Geometric detached breakwaters indicators on the Spanish North East coastline

Abstract

Many beaches have been eroded and the obvious environmental and landscape degradation of many coastal stretches are problems that coastal engineers are spending time solving. With this in mind, different protection methods have been used over time, most on the basis of the artificial nourishment of beaches and the building structures such as groynes and detached breakwaters. Detached breakwaters are artificial structures, generally parallel to the coastline, inspired by the working of natural formations, protecting a certain stretch from wave action and being able to create accretion areas. This is why these structures have been in general use, with different results, since the 1970s in countries such as Japan, the United States, Israel, Spain, Italy, and Australia. The study undertaken for this research focuses precisely on this type of structure, with the purpose of providing an overall view of the state of the art in this field. In addition, the effects of a detached breakwater on the shoreline for a series of real cases on the Spanish coastline were analysed to check whether the empirical relations given by different researchers for classifying the shoreline’s type of response were fulfilled for them all or not. This study only takes formulas on the basis of the geometrical characteristics of breakwaters into consideration as being the most used by design engineers for predesigning a construction. All the formulas studied are based on the nondimensional B/X monomial, which is a ratio between the two most important geometric breakwater parameters (the length of the detached breakwater, B, and its distance to the initial coastline, X), so the result of this work led us to propose the following geometric model for the case of the Catalonian coastline: tombolo formation if B/X _ 1.3; salient formation if 1.3 _ B/X _ 0.5; limited shore response if 0.5 _ B/X.