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| Author(s): |
Cassia Pianca Barroso
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Instituto Oceanográfico (IO/DIDC) |
| Defense date: | 2009-12-15 |
| Examining board members: |
Eduardo Siegle;
Luiz Bruner de Miranda;
Elirio Ernestino Toldo Junior
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| Advisor: | Eduardo Siegle |
| Abstract | |
Tidal inlets are highly dynamic environments with their sedimentary features representing the complex interaction of tidal currents, river discharge, waves and the local bathymetry. These sedimentary features have a strong influence in morphological changes of coastal regions, affecting the stability of the adjacent environment such as beaches and estuarine systems. The aim of this study is to better understand the relative influence of the main processes controlling the morphological evolution of sandbars and sandspits associated to the inlet system of the Caravelas estuary. The Caravelas estuarine system comprises several meandering channels connected to the ocean by a double inlet system located in front of the Abrolhos reef in the south of Bahia. Based on the data collected during two 16-day field experiments in the estuarine system, the numerical model MIKE21 FM (DHI Water \\& Environment) has been applied and validated in order to assess quantitatively the processes that control the system. The hydrodynamic, wave propagation and sediment transport modules of the numerical model were used in this study. The model includes the feedback of morphological changes on hydrodynamic, wave and sediment transport calculations. Numerical experiments aiming to assess the relative importance of the physical forcings on the environment include ten sets of boundary conditions. These include the extreme energetic conditions, for high (large wave heights, river discharge and spring tides) and low energy (small wave heights, river discharge and neap tides) under a range of wave directions; and two additional periods that include the measured conditions (2008 period and 2007 period). Satellite images (LANDSAT and CBERS) were also used to observe the morphological changes of the sandspits and adjacent coastline during the last years. The results from the calibration and validation of the numerical model showed that in the region of interest and the inner shelf the model represents the hydrodynamic patterns. Results show that the local morphodynamics is controlled by the interaction of the main physical processes, being however its relative importance variable along the different regions of the system. Tidal flows control the sediment transport and morphology of the main inlet channel. The sandbars that form the ebb-tidal delta are also tide-dominated, although wave driven currents drive an onshore sediment transport component. The sandspit is influenced by waves and tides. The sediment transport along the sandspit is controlled by longshore drift and then redistributed by tidal currents. Satellite images show the sandspit growing in length, and becoming narrower with a recurved tip. The design of the recurved spits that comprise the inlet is a consequence of the wave generated longshore drift which varies at different time scales: a daily cross-shore variation due to the varying water level and seasonally due to variations in the direction of wave incidence. (AU) | |