Walter C. Dragani

A Set of 3-D Nested Models for Tidal Propagation from the Argentinean Continental Shelf to the Río de la Plata Estuary—Part I. M2

Abstract As a contribution to the UNDP/GEF project ‘Environmental Protection of the Río de la Plata and its Maritime Front’, the three-dimensional primitive equation Hamburg Shelf Ocean Model is being implemented for forecasting purposes. As a first step a study of the tidal propagation was done. Data for the estuary were gained through a set of three one-way nested models. Simulations were started with a large-scale model covering the Argentinean and Uruguayan and part of the Brazilian continental shelves. This model provides boundary conditions to a smaller scale model of the Río de la Plata and adjacent continental shelf, which in turn is used to force a small-scale high-resolution model of the Río de la Plata estuary. Model sensitivity to different boundary conditions and to model parameters was investigated. Solutions are not sensitive to the two different boundary conditions tested, derived from global data assimilating models. It results also not sensitive to lateral diffusion but to bottom friction. M2 tidal wave propagates northwards as a Kelvin wave, with amplitudes reaching almost 4 m in Southern Patagonia and a few centimeters at the Río de la Plata estuary. Simulation results for the M2 component propagation were validated using all tidal gauge data available and several currents observations, resulting in a very good agreement. These simulations have permitted, therefore, the construction of more reliable model derived cotidal, corange and tidal currents charts. The nonlinear transfer of energy from semidiurnal to higher order harmonics was mapped. It can reach very high values at some locations of the Patagonian coast. Tidal energy dissipation derived from the simulations shows that it constitutes an important amount of the globally estimated one.

Modeling Ocean Tides and Their Energetics in the North Patagonia Gulfs of Argentina

Abstract During the last decade, global tidal models have spectacularly improved. However, they still have difficulties in resolving tides over continental shelves and near coastlines. This study of tidal propagation from the continental shelf to the North Patagonia Gulfs of Argentina applies a set of three nested high resolution models based on the Hamburg shelf ocean model (HamSOM), where particular attention was paid to the bathymetry and the coast line. The study is complemented by the use of all the tidal gauge and tidal current observations available. Simulations display good agreement with observations, permitting the construction of higher resolution and more reliable cotidal and corange charts. The tidal regime in the area is essentially semidiurnal and dominated by M2. This constituent propagates northward as a Kelvin wave and reaches the gulfs from the south. In their interior an important amplification is observed. Tidal currents are large at the mouths of the gulfs, and weaken toward their interior. The nonlinear transfer of energy from the semidiurnal to higher order harmonics was analyzed. This can be very important in the interior of the gulfs, particularly in Nuevo Gulf and in the northwestern San Matías Gulf, close to San Antonio. Energy flux and energy dissipation by bottom friction has been computed and indicate that this region dissipates 17% of the total energy dissipated on the Patagonian Shelf which, in turn, is one of the most dissipative areas of the world ocean. The Simpson-Hunter parameter computed from the simulations shows that in the mouth of the gulfs, particularly in San Matías and east of the Península de Valdés, the tides are energetic enough to overcome stratification and produce tidal fronts. The locations where tidal fronts are located are highly consistent with results from sea surface temperature and primary productivity data analyzed by other authors.

Tidal Hydrodynamics in Golfo Nuevo, Argentina, and the Adjacent Continental Shelf

