Mónica Fiore

Return periods of extreme water levels estimated for some vulnerable areas of Buenos Aires

Abstract In Argentina, particularly in the province of Buenos Aires, densely populated areas are affected by swell inundations. This paper estimates the return periods of extreme levels, including those fixed by the Direccion Nacional de Planeamiento y Proteccion Civil (DNPPC) as evacuation warnings. The analysis combines the probability density functions (pdf) of tides and surges, provided their independence. The tidal pdf is generated from an hourly prediction for 19xa0yr. The surge pdf is obtained applying the generalized extreme value (GEV) distribution to a set of extreme surges generated by removing tides from a series of 89xa0yr of annual maxima. This set is chosen in order to make best use of the historical information since hourly water levels are not available for a long enough period. It is shown that in this case, the probability distribution which best fits to the surge data is that of Gumbel Type I. For an evacuation warning level of 3.30xa0m the estimated return period is 5xa0yr. The last 89xa0yr maximum (4.44xa0m) has a recurrence of approximately 265xa0yr. Estimated return periods are compared with those computed by the classical annual maxima method for the same period. The extreme levels and return periods estimated herein strongly justify the undertaking of actions in order to mitigate the serious consequences caused by floods in these low-lying areas.

Changes in the Regime of Storm Surges at Buenos Aires, Argentina

Abstract Located on the west margin of the Rio de la Plata estuary, the capital city of Buenos Aires is often affected by positive and negative storm surges due to strong southeasterly and northwesterly winds, respectively, which sweep the estuary. While positive surges cause severe flooding, negative surges affect navigation and drinking water supply. Since Buenos Aires is densely populated, a quantitative assessment of the variations in the regime of storm surges will help to develop policies for reducing their impacts. Changes in frequency, duration, and height of storm surges over the period 1905–2003 were determined from statistical analyses of hourly water levels. Calculations of the tidal constants used harmonic analyses of 19 y periods to account for any variation in the astronomical tide. Positive and negative surges were chosen from the residuals between observed levels and the predicted tide. The results show that the decadal averages of frequency and duration for positive surges have increased in the last three decades, but they have decreased for negative surges. The average decadal trends of the maximum positive and negative surges in each year, +1.46 ± 0.08 mm/y and +1.02 ± 0.09 mm/y, respectively, compare well with the relative mean water-level rise for Buenos Aires: +1.68 ± 0.05 mm/y. However, the height of positive surges has decreased in the last decade, and negative surges have become more intense in the last two decades.

Environmental impacts and simultaneity of positive and negative storm surges on the coast of the Province of Buenos Aires, Argentina

The Argentine shore of the Rio de la Plata estuary and its southwards adjacent maritime front are normally affected by extratropical positive and negative storm surges that affect human activities seriously. Positive surges can raise the water level in the estuary by more than 3xa0m over the predicted tide; thus, flooding the coastal plain where over 13 million people live and causing extensive property damage. Sometimes, there has been loss of life too. Although less populated than the coastal plain, the maritime front has many important tourist resorts and also undergoes severe beach erosion processes and loss of property owing to positive surges. Negative surges are particularly troublesome in the Rio de la Plata because they critically affect navigation safety and drinking water supply by lowering the predicted water level in an amount that sometimes reached more than 4xa0m. A remarkable point is that the same storm event can simultaneously give rise to a positive surge on the maritime front and a negative one in the Rio de la Plata. The environmental impacts of positive storm surges are strongly aggravated by human intervention. At the same time, sea level rise due to global climatic change has also its influence.

Simultaneous meteorological tsunamis and storm surges at Buenos Aires coast, southeastern South America

Meteorological tsunamis are frequently observed in different tide stations at the southeastern coast of South America. They are associated with the occurrence of atmospheric gravity waves during the passages of cold fronts over the Buenos Aires Province continental shelf. On the other hand, storm surges are also frequent in the region, and they are associated with strong and persistent southerlies, which are also frequent during cold front passages. The impact of meteorological tsunamis in coastal erosion and in the statistics of storm surge trends is discussed in this paper. For this study, fifteen meteorological tsunamis (with maximum wave heights higher than 0.20xa0m), seven of them simultaneous to the occurrence of storm surge events (with extreme levels higher than |±0.60xa0m|), are selected from April 2010 to January 2013. The impact of meteorological tsunamis in the storm erosion potential index (SEPI) is evaluated. Not significant differences are obtained between SEPI calculated with and without filtering the meteorological tsunami signal from the storm surge data series. Moreover, several experiments are carried out computing SEPI from synthetic sea level data series, but very low changes (lower than 4xa0%) are also obtained. It is concluded that the presence of moderate meteorological tsunamis on sea level records would not enhance this index at the Buenos Aires Province coast. On the other hand, taking into account that meteorological tsunamis can reach up the 20–30xa0% of the storm surge height, it was concluded that the statistics of storm surge trends (and their uncertainties) should be revised for Mar del Plata data series.

