Title: SEDIMENT TRANSPORT AND MORPHOLOGY MODELING OF SHIP ISLAND,
MISSISSIPPI FOR NORMAL WAVE CONDITIONS
Cilia Swinkels1, Jaap van Thiel de Vries1, Frank Dekker2, Arjen Luijendijk1, Dirk-Jan Walstra1
1
Deltares, The Netherlands, 2 DHV, The Netherlands
Presenter: Cilia Swinkels
Deltares, Department of Harbours and Coastal Engineering
Rotterdamseweg 168, Delft, The Netherlands
Telephone: +31 335 8628
cilia.swinkels@deltares.nl
The U.S. Army Corps of Engineers has recently undertaken several comprehensive coastal
restoration and hurricane protection measures. The Mississippi Coastal Improvements Program,
budgeted at nearly 500 million dollars, is a multi-faceted project with a focus on the restoration
of select barrier islands within the Mississippi Sound. After Hurricane Katrina, it became widely
accepted by the public that if the Mississippi barrier islands had been in a “pre-Hurricane
Camille” condition, there would have been much less storm damage as a result of Hurricane
Katrina (MSCIP 2009). This presentation will focus on the application of a depth-integrated
2DH sediment transport and morphodynamic model, Delft3D, that is used to predict the
sediment pathways and morphological response resulting from a “pre-Hurricane Camille” Ship
Island restoration to normal wave conditions (i.e. yearly averaged conditions excluding
hurricanes). The restored pre-Camille modeling template includes the placement of
approximately 20 Million m3 of sand for the closure of Camille Cut as well as an increased
island footprint and sand placement into the local littoral zone.
The averaged normal offshore wave conditions in the Northern Gulf of Mexico are characterized
by fairly low energetic waves (Hs,av ~ 1m, Tp,av ~ 5-6s) coming from a predominant SSE
direction. Wave modelling is performed with the SWAN model to transform the offshore wave
climate to nearshore. Subsequently, a regional transport model is considered in which wave-,
wind- and tidal- driven transports are included in order to investigate the general sediment
pathways along the Mississippi Barrier Islands and over the tidal passes.
The dominant nearshore wave direction shows a large angle of attack, which causes a nett
westward driven littoral transport along the barrier islands. The E-W decrease in wave energy
due to the sheltering by the Chandeleur Islands leads to a gradual reduction in transport rates
from Dauphin Island in the East to Ship Island in the West. By analysing the sediment pathways,
sediment sinks and sources in the system have been identified. Furthermore, a comparison is
made with the sediment pathways derived from long-term bathymetric data analysis (Byrnes,
2011), with annual dredging records and with shoreline changes derived from LIDAR data.
A more detailed local model covering Ship Island is subsequently developed and calibrated in
order to investigate the morphodynamic development of the Ship Island restoration under forcing
of normal wave conditions. With the calibrated model, the morphodynamic impact of an offshore
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borrow area and nearshore sand placement is investigated as well as the effectiveness of a
terminal groin in preventing sediment losses to the Gulfport navigation channel.
A sensitivity of the computed sediment pathways and morphology model predictions will be
presented for a variety of model parameters, including variations in the Camille Cut restoration
grain size, bed composition and model forcings. Furthermore, an interpretation of the sediment
transports due to normal conditions is made with respect to extreme events (hurricanes) to gain
insight in their relative contributions to the overall sediment budget.
Bio: Cilia Swinkels is a Researcher at Deltares, The Netherlands, working in numerical
modeling of coastal morphology. She has a Master of Science degree in Environmental Coastal
Engineering from the University of Southampton, UK. She has been with Deltares for over 4
years and is involved in national and international projects in the field of coastal engineering and
morphology.
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