Back Analysis of the Draining Process of the Tangjiashan Barrier Lake

This study attempts to use a dam breach model to reproduce the well-monitored outflow hydrograph obtained during the dam breaching process of the Tangjiashan barrier lake, which was formed by a landslide triggered by the Wenchuan earthquake on May 12, 2008 in China. The key parameters that affect the model results, such as soil erosion and breach lateral enlargement, are reviewed by using field measurements followed by extensive sensitivity studies. The present paper advocates a hyperbolic model for soil erosion rate and a circular slip surface approach for breach lateral enlargement, which contribute to more reliable model results. The governing equations are solved using a numerical method that allows straightforward calculations coded in an Excel 2007 spreadsheet. This provides an easy, transparent, and robust tool that could enable practicing engineers to perform dam breach analyses with a comprehensive understanding of the uncertainties involved. This back analysis confirms that the peak outflow can be predicted with reasonable accuracy if the input values of the key model parameters are within well-understood ranges.