Abstract

Espichel-Sines is an embayed coast in SW Portugal, consisting of two capes at both extremities, a tidal inlet and associated ebb tidal delta, a barrier spit, sandy beaches, sea cliffs, and a submarine canyon. Beach berm, backshore, near shore and inner shelf sediment samples were taken. Samples were analyzed for their grain-size compositions. This study ranks the hypothetical sediment sources influences on the sediment distributions in the study area using the multivariate Empirical Orthogonal Function (EOF) techniques. Transport pathways in this study were independently identified using the grain size trend analysis (GSTA) technique to verify the EOF findings. The results show that the cliff-erosion sediment is composed of pebbles and sand and is the most important sediment source for the entire embayment. The sediment at the inlet mouth is a mixture of pebbles, sand, silt, and clay, which is a minor sediment source that only has local influence. The overall grain-size distributions on the shelf are dominated by the sand except for the high mud content around the tidal delta front in the northern embayment. Sediment transport patterns on the inner shelf at the landward and north sides of the canyon head are landward and northward along the barrier spit, respectively. On the south side of the canyon head, the prevailing sediment transport is seaward. Sediment transport occurs in both directions along the shore.

Highlights

  • Each year about 28 Gt of sediment is transported from the land into the oceans (Syvitski 2003)

  • The geochemical properties of sediment, such as the clay minerals, magnetic minerals, heavy minerals and particle adsorbed radioactive elements and organic substances composition may be used as tracers for sediment transport and deposition

  • The former proposed trend vectors based on a sampling grid that compares each sample with its neighboring samples within a characteristic distance

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Summary

Introduction

Each year about 28 Gt of sediment is transported from the land into the oceans (Syvitski 2003). Based on the McLaren model two-dimensional approaches were proposed by Gao et al (1991) and Gao and Collins (1992, 1994) and Le Roux (1994a, b) The former proposed trend vectors based on a sampling grid that compares each sample with its neighboring samples within a characteristic distance. The latter assumes that sediment transport takes place across wide unidirectional fronts rather than from point to point. Using geostatistical tools Asselman (1999) modified the Gao-Collins method and implemented a Geographic Information System (GIS) methodology This method employs initially irregularly spaced data set interpretation to produce a regular grid of grain-size parameters using a Monte Carlo simulation to carry out a statistical test on the trend vectors. The latter definition for characteristic distance is more rigorous, taking into account the spatial change in the statistical parameters as the relative change in the parameter value itself. Poizot and Méar (2010) developed new GIS software that accounts for the presence of rocky outcrops in calculating the trend vectors

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