Modelling NH4+ Dispersion from Wastewater of Urban Drainage to the Coastal Area of Danang City, Vietnam

With the fast-urban development in all the country, Vietnam cities are currently facing aging problems on networks and frequent flooding events that are significantly affecting the populations and cities activities. In most of the cases, combined solutions have been implemented, the wastewaters are treated in treatment plants before discharging into the natural environment such as rivers, lakes or coastal areas. Unfortunately, in the South-East and North-West areas of Danang city, the wastewaters from the drainage system are discharged directly into nearby water environment that is the coast of the East sea at the mouth of Han river. The selected approach combines modeling tools—Mike Urban and Mike 21 FM EcoLab—that allow to simulate jointly the behavior of the sewage system, the production of pollutants and their impact within the coastal area. NH4+ is chosen to simulate the coastal water quality. A hypothesis has been formulated for the event observed in July 2016 in Danang city. Through the results of simulation in the dry season, the ammonium concentration distribution along the coast of Danang is higher than 0.5 mg/l—the standard limited value of National Technical Regulation on marine water quality of Vietnam with a small area approximately 0.03 km2 during a short time. On the other hand, the high NH4+ concentration will disperse in larger areas after rainy events following a dry period. Findings indicated that 0.3 km2 areas are covered over 0.5 mg/l NH4+ after a rainfall of 8 mm/h. In addition, the 4 km2 area in the coast of Danang is covered by 0.14–0.5 mg/l NH4+.