masterThesis
Morfodinâmica de sistemas de ilhas barreiras tropicais, litoral setentrional-RN
Fecha
2019-08-23Registro en:
SILVA, Filipe Ezequiel da. Morfodinâmica de sistemas de ilhas barreiras tropicais, litoral setentrional-RN. 2019. 95f. Dissertação (Mestrado em Geodinâmica e Geofísica) - Centro de Ciências Exatas e da Terra, Universidade Federal do Rio Grande do Norte, Natal, 2019.
Autor
Silva, Filipe Ezequiel da
Resumen
The northern littoral of Rio Grande do Norte State (RN) is a tropical mixed energy coast
where geological conditioning favors the maintenance of barrier island systems. These
systems include barrier islands, sandy spits, ebb tidal deltas, mangrove forests, tidal inlets
and plains. Coastal dynamics in these systems is intense, which causes large shoreline
retreat, sandy spits growth, as well opening and closure of tidal inlets in a short time. This
dynamic directly affects onshore oil exploration, and for this reason, several studies have
been conducted in the region in recent decades, in order to better understand its
morphodynamic aspects. However, much remains to be understood, especially when
considering the extension of these systems. This work aimed to evaluate the
morphodynamics of the barrier islands systems of the northern coast of RN through
quantitative data obtained from multitemporal analysis of orbital images of Landsat 5 TM
and Landsat 8 OLI sensors, and associated knowledge of coastal processes as well. The
analysis were carried in a period of 33 years (1984 to 2016), with 4-year sampling
intervals for the low frequency analysis, and 1 year for the high frequency analysis. The
results indicate a great influence of the sampling interval on the interpretation of the
evolutionary behavior of these barrier islands and sandy spits, so that low frequency
analysis does not represent the actual evolution of the barriers, leading to
misinterpretations. This is related to the considerably dynamic behavior of these barriers
which over a period of 1 year may present a 3 km² magnification. In addition, the
successive alternations between enlargement and shrinkage in the area of these barriers
correspond to uninterrupted accretion and erosion cycles that nullify any trends of growth
or decrease in these areas. The morphodynamic analysis allowed differentiating two types
of barriers: migrant and stationary. The migration movement results from the joint action
of the meteo-oceanographic forcing that causes continuous updrift sediment loss followed
by downdrift sediment gain. This process pushes the whole barrier westward at rates of
up to 100 meters per year, however preserving its shape. The migration of barriers can
cause opening, rotation, translation and closure of tidal channels. The stationary barriers,
in turn, have features that attenuate the energy of waves and currents, avoiding large
sediment losses and, consequently, their migration. The barriers also act as sediment
source for the transgressive dune fields. Therefore, migrating islands may coalesce with
the shoreline providing sediment to adjacent dune fields.