The internal structure of modern barchan dunes of the Ebro River Delta (Spain) from ground penetrating radar

Abstract

Ground penetrating radar is a non-invasive technique that allows the study of the structure of dune systems when outcrops are limited or protected. GPR response of sand dunes of the Holocene aeolian dunes of the Ebro River Delta (Spain) has been analyzed in this study in order to: characterise their internal architecture, determine their development and recent evolution, and calculate electromagnetic (EM) waves mean velocities in fine-grained sedimentary deposits. Several GPR profiles carried out in different representative areas have revealed the existence of different reflector packages that are related to differences in barchan-type dune activity. The area with a highest sand movement activity is characterized by small dunes, with overlapping reflector packages exhibiting reflections which dip up to 25°. When dune activity is moderate, dunes are higher (up to 5 m height) and their internal structure shows low-angle dip reflections except for the avalanche face, where dips up to 22° are identified. The area with the lowest sand movement, nearest to the coast line, is represented by small dunes with internal geometry consisting of partially overlapping elongated reflector packages defined by subhorizontal reflections. In all cases, a reflection associated to the location of the water table has been recognized at about 0.7 m depth. The results obtained from the GPR survey have allowed us to improve our knowledge about the dynamics of the coastal dune field and its relative evolution. They have shown that the morphology and geometry of the dune bodies adapt themselves to wind conditions, which permits the construction of coastal dune development models in order to establish the evolution of dunes.