ABSTRACT

Nascimento, A. T. and Pereira, L.C.C., 2016. Morphodynamic Processes on a Macrotidal Beach in the eastern Amazon. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 427–431. Coconut Creek (Florida), ISSN 0749-0208.

This study analyzes the spatial and temporal variation in the morphodynamic processes and states of a macrotidal beach. Two intensive campaigns (9 days under spring/neap tide condition) were conducted to determine wave and weather conditions, in November/December 2013 (end of the dry season, characterized by strong winds) and March/April 2014 (rainy season, equinoctial period). Topographic surveys of two beach profiles were also conducted during the study period. Surface sediment samples were collected along each beach profile. Sediment grain sizes were later determined by laser diffraction. Ajuruteua is a sandy beach characterized by macrotides (up to 6.0 m), moderate wave energy (Hs of as much as 2.0 m), and strong winds (mean velocities of up to 4.5 m s−1). The beach is sheltered from waves by sandbanks and sandbars around low tide during both neap and spring tides. This results in a delay in the flood tide in the inshore areas, resulting in the prolongation of the ebb tides, primarily during the equinoctial period. During this period, modal breaker heights on Ajuruteua beach were minimal (Hb < 0.2), which, due to the longer ebb tides, combined with the higher tidal range, resulted in a scenario of tide-dominated tidal flats. By contrast, during neap tides an ultradissipative state dominated. Our results indicate that the characteristics of Ajuruteua beach are influenced primarily by macrotides and moderate wave energy, although the influence of the waves is restricted to the period around high tide, when the water is propagated towards the shoreline.

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