Landslide-dammed lake at Tangjiashan, Sichuan province, China (triggered by the Wenchuan Earthquake, May 12, 2008): risk assessment, mitigation strategy, and lessons learned

Abstract

Landslides and rock avalanches triggered by the 2008 Wenchuan Earthquake produced 257 landslide dams, mainly situated along the eastern boundary of the Qinghai-Tibet Plateau where rivers descend approximately 3,000 m into the Sichuan Basin. The largest of these dams blocked the Tongkou River (a tributary of the Fujiang River) at Tangjiashan. The blockage, consisting of 2.04 9 10 7 m 3 of landslide debris, impounded a lake with a projected maximum volume of 3.15 9 10 8 m 3 , potentially inundating 8.92 km 2 of terrain. Its creation during the rainy season and the possibility of an uncontrolled release posed a serious, impending threat to at least 1.3 million people downstream that could add substantially to the total of 69,200 individuals directly killed by the earthquake. Risk assessment of the blockage indicated that it was unlikely to collapse suddenly, and that eventual overtopping could be mitigated by notching the structure in order to create an engineered breach and achieve safe drainage of the lake. In addition to the installation of monitoring and warning instrumentation, for emergency planning we estimated several outburst scenarios equivalent to 20, 25, 33, and 50% of the dam failing suddenly, creating, respectively, 3.35, 3.84, 4.22, and 4.65 km 2 of flooded area, and overbank water depths of 4.6, 5.1, 5.7, and 6.2 m, respectively, in Mianyang, the second largest city in Sichuan Province, 48 km downstream from the blockage. Based on these scenarios, recommendations and plans for excavating a sluiceway, draining the lake, and downstream evacuation were proposed and later were implemented successfully, with the blockage breached by overtopping on June 10, less than a month after dam emplacement. The peak discharge of the release only slightly exceeded the flood of record at Mianyang City. No lives were lost, and significant property damage was avoided. Post-breaching evaluation reveals how future similar mitigation can be improved. Although initial breach erosion was slow, later erosion was judged uncontrollably rapid; increased slope of the engineered channel and adoption of a compound, trapezoid-triangular cross-section can be considered, as can other measures to control the rate of breach incision. Evacuees from Mianyang City spent an unnecessarily long time (12 days) in temporary settlements; more precise risk management planning can reduce this time in the future.

River Courses Affected by Landslides and Implications for Hazard Assessment: A High Resolution Remote Sensing Case Study in NE Iraq–W Iran

“…Landslides also modify natural environments, such as valley systems. The best example is landslide dams, including the 2010 Attabad Lake in northern Pakistan [6], the 2008 Tangjiashan Lake in China [7], and the 2,200-year-old Waikaremoana Lake in New Zealand [8][9][10], which usually occur when a landslide blocks the flow of a stream, causing a lake to form behind the dam [11]. The 300-meter-high Usoi landslide dam located in the Pamir Mountains (SE Tajikistan) is the highest dam, natural or man-made, in the world [12].…”

Experimental study on the applicability of Westergaard’s formula for calculating earthquake-induced hydrodynamic pressure in small lake

“…Therefore, the sinusoidal waves with frequency ranging from 2 to 6 Hz were used to study the characteristics of hydrodynamic pressures. And the seismic wave adopted the real-time records of the Wenchuan Ms 8.0 earthquake on May 12, 2008, 3 Experimental results and discussion 3.1 Fluctuation characteristics of hydrodynamic pressure Figure 6 shows the change of hydrodynamic pressure recorded by P 1 pulsating water pressure sensor. Then, FFT was used to derive the pressure spectrum, and the water fundamental frequency is 0.3325 Hz (Fig.…”

“…In addition, the moraine dams are formed by an unconsolidated, poorly sorted rock debris or highly heterogeneous mixture of particles [16][17][18]. The pressure loads acting on this type of dams may lead to failure of the dams and become a critical factor causing the dam to break in the earthquake areas [19].…”

Formation, breaching and flood consequences of a landslide dam near Bujumbura, Burundi

“…The formation of landslide dams is caused by the combination of several factors. Many spectacular cases were reported in which earthquakes were a major trigger (Adams, 1981;Cui et al, 2012). For example, the Wenchuan earthquake in 2008 caused up to 828 landslide dams (Fan et al, 2012(Fan et al, , 2017.…”