Impact of earthquake-induced dammed lakes on channel evolution and bed mobility: case study of the Tsaoling landslide dammed lake.

Summary On May 12, 2008, a mega earthquake measuring 8.0 on the Richter scale hit Wenchuan, Sichuan province of China, causing severe casualties and damages. The tremor was felt by nearly all of Asia. The quake-induced landslides and sliding slopes also formed 34 dammed lakes of various sizes, each of which may bring serious potential disasters. Understandably, the earthquake-triggered dammed lakes and their ensuing disasters cause grave concerns worldwide. Similar devastation took place in Taiwan on September 21, 1999, when an earthquake of 7.3 on the Richter scale occurred with the epic center at Jiji in central Taiwan. The earthquake affected changes in the channel course and induced landslides to form several dammed lakes, among which a large dammed lake was created in the upstream Chingshui River with reservoir capacity of 42,000,000 m 3 . Its size and potential problems therefore caused serious apprehension. A series of subsequent typhoon-induced torrential flooding events affected the channel forming processes to diverge drastically between the dammed lake and the landslide area, which presented a rare phenomenon for data observation and research. In the last century five dammed lakes had been formed in the area due to landslides, suggesting high possibility of future recurrence, particularly from earthquake activities. An investigation of the channel evolution in this area prior and post a quake, therefore, can assist in current disaster handling protocols and provide policy guidelines for future crisis management when landslides occur. Topographic changes in the study watershed, historical channel surveys, and past studies were gathered to aid the geomorphologic analysis. Channel evolution in the Tsaoling dammed lake and the landslide area was also investigated using a NETSTARS channel scour-deposition model by simulating the trends of erosion and deposition patterns under the influence of different recurrence interval flood peaks and streamflow time series. This simulation analysis demonstrated that the modeling not only successfully predicted the variations of hydraulics and sedimentation along the steep reaches under the influence of various streamflow conditions, but also properly reflected the trend of scouring and deposition in the entire study reach and the upstream migration of head-cut.