Morphometric analysis of debris flows and their source areas using GIS

Important factors for the initiation of debris flows include available loose sediment, torrential rainfall, and topographic conditions. The objective of this study is to identify topographic features of debris flows and conditions favorable for debris-flow initiation based on geomorphological analyses of 11 river basins in northern and central Taiwan. Morphometric indices were derived from 10-m grid digital terrain models before and after debris flow events using GIS. The indices include the stream power index (SPI), topographic wetness index (TWI), sediment transport capacity index, elevation–relief ratio, form factor, effective basin area, and slope gradient. The results show that debris flows tend to initiate from steep slopes or landslides with higher TWI values. Debris flows are expected in basins with higher SPI and TWI. Basins with lower slope gradients and SPI but higher TWI may also have a high potential for debris flow. SPI changes most significantly due to a debris flow event particularly in steep basins.