Modular Hybrid Coastal Protection Structure

Abstract

Tourism is one of the main sources of income of Jamaica. . However, at the moment the beaches are retreating. An example is the erosion of Hellshire Beach, showing a retreat of ten meters in only seven years. To preserve the beaches effectively, a new concept is requested. The main requirements of the system are wave attenuation and the marine life enhancement. The literature study showed, a variety of coastal management techniques exist. However, none of those solutions are capable of attenuating waves and enhancing marine life in an effective way. Ranking criteria are given and the following concept groups are generated: boulders, gabions, marine blocks, big (open) blocks and 'lego' (interlocking) blocks. The Multi-Criteria Analysis shows that the big (open) blocks are the most viable and two concepts are designed within this concept group: a triangular and a hexagonal block structure. In the hydrodynamic and wave models (Delft3D), a study is performed to find the relation between breakwater dimensions and wave attenuation. Also, three different conditions are modelled: daily conditions, hurricane conditions, and one-year storm conditions at the Hip-Strip in Montego Bay. Using the results from the hurricane model, the flow- and wave forces are calculated using the Morison equations for lift and drag. Three lay-outs for submerged breakwaters are tested in the model. This led to the final lay-out which is a combination of the three tested breakwaters. Following the Delft3D models, a structural analysis is done with the flow- and wave forces from the Morison equation. The structural analysis focuses on the sliding and uplift of the submerged breakwater. The hexagonal structure shows a better stability than the triangular blocks in hurricane conditions and therefore chosen as the final concept. A sensitivity analysis is performed with regard to the friction coefficient, the force-time profile and the placement errors. The placement errors turn out to be crucial and a connection between the top block and the base is needed to retain stability. The final dimensions (l x w x h) of the hexagonal blocks are 3 x 0.75 x 0.93 meter. The blocks can be made from a low strength class concrete and reinforcement is needed to provide strength during lifting. To enhance the marine life enhancement properties, fish condos of 4" and 6" are provided, the surface is made more permeable and the pH of the concrete is altered by curing. The structure shows great future potential and can be built soon. It is a state of the art structure, the stability is high, it enhances the marine life, the final dimensions will precisely agree with the drawings and there is no need for a nearby quarry. However, to all this benefits, there is also a drawback; the cost. The cost is a multiple of the conventional armour stones. Recommendations are given to bring expenses down. Placement in shallow water is preferred and replacing steel reinforcement by fibre reinforcement is worth investigating. Those recommendations will decrease the cost and will increase the viability of the Honeycomb block concept.