Evolution process of sediment supply for debris flow occurrence in the Longchi area of Dujiangyan City after the Wenchuan earthquake

In order to analyze the changes in the sediment budget after the Wenchuan earthquake and after the heavy rain events in the following years, 12 debris flow gullies in the Longchi Dujiangyan County were selected. A comparison of the TM images taken on 18 September 2007 (before the 5.12 Wenchuan earthquake) with the SPOT5 images taken on 10 February 2009 (after the 5.12 Wenchuan earthquake) indicates that the landslide area in the 12 debris flow watersheds increased from 83.1 x 10(3) m(2) to 3126.5 x 10(3) m(2). Also, the gully length increased by 60.55 %, and the area with deposits in the channel bed increased by 134.80 %. A comparison of the SPOT5 images taken on 10 February 2009 (after the 5.12 Wenchuan earthquake) with the WorldView-2 images taken on 26 April 2011 (after the large rainstorm event in August 2011) showed that the landslide area increased by 24.8 % from 3126.5 x 10(3) m(2) to 3902.8 x 10(3) m(2) while the gully length increased by 26 % and the channel deposits by 12 %. A comparison of the WorldView-2 images taken on 26 April 2011 with the WorldView-2 images taken on 14 July 2011 indicated that the landslide area increased in this relatively dry period by only 2.3 %.