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Shamrock Island

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Shamrock Island is in eastern Corpus Christi Bay, about 2 miles west of Mustang Island, a barrier island that separates the bay from the Gulf of Mexico.  Shamrock Island is undeveloped and is widely regarded as some of the best aquatic and colonial waterbird habitat in South Texas. The island was formed as a spit and was once connected to Mustang Island by the “land bridge” as its north end, but became detached following construction of navigation channels through the island in approximately 1951 and erosion by Hurricane Celia in 1970.  Since detachment from Mustang Island, the north and northwest areas of Shamrock Island have experienced considerable beach erosion and loss of wetlands, losing approximately 17 acres between 1950 and 1997.  Without proactive measures, this trend of erosion would have continued, resulting in the loss of all valuable habitats found on the Island, including submerged and emergent wetlands, beach areas, and adjacent uplands.

The critical ecological importance of Shamrock Island was recognized in the early 1990s when the Texas Nature Conservancy (TNC) led an effort to acquire the Island, which has always been in private ownership, to absolutely ensure its protection from development.

The TNC worked with several agencies and sources including the U.S. Fish and Wildlife Service, the Corps of Engineers, Texas Audubon Society and the Coastal Bend Bays Foundation to generate funds needed for protective and enhancement measures.  The Land Office took the administrative lead and engaged Shiner Moseley and Associates to develop alternatives, obtain permits, prepare detailed designs and specifications, and provide construction observation assistance.

Determination of the proper remedy required a combination of careful scientific evaluation of physical processes and habitat characterization coupled with practical engineering design and construction considerations.   The solution involved the following components:

  • An offshore breakwater along the north and northwest end of Shamrock Island consisting of a 4,000 linear feet geotextile tube filled with approximately 8,000 cu yd of sand.
  • Creation of approximately five acres of shallow water habitat/wetlands between the geotube and Shamrock Island’s shoreline requiring 10,000 cu yd of fill.
  • Construction of a 72,000 cu yd feeder beach outside the breakwater to ensure the continuation of the longshore flow of sand to the beach at the south end of the Island.

Construction began in December 1998, and was completed in March 1999.  This project's total cost was approximately $750,000.