Characteristics and Longevity of Beach Nourishment at Praia da Rocha, Portugal

Abstract

Beach fill instances on the Atlantic coast of the U.S.A. generally have a life expectancy of less than five years. Although beach nourishment is viewed as viable and is often preferred to hard structures, the geomorphologic life of the fill is an important variable in evaluating the success of the venture. Two adjacent, nourished beaches on the diffed south coast of Portugal are examined to determine their morphologies following the fill and the variables that condition their temporal and spatial responses. The differential exposure to the ambient wave conditions and the nearshore circulation system differences caused by stacks and a very long jetty help to explain the contrasting history of beach fill in the two areas. Shoreline changes, surface morphologies, and sediment redistributions are traced through aerial photos, ground surveys, and a large collection of postcard views of the growing tourist area. The interpretation of this heterogeneous data set is that Praia da Rocha is regarded to be losing sediment very slowly, 2-5% per year, whereas the adjacent Praia dos Tres Castelos is losing its emplaced sediment at a rate of about 15-20% per year. Within a distance of a few hundred meters, one nourishment episode is an unqualified success because much of the beach remains after two separate periods of filling (1970 and 1983), whereas the other beach has returned to its pre-fill (1983) narrow condition within 5 years.