PhD thesis presented at University of Minho by António M. Caetano Alves, 1997

Abstract
The subject of this dissertation is the morphosedimentary characterization and the analysis of the recent evolution of the coastal area between the Minho and Neiva rivers, including the estuaries of the two main rivers in the region, the Minho and Lima rivers.

For this purpose three types of environment were studied: the coastal zone, dunes and estuaries. The main aims of their study were:

1. characterization of the deposits' sediments by textural analysis, study of the heavy and light minerals, morphoscopy and exoscopy of the quartz sand grains;
2. analysis of the marine and estuarine dynamics through refraction diagrams and the study of the estuarine tidal currents;
3. determination and analysis of the shoreline recent evolutionary trend based on the comparison of maps of different periods, aerial photography, periodical survey of the beach profiles and monitoring of the cliffs' retreat;
4. summarize the geological causes and processes responsible for the shoreline's recent evolution and its present evolutionary trend in order to establish the areas of different sensibility to human occupation.

The beach sediments show variations in textural characteristics that permit to identify the littoral drift direction, from N to S, and to distinguish areas of different energy and the inversion drift zones.

The coastal type depends on the lithostructural characteristics of the basement rocks. At present the shoreline occupies an abrasion platform conditioned by the contact between Hercynian granites and Pre-Mesozoic metasedimentary formations. In the beach areas the contact zone lies in the littoral platform; therefore the beach develops over the abrasion platform. In the rocky coast areas the contact is made in submerged areas and there are no beaches due to the pronounced dip of the adjoining continental area.

The net drift is very reduced, only about 1/4, of that recognised as the potential drift in the Portuguese west coast. At present the rivers give a weak contribution to providing coarse materials; some of these may be issued from the continental shelf deposits by seasonal transversal supply to the coast.

During the Holocene the sea level rose above the present level allowing the formation of fine deposits, such as the muddy sands, preserved at the top of the islets and estuary borders.

Human influence is the primary cause in the lack of stability of the coastal equilibrium and it normally urges the need for new interferences, usually just transferring the problem.