Morphologic Changes caused by Hurricane Bonnie

In advance of Bonnie's arrival, four profile lines were surveyed by the CRAB. Line 62, located about 500 m north of the FRF's research pier is shown in the figure below. Although there was little change to the beachface, an inner sandbar formed at 190 m offshore, and the outer sandbar moved ~50 m seaward. The presence of the wide outer bar before the storm likely contributed to the stability of the beachface. The offshore movement of the outer bar caused deposition to occur to a depth of 5.8 m NGVD (National Geodetic Vertical Datum of 1929). The development of the inner bar and the offshore movement of the outer bar can also be seen in the video time exposures. Acoustic altimeters located near Line 62 at depths of 5.5, 8 and 13 m revealed bottom changes up to 20 cm during the peak of the storm, but negligible net change at -5.5 m and about -10 cm both at 8 and 13 m depth.

The figure below shows the bathymetry on August 29 following Bonnie and the change in bathymetry since 13 August 1998 centered around the FRF research pier (download a sharp postscript image). In the change diagram, green indicates accretion and red erosion at 0.25 m contour intervals. Close examination indicates cross-shore changes similar to Line 62 (shown above) at distances about 250 m north and south of the pier. Closer to the pier there was deposition to the south and erosion (up to -2.5 m) on the north side. This is typical for storm waves arriving from the SE.

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