ABSTRACT

Middle America, as used here, includes the shores of the Caribbean Sea and the Gulf of Mexico, plus nearby parts of the Pacific coast of Mexico and Central America, and nearby parts of the Atlantic coast of the southeastern states in the U.S. Various papers in this symposium present detailed historical data on beach accretion or retreat in South Carolina, Georgia, Florida, Alabama, Mississippi and Louisiana. The introduction surveys shores of other parts of Middle America, where actual measurement of rates of change have not been undertaken, or cannot be undertaken. This overview of poorly-studied parts of the region is based largely on field observation, supported by air photo study and aerial reconnaissance, and is necessarily far from complete, even as a summary.

Nevertheless, the data so obtained agree, in general, with the results of more detailed studies made in the U.S.: erosion is very important along most of the coast, but is not universal; and rates change (and even reverse algebraic sign) from place to place and from time to time. The general picture is one of coastal erosion, with stable and accreting shores being less important.

Even large and important rivers commonly do not provide for significant growth of new land (examples from Mexico and Columbia). Much of the local depositional regime of the late Holocene has changed, in the last five centuries, to erosion, or is now so changing; this shift, however, has not been synchronous throughout the area. The status of the littoral sand account is, currently: more loss than gain.

Six possible causes for regional beach erosion are examined, and four are rejected, based on the data. The two that remain are: changes in the wave climate, and maturing of the system. The other four might be important locally.