In this study

a two-dimensional water dynamic and water quality model based on MIKE21 was developed to simulate the water quality at the intake of Dongshen water supply project. The study was carried out in the tidal reach between the Dongjiang HydroProject and Shilong in the downstream of the Dongjiang River

and NH-3-N was taken as the water quality indicator. Different scenarios of flood discharge from the Shima River and the release discharge of the Dongjiang Hydro-Project were used to drive the model for the simulation of the water quality at the intake of the Dongshen water supply project. The results indicate that: ① the change of the NH-3-N concentration at the intake is related to the tidal change

the NH-3-N concentration over-standard occurs during higher high water level period; ② flood tide is the main factor which impacts the water quality at the intake

and the NH-3-N concentration is more than 0.5mg/L during higher high water lever period; ③ more flood discharge from Shima River has the greater effect on the water quality

and the water regulation of the Dongjiang Hydro-Project can cause a significant improvement on water quality in the downstream. The results of this study contribute to the decision-making for the joint operation of the flood discharge from Shima River and the intake of Dongshen water supply project

also have great significance for the emergency operation of the Dongjiang Hydro-Project.