Investigation of Scour Adjacent to Submerged Geotextiles Used for Shore Protection
Alicia M. Gorton, Thomas O. Herrington and Ernest R. Smith
This study presents the results of an experimental investigation of morphology change in the vicinity of submerged sand-filled geotextile tubes placed within the surf zone. The study was motivated by the emerging use of submerged geotextile tubes for shore protection, shoreline stabilization, and surf amenity enhancement and the need to understand the mechanisms responsible for seabed changes near these structures. A movable bed physical model experiment was conducted at the U.S. Army Engineer Research and Development Center’s Large-scale Sediment Transport Facility (LSTF) to investigate macro-scale bed form changes adjacent to submerged geotextile tubes. A limited number of high-resolution wave, current, and scour measurements adjacent to the tubes are analyzed to gain insight into the structure-seabed interactions under oblique wave-breaking conditions. The data are used to develop empirical formulations to predict the mean scour depth adjacent to the sand-filled geotextile tubes as a function of the maximum Keulegan-Carpenter, Shields, and Reynolds numbers. The observed scour near the sand-filled geotextile tubes is compared to a previous study of scour in the vicinity of submerged cylinders. Formulations developed by Cataño-Lopera and García (2006) relating the Keulegan-Carpenter, Shields, and Reynolds numbers to the scour depth were used to predict the scour observed during the LSTF experiment. Results show that the formulations of Cataño-Lopera and García (2006) over-predict the observed scour when calculated using the maximum Keulegan-Carpenter, Shields, and Reynolds numbers. New, modified expressions of Cataño-Lopera and García (2006) are proposed for use in oblique random wave fields.
Keywords: Sediment transport, morphology change, scour, physical model, geotextile, shore protection