Emergency response to the Tangjiashan landslide-dammed lake resulting from the 2008 Wenchuan Earthquake, China

Natural landslide dams triggered by earthquakes are a common feature and a significant hazard in high-relief, tectonically active areas. The great Wenchuan Earthquake of May 12, 2008 created 256 natural dams, of which 34 presented significant risks to downstream areas in the event of their uncontrolled failure. Out of the 34 large landslide dams that warranted mitigation, we discuss Tangjiashan landslide dam in detail. Emergency response to the Tangjiashan landslide-dammed lake in the following weeks and months successfully reduced the risk, and the advantages and disadvantages of various countermeasures that were applied are summarized here. Successful strategies relied on accurate scientific assessments, on timely execution of the countermeasures, and on the correct design of sluiceway (spillway) channels across the landslide dams. Retrospective assessment indicates that the following improvements would be more beneficial: (1) Sluiceway channels utilizing a combination of cross-section types, rather than simply trapezoidal in shape; (2) increased channel slope, which is more than the original gradient of the river; (3) better protection of inlets and outlets to control the planned incision rates; and (4) channels lined to better control the incision rate. We discuss applications of the concept of artificially controlled failure, and we submit these observations for the benefit of those responding to future seismic catastrophes.