Evolution of the surface roughness of a coarse sand after a beach nourishment

Abstract

Beach nourishment with material from quarries is an increasingly common practice. These materials are usually coarse sands or fine gravels, and the particles show a very angular and rough surface. In this work, research on the evolution of the surface roughness of coarse sand particles that were dumped in January 2020 at Los Locos beach in Torrevieja (Alicante, Spain) is conducted. This sample came from a quarry and presented a high angularity and roughness on the surface of its particles. Samples were taken monthly for a year and a half (from January 2020 to June 2021), always at the same sampling point. Due to restrictions caused by the Covid-19 pandemic, samples could not be collected for 6 months. Once the samples were collected they were taken to the laboratory where the grain-size analysis of the complete sample was performed, and 108 particles of each of the most significant sieves (1.60 mm, 1.25 mm and 1.00 mm) of the coarse sand (from a quarry) were photographed. The contras, angular second moment (also known as energy), inverse difference moment, correlation and entropy were obtained (for each particle) from the photographs. Also, the swell that occurred throughout the study period was obtained from the SIMAR point 2077096 (the closest point to the study area). The significant wave height, period and direction of the waves affecting the sampling point were analyzed. The results show a decreasing trend in all the parameters studied (median sediment size, contrast, entropy, etc.). Some increases are observed due to the swell that moves the sediments from the backshore to the swash zone. These variations are first observed in the median size but are not seen until the following month in the textural parameters (contrast and entropy). When relating the parameters obtained from the photographs to the particles (contrast, entropy) with the surface texture of the particles, it is observed that they cannot be analyzed separately but must all be considered together. Thus the decrease in contrast and entropy shows a decrease in the superficial roughness of the particles, but the greater the difference between these two parameters, the greater the smoothness of the surface. After a year and a half of dumping the quarry material on the beach, a high degree of decrease in the roughness of the particles is observed; however, to reach the degree of polishing that the particles of a natural beach have, a longer period is necessary.