Abstract A numerical, non-linear, barotropic, two-dimensional tidal model was implemented and used to simulate the M2, S2, N2, K1, O1 and M4 constituents in Golfo Nuevo (Argentina) and the adjacent continental shelf. The model includes the calculation of the vertical distribution of flow velocities using the linear three-dimensional equations. The tidal circulation was modeled by forcing at the open boundaries. Field measurements have shown that the hydrodynamics of Golfo Nuevo is basically of a semidiurnal character. Because of the difference in magnitude between M2 and the other constituents the M2 tide induces the strongest currents. These are strong on the shelf, with speeds exceeding 50 cm/s at maximum flood and ebb, but close to the coast become parallel to it and somewhat weaker, except at Golfo Nuevo mouth and near Punta Delgada. The direction of maximum current is almost constant in the vertical at the adjacent continental shelf, whereas in the middle of Golfo Nuevo the axes of the ellipse at the bottom appear rotated 24° counterclockwise with respect to those at the surface. Calculated tidal currents within Golfo Nuevo are reduced by a factor of about 5 with respect to those on the adjacent shelf. The resulting sea levels and currents compare well with the limited observation available. Cotidal and corange lines and the axes of the tidal current ellipses are also presented. RESUMEN Se desarrolló un modelo hidrodinámico numérico no lineal, bidimensional y barotrópico para simular el comportamiento de las componentes M2, S2, N2, K1, O1 y M4 de la marea en Golfo Nuevo, Argentina, y la plataforma continental adyacente. El modelo calcula la distribución vertical de la velocidad de las corrientes utilizando las ecuaciones lineales tridimensionales. La circulación se simuló forzando el modelo en los contornos abiertos. Las mediciones de campo demostraron que la hidrodinámica del Golfo Nuevo es esencialmente semidiurna. Las corrientes más fuertes están inducidas por la M2 porque su amplitud es mucho mayor que la de las demás componentes. Estas corrientes son fuertes en la plataforma continental, con velocidades superiores a 50 cm/s en los máximos de flujo y reflujo, pero en las proximidades de la costa se hacen paralelas a ella y algo menos intensas, excepto en la boca del Golfo Nuevo y en Punta Delgada. En la plataforma, la dirección de la máxima corriente es prácticamente constante en la vertical, pero en el medio del Golfo Nuevo los ejes de la elipse de corriente en el fondo exhiben una rotación antihoraria de 24° respecto de los ejes correspondientes a la elipse de superficie. Las corrientes calculadas en el interior del Golfo Nuevo están notablemente reducidas en relación con las de la plataforma adyacente. Tanto las alturas de marea como las corrientes muestran un buen acuerdo con el limitado conjunto de mediciones disponibles. Se presentan las líneas cotidales y de isoamplitud y los ejes de las elipses de corriente.

Tide Gauge Observations of the Indian Ocean Tsunami, December 26, 2004, at the Rio De La Plata Estuary, Argentina

The Rio de la Plata (RDP), located on the eastern coast of southern South America at approximately 35°S (Fig. 1), is one of the largest estuaries of the world (Shiklomanov, 1998). It has a northwest to southeast oriented funnel shape approximately 300 km long that narrows from 220 km at its mouth to 40 km at its upper end (Balay, 1961). The estuarine area is 35,000 km2 and the fluvial drainage area is 3.1 x 106 km2. The system drains the waters of the Parana and Uruguay rivers, which constitutes the second largest basin of South America. Therefore, it has a large discharge with a mean of around 25,000 m3 s-1, and maximum values as high as 50,000 m3 s-1 under extreme conditions (Jaime et al., 2002). The RDP can be divided into three regions: upper, with an averaged depth of less than 3–5 m, intermediate, 5–8 m deep, characterized by the presence of several shallow sand banks and an outer region with depths ranging from 10 to 20 m (Dragani & Romero, 2004). Throughout its system of dredged channels the RDP estuary constitutes the main maritime access to Argentina and Uruguay. Water level stations located along the estuary constitute a tide gauge network with the main purpose of recording water level heights associated not only with tides but also with the atmospheric forcing which produces storm surges (D’Onofrio et al., 1999). Tides in the RDP present a mixed, primarily-semidiurnal regime. Tides have a spring range of 1.58 m at Santa Teresita (Argentina) and 0.38 m at Punta del Este (Uruguay) located on the Atlantic coast, at the south-western and north-eastern side of the RDP mouth, respectively. The tidal range increases north-westward: 0.72 m at Punta Indio Channel, 1.01 m at La Plata and 1.10 m at Buenos Aires (Fig. 2), along the RDP southern coast. On the other hand, along the Uruguayan coast, the tidal range varies: 0.68 m at Montevideo, 0.66 m at Colonia del Sacramento (known as Colonia) and 0.76 m at Martin Garcia Island (SHN, 2010). The coincidence of large or even moderate high tides and large meteorologically induced surges has historically caused catastrophic floods in many coastal areas of the Buenos Aires Province (D’Onofrio et al., 1999). Sea level oscillations in the frequency band from a few minutes to almost two hours have been frequently observed at different tide stations along the Buenos Aires coast (Balay, 1955; Inman et al., 1962; Dragani et al., 2002; Dragani et al., 2009). Dragani (1988) studied a

