Development and application of a Coupled-Ocean-Atmosphere-Waves-Sediment Transport (COAWST) Modeling System

John C. Warner, Brandy Armstrong and Maitane Olabarrieta
U.S. Geological Survey, 384 Woods Hole Rd, Woods Hole, MA

Ruoying He and Joseph Zambon
Marine, Earth & Atmospheric Sciences, North Carolina State University, Raleigh, NC

George Voulgaris and Nirnimesh Kumar
Department of Earth & Ocean Sciences, University of South Carolina, Columbia, SC

Kevin Haas
Dept. of Civil and Environmental Engineering, Georgia Institute of Technology, Savannah, GA

Understanding the processes responsible for coastal change is important for managing both our natural and economic coastal resources. The current scientific understanding of coastal sediment transport and geology suggests that examining coastal processes at sub-regional to regional scales can lead to significant insight into how the coastal zone evolves. In the coastal zone, storms are one of the primary driving forces resulting in coastal change. Understanding the processes that drive coastal change will increase our capability to predict impacts of storms on coastal systems.

Here we describe a numerical modeling approach to investigate the dynamics of coastal storm impacts. We use the newly developed Coupled Ocean – Atmosphere – Wave – Sediment Transport (COAWST) Modeling System that is based on the Model Coupling Toolkit to exchange prognostic variables between the ocean model ROMS, atmosphere model WRF, wave model SWAN, and the Community Sediment Transport Modeling System (CSTMS) sediment routines. The models exchange fields of sea surface temperature, ocean currents, water levels, bathymetry, wave heights, lengths, periods, bottom orbital velocities, and atmosphere radiation fluxes, winds, atmospheric pressure, relative humidity, precipitation, and cloud cover. Data field exchanges are regridded using sparse matrix interpolation with weights from SCRIP.

We describe the modeling components and the model field exchange methods. As part of the system, the wave and ocean models are run with cascading, refined, spatial grids to resolve nearshore processes driven within a larger, coarser-scale coastal modeling system. This facilitates seamless modeling from the shelf break across the inner shelf and through the surf zone. The modeling system is applied to the U.S. East coast with a focus on the Carolinas coastal region to investigate nearshore and inner-shelf processes and how these are connected. The importance of utilizing larger-scale forcing to drive nested models is identified by showing the spatial variability of the forcing and how that interacts with coastal orientation. Because the waves are a dominant mechanism for sediment mobility and the currents are then responsible for the transport, a coupled system is necessary. Also presented will be some of the challenges faced to develop the modeling system.