Coastal Barrier Reservoirs

Abstract

Coastal barriers are long, narrow, wave-built, sandy islands parallel to the shore. Part of the island has a beach, but may parallel to the shore. Part of the island has a beach, but may have sand dunes and areas of vegetation above the high-tide line. A lagoon or estuary is behind the barrier on the protected side away from the ocean, as shown in Fig. 1. Coastal barrier reservoirs can hold major accumulations of oil and gas. Coastal barriers can build by three major processes: addition of sand washed onto the beach from breaker bars, addition on one end by sand washed from the other end and moved by riptides, and deposition of sand into the lagoon by waves breaking over the barrier during storms. Tidal channels that form at the ends of the barriers tend to migrate laterally and fill with sand from the barriers (see Fig. 1). Wind-blown (aeolean) dunes are usually minor parts of the barrier deposits. Galveston Island, offshore Texas, is a good example of a modern coastal barrier. Waves in the Gulf of Mexico have sufficient energy to transport and deposit fine-grained sand on Galveston Island. (Fine-grained sand is the coarsest sand available in upper Texas coastal waters.) Other examples of modern coastal barriers are found in the Gulf of California, where medium-sized sands are deposited. An example of an ancient deposit was found in the Elk City field, where the barrier beach was composed of well-sorted gravel and coarse sand. P. 1127