Sand-spit erosion following interruption of longshore sediment transport: Shamrock Island, Texas

Abstract

Shamrock Island, located in Corpus Christi Bay, Texas, is a former sand spit that was detached from Mustang Island by navigation channels constructed in the early 1950s. The navigation channels effectively eliminated longshore sediment transport to the island, resulting in severe and ongoing erosion of the island's north shore. This study documents long-term shoreline change, based on analysis of aerial photographs from 1938, 1948, 1950, 1952, 1956, 1967, 1975, 1979, 1985, 1990, and 1995. Shamrock Island grew steadily to the south prior to 1956, while the north shore of the island was relatively stable. After 1956, the north shore eroded rapidly, while the south shore continued to grow, probably because sand eroded from the north was redistributed to the south. By 1995, up to 156 m of retreat had occurred on the north shore. The island was recently acquired by the Nature Conservancy of Texas for use as a nature preserve. Erosion now threatens to breach the island, which may result in degradation of an interior lagoon and loss of valuable wildlife habitats. Therefore, in addition to documenting long-term erosion following interruption of longshore sediment transport, this study also illustrates how human modification of the coastal zone can have important and unforseen ramifications affecting future shoreline uses for many decades.