Beach ridges are linear sand ridges that were deposited along the beach face in areas characterized by a gentle offshore slope, low wave energy, and an abundant sand supply. Beach ridges form only on accreting beaches. Because they form on the beach face, they indicate the location and orientation of the coastline, as well as the approximate sea level (in areas that have not been tectonically uplifted or depressed) at the time they were formed. Several spectacular beach-ridge plains have formed in Florida. Among the most spectacular were Sanibel Island, Cape Canaveral and St. Vincent Island. Of these St. Vincent is the only one still preserved in pristine condition.
Beach ridges are constructed by the process of wave run-up in the swash zone by waves that fall in the long-term "maximum wave energy" category (Stapor and Tanner, 1972). The internal structure of beach ridges indicates that all or almost all of the ridge is constructed by wave run-up, with very little washover (Tanner and Stapor, 1972). Internal bedding is almost exclusively composed of planar, seaward-dipping cross beds. The ridge grows upward and seaward as material is deposited. In Florida beach ridges typically have heights of 1-3 meters, with spacings of tens of meters.
Stapor (1973) described several basic types of beach-ridge patterns, each of which is indicative of specific depositional environments. Stapor's categories are: 1) ridges convex seaward, occurring at the distal prograding tip of spits; 2) ridges concave seaward, which are being actively eroded perpendicular to their ridge and swale orientation; 3) ridges concave seaward deposited in embayed sections of the coast; and 4) ridges convex seaward, which represent net seaward growth, not lateral extension. Category 3 beach ridges predominate on St. Vincent Island. Beach ridges that are essentially parallel indicate that sediment was transported from offshore without significant longshore transport. Splayed ridges (increasing ridge crest spacing from one end to the other) indicate that longshore drift supplied the sediment for their construction. According to Stapor the direction of decreasing ridge crest spacing indicates the direction of the longshore drift.
Florida has numerous areas where beach ridges have been deposited in the past; however, there are few areas where ridges are being deposited today because of a long-term shortage of sediment for their construction. This is evidenced by the predominance of eroding coastline over stable or accreting coastline in Florida.
Many beach ridges evident on aerial photographs are difficult or impossible to locate in the field. The topographic expression of ridges and swales is degraded through time by a variety of geomorphic processes. Erosion by wind and rain, and karst dissolution of calcareous sediments within and beneath the ridge reduce ridge slope and height. Development of dunes on the surface of the ridge can further mask the characteristic shape of the ridge. On older ridges the topographic expression may be completely gone. These ridges show up in aerial photographs due to the different sediments and moisture regimes of the ridges and swales and the differences in vegetation on the ridges versus the swales. Swales collect fine grained sediments, organic material and are wetter compared to the sandy and drier ridges. The sedimentologic and vegetation signature remains even after the topographic expression of ridge and swale has deteriorated.
