Abstract
In the Citadel area of Hue city, Vietnam, the discharge of septic tank effluent and untreated wastewater might cause fecal pollution in canals. However, it is difficult to assess the water pollution dynamics in the canal system which is affected by tidal action from an adjacent river. By sampling campaign, the concentration of E.coli exceeded the Vietnamese standard at all the points and it was found that the averages of EC and NH4-N concentration at the inner canal were higher than the surrounding outer canal which is connected to the river. At the inner canal, continuous monitoring results showed the existence of polluted water mass at the center part where EC kept higher than the boundary points between the inner and outer canals. In addition, near the downstream boundary, EC becomes high during ebb tide and low during flood tide. The 1D water quality model was constructed to discuss the behavior of the polluted water mass. The model simulation reproduced the tendency of EC change at the inner canal and showed that the polluted water mass would vanish due to increased canal flow rate by width enlargement at the upstream boundary.
