Modeling the sediment yield from landslides in the Shihmen Reservoir watershed, Taiwan

Landslides generate enormous volumes of sediment in mountainous watersheds; however, quantifying the downstream transport of landslide-derived sediment remains a challenge. Landslide erosion and sediment delivery to the Shihmen Reservoir watershed in Taiwanwas estimated using empirical landslide frequency–area and volume–area relationships, empirical landslide runout models, and the Hydrological Simulation ProgramFORTRAN (HSPF). Landslide erosion rates ranged from 0.4mmyr to 2.2mmyr during the period 1986–2003, but increased to 7.9mmyr following Typhoon Aere in 2004. The percentage of landslide sediment delivered to streams decreased from 78% during the period 1986–1997 to 55% in 2004. Although the delivery ratio was lower, the volume of landslide sediment delivered to streams was 2.81 10Mgyr in 1986–1997 and 8.60 10Mgyr in 2004. Model simulations indicate that only a small proportion of the landslidematerial was delivered downstream. An average of 13% of the landslide material delivered to rivers was moved downstream during the period 1986–1997. In 2004, the period including Typhoon Aere, the annual fluvial sediment yield accounted for approximately 23% of the landslide material delivered to streams. In general, the transfer of sediment in the fluvial system in the Shihmen Reservoir watershed is dominantly transport limited. The imbalance between sediment supply and transport capacity has resulted in a considerable quantity of landslide material remaining in the upper-stream regions of the watershed. Copyright © 2012 John Wiley & Sons, Ltd.