosion rates in these two study areas insoutheastern Taiwan.
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