Environmental Engineering Reference
In-Depth Information
FIGURE 7.48
Beach ridges of an emerging shoreline, Ormond Beach, Florida. (Courtesy of USGS.)
apparent. The oldest beach ridge in the figure, now 100 ft above sea level, migrated inland
and its tidal lagoon filled in; the land uplifted and a second beach ridge formed.
Eventually its lagoon filled and a third beach ridge formed as a barrier beach. The offshore
waters at this location are very shallow, indicative, along with the beach ridges, of an
emerging shoreline.
Combined Shorelines
The features of a structurally shaped coast along the ocean and a subaerial erosion and
marine depositional coast on a large bay are shown in
Figure 7.49.
The geologic formations
inland are primarily rock, such as quartz diorite. On the ocean side, strong wave forces
have cut a linear cliff in the rock; a narrow beach has been formed and fine sands from the
beach blow inland to form dunes. In Drakes Bay, longshore currents deposit sands to form
a bay bar and spits. The drowned valley (Schooner Bay) has been filled with sediments to
form shallow waters. Current in the bay is minimal and deposition is limited to fine-
grained soils forming mud flats. The relatively steep slopes and high elevations of the
adjacent hills indicate that the bay deposits may be as thick as 100 ft. At Drakes Beach, a
bayhead bar has formed, blocking the flow of a small stream into the bay. The lagoon
behind the bay bar fills with fine sediments from landward.
