FLOOD INUNDATION ANALYSIS IN DOWNSTREAM OF SMALL HYDROPOWER PLANT: A CASE STUDY IN LANG SON PROVINCE, VIETNAM

Abstract

Hydropower is well known as one of the most economical traditional energy sources, and it is clean and renewable in the world so far. This resource has been harnessed for socio-economic development and energy security in Vietnam. Small hydropower projects have contributed significant power to the national power grid thanks to their economic investment and environmental friendliness. However, the small hydropower was restrictive on flood regulations and risked potential incidents such as dam breaks during operation. Therefore, it is necessary to study the risk of downstream inundation due to flood discharge or dam break. This study uses HEC-RAS software to map flood inundation applied downstream of Thac Xang hydropower (Lang Son, Vietnam) at three (03) active flood discharge scenarios and two (02) dam break scenarios. The results show that the hydropower reservoir can help reduce flood peaks by 6.54% for a flood frequency of 1% but does not help reduce flood peaks in the case of flood frequency of 0.2% and 0.1%. In addition, the flood peak time is also delayed from 1.0 to 1.8 hours. The inundation map results show that in the event of a dam break during flood discharge, the flooded area will increase by 9.89%, the flooded residential area will increase by 12.47%, and the flooded depth will increase by 13.08%.