Confirmation of beach accretion by grain-size trend analysis: Camposoto beach, Cádiz, SW Spain

Abstract

An application of the grain size trend analysis (GSTA) is used in an exploratory approach to characterize sediment transport on Camposoto beach (Cádiz, SW Spain). In May 2009 the mesotidal beach showed a well-developed swash bar on the upper foreshore, which was associated with fair-weather conditions prevailing just before and during the field survey. The results were tested by means of an autocorrelation statistical test (index I of Moran). Two sedimentological trends were recognized, i.e. development towards finer, better sorted and more negatively skewed sediment (FB-), and towards finer, better sorted and less negatively or more positively skewed sediment (FB+). Both vector fields were compared with results obtained from more classical approaches (sand tracers, microtopography and current measurements). This revealed that both trends can be considered as realistic, the FB+ trend being identified for the first time in a beach environment. The data demonstrate that, on the well-developed swash bar, sediment transported onshore becomes both finer and better sorted towards the coast. On the lower foreshore, which exhibits a steeper slope produced by breaking waves, the higherenergy processes winnow out finer particles and thereby produce negatively skewed grain-size distributions. The upper foreshore, which has a flatter and smoother slope, is controlled by lower-energy swash-backwash and overwash processes. As a result, the skewness of the grain-size distributions evolves towards less negative or more positive values. The skewness parameter appears to be distributed as a function of the beach slope and, thus, reflects variations in hydrodynamic energy. This has novel implications for coastal management.

Beach nourishment effects on sand porosity variability

“…1) and faces the Atlantic Ocean (Victoria and Camposoto beaches) and the Mediterranean Sea (Atunara beach). Both the Victoria and Camposoto beaches, the former located in the city of Cadiz, are dissipative beaches (Muñoz-Pérez and Medina, 2000;Poizot et al, 2013) composed of medium and fine moderately sorted sands. However, whereas Victoria has a seaside promenade, Camposoto is a natural beach with a backshore dune ecosystem.…”

“…The porosity is a primary determinant of the density and permeability of sediments; therefore, the porosity is a vital input for basin modelling (Chuhan et al, 2002). According to Poizot et al (2013), the permeability of a sand bed may also be correlated with the sand grains' size (mean, sorting and skewness) and sphericity in addition to the bed porosity.…”

Reply to J.J. Muñoz-Perez et al. Comments on “Confirmation of beach accretion by grain-size trend analysis: Camposoto beach, Cádiz, SW Spain” by E. Poizot et al. (2013) Geo-Marine Letters 33(4)

“…Muñoz-Perez et al (2014) have updated the information concerning the total volume and cost of nourishment operations at Camposoto beach and it is, of course, important to operate with precise and up-to-date information when assessing the cost of environmental operations such as beach nourishment. In the case of the "older" data cited in Poizot et al (2013), the conclusions nevertheless remain valid as they overall do reflect the physical and financial effort invested by national and local governmental authorities to support economic activities in the "sea-sun-sand" context.…”

“…Poizot et al 2006;Poizot and Méar 2010) which also allow the investigation of sedimentological processes prevalent on beaches. A first result dealing with a beach in recovery was reported by Poizot et al (2013).…”

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Abstract In a novel finding for a beach environment, Poizot et al (2013) identified an FB+ trend (sediments becoming finer, better sorted and more positively skewed upshore) on a well-developed swash bar on the upper foreshore of the Camposoto beach of Cádiz in SW Spain. In their Discussion of that paper, Muñoz-Perez et al (2014) provide some supporting arguments and also report grain-size, beach profile and other data from nearby beaches which differ from those of Poizot and colleagues for Camposoto beach, pointing out that a trend observed on one beach may not apply to a neighbouring beach.

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