A Numerical Modeling Study of Turbulence and Sediment Resuspension in the Near Field of River Plumes

Abstract:

To understand the dominant mechanisms controlling the delivery of sediment in the near field of river plumes, a numerical study is carried out using Regional Ocean Modeling System (ROMS) with an idealized river mouth domain. The domain is designed to be sufficiently simple such that it can be described by several nondimensional parameters but sufficiently complex to capture the key features of a given river mouth. Motivated by a recent multi-institutional study at the mouth of Columbia River, we first apply the idealized model similar to the Columbia River month during the month of May 2013 when the field observation was conducted. Field observation shows interesting asymmetry of near bed turbidity with significantly higher turbidity observed during flood, which follows the landward migrating front. Numerical model predicts a significantly higher turbulent kinetic energy (TKE) following the landward-migrating front during flood, consistent with the location where high turbidity is observed. Preliminary analysis shows that the predicted high near bed TKE level is associated with the stratified two-layer flow established during flood. The two-layer system establishes high flow shear at the interface and enhances TKE in the lower layer. During ebb, the flow becomes much less stratified with a very low gradient Richardson number, and the TKE distribution more or less follows the classic logarithmic law. More thorough analysis including simulations with different composition of sediment resuspended from the plume nearfield and/or supplied by the river outflow will be discussed.