||This study used the sediment samples collected in May (dry season) and September (wet season) 2010 in a river delta and tidal flat complex around Jhoushuei River mouth in Central Taiwan to examine seasonal sediment transport pathways and sources. Four different approaches were used in the analysis of grain-size distribution pattern. They include (1) the McLaren-Bowles method, and (2) the transport vector technique (Gao-Collins method), and (3) a combination of `filtering' and the empirical orthogonal (eigen) function (EOF) analysis technique, and (4) C/N elemental ratios of organic sediments.|
The results of surface grain size distributions of sediment range from clay to medium sand towards the sea, and very fine sand deposited in the river delta. On the upper tidal flat, mud content of the wet season is higher than dry season due to higher river output of organic sediment and low-energy sediment transport. In wet season, according to the fine-grained sediment from the Jhoushuei River is therefore mainly discharged to the offshore area and little remain around the tidal flat, the influence of river on the grain-size distribution is the least.
The results based on McLaren-Bowles method indicate that there were two type sediment transport pathways, (1) the river carried sediment to the coast, then alone the northeast-southwest direction by the longshore current, and (2) during the flood tide, the riverine sediment move to northeast and east through the river delta and tidal creek to the upper tidal flat, respectively. The results based on Gao-Collins method indicate that there was possible seasonal variation of sediment transport pathways on the river delta front, where the significant transport was seaward in the wet season whereas the transport was the opposite in the dry season. On the tidal flat, the model results indicate that seaward transport seems to be controlled by ebb tidal current perhaps due to the sampling at low-tide.