A coupled wave, circulation, and sediment transport modeling system was applied to an
idealized inlet and ebb shoal to examine the physical response to tide and wave forcing. The
idealized inlet was patterned after Shinnecock Inlet, New York, in dimensions, geometry, jetty
configuration, bay area, and morphology. Five simulations were conducted for combinations of
tide, fair-weather waves, and storm waves. Wave direction was specified at 30 deg to produce
exaggerated and rapid response from the modeling system to allow multiple simulations over
brief time intervals. Changes in depth from wave forcing were greater than would be expected
over the same duration at a real inlet.
Patterns of response of the current to tide and waves reproduced those that are commonly
observed to occur at tidal inlets stabilized by jetties. Well-defined longshore currents developed
nearshore. The longshore current speed increased with larger waves, and the surf zone and
location of peak current moved further offshore. Wave refraction and breaking on the ebb shoal
produced strong and complex currents. For both fair-weather and storm waves, a strong north
directed flow was produced on the central and northern portion of the ebb shoal, while a south-
directed current formed on the outer shoal.
Calculation of morphology change showed realistic patterns for both wave and tidal forcing.
Erosion at the jetty tips took place under tidal flow, as well as formation of tip shoals. Sand
transport by waves impounded material against the south jetty during fair-weather conditions.
During storm conditions, sand from the updrift nearshore region was moved to a deltaic
formation off the tip off the south jetty. Both storm and fair-weather waves eroded the top of the
ebb shoal and deposited material along its north and western perimeter. Fair-weather waves
produced a split deposition pattern on the ebb shoal perimeter, whereas storm waves produced a
spatially continuous band of deposition. These patterns resulted in a skewed ebb shoal. Storm
waves produced scour at the tip of the downdrift jetty, in part controlled by phasing of the tide
Updrift and downdrift bypassing bars formed under wave action. The modeling results thus
give support to the Reservoir Model (Kraus 2000) concept of ebb shoal morphology genesis, in
which the ebb shoal proper is developed by transport from the ebb jet, and the bypassing bars
and lobes of the ebb shoal are created by transport under wave action.
This paper was prepared under the Inlet Modeling System Work Unit of the Coastal Inlets
Research Program, U.S. Army Corps of Engineers. Permission was granted by Headquarters,
U.S. Army Corps of Engineers, to publish this information.
Bruun, P., and Gerritsen, F. 1959. Natural By-Passing of Sand at Coastal Inlets. J. of
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Gaudiano, D. J., and Kana, T. W. 2000. Shoal Bypassing in South Carolina Tidal Inlets:
Geomorphic variables and empirical predictions for nine mesoscale inlets," Journal of
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Kraus, N. C. 2000. Reservoir Model of Ebb-Tidal Shoal Evolution and Sand Bypassing.
Journal of Waterway, Port, Coastal, and Ocean Engineering, 126(3), 305-313.
Militello and Kraus