NEARS SHORE SEDIMENT TRANSPORT AT MYRTLE BEACH, SC

The objective of this project, funded by the US Geological Survey and the South Carolina Sea Grant Consortium is to describe the processes governing the circulation, wave propagation and sediment transport along the northern South Carolina coast. This talk will focus on the development and validation of a nearshore sediment transport model within this project. The model is applied at a range of a few km in the longshore direction and to a depth of 10 m and has a temporal scale up to weeks.

As part of the study, wave and current data were collected offshore of Myrtle Beach, SC in three field measurement campaigns since 2001. During the latest experiment that took 6 months at nine different stations various instruments were used to measure waves, currents and sediment concentrations.

Two nearshore experiments were also conducted during December 2003 and December 2005. Bathymetric data was collected using differential GPS and total station, waves and currents were measured along a cross-shore profile with four instruments and sediment samples were taken. Digital imagery was acquired throughout the experiments which was used to infer additional hydrodynamic information such as wave directions and longshore currents.

A process-based sediment transport model was developed to predict the bathymetric changes in the nearshore region. The model solves for the diffusion of the sediment over the water column after it is picked up from the bottom. The movement of the sediment below the pickup layer is also accounted for using empirical velocity and concentration profiles.

The sediment transport model requires detailed hydrodynamic input at every point of the model grid. REF/DIF-S is used to model the wave transformation while SHORECIRC is used for predicting the circulation. Velocities within the wave boundary layer are predicted with another model developed for this study, since the models mentioned above do not resolve the wave boundary layer.

The hydrodynamic and sediment transport models were tuned and tested using data collected in this study and others available in the literature. The performance of the model is evaluated on its ability to predict the formation of bars, on/offshore movement of bars, erosional and accretional profiles, response to tide and quantity of cross-shore and longshore sediment transport rates.