Impact Assessment of New Dam Construction in Nam Ngum Watershed on Electric Generation at Num Ngum 1 Dam

Abstract

Lao PDR is a landlocked country and around 90% of the country is located in Mekong River Basin. Average annual rainfall is around 1,900 mm and 35% of the annual flow in the Mekong River is from Lao tributaries. Given the abundance of water resources in Laos, many hydropower dams have been constructed in the country. The generated electricity is exported to Thailand and other surrounding countries and has become an important means of earning foreign currency for Laos. In particular, the Nam Ngum 1 dam has been in operation since 1971 in the Nam Ngum watershed near Vientiane, the capital of Laos, and several additional dams have been completed in this watershed since 2010. Hydropower has great potential to boost the national income and raise living standards in Lao PDR. At the same time, hydropower reservoirs have a large number of potential cross-sector impacts, including changes in the downstream water environment. The purpose of the current study was to evaluate the impact of the construction of multiple dams in the Nam Ngum watershed on the river flow regime, as well as on the hydropower generation of the preceding Nam Ngum 1 dam. In this study, the fully distributed TOPMODEL was developed and applied to analyze the water flow in the Nam Ngum watershed with a spatial resolution of 1 km X 1 km. Simulated river discharge and dam storage were in good agreement with observed data. Subsequently, we investigated the impact of the construction of the Nam Lik 1/2, Nam Ngum 2, and Nam Ngum 5 dams, which were newly developed after 2010. Results indicated that new dam construction has positive effects in decreasing flood flow during the rainy season and increasing discharge in the dry season, while electricity generation at the Nam Ngum1 dam also increased by 6.8%.