Navegando por Autor "Winterwerp, Johan Chistian"

Agora exibindo 1 - 2 de 2

Item
Determination of the wave climate for the southern brazilian shelf
(2009) Cuchiara, Débora Copstein; Fernandes, Elisa Helena Leão; Strauch, João Carlos da Silva; Winterwerp, Johan Chistian; Calliari, Lauro Júlio
The main objective of this study is the characterization of the waveclimate in the SouthernBrazilianShelf (SBS) based on a thorough review of existing field data and on numerical modeling experiments. A quantitative knowledge about the waveclimate of this area is important to understand the mechanisms driving episodic mud bank attachments to the sandy shore, and the interaction of these banks with the flow and waves. The statistical analysis of existent data on the waveclimate throughout the SBS indicates that the predominant wave directions are 100° and 160° (E–SE), with wave heights varying between 1 and 1.50 m. The wave period varies between 6 and 14 s, with predominance of mean wave period of 8 s (sea conditions) and 12 s (swell conditions). The spectral wave model SWAN version 40.41 [Booij, N., Haagsma, I.J.G., Holthuijsen, L.H., Kieftenburg, A.T.M.M., Ris, R.C., van der Westhuysen, A.J., Zijlema, M., 2004. SWAN Cycle III Version 40.41 Users Manual, Delft University of Technology, Delft, The Netherlands, p. 118, http://fluidmechanics.tudel /swan/index.htm] is used to simulate the waveclimate for the region. Special attention is given to Cassino Beach, describing the waveclimate observed during the Cassino Experiment, carried out in 2005. The verification of the standard SWAN model was carried out based on the comparison between numerical modeling results and available data of significant wave height, peak period, mean wave direction and energy density for the period relative to February of 1998. Results showed satisfactory model predictions of significant wave height and reasonably accurate predictions of peak spectral wave period and direction. The model performance is also considered satisfactory in the representation of the waveclimate of the region when the wave spectrum has only one spectral peak, but presents limitations for bimodal wave spectrum. When two spectral peaks are observed, the SWAN model agrees with the spectral level observed in the low frequency, but underestimates the spectral level in the high-frequency band. When considering the presence of mud deposits in the area, model results predict that although the presence of mud attenuates most of the wave energy on the low frequency peak, it has a smaller effect in attenuating the wave energy on the high frequency peak. The comparison between significant wave heights calculated by the SWAN model (with and without mud) and measured with an Nortek acoustic doppler profiler (NDP) for the NDP localization point, and with data from a waverider relative to the 2005 survey for the studied period showed that all the time series have a similar pattern. Observed and calculated results without mud are in agreement, following the expected behavior. By considering the presence of mud in the whole domain, the model with mud shows a clear decrease of the significant wave height in relation to the NDP localization point. Furthermore, the significant wave height is underestimated due to the consideration of a constant mud thickness, extent, density and viscosity in the whole domain.
Item
Fine grain sediment transport and deposition in the Patos Lagoon Cassino beach sedimentary system
(2008) Calliari, Lauro Júlio; Winterwerp, Johan Chistian; Fernandes, Elisa Helena Leão; Cuchiara, Débora Copstein; Vinzon, Susana Beatriz; Dias, Marcelo Sperle; Holland, Todd
Extensive mud deposits superimposed on the predominantly sandy inner continental shelf adjacent tothe Patos Lagoon estuary, indicates that the Lagoon is a potential source of ﬁne sediments to the coastal sedimentary system. The lagoon is large and shallow, and the water movement is mainly controlled by wind-driven set-up and set-down. The mean river inﬂow is around 2000 m3 s1, although peak ﬂowrates exceeding 20,000 m3s 1have been observed during El Nin˜o periods. Though the tidal elevations are small, tidal velocities in the lagoon’s inlet can be signiﬁcant due to the large extension of the backwaters. Moreover, signiﬁcant exchange ﬂows can be generated between the estuary and coastal area due to barotropic pressure gradients established as a function of wind and freshwater discharge.The predominant net ﬂow is seawards, but opposite near-bed ﬂows due to pronounced vertical salinity stratiﬁcation can also be observed. The coastal area is characterized by small tidal effects, large scale ocean circulation, wind-induced residual ﬂows and wave-driven currents, where the waves originate from swell or are locally generated. Fine sediment is brought into the Patos Lagoon by the rivers and its deposits are likely to have long residence times. These ﬁne sediment deposits can be remobilized by locally generated waves, and driven towards the channels and lagoon 0s shallow bays. Suspended particulate matter (SPM) concentrations within the lagoon do not exceed a few 10 mg l1, though higher values have beenmeasured occasionally. In the southern estuarine part of the lagoon, ﬁne sediments may accumulatedue to gravitational circulation effects, yielding SPM concentrations of a few 100 mg l 1. The export of ﬁne sediment from the lagoon to the coastal area occurs predominantly during NE winds. This explains why the majority of the off shore sediment deposits, known as the Patos Facies, are more widespread towards the southern portion of the inner continental shelf. These sediments deposit in the form of ﬂuid and more compacted mud, between the 6 and 20 m isobath, in layers with thickness varying between a few dm to 2 m causing marked lateral differences in grain size. Recent sediment core data, indicates that ﬂuid mud occurrence increases towards the shore and that the mud depocenter remains in the same area as previously mapped two decades before. On a long-term basis, this lateral heterogeneity in sediment properties controls the geomorphology of the inner continental shelf and shoreface, and inﬂuences the shoreline accretion rate and beach morphodynamic south of the inlet. Short-term effects are associated with episodic events of mud deposition on the beach during heavy storms that often result in strong gradients in hydrodynamic processes. These gradients in turn inﬂuence the morphodynamic behavior on the sectors affected by the mud deposits and can create coastal hazards relating to beach usage.