Winter Storms Impact on the Hydrodynamics of Sabine Bank, off Louisiana-Texas Coast, USA

Sabine Bank, located off the Louisiana-Texas has been identified as a prospective source of sand for beach nourishment and coastal protection projects along western Louisiana. The bank is located at the approximate 12 m isobath and is surrounded by marine mud. The present study employs a fully spectral finite volume wave model to estimate the wave transformation over the shoal due to cold front generated, extra-tropical storms. Also, in situ observations were conducted using wave and current arrays. The MIKE 21 spectral wave module is implemented for the shoal at a high resolution scale (200m), to estimate wave attenuation over the shoal and to calculate the sediment transport induced by frequent winter storms. The fine resolution computational grid is nested within a regional wave model for the Gulf of Mexico. Forty-three days of NCEP re-analysed wind data is used for driving the wave model and the spatial distribution of bottom sediments are also included in the model to develop friction factors.

An extensive array of bottom boundary layer instrumentation was deployed for the same duration as the modelling period, across a transect of the shoal. The instrument array mainly consisted of Acoustic Doppler Velocimeters (ADVs), PC-ADP, OBS and pressure sensors. Also, bottom sediment samples were collected for calibrating the OBS sensors. The model simulations were in excellent agreement with in situ observations obtained from two bottom boundary layer arrays deployed at the shoal. The model results were also validated using time series and spectral wave data collected from NDBC Buoy 42035. It was found that the shoal could significantly dissipate storm waves during propagation across the shoal. The OBS data also showed that, during high energetic winter storm events, bottom sediments were resuspended and transported in various directions as a function of veering wind/wave fields.