Upstream effects on salinity dynamics in the red river delta

Abstract

The Red – Thai Binh river system is largest one in the North of Vietnam and as the matter of fact, water consumption and water quality are highly stressed in the delta areas. The research has collected available data of discharge, water level and salt concentration in the river network since 1960 (before reservoir operation) to examine salinity dynamics temporally and spatially. After the base assessment of seawater intrusion throughout the years and space, the study applied numerical modeling to simulate salinity dynamics in respond to different discharge level at Son Tay station during dry season. In general, the smaller discharge at Son Tay, the higher salt concentration in most of the branches. The least discharge of 900 m3/s leads to salinity thresholds up to 30 km in most of the branches, while salinity could be found at the distance of less than 23 km with the 1700 m3/s discharge. Salt concentration varies at different locations and ranges but highly fluctuate over the distance from about 10 – 20 km. Thai Binh river shows most complicated and uncertainty salinity dynamics due to the connection with Hoa and Moi river. The longer lowest discharge to maintain, the worse salinity could occur causing freshwater scarcity at downstream areas.