A Study of Field Measurements of Suspended Sediment Concentration in the Gaoping River and Numerical Simulation of Hyperpycnal Turbidity Currents in the Gaoping Submarine Canyon
Abstract:
https://agu.confex.com/agu/osm20/prelim.cgi/Session/85715
A Study of Field Measurements of Suspended Sediment Concentration in the Gaoping River and Numerical Simulation of Hyperpycnal Turbidity Currents in the Gaoping Submarine Canyon
Yu-Chi Lin1, Jia-Lin Chen1, James Liu2
1 National Cheng Kung University 2Department of Oceanography, NSYSU
This research aims to understand the mechanisms control the formation of the hyperpycnal turbidity current (HTC) in small mountainous rivers. It was known that when river-borne sediment concentration exceeds Ccrit=40~45 g/l, the bulk density of the river plume becomes greater than that of the ambient seawater and the plume descends to the seabed as HTC (Mulder and Syvitski 1995). In order to understand the formation of HTC at Gaoping River, this study obtains the information of grain size distribution and suspended sediment concentration (SSC) in the Gaoping River by field observation as a basis for numerical simulation. The suspended sediment concentration of the Gaoping River during Typhoon Soudelor was lower than 20 g/l according to the real time SSC estimated through the rating curve between turbidity and SSC. The median grain size of the suspended sediments was calculated as 15.15μm, which indicated that the silt accounted for a large proportion. The observed grain-size distribution and SSC are applied to the numerical model to examine the possibility of the occurrence of HTC. Model results show that the submarine canyon confines the path and width of the HTC so the HTC has enough gravitational force to keep moving in the deep sea through the steep slope of the submarine canyon. In addition, to investigate the impact of sediment grain size on the occurrence of HTC, the cases with different settling velocities were simulated in the numerical model. The simulation results show that the SSC of HTC increases while the grain size of riverine sediment decreases. However, if the grain size of sediment is smaller than 4 (clay), most of suspended sediments will flow on the sea surface as the surface plume.