Modelling of a Landslide Dam Breach using 1-D Hydrodynamic Model

Abstract

The formation of landslide dams is a very common phenomenon around the world, especially in mountainous regions having steep narrow valleys. The formation and breach of these dams pose a great threat to the people and infrastructure both upstream and downstream. A great earthquake of 8.0 hit the Sichuan province of China in 2008. It resulted in almost 37 landslide dams. Tangjiashan Landslide dam is one of them. Tangjiashan Dam is formed across the Jiang valley and blocked the Tongkou River forming a barrier lake behind it. The estimated volume of the barrier lake was 3.1 × 108 m3. Due to the rainy season, the lake water level was continuously increasing at the rate of 1.2m/day. The dam was highly probable to breach causing a serious threat to 2.5 million people living in Mianyang city downstream of the Tangjiashan area. Thus the Chinese government decided to excavate a spillway for draining the lake water in a controlled way. This present research study aims to simulate the breaching process of the Tangjiashan Landslide Dam. The disastrous scenario of dam breach is recreated by using data from past studies. Sedimentation and River Hydraulics – One Dimension (SRH-1D) model is used to perform the modeling. A discharge hydrograph is applied to breach the landslide dam and the resultant effects of a breach like erosion and deposition are studied. The results of the model show that the channel bed eroded down to 718m at the entrance and the downstream river bed aggraded to 680 m. 1.2 × 108 m3 of water is carried to the d/s area. 3.8 × 105 m3 of sediment is eroded out of which 2.7 × 105 m3 material is deposited downstream the river reach. It is concluded that SRH-1D produced reasonably accurate results in simulating the landslide dam breach. The model produced physically correct behavior as it eroded where the slope was steep and deposited where the slope was flat. The 1D model is very fast with each simulation spanning a few minutes. This is advantageous as more simulations can be carried out to assess the influence of various parameters. The use of a computationally inexpensive model to simulate the dam breach on a field case and its validation suggests that it can be used in other comparable situations with a degree of confidence.