Nam Gnouang Dam Failure Hydraulic Analysis for Emergency Response Plan (Laos)

Introduction

The Nam Gnouang (NG) Dam, Bolikhamxai Province, Laos, is built on a major tributary of the Nam Theun/Kading river system; it is located approximately 27 km upstream of the first Theun-Hinboun (TH) Diversion Dam and 9 km upstream of the confluence. The reservoir behind the dam extends approximately 40 km upstream and covers 105 square km at full storage. The dam is operated by the Theun-Hinboun Power Company (THPC). DSI performed a hydraulic analysis for possible failure of the NG Dam as part of the THPC’s Theun-Hinboun Expansion Project (THXP).

Project Goal

The NG Dam failure analysis was required to support the preparation of an Emergency Response Plan (ERP). The ERP helps facilitate the management of potential floods caused or exacerbated by dam operations or dam failure, and to reduce the risk to lives and property as a consequence of dam failure.

Phase 1 of the study was a preliminary assessment for several NG Dam failure scenarios using the HEC-RAS model of the TH Reservoir. Based on the results of Phase 1, additional work was recommended for Phase 2 of the study, including further data collection and an extension of the HEC-RAS model to avoid the downstream boundary effect and properly represent the floodplain. Following the recommendations from Phase 1, the HEC-RAS model was revised and used for the analysis of the NG Dam failure scenarios.

Nam Gnouang (NG) Dam in Bolikhamxai Province, Lao PDR

Application

DSI conducted hydraulic analysis and developed inundation maps for a range of scenarios. Inundation levels and areal extents were needed to support the assess- ment, which followed USA Federal Emergency Management Agency (FEMA) dam failure guidance. Based on the results of the analysis, a series of flooding maps were prepared for the ERP.