Abstract
Abstract. A combination of a three-dimensional Eulerian ocean circulation model (Princeton ocean model, POM) and a Lagrangian particle-tracking model (Surface-Trapped River Plume Evolution, STRiPE) is used to study the fate of fine river sediments discharged by the Peinan River at the southeastern coast of the island of Taiwan. The composite model is verified against in situ measurements and applied to simulate primary sediment deposition under freshet and typhoon discharge conditions of the Peinan River. It is shown that local wind plays a crucial role in sediment transport and settling in the coastal area through its influence on the river plume dynamics and turbulent mixing in the upper layer. Wind forcing conditions generally determine the location of the sediment deposit area, while its final pattern is defined by coastal circulation as modulated by the geometry of the coast and local bathymetry. In the study, region river-borne sediments are deposited to the sea floor, mainly in the shallow shelf areas. A significant portion of discharged fine sediments is moved offshore to the deeper ocean where it is further advected and dispersed by strong coastal circulation, mainly governed by the Kuroshio Current.The performed numerical experiments showed that sediment accumulation rate under typhoon conditions is about 2 orders of magnitude greater compared to freshet conditions. Based on the simulation results, we identified areas of continental shelf and continental slope adjacent to the Peinan River estuary which exhibit a high risk of formation of submarine landslides during and shortly after the typhoon events.
Highlights
Small rivers transport a significant volume of terrigenous sediment to the ocean on the global scale (Milliman and Syvitski, 1992) and affect short-term and long-term coastal and seabed characteristics (Syvitski and Saito, 2007; Milliman et al, 2007)
The detailed description of the Surface-Trapped River Plume Evolution (STRiPE) is given in Osadchiev and Zavialov (2013). This model coupled with Princeton ocean model (POM) was recently used to study dynamical features of the Zhuoshui and Wu river plumes located on the western part of the Taiwan coast (Korotenko et al, 2014)
This study is focused on the influence of external forcing conditions on the transport and deposition of fine sediment discharged from the Peinan River on the steep northeastern coast of Taiwan
Summary
Small rivers transport a significant volume of terrigenous sediment to the ocean on the global scale (Milliman and Syvitski, 1992) and affect short-term and long-term coastal and seabed characteristics (Syvitski and Saito, 2007; Milliman et al, 2007). Taiwan rivers are characterized by high concentrations of total particulate organic carbon (Kao and Liu, 1996; Hilton et al, 2008); turbidity currents at the Taiwan shelf play an important role in the burial of organic carbon They have caused a number of destruction events of underwater pipelines, telecommunication cables, and other artificial structures at the continental shelf and continental slope (Carter et al, 2014). Much less attention was paid to the second mechanism which can be induced by elevated sediment load during and shortly after typhoon events It has a significantly longer preconditioning period and is characterized by distributed potential sources of turbidity flows (Carter et al, 2014). The present work is focused on the fate of fine sediment discharged by the Peinan River at the northeastern coast of Taiwan and related identification of areas of potential formation of submarine landslides, based on the simulated mass distribution of sediment deposit at the seafloor.
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