The influence of suspended sediments on the plume of a small mountainous river

A comprehensive field experiment was conducted to monitor the plume of the Tsengwen River, a monsoon-regulated small mountainous river located on a wa ve-dominated micro-tidal coast in southern Taiwan. The field work included the deployment of a tripod near the river mouth that measured the salinity, temperature, tide, waves, current, and turbidity at 1 m above the bed. Shi pboard profiling of the salinity, temperature, and turbidity was also condu cted. In addition to the ground survey, a Landsat TM image taken during the time of the field work was converted to a map for suspended sediment distr ibution in the study area. Our results show that the expansion and contract ion of the river plume is largely controlled by the river discharge, tidal phase, and the wind field. Horizontal advection, downward settling, and the resuspension are the three mechanisms that control the near-bed suspended sediment concentration near the river mouth. Both forms of hypopycnal and h yperpycnal plumes from the river have been documented. Our study shows the type of plume of small rivers not particularly rich in suspended sediments on wave-dominated coasts have greater variability and is subject to the inf luence of the suspended sediment dynamics. In the presence of weakened runo ff and absence of runoff, stratification can become unstable in the farfiel d when vertical movements of suspended sediments are present. In summary, t he plumes observed in this study represent three types of plumes in terms o f relative dominance between the river and nearshore suspended sediment dyn amics.