1 TIDAL HYDRODYNAMICS OF DA RANG RIVER MOUTH IN CENTRAL VIETNAM PHAM THU HUONG†(*) NGUYEN BA QUY(*)

The Da Rang river mouth is one of the biggest rivers in the Southern Central Area of Vietnam and it has a typical lagoon type. It usually opens for 3- 4 months during the rainy season and closes for 6-7 months during the dry season. In recent years, the topographic change of Da Rang river mouth increases its rate with time. This phenomenon is governed by a micro-tidal regime and a wave dominant coastal dynamics. Strong seasonal variation of the river discharge and the incident wave climate are important factors. The closure of the river mouth during the dry season causes a lot of problems to the socio-economic developments in the area including navigation and flood water discharging. This paper presents an analysis of the morpho-dynamics and the mechanism of seasonally and yearly topographic change of the Da Rang river mouth, which was affected by exogenous causes such as river floods, ocean waves and currents. The calculation results of longshore sediment transport and morphological changes by application of Delft3D models (WL | Delft Hydraulics, 2006) is discussed. Subsequently, this paper points out a trend of sediment movement in the Da Rang river mouth based on the analysis of the Da Rang river mouth using available historical maps, aerial photographs and satellite images. The results show that the Da Rang river mouth has a trend of accretion in long term. 1