Date of Award
Open Access Dissertation
Wind stress and surface gravity waves play an important role in creating and modifying flows on the shelf. The importance of surface waves increases in shallow waters especially within the inner shelf and the surf zone. Understanding the generation and maintenance mechanisms of these flow patterns is a requirement for a number of environmental and ecological processes including the transport and fate of sediment, pollutants, buoyant river discharge and anthropogenic material introduced to the coastal zone. This dissertation examines inner shelf and surf zone circulation patterns through: (a) the development and validation of appropriate techniques to incorporate the effect of surface gravity waves on mean flows using the modeling framework of Regional Ocean Modeling System (ROMS) and the wave propagation model Simulating Waves Nearshore; and (b) a combination of field observations from acoustic instruments, High Frequency (HF) radars and coupled wave-current interaction based modeling system.
In the first chapter of this dissertation, the circulation module is extended for surf zone applications through modification and implementation of depth dependent radiation stress formulations which are used to simulate three-dimensional flows due to depth-limited breaking of incoming waves and their interaction with non-uniform bathymetry. It is identified that the radiation stress approach can perform satisfactorily inside the surf zone, but creates incorrect flow patterns outside the surf zone for shoaling and non-breaking waves.
In the second chapter, the aforementioned short-comings of the radiation stress formulation are addressed by implementation of the Vortex Force (hereinafter VF) Formalism within the framework of the coupled ROMS-SWAN modeling system. This modification is shown to allow for the correct incorporation of surface wave effects and enabling the updated modeling system to work seamlessly from the inner shelf all the way to the surf zone. The VF formalism is evaluated against field data for wave breaking driven currents and also for non-breaking wave driven flows outside the surf zone and is shown to perform exceptionally well.
In the third chapter, a practical application of the modified modeling system is presented where the model can be used as a rip current forecasting system. Although this application is presented using the Radiation Stress formulation, the same methodology can be used with the Vortex Force formalism. As a part of this work a methodology for incorporating bathymetry uncertainties in such prediction system is also presented.
In the fourth chapter in-situ point measurements of waves and currents obtained at various locations throughout the nearshore region of Cape Hatteras, North Carolina (USA) are presented. The data are used to reveal the alongshore momentum balance around a cuspate foreland system. The analysis indicates that on the windward side of the cape, a balance between wind and bottom stress is present in deeper waters, while on the leeward side, no balance exists between wind and bottom stress. Closure of the balance requires development of a pressure gradient in response to wind forcing. In shallower waters, wave breaking, VF, and nonlinear advective acceleration terms are found to be important as well.
A similar momentum balance analysis is carried out using the results of the Coupled Ocean-Atmosphere-Wave-Sediment transport modeling system which is set up in a nested framework capable of resolving wave variability and flows throughout the inner shelf to coastline, including the surf zone. Analysis of the simulated results reveals a contribution of pressure gradient term on both sides of Cape Hatteras. On the windward side, pressure gradient and wind stress balance the bottom stress, while on the leeward side the wind stress is balanced by the pressure gradient. The shallow shoal complex extending seaward from Cape Hatteras point acts like a coastline in regulating wave propagation and flow pattern for different synoptic wind and wave conditions.
Kumar, N.(2013). Measurement and Three-Dimensional Modeling of Hydrodynamic Processes In the Inner Shelf and Surf Zone. (Doctoral dissertation). Retrieved from http://scholarcommons.sc.edu/etd/2343