Geotubes Along the Gulf Shoreline of the Upper Texas Coast: Observations During 2001

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In September 1998, Tropical Storm Frances caused severe beach and dune erosion along the Gulf shoreline of the southeast Texas coast. This erosion placed many beach houses in danger of being undermined or damaged during subsequent storms and gradual shoreline retreat. To help prevent such damage, shore-parallel geotextile tubes (geotubes) were installed. The geotubes are sediment-filled sleeves of geotextile fabric having an oval cross section of approximately 12 ft. They rest on a fabric scour apron that has sediment-filled anchor tubes along each edge. Geotubes are placed in a trench parallel to shore along the back beach or foredunes, and project designs call for sand and natural beach vegetation to cover them. Currently, nine separate geotube projects cover a total of 7.3 mi of the Gulf shoreline from Follets Island to High Island.

This study provides a quantitative evaluation of these projects on the basis of observations made during 2001. Three field surveys were conducted that included ground surveys (beach profiles), visual inspection of geotube exposure and damage, and an airborne topographic survey (lidar) of the projects and adjacent beaches and dunes. Wave and water-level data were also compiled. Results from this study will aid the design of future erosion-control projects, such as beach nourishment and other geotube projects in the area. Results, data, and maps are reported on the Bureau of Economic Geology website.

The geotubes are intended to serve as temporary storm-surge protection and erosion-control structures. Their effectiveness in protecting against storm surge is untested. Tropical Storm Allison struck the coast in June 2001, but the storm was not a significant event with regard to storm surge and beach erosion. Geotubes are effective only for temporary erosion control, and they will fail when exposed to direct wave attack and undermining. Also during 2001, one of the Treasure Island (on Follets Island) geotubes failed, and holes were found along the Gilchrist West project. To prevent failure, it is critical to (1) keep the geotubes covered with sand, (2) maintain a beach in front of them through beach nourishment, and (3) repair holes in the fabric as soon as possible. Although Allison did not test the storm-surge-protection function of the geotubes, the storm was largely responsible for eroding sand cover and fully exposing seaward faces of 44% of the combined lengths of the projects, for a total of 14,193 ft. Fair weather and transportation of sand from borrow sites allowed 85% of the geotubes to be covered by November. Because the geotubes cannot be recovered through natural processes, covering them requires a significant effort. Furthermore, maintaining even a sparse vegetation cover on at least half of the project lengths has been impossible. Besides the Treasure Island projects, the Gilchrist West project on Bolivar Peninsula has been the hardest to maintain. In contrast, the Pirates Beach project on Galveston Island has fared well with respect to keeping a vegetated sand cover. Analysis of pre-Allison data and future monitoring will reveal why.


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