Risk analysis and emergency actions for Hongshiyan barrier lake

Abstract

This paper presents the emergency response to the barrier lake created by the Mw 6.5 earthquake on August 3, 2014, in Niulan River which is situated in Yunnan Province, southwest China. The lake, behind 83- to 103-m-high landslide dam, has a storage capacity of 260 million m3. The Hongshiyan hydropower station, situated just upstream of the landslide dam, was submerged by the lake water. The rescue actions include building an 8-m-deep drainage channel in the flood season, draining the lake water via a water release tunnel and rebuilding the landslide dam as a permanent structure. This paper presents the considerations and processes in deciding on the emergency actions. One major consideration is to minimize the hazards caused by a possible dam break flood induced by Hongshiyan barrier lake in the flood season. It was found that the barrier lake is classified as “grade I: extremely high risk” in which the 5- and 20-year floods should be used for design and check purposes of emergency works, respectively. The dam break flood evaluations indicated that an 8-m-deep diversion channel should be constructed in order to reduce the total amount of the released reservoir storage and to prevent possible overtopping of the downstream Huangjiaoshu rockfill dam. This study was based on an improved analytical approach to dam break flood modeling and a handy spread sheet developed by the authors. The considerations on various risks and the key analytical technology for dam break flood predictions described in this paper may be useful for other similar cases.