![]() Where Kt is the wave transmission coefficient, Ht is the transmitted wave height shoreward side of the submerged structure, and Hi is the incident wave height on seaward side of the submerged structure. Army Corps of Engineers (1984), wave energy reduction is defined in terms of the energy transmission coefficient: In these cases, incident wave energy may be reduced to conditions that generate a balanced beach profile by submerged structures, so sand accumulates without interrupting alongshore transport. When it is too high, related to the littoral drift, the erosion process causes shoreline regression. The hydraulic load on the coast governs morphological response to wave climate and shoreline control. In critical segments, free sediment motion was not enough. Evidently, the beaches never recovered their original dimensions but in some segments, they were naturally stabilized solely by the free sediment motion. With these actions, alongshore sediment transport was partially recovered to natural conditions. Originally, the solution consisted of: (1) the elimination of structures perpendicular to shoreline (groins) (2) beach nourishment from inland material banks, so actions in the seabed were fully avoided and (3) implementation of sediment bypass techniques for the various harbors along the coast. Under these requirements, the final objective of the beach restoration project was to re-establish the natural conditions that govern the littoral drift. Based on local experience in the past 20 years, any beach restoration action has to be environmentally friendly, reducing as much as possible any changes to littoral dynamics and it also needs to consider possible negative impacts on adjacent beaches. The combination of wave climate, currents, tides, and storm surges is the main cause of beach erosion. By the end of 2002 the situation was critical, since many beaches were almost fully eroded (Photo 1) and many faced the risk of permanent destruction due to extreme waves induced by any hurricane with a path through the Gulf of Mexico. The first attempts to control beach erosion were individual actions undertaken to retain sediment for beach stabilization without considering other consequences along the coast. However, as a particularity of this beach system, there are not many natural sediment sources such as river discharges, so littoral balance may be easily broken by infrastructure such as small harbors, piers, and groins. The most-developed zone, near the city of Progreso, was originally limited by a vigorous and balanced beach 30m to 100m wide. The case discussed in this paper refers to a beach system defined as Barrier Island, formed by alongshore transport of sediments running parallel to the coast. By September 2005, 4km of geotextile tubes were installed. The main goal was to generate a balanced beach profile integrated to natural littoral dynamics. Their main function was to reduce the incident wave energy on the beach, by controlling the wave-breaking process, to the required level that maintains the dynamic balance on the shoreline (Figure 1).īased on these criteria and using a maritime field database processed by federal and state authorities, geotextile tubes were designed according to coastal engineering theories regarding wave propagation, the breaking process, and their relation to sediment transport. Woven polypropylene geotextile tubes were designed to work as low-crested submerged structures. Under these conditions and for critical points, geosynthetics were considered optimal for the beach-restoration project. Also, the solution had to be as flexible as possible, avoiding any rigid structures, so it would easily absorb any physical media modification. The philosophy behind the solution was to generate a sand accumulation process without interrupting alongshore sediment transport. For a long-term solution, it was imperative that any restorative actions not affect the natural dynamic process that relates wave climate/bathymetry/sediments. In 2001, federal authorities from the Ministry of the Environment in Yucatan initiated a Beach Rehabilitation Program. Proposed actions for improving knowledge of this application are also discussed. This paper describes the technical solution adopted using geotextile tubes, as low-crested structures, along 4km of beach.
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