The role of meteorological tsunamis on beach erosion in the buenos aires coast: some numerical experiments

ABSTRACT Meteorological tsunamis (meteotsunamis) are very similar to ordinary tsunamis but are produced by atmospheric processes. In this work, some numerical experiments are performed using XBeach numerical model investigate the role of moderate meteorological tsunamis on a sandy beach. The model was forced using tide, a moderate storm surge event, wave height data series and a meteorological tsunami event recorded in the Buenos Aires coast, Argentina. Several numerical experiments were carried out considering different time lags between the peak level of the meteotsunami event and the highest sea level (storm surge and tide). In these experiments, the volumes of moved sand were quite similar, although different erosion patterns on the beach were appreciated. Numerical experiments presented in this work constitute the first indication that the occurrence of regular meteotsunamis during moderate storm conditions could change the erosion pattern on sandy beaches in the coast of Buenos Aires.

Evolución geomorfológica de Punta Rasa, Pcia. de Buenos Aires, Argentina

The spatial and temporal variability observed during the last 25 years at Punta Rasa sandspit is studied in this work. Five images Lansat TM (30 m spatial resolution) corresponding to the years 1987, 1994, 2001, 2007 and 2011 were selected in this study. Each one covers an area of 185 km x 172 km but, for this analysis, a smaller area from latitude 36°19´40” to 36°17´08” S and from longitude 56°44´10” to 56°47´25” S was selected. A remarkable retrogression of the sandspit and a gradual widening of the sector located adjacently southward the sandspit was observed by comparison of the selected images. The hypothesis discussed in this work is that such variability would be associated to a change in the wind wave climate which arose a slight change in the long shore wave energy flux and in sand transport. Finally, it is highlighted that the mean sea level rise and the increasing in frequencies and intensities of storm surges in the Rio de la Plata could play an important role in the observed erosion.

Numerical simulation of wind waves on the Río de la Plata: evaluation of four global atmospheric databases

Na regiao do Rio de la Plata, o desempenho das reanalises globais do NCEP/NCAR I, NCEP/DOE II, JRA-25 e ERAInterim implementadas como forcantes atmosfericas do modelo SWAN foram quantitativamente acessados atraves do vies, erro quadratico medio, coeficiente de determinacao e inclinacao da reta. Estes indices foram obtidos dos parâmetros de ondas observados e simulados (alturas significativas de ondas, periodo principal e direcao). Embora as estimativas estatisticas nao mostrem diferencas evidentes para periodos e direcoes, algumas diferencas notaveis foram obtidas para altura de ondas simuladas, dependendo do vento utilizado. O menor vies para altura significativa (0.22 m) foi obtido quando o SWAM foi forcado com a ERAInterim, enquanto o NCEP/NCAR I (0.16 m) e NCEP/DOE II (0.19 m) forneceram menor erro quadratico medio. A melhor inclinacao da reta entre simulacao e observacao de altura significativa (0.79) foi obtida usando NCEP/DOE II. No periodo de estudo, o maior episodio de onda registrado na boca do Rio de la Plata foi analisado e discutido. Neste evento de condicoes atmosfericas energeticas o melhor ajuste foi alcancado utilizando os ventos do NCEP/DOE II como forcante. Conclui-se que a base de dados NCEP/DOE II e forcante atmosferica mais adequada para simular alturas significativas de ondas com o modelo SWAN na regiao estudada.