![]() 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. 10.6.2).This paper describes the technical solution adopted using geotextile tubes, as low-crested structures, along 4km of beach. In addition, protection measures may be required against local toe scour in front of the breakwater, just as for seawalls (see Sect. This can be established by creating a transitional zone with gradually increasing gap lengths and/or decreasing crest levels. Attention should further be paid to mitigation of downdrift (leeside) erosion. ![]() ![]() If a submerged or low-crested emerged breakwater is not designed properly, additional negative morphological effects such as local scour and shoreline erosion may easily occur. A successful project may involve an initial design phase based on mathematical and physical modelling, the testing of the design by means of a field pilot project including a detailed monitoring programme and the fine-tuning of the design by modification of breakwater lengths based on the field experiences. Waves from different directions and tidal effects (water level and currents) also seriously complicate the situation. ![]() The fine-tuning of series of offshore breakwaters is a very difficult task, especially for submerged breakwaters. In conclusion, in this paragraph the morphological consequences of detached shore parallel offshore breakwater were discussed. Sometimes, submerged breakwaters are constructed as sills between the tip of groynes to support the seaward toe of beach fills (perched beaches, see Fig. Supplementary beach nourishments may be required to deal with local storm-induced shoreline erosion, especially opposite to gaps, where under storm conditions large amounts of sediment may irrevocably be carried seaward. Submerged structures have only a limited effect on storm-induced erosion, as most of the storm waves can be expected to pass over the structure and attack the dune or cliff front. Any attempt to understand and model the morphodynamic impact of (submerged) structures requires the explicit consideration of the complicated circulation currents. Clearly, the successful application of submerged breakwater requires a better understanding of the shoreline response. Unfortunately very few guidelines are available for submerged breakwater design, as yet. Hence, shoreline erosion may occur, for instance, if a submerged breakwater is built too close to the shore. The erosional current pattern becomes stronger for decreasing distance between the breakwater and the shore. This current pattern can transport a lot of sediment outside the area and counteract the accretional tendency. Along the end sections of (segmented) breakwaters, the currents escape in the seaward direction (see Fig. However, wave breaking on the structure drives a current pattern with diverging shore-parallel currents in the shadow zone of the breakwater (see Sects. As for emerged structures, this may result in accretion behind the structure. (1997) a striking example is described where the application of offshore breakwaters yields more erosion than without this ‘protection’ measure: a single submerged breakwater built on the lower east coast of Florida (USA), approximately 7 km south of the entrance of the Port of Palm Beach was later (1995) removed because of excessive erosion problems in the lee of the breakwater.Ī submerged breakwater parallel to and at some distance from the shoreline will undoubtedly reduce the wave heights landward of the submerged breakwater (depending on the wave climate, the positioning and the crest height relative to the still water level). Therefore, depending on the crest levels above MSL, tidal range and storm surge levels, large storm waves may still pass over the structure, such that storm erosion cannot be completely stopped.Įxamples are known from field and laboratory tests in which severe erosion is generated landward of submerged breakwaters. However, the still water level during a storm often increases (storm surge, see Sect. L > 1\) to 1.5).įrom the above, it follows that the optimal emerged breakwaters in terms of coastal protection are built close to the shore with a high crest level and small gap lengths, but such a structure will largely block the horizon and is not attractive in terms of beach recreation.Įmerged breakwaters also reduce storm-induced beach and dune erosion to a certain extent.
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