Carlos Antunes

Point Mass Method Applied to the Regional Gravimetric Determination of the Geoid

The determination of the local gravity field by means of the point mass inversion method can be performed as an alternative to conventional numerical methods, such as the least-squares collocation. Based on the first derivative of the inverse-distance Newtonian potential for the representation of the gravity anomaly data, it is possible to compute any wavelength component of the geoid in planar approximation with sufficient accuracy. In order to exemplify the theoretical concept, two applications are presented of the computation of two different wavelength components of the geoid, the long wavelength component in a local solution and the short wavelength component in a regional solution. The results are compared with corresponding least-squares collocation solutions, using a global geopotential model to remove and to restore the long wavelength component.

Geomorphological response of the salt-marshes in the Tagus estuary to sea level rise

ABSTRACT Silva, T.A., Freitas, M.C., Andrade, C., Taborda, R., Freire, P., Schmidt, S., Antunes, C., 2013. Geomorphological response of the salt-marshes in the Tagus estuary to sea level rise. Salt-marshes are highly valuable ecosystems due to their role in supporting the aquatic and bird life. Furthermore, many anthropogenic activities such as agriculture, salt production or aquaculture targets these areas. They also act as protective barriers to shores, given their ability to dissipate most of the wave and current energy in high tide. Sea level rise can place these intertidal zones at risk, reinforcing the need to understand their morphosedimentary and dynamic response to the variations on the forcing factors, thus allowing for a better management of these environments. Large expansions of salt-marshes and tidal flats are among the morphodynamic contents of the Tagus estuary. This study focuses on the recent past evolution of Tagus marsh areas in order to understand their geomorphological response to higher sea level scenarios. Cores were taken in four contrasting high salt-marsh expansions in estuarine margins (Trancão – TR, Mouchão da Póvoa – MP, Pancas – PA and Corroios - CO). Marsh surfaces were surveyed using DGPS-RTK and tidal regime characterized at each location. The cores reached at least 1.20m in depth and were sub-sampled every cm for 210Pb and 137Cs radioisotope determination, allowing the derivation of sedimentation rates. In all locations, accretion rates clearly exceed the post-1920 mean rate of sea level rise (+0.21cm/year, Cascais gauge). Their linear extrapolation into the future, until reaching the upper threshold of marsh surface aggradation (MSHT), suggests that Tagus marginal marshes will not drown under the projected sea level elevation scenarios for the end of the 21th century.

Understanding the coastal variability at Norte beach, Portugal

ABSTRACT Silva, A.N., Taborda, R., Antunes, C., Catalão, J. and Duarte, J. 2013. Understanding the coastal variability at Norte beach, Portugal Norte beach stands in a coastal stretch fully exposed to the high energetic North Atlantic wave regime. The beach is located updrift of the Nazaré submarine canyon head, a sedimentary sink that captures the southward directed longshore drift. Systematic monitoring of Norte beach has been conducted by a coastal video monitoring system since 2008. A total of 31 monthly coastlines were extracted and analyzed in the period between December 2008 and May 2012. Results show a rare high seasonal coastline variability which exceeds 160 m in the southward sector (adjacent to the headland) and 70 m at the central and north sectors. These coastline variations are related with modifications in the planform beach configuration: beach oscillates between a straight (generally from June to August) and an arcuate configuration (during the remaining months of the year). Results suggest that Norte beach variability depends mainly on longshore drift gradients rather than with cross-shore sedimentary transfers. The intense wave refraction over the canyon head, associated with the westerly swell waves, generates a sedimentary convergence at the centre of the beach promoting the increase of the beach curvature, while, northern and/or short waves (more frequent in summer) tend to linearize the beach. This work contributed with valuable information about the sedimentary dynamics of the Norte beach and showed that this site is a suitable candidate to evaluate longshore drift from shoreline changes.

Effect of inlet morphology and wave action on pollutant pathways and sediment dynamics in a coastal stream

Hydrodynamics and water renewal of intermittent coa stal streams are highly variable, at various time scales, due to the very active morphod ynamic behavior of their inlets. Due to this strong dynamics, the pathways of water-born e materials – and the consequences of contaminated discharges – can depend strongly on the morphology and environmental conditions. Predicting the fate of contaminants in these systems requires coupled numerical models accounting for the major physical and water quality processes. We aim at improving the understanding of the impact of inlet morphology and wave action on the pollutant and sediment pathways of th ese small coastal systems, based on a suite of calibrated and validated coupled models. T wo analyses, based on particle simulations, are presented to assess sediment dynam ics and pollutant pathways for several conditions. Results show that waves have a major effect on the fate of waterborne materials in the estuary. Wave-induced curren ts sweep away materials coming out of the estuary, while wave-induced setup has a prof ound effect on tidal propagation, water levels and velocities in the estuary, promoti ng he upstream transport of pollutants. 1 National Laboratory for Civil Engineering, Av. do B rasil, 101, 1700-066 Lisbon, Portugal; {aoliveira, afortunato, mguerreiro, xbertin, nbrune au, mfrodrigues, pfreire, lsimoes, gdodet, amendes}@lnec.pt. 2 Faculdade de Ciências da Universidade de Lisboa, Ca mpo Grande, Ed. C6, 1749-016 Lisboa, Portugal; {rtaborda, candrade, amasilva, cm antunes}@fc.ul.pt. 3 CIMA, Universidade do Algarve, Campus de Gambelas, Ed. 7, 8005-139 Faro, Portugal; cloureiro@ualg.pt.