Impact of Pluvial First Flush – Application to Danang City, Vietnam

Abstract

Abstract As cities in Vietnam, a combined drainage system has been building in Danang City. In recent years, Danang City has been extensively developing. However, additional wastewater treatment plants have not been built. As a result, wastewater and rainwater are discharged directly into the coastal areas. The initial period of the runoff after first rainfall events can be called the first flush, which has higher pollutants. So the contribution of pollutants from the first flush must be considered in order to correctly make an environmental preservation method for the coastal area. This study uses Mike Urban with modelling water quality to analysis the sensitivity of the NH4 + concentration in the first flush of the areas. In addition, rainfall intensity and Antecedent Dry Weather Period are two key factors influencing the pollutants of the first flush. Through the results of the simulation, the NH4 + concentration increase follows the rainfall intensity with maximum concentration appearing when rainfall intensity reaches 19 mm/h. However, NH4 + concentration then decreases even when rainfall intensity increases. NH4 + concentration reaches up to around 15 mg/l every 5 days dry period with 30 mm/h rainfall intensity.