Simplified empirical astronomical tide model-An application for the Río de la Plata estuary

The Rio de la Plata has a complex astronomical tide due to the effect of the shallow depth of this extensive estuary, the complicated geometry and bathymetry and the huge discharge of the rivers Parana and Uruguay and therefore the simulation of the astronomical tide is complicated. This paper presents a Simplified Empirical Astronomical Tide model (SEAT) which overcomes the foreseen difficulties in a straightforward way. The program developed can be applied to other regions by only changing a file of the dynamic-link library. SEAT provides predictions, harmonic constants and the mean water level referred to the tidal datum used to calculate the prediction. The storage of information in the form of images reduces the size of the application. The equations considered for the prediction do not require the use of special computer processors. A personal computer with minimum hardware that supports Microsoft Framework 3.5 is suitable to run SEAT.

Non-Tidal Ocean Loading Correction for the Argentinean-German Geodetic Observatory Using an Empirical Model of Storm Surge for the Río de la Plata

The Argentinean-German Geodetic Observatory is located 13xa0km from the Río de la Plata, in an area that is frequently affected by storm surges that can vary the level of the river over ±3xa0m. Water-level information from seven tide gauge stations located in the Río de la Plata are used to calculate every hour an empirical model of water heights (tidalxa0+xa0non-tidal component) and an empirical model of storm surge (non-tidal component) for the period 01/2016–12/2016. Using the SPOTL software, the gravimetric response of the models and the tidal response are calculated, obtaining that for the observatory location, the range of the tidal component (3.6xa0nm/s2) is only 12% of the range of the non-tidal component (29.4xa0nm/s2). The gravimetric response of the storm surge model is subtracted from the superconducting gravimeter observations, after applying the traditional corrections, and a reduction of 7% of the RMS is obtained. The wavelet transform is applied to the same series, before and after the non-tidal correction, and a clear decrease in the spectral energy in the periods between 2 and 12xa0days is identify between the series. Using the same software East, North and Up displacements are calculated, and a range of 3, 2, and 11xa0mm is obtained, respectively. The residuals obtained after applying the non-tidal correction allow to clearly identify the influence of rain events in the superconducting gravimeter observations, indicating the need of the analysis of this, and others, hydrological and geophysical effects.

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

Sea-Level Trend at the Southernmost Region of South America

ABSTRACT Dragani, W.C.; DOnofrio, E.; Alonso, G.; Fiore, M., and Oreiro, F., 2014. Sea-level trend at the southernmost region of South America. Tide gauge data were used to estimate the sea-level trend at the Ushuaia tidal station (54°49′ S, 68°13′ W), located at the southernmost city in the world. The Ushuaia tidal station began working in 1951 but was relocated in 1970 approximately 900 m from its original location. Special care was taken in linking both data series to compose a single and reliable sea-level record gathered from 1952 to 2005. The least-square regression line for annual mean sea level (relative to the benchmark) was fitted, and the computed slope that resulted was not significantly different from zero. A low-pass filter was applied to the annual sea-level data series to smooth the constituents of tide longer than 1 year, which could mislead the trend of the mean sea level. The trend of the best fit line computed from the filtered data was −0.2 mm y−1, which was not significantly different from zero. Taking into account the Peltier glacial isostatic adjustment prediction, a corrected sea-level trend was estimated in +1 mm y−1 for the Ushuaia tidal station. The sea-level trend was also estimated by processing the altimetry data series gathered at five satellite track crossings located in the adjacent ocean (analyzed period 1992–2011). Resulting sea-level trends computed from altimetry data presented high spatial variability (from −0.9 to +3.1 mm y−1), which is likely associated with the rather short length of the processed data series. The authors of this technical communication foresee that these results will contribute to our knowledge of sea-level change in the Southern Hemisphere, especially southward of 50°S, where long sea-level data series are considerably scarce.