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

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 Direcciَn Nacional de Planeamiento y Protecciَn 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 19 yr. 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 89 yr 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 3.30 m the estimated return period is 5 yr. The last 89 yr maximum (4.44 m) has a recurrence of approximately 265 yr. 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.