Hydrosedimentological controls on bedform development in a mesotidal environment

Abstract

The Bahía Blanca Estuary, located in the southern sector of Buenos Aires Province (Argentina), exhibits a wide variety of bedforms generated by the interaction among hydrodynamic and sedimentary processes. The aim of this study is to analyze these geomorphic features by identifying their sedimentary characteristics, their spatio-temporal evolution, and their relationship with the prevailing hydrodynamic conditions within the estuary. To this end, data acquired in the outer sector of the estuarine inlet were integrated, including side-scan sonar records, high-resolution seismic profiles, surface sediment samples, and hydrodynamic information. The identified bedforms include sand ribbons, with and without superimposed dunes, comet marks with different geometries, and asymmetric dunes of various dimensions. The distribution and type of bedforms reflect the interaction between sediment supply and the dominant hydrodynamic regime. The availability of sediment transported as bedload constitutes the main factor controlling their morphological configuration, spatial distribution, and dynamic behavior. Dunes develop in sectors where sandy thicknesses exceed 1 m, whereas intermediate thicknesses (0.5–1 m) allow the formation of sand ribbons with superimposed dunes and smaller-scale dunes. In contrast, sediment thicknesses below 0.5 m are associated with sand ribbons without dunes and comet marks. The morphological characteristics of the recorded bedforms, together with the measured current velocity patterns, indicate a marked dominance of the ebbrent, with values exceeding 1 m/s.