Analysis of sediment distribution and transport for mitigation of sand deposition hazard in Tam Quan estuary, Vietnam

Tam Quan estuary in the Binh Dinh Province of Vietnam provides shelter for about 2000 boats. Recently, erosion and accretion associated with the mouth of the estuary have badly affected marine transportation and economic development. An 850-m-long jetty was constructed to mitigate the hazard. However, sand deposition still continues to be an ongoing problem. This paper aimed to assess the reasons for sand deposition in the estuary based on sediment distributions and transport pathways. Following an investigation of topography, geological and hydrodynamic conditions, and sediment characteristics, an analysis of sediment transport trends was undertaken. Results show that medium sand is distributed along the coast from the shoreline to 2.5 m water depth. Fine sands are found in deeper areas of 10-13 m where there are also medium sand deposits thought to be of ancient origin. Sand deposition has intensively occurred in the estuary due to a dominant north-to-south longshore sediment transport regime. Sediment from this regime is presently trapped by the jetty and deposited in the navigation channel. As a solution, it is suggested that a properly designed jetty stemming from the headland on the north side of the estuary could effectively control the patterns of sediment transport enabling the sand to bypass the entrance, thereby avoiding entrapment inside its mouth.