Walter Grismeyer

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