The Cantabrian Coast (N. of the Iberian Peninsula) is characterised by its erosive nature and its high cliffs sectioned by narrow and inland-extended estuaries, which are several hundred metres width and less than 15 km long. The origin of these estuaries can be traced back to a series of river beds engagements on the raised coast as well as to further fillings related to sea level eustatic variations during the general Holecene transgression.
Although there is a general tendency in the Cantabrian coast estuaries to repository backfilling, human activity has contributed to speed up this process by the construction of some elements which avoid or refrain sea waters access. Consequently, its elements reduce the tide lands floor in favour of land used for agricultural and stockbreeding purposes. This phenomenon has been especially intense throughout the 20th Century and has caused an impact on the estuarine natural environment. The analysis and recovery of this impact requires knowing the extent of the tidal dynamics and the accurate demarcation, from a dynamic viewpoint, of the estuaries zones as well as their anthropic alteration.
The zoning of two important estuaries in the central sector of the Cantabrian Coast, the Ribadesella and the Tinamayor ones, highlights the difficulties in approaching this type of study and shows the most valid geomorphologic criteria for zoning. The detailed geomorphologic cartography and the range of the tidal wave during the present spring high tides, shows that the tideways extension, their typology and the existence of scarps between areas located at different heights in the estuarine deposit and the alluvial plain allow us to identify three units: low, middle and high terraces. These units have shown an ever decreasing tidal influence. The supplementary analysis of aerial photographs from the last 40 years contributes to clarify the mentioned zoning and to characterise some recent anthropic impacts.