The surf zone is a spatially limited but highly energetic region of the near-shore ocean where waves shoal, break and dissipate energy through to the shoreline. Here, nonlinear surface wave profiles deviate strongly from the linear superposition of sinusoids assumed in deeper waters, with super-harmonic phase-locking leading to sharper, higher, crests and flatter troughs, while subharmonic interactions generate low frequency motions that can dominate dynamics in the inner surf and swash (run-up) zones. The surf zone becomes especially important in severe storms such as hurricanes where large wind waves can combine with fast currents, and water levels may be much higher than normal. The consequences of the wind wave-current interaction during hurricanes can affect inland wind wave propagation, can influence flooding far inland, and can change the sediment dynamics and therefore the shape of the coast. Unfortunately, the ability to model accurately and in detail this highly energetic and important zone has been limited due to requirements for very high levels of mesh resolution, complex governing equations and prohibitive computational costs. Intellectual merit: The long-term objective of this project is to improve the accuracy of hurricane inundation, current and wave climate models by locally incorporating the appropriate physics and levels of resolution. To significantly advance this goal, a multi-process, multi-scale framework which integrates new Green-Naghdi (GN) phase resolving wave (PRW) models with existing coupled wave action/long wave circulation models will be developed: this will greatly improve the ability to simulate detailed near-shore hydrodynamics during severe storms and other highly energetic events. Different physics and levels of resolution will be applied and coupled in the various portions of the global domain. In regions where rapid wave transformation does not occur, the standard shallow water equation combined with a non-phase resolving wave energy equation formulation will be applied. The new GN combined current and phase resolving wave equations will model the wave and current hydrodynamics in narrow zones where near-shore and/or structure induced wave breaking and run-up occurs. Numerous research issues relating to the algorithms, coupling mechanisms, physics and code design will be investigated. Verification and validation exercises will confirm the adequacy of the selected physics and algorithms while code performance studies will demonstrate the efficiency of the techniques. The project brings together expertise in mathematics, computational science, shallow water hydrodynamics, wave physics, coastal engineering and storm surge modeling. Broader impacts: The study will improve the ability to predict waves, water levels, and currents near and behind features such as barrier islands, dunes, near-shore breaking zones, inland roads and levees. Broader impacts of this work include improvements in the ability to: 1) evaluate flood risk behind a barrier or levee; 2) assess the actual degradation of dunes, barrier islands, levees, roads and railroads; 3) compute wave run-up behind wave breaking zones; 4) determine nonlinear wave climate around coastal structures such as levees, bridges and buildings; and 5) forecast storm surge and waves so as to help plan evacuations, assess coastal risk, design levees and closures, and operate shipping by federal and state agencies including FEMA, NOAA, the USACE, and the U.S. Navy. The algorithms and computational infrastructure developed under this project may be applicable to other problems in near-shore oceanography and coastal engineering, including water quality, shipping and ports operations, naval operations, marine ecology, weather and climate change, and wetland degradation and rebuilding. On a broader level, the computational techniques to be studied under this project apply to many other types of compressible and incompressible flow problems.
Intellectual Merit This project focused on the development, testing, and application of theories and models to simulate detailed wave and surge processes in the surf zone. Two sets of Boussinesq-type wave models were investigated and optimized, each having its own advantages. Discontinuous Galerkin finite element and finite difference implementations of these models were created and tested. Models were extended to include surf zone and wave runup processes, and to provide improved wave generation/absorption for nonlinear waves. Broader Impacts The models developed under this project will prove useful in computing storm processes in nearshore and overland regions, and will help to increase understanding of damages, and reduce losses. Models were implemented for Hurricane Sandy to examine wave and surge processes during the storm. These results were related to observed damage in Ortley Beach, New Jersey and used to evaluate conditions most likely to cause specific damage levels to homes near the shore. The same models were used to evaluate wave runup during Super Typhoon Haiyan in the Philippines, and to drive models to simulate the transport of very large (>5m) boulders during the storm. Additional geophysical and engineering applications are currently in progress using models developed and tested during this project.
