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2014/11/18 14:00 Dr. Julia Chen（Civil and Environmental Engineering, University of Delaware, USA）
Seminar
Poster： ╱ Post date：2014-11-13NCU IHOS Seminar Announcemnet
Speaker：Dr. Julia Chen
Place：S-325, Science Building 1
Abstract：
Title：Hydrodynamics, Sediment Transport and Morphodynamics at inlets and river mouths - A numerical investigation
Speaker：Dr. Julia Chen
Civil and Environmental Engineering, University of Delaware, USA
Time：11/18（Tue.）14：00
Place：S-325, Science Building 1
Abstract：
Inlets and river mouths are among the most important coastal zones in terms of their economic, ecological and societal values. However, our current predictive capability on the hydrodynamics, sediment delivery and morphological evolution of inlets and river mouths remains qualitative. The overarching goal of this study is to enhance the physical understanding and model development of inlet/river mouth dynamics. The newly developed nearshore circulation model, SHORECIRC, using a hybrid finite-difference finite-volume TVD-type scheme, is coupled with the wave model SWAN and several sediment transport model. This new nearshore modeling system is called NearCoM-TVD. The capability and limitation of NearCoM-TVD for several coastal applications, including tidal inlet hydrodynamics, nearshore wave-current interaction and sandbar migration are evaluated.
The interactions between waves, tidal currents, and bathymetry near New River Inlet, NC, USA are then investigated to understand the effects on the resulting hydrodynamics and sediment transport. Using NearCoM-TVD, the model is validated with observations of waves and currents at 30 locations, including in a recently dredged navigation channel and a shallower channel, and on the ebb tidal deltas, for a range of flow and offshore wave conditions during May 2012. Model results reveal the existence of a sharp transition of flow field, which coincides with the location of the breaker zone over the ebb tidal deltas. This region is modulated by semi-diurnal tides and by wave intensity. The modeled tidally averaged residual flow patterns show that waves play an important role in generating vortices and landward-directed currents near the inlet entrance. Numerical experiments suggest that these flow patterns are associated with the channel-shoal bathymetry near the inlet, similar to the generation of rip currents. Model results further show that wave intensity and direction play a critical role in controlling the morphological evolution of the ebb tidal deltas.
To further understand the dominant mechanisms controlling the delivery of sediment in a stratified river mouth, a numerical study is carried out using Regional Ocean Modeling System (ROMS) with an idealized river mouth domain. Motivated by a recent multi-institutional study at the mouth of Columbia River (MCR), we first apply the idealized model similar to the high discharge flow condition of MCR during the month of May 2013 when the field observation was conducted. Field observation reveals an interesting asymmetry of near bed turbidity with significantly higher turbidity observed during flood, which follows the landward migrating front. The numerical model captures the observed high turbidity region during flood. Model results further reveal that the high turbidity is associated with significantly higher turbulent kinetic energy (TKE) following the landward-migrating front during flood. An analysis of model results shows that the predicted high near bed TKE level is associated with the stratified two-layer flow established during flood, which is absent during ebb. The newly established idealized river mouth system is quantified by two nondimensional parameters and hence it can be used as an analytical tool to study the flow structures and the resulting turbulent mixing and sediment transport processes for different river mouth systems.
Last modification time：2014-11-13 AM 11:07
