In the last decade, the concern about the effects of the sea level rise as a result of climate change has been accepted not only by the scientific community, but also by governments and international institutions, multiplying the works that have attempted to assess the consequences of such increase in all types of coasts in the world (e.g. IPCC 2007; EEA 2010). Some of these institutions (e.g. International Panel on Climate Change, IPCC 2007; European Environmental Agency, EEA 2010) have encouraged the development of analysis at regional and local scales in order to evaluate and assess the effects of the sea level rise on different coastal areas of the planet. Even there have been many approaches, most of the works (Titus y Richmann, 2000, Marfai y King, 2005, Zhang, 2011, Fraile et al. 2012a) coincide in considering as inundated those areas of a DEM which height are under a marine inundation local level. This level is usually calculated as the integration of a few variables as the future sea level rise (from climate change numeric models), the tide and the topographic datum. In summarize, most of the techniques agree in the necessity of modeling two surfaces: i) a topographic surface (generally known by means of a DEM), which often is referred to an official altimetry datum (NMMA in Spain); and ii) a sea surface, the local mean sea level (NMML), which is defined as the vertical difference between a local sea level (generally an averaged value) and NMMA level. Tide gauges are often used to calculate NMML. NMMA is the altimetry reference (0 m level) in the topographic maps and DEMs in Spain. Nevertheless, this value does not necessary match with NMML. This discrepancy makes differences in the calculation of marine inundation local levels. It might involve significant difference in the calculation of inundated areas. Although different approaches to calculate NMML have been used (Wyrtki y Mitchum, 1990; Woodworth et. al, 1999; Woodworth et. al, 2009), none of them studied the importance of the period and the method to calculate it.