Wave attenuation by rigid and flexible-membrane submerged breakwaters

This research investigates the use of rigid and flexible-membrane submerged breakwaters for wave energy attenuation. A comprehensive review of breakwater design criteria and previous research on submerged breakwaters is included. Physical model laboratory studies conducted by the author and other researchers are investigated as a means for obtaining formulations for wave transmission coefficients. The mechanisms by which waves are attenuated and break are analyzed using video photography of the wave tank tests. The primary objective of this doctoral research was to determine and compare the wave attenuation of non-conventional rigid and flexible-membrane type submerged breakwaters. Physical model tests were performed using the wave tank facilities at Florida Institute of Technology located in Melbourne, Florida. Six different breakwater cross-sections used were: (1) rectangular, (2) triangular, (3) P.E.P.-$Reef\sp{TM}$, (4) single sand-filled container, (5) three stacked sand-filled containers, and (6) one single water-filled container. The first three breakwater units were rigid (or monolithic), and the last three units are flexible-membrane breakwater units. All six units tested had the same height, length (longshore), and base width (cross-shore), with different cross-sections and shapes, and were composed of different materials. A new classification scheme was developed for breakwaters and artificial reefs, based on water depth, structure height, and wave heights. The wave-structure interaction resulting in the wave breaking on the submerged breakwaters was documented, and the observations were analyzed. Wave transmission coefficients were computed for the six different breakwater models tested, and comparisons between the different models were made. Conclusions regarding the primary factors affecting the effectiveness of rigid and flexible-membrane submerged breakwaters were developed, as were recommendations for further research.