Abstract
The sediment yield from numerous landslides triggered in Taiwan’s mountainous regions by 2009 Typhoon Morakot have had substantial long-term impacts on the evolution of rivers. This study evaluated the long-term evolution of landslides induced by 2001 Typhoon Nari and 2009 Typhoon Morakot in the Tsengwen Reservoir Watershed by using multiannual landslide inventories and rainfall records for the 2001–2017 period. The landslide activity, vegetation recovery time, and the landslide spatiotemporal hotspot analyses were used in the study. Severe landslides most commonly occurred on 35–45° slopes at elevations of 1400–2000 m located within 500 m of the rivers. The average vegetation recovery time was 2.29 years, and landslides with vegetation recovery times exceeding 10 years were most frequently retrogressive landslide, riverbank landslides in sinuous reaches, and the core area of large landslides. The annual landslide area decline ratios after 2009 Typhoon Morakot in Southern Taiwan was 4.75% to 7.45%, and the time of landslide recovery in the Tsengwen reservoir watershed was predicted to be 28.48 years. Oscillating hotspots and coldspots occupied 95.8% of spatiotemporal patterns in the watershed area. The results indicate that landslides moved from hillslopes to rivers in the 2001–2017 period because the enormous amount of sediment deposited in rivers resulted in the change of river geomorphology and the riverbank landslides.
Highlights
Those landslides were most commonly retrogressive landslide or riverbank landslides in the sinuous reaches and the core area of Frequency and Vegetation Recovery Time the Landslide large landslide cases
The area with landslide frequency greater than 10 constituted 0.394 km2. Those landslides were most commonly retrogressive landslide or riverbank landslides in the sinuous reaches and the core area of the large landslide cases
This study evaluated landslide activity and vegetation recovery time and detected the spatiotemporal hotspots of extreme rainfall-induced landslides in the Tsengwen Reservoir Watershed (TRW) by using annual landslide inventories and long-term rainfall records from 2001 to 2017
Summary
The sediment yield from numerous landslides triggered in Taiwan’s mountainous regions by 2009 Typhoon Morakot have had substantial long-term impacts on the evolution of rivers. Typhoon Morakot in the Tsengwen Reservoir Watershed by using multiannual landslide inventories and rainfall records for the 2001–2017 period. The landslide activity, vegetation recovery time, and the landslide spatiotemporal hotspot analyses were used in the study. Typhoon Morakot in Southern Taiwan was 4.75% to 7.45%, and the time of landslide recovery in the Tsengwen reservoir watershed was predicted to be 28.48 years. The return period of heavy rainfall brought by Typhoon Morakot (5–10 August 2009), which caused approximately 45,000 landslides concentrated in central and southern Taiwan, was estimated to be over 200 years [3]. Loose deposits from the numerous landslides in mountainous areas continues to affect watershed evolution and landslide recovery.
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