Barrier formation on an actively prograding delta system: The Red River Delta, Vietnam

Abstract

An extensive barrier-spit system 20 to 30 km long developed on the delta front platform of the Ba lat Delta within a relatively short period (10–20 years). However, it was not evident whether the formation was related to river floods, typhoons or calm weather conditions, or to cross-shore or alongshore sediment transport mechanisms. Therefore a process-based numerical model that simulates sediment transport and morphologic changes by waves, tides, wind, and river flow, is used to analyze the processes that govern this barrier formation. The mechanism that initiates the barrier formation is concluded to be onshore transport by wave asymmetry of sediment previously transported seaward in the buoyant river plume. The main mechanism that counteracts the barrier formation is probably destruction of the barrier by river flow. During the subsequent transformation from a subaqueous barrier into a sub-aerial barrier-spit system, overwashes and alongshore sediment transport become increasingly important. This spit system therefore appears to be dominated by alongshore processes, even though its initial formation is more strongly regulated by cross-shore processes. The importance of cross-shore processes results in a minor contribution of typhoons to the initial formation of these barriers. Typhoons are not very important to destruction of barriers as well, because wave energy is gradually dissipated over the gentle offshore profile, which in turn results from river plume sedimentation.