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Marine action and control
Published in F.G. Bell, Geological Hazards, 1999
Those waves with a period of approximately 4 s are usually destructive, while those with a lower frequency, that is, a period of about 7 s or over, are constructive. When high-frequency waves collapse they form plunging breakers and the mass of water is accordingly directed downwards at the beach. In such instances, swash action is weak and, because of the high frequency of the waves, is impeded by the backwash. As a consequence, material is removed from the top of the beach. The motion within waves that have a lower frequency is more elliptical and produces a strong swash, which drives material up the beach. In this case the backwash is reduced in strength because water percolates into the beach deposits and therefore little material is returned down the beach. Although large waves may throw material above the high-water level and thus act as constructive agents, they nevertheless have an overall tendency to erode the beach, while small waves are constructive. For example, when steep storm waves attack a sand beach they are usually entirely destructive, and the coarser the sand the greater the quantity that is removed to form a submarine bar offshore. In some instances a vertical scarp is left on the beach at the high-tide limit. It is by no means a rarity for the whole beach to be removed by storm waves: witness the disappearance of sand from some of the beaches along the Lincolnshire coast of England after the storm flood of January—February 1953, which exposed their clay base. Storm waves breaking on shingle throw some shingle to the backshore to form a storm beach ridge, which may extend far above high-tide level. Chesil Beach in southern England provides an example, extending 13 m above high-tide level at its eastern end. Storm waves may also bring shingle down the foreshore, so that a step is developed at their break point.
The role of meteorological tsunamis on beach erosion in the buenos aires coast: some numerical experiments
Published in Coastal Engineering Journal, 2018
Guadalupe Alonso, Walter Dragani, Iael Pérez
The role of a moderate meteorological tsunami on a sandy beach profile during regular storm conditions was studied by means of the XBeach numerical model. The forcing was constructed superimposing tide, a moderate storm surge event, wave height data series representative of an ordinary wind wave condition and a regular meteorological tsunami event. Meteotsunami data series were located at different times along the tidal cycle to generate a set numerical experiments. Even though the volumes of relocated sand were quite similar (ranged from 1.25 to 1.34 m3/m2), different erosion patterns on the beach were obtained depending on the lags between the instants of occurrence of the meteotsunami peak and the wave data series, storm surge and tide maxima. Then, these results constitute the first indication that the occurrence of regular meteotsunamis during moderate storm conditions could change the erosion pattern on sandy beaches in the coast of Buenos Aires. Unfortunately, the lack of simultaneous pre and post full storm beach profiles, high-resolution sea level data and wave observations precludes advancing in the calibration and validation of XBeach model in order to reach a better understanding of this subject in the study region.