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Bathymetry

Depths in the main channel range from 4 to 14 ft below sea level and average about 8 ft (fig. 3). The channel is narrow and irregular with wide and shallow areas along the shorelines of Cape Coral and Pine Island. Many oyster beds are present, indicating freshwater-saltwater mixing zones between the Caloosahatchee River and the Gulf of Mexico. Variable velocities are also indicated by sandbar deposition outside the narrow channels. Sandbars and oyster beds in the southern end of the pass (fig. 3) can be exposed at low tide.

Velocities capable of maintaining channel depths greater than 5 ft (fig. 3) occur from San Carlos Bay to the southern end of Little Pine Island. In the middle of Matlacha Pass adjacent to Little Pine Island, depths average less than 4 ft across a wide section of the pass and about 2 ft along the mangrove shoreline (fig. 3). A tidal division occurs at State Road 78 near the center of Matlacha Pass, and tidal stages are affected more by tidal currents from upper Charlotte Harbor rather than from San Carlos Bay. This mixing or dampening of tidal stage lowers tidal velocities and promotes a deposition of sediment.