Figure 7. Above: Plot of the relative strength of the wave-induced current (black line) and suspended sediment concentration (red line) at the bottom at the long-term monitoring station near the site of the future outfall. Increased sediment concentrations occur in the water whenever wave-induced currents are large.
Below: Sequence of bottom photographs taken before, during, and after the April 1, 1997, storm. During the storm (middle photograph), material in suspension obscures the sea floor from view. By the end of the storm, several of the large cobbles on the sea floor have moved (the frame holding the camera also moved during the storm, slightly changing the field of view). |
Figure 8. Mean wind (in m/s) and currents (in cm/s) measured near the future outfall site during strong storms that resuspend and transport bottom sediments. Winds from the northeast drive near-surface currents at this location to the south toward Cape Cod Bay and near-bottom current to the southeast offshore toward Stellwagen Basin. |
Figure 9. Modeled wind-induced currents (arrows) and contours of near-bottom wave current speed driven by a northeasterly wind of 14 m/s (28 knots). Near-bottom wave speeds in excess of about 10 cm/s are sufficient to resuspend fine-grained sediments. During major northeasters, fine sediments along the western shore of Massachusetts Bay are resuspended by the wave currents and transported by the wind-driven flow to the southeast toward Cape Cod Bay, where they settle. They are protected from the influence of subsequent storms by water depth and and basin geometry. The numerical circulation models provide predictions of the basinwide storm response, which would be very difficult to observe directly. |
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Maintained by Jim Robb
Last revised 6-24-98