COASTLINE CHANGES NEAR A TIDAL INLET

Abstract

Extensive coastline changes around the Ponce de Leon Tidal Inlet, Florida, are described, discussed and explained. These changes started developing immediately after the beginning of the construction of two jetties on both sides of the inlet forming part of a plan to stabilize the inlet, improve navigation conditions and bypass sand effectively. The mean annual littoral transport of sand was considered to be from north to south. Rapid sand accretion south of the south jetty started immediately after the beginning of its construction in 1969, reaching by November, 1971, a volume of approximately 1,400,000 cu. yds. Aerial photographs suggest that the sand was transported there from the south during the summer periods of northerly drift and from the offshore bar by refracted waves from the north. The accumulated sand is well protected by the south jetty during the winter storms from the northeast. Coastline and duneline recession occurred north of the inlet due, at least partially, to the described sand retention. It is concluded that for inlets where the littoral drift reverses its direction, the net annual rate of littoral transport is not a unique design criterion. Instead the total sand volumes transported annually in either direction should be considered.