Figure 4. Sites included in the present study.
The study was supported by the National Geographic Research and Exploration Committee and the National Sea Grant Program.
From 1940 to 1977, the shoreline at Arecibo underwent continuous retreat at an average rate of 1.5 to 1.7 meters per year (Morelock, 1984), resulting in a net loss of more than 55 meters of shoreline. From 1977 to 1985, the shoreline was stable except for changes at the mouth of the old river channel. The stability of the coast for this eight-year period may indicate that the shoreline adjusted to the changed conditions that led to the original erosion, which were:
damming of the river upstream, with reduced sediment carried to the beach
construction of the harbor breakwater and a change in the wave regime
harbor dredging and removal of bottom sediments
changes in position of the river mouth
In 1980, construction was started on a small jetty north of the relict river mouth, and the channel was dredged for access to the Arecibo Yacht Club. The work was completed in 1982. The shore north of the jetty is almost 30 meters seaward of the 1977 shoreline (Figure 5). By 1987, there was only minor accretion and erosion when compared to the 1977 photo. The stability was upset by the jetty between 1987 and 1999 and the resultant erosion begins just south of the channel and spreads westward (Figure 6). Field observations showed that high waves accompanying Hurricane Gladys have started this process.