Bedforms Characterization of the Magdalena River Estuary: A Comparative Analysis Using the Mahalanobis Distance

This study presents the first detailed characterization of bedforms within the Magdalena River Estuary (MRE), a large tropical estuary with marked seasonal variability. Three sets of high-resolution bathymetric surveys conducted under contrasting climatological conditions were used to quantify bedform morphology and analyze their temporal and spatial variability. Bedform dynamics were linked to hydrodynamic and sedimentologic processes previously documented for the MRE. The bedforms of the MRE were compared with those of several estuaries and rivers using a newly introduced statistical approach based on the Mahalanobis distance applied to bedform geometric parameters. This statistical method measures the difference between a set of features and a reference group, allowing for the comparison of bedform characteristics across systems. The results show that during the low-discharge season, salt-wedge intrusion into the MRE inhibits the development of bedforms, resulting in a lower-stage plane bed, whereas larger dunes become predominant along the river channel when the salt wedge is flushed out of the estuary during high discharges. However, the symmetric shape of these dunes reflects the tidal influence on the river channel dynamics even during high discharges. The Mahalanobis distance demonstrated a quantitative framework for discriminating between fluvial (unidirectional) and estuarine (bidirectional) flow regimes based on bedform geometry. This research also proposes a nomenclature for standardizing geometric features in bedform